A restoration of Saurolophus angustirostris based upon skeletal and soft-tissue fossils. Art by L. Xing and Y. Liu, from Bell, 2012.

We love to bring dinosaurs back to life. From museum displays and academic papers to big-budget movies, we have an obsession with putting flesh on old bones. How much anatomical conjecture and artistic license is required to do so varies from dinosaur to dinosaur.

Some dinosaurs are known from a paltry collection of fragments and require a considerable among of reconstruction and restoration on the basis of better-known specimens of related species. Other dinosaurs are known from complete skeletons and require less osteological wrangling, but they still present the challenge of filling in the soft tissue anatomy that the skeleton supported in life. Every now and then, though, paleontologists discover skin impressions associated with the bones of dinosaurs. These rare fossils can give us a better idea of what the outside of some dinosaurs looked like.

Skin impressions are found most often with hadrosaurs. These herbivores, such as Edmontosaurus and the crested Corythosaurus, were plentiful and seemed to dwell in habitats where deceased dinosaurs could be buried rapidly by sediment, a key to the preservation of soft-tissue anatomy. In the roughly 68-million-year-old strata of Canada and Mongolia, for example, skeletons of two different species of the hadrosaur Saurolophus have been found associated with skin impressions. But these fossils can do more than help use restore the outer appearance. According to a new paper by University of Alberta paleontologist Phil Bell, subtle differences in Saurolophus skin traces can help paleontologists distinguish one species of dinosaur from on another on the basis of soft tissue anatomy alone.

In 1912, professional dinosaur hunter Barnum Brown named the hadrosaur Saurolophus osborni from skeletons found in Alberta’s Horseshoe Canyon Formation. Although not mentioned at the time, three skeletons of this species were associated with skin impressions from various parts of the body, including the jaw, hips, foot and tail. Forty years later, from skeletons found in a huge bonebed called the “Dragon’s Tomb” in Mongolia’s Nemegt Formation, paleontologist Anatoly Konstantinovich Rozhdestvensky named a second species, Saurolophus angustirostris. Numerous skin impressions were found with skeletons of this species, too. The fact that two Saurolophus species had been found with intact skin impressions provided Bell with a unique opportunity to compare the outer anatomy of two closely related dinosaurs.

Both Saurolophus species had pebbly skin. Like other hadrosaurs, the skin of these dinosaurs was primarily composed of non-overlapping scales or tubercles of varying shape. In detail, though, Bell ascertained that the skin of the two species differed enough that one species can be readily distinguished from the other.

Along the base of the tail, the North American species (S. osborni) had mosaic-like clusters of scales, while the species from Mongolia (S. angustirostris) seemed to have vertical bands of specialized scales interspersed with larger, rounded scales Bell terms “feature scales.” This pattern in S. angustirostris remained consistent in young and old individuals—evidence that this was a real pattern peculiar to this species and not just a matter of variation among individuals.

Frustratingly, the skin impressions from the North American species cover less of the body and come from fewer specimens than those from the Dragon’s Tomb. That limits the possible comparisons between the species. Still, based on the consistent differences between the Saurolophus species in the skin at the base of the tail, it appears that paleontologists might be able to use soft-tissue anatomy to identify and diagnose particular dinosaur species. This could be especially useful for the study of hadrosaurs. These dinosaurs are notoriously difficult to tell apart on the basis of their post-cranial skeleton, but Bell’s study hints that skin impressions might show prominent differences. Judging a dinosaur by its cover might not be such a bad idea.

References:

Bell, P. (2012). Standardized Terminology and Potential Taxonomic Utility for Hadrosaurid Skin Impressions: A Case Study for Saurolophus from Canada and Mongolia PLoS ONE, 7 (2) DOI: 10.1371/journal.pone.0031295

A reconstruction of Velociraptor, complete with a scleral ring in the eye, at the Wyoming Dinosaur Center in Thermopolis, WY. Photo by the author.

What’s scarier than a Velociraptor? A Velociraptor at night. That’s the hook I used last spring when a study published in Science used the fossilized bony rings that once supported dinosaur eyes to discern which species might have run around during the day and which stalked the night. (In truth, you wouldn’t have much to fear from Velociraptor at either time—the feathered dinosaur was about the size of a turkey and probably specialized in prey smaller than themselves.) Since the time that study was published, however, other researchers have raised questions about whether or not we can really use remnants of dinosaur eyes to study their behavior.

The idea behind the 2011 Science study by paleontologists Lars Schmitz and Ryosuke Motani was relatively simple. In dinosaurs, as in many other vertebrates except mammals and crocodylians, a ring of small bones helped support the pupil and iris of the eye. The structure is technically known as a scleral ring and acts not only as a proxy for eye size. A wider hole in the middle of the ring would indicate an ability to take in more light, and thus would be consistent with noctural habits, while a relatively smaller window would be more consistent with daytime behavior. Applied to dinosaurs, the study seemed to show that many predators hunted at night while large herbivores were most active during the mornings and evenings.

In a comment published in December last year, however, researchers Margaret Hall, Christopher Kirk, Jason Kamilar and Matthew Carrano pointed out that this correspondence may not be so simple. In addition to questioning the statistical analysis used by Schmitz and Motani, Hall and co-authors noted that there is a considerable degree of overlap in scleral ring anatomy between animals active at night and those active during the day. Among birds and lizards, for example, the scleral rings of some day-dwelling species are very much like those of nocturnal ones. The anatomy of the scleral rings may not be a clear-cut predictor of behavior.

That isn’t to say that the scleral rings can’t tell us some important things about the eyes of extinct animals. Hall and collaborators remarked that the inner diameter of the scleral ring corresponds to the diameter of the cornea—an essential measurement for figuring out how much light can enter the eye. The problem is that another measurement—axial length, or the distance from the front to the back of the eye—is essential for gauging the vision of dinosaurs, but no known specimen has the preserved soft tissue anatomy required to figure this out. Until other anatomical markers of eye shape and size are found, our inferences about whether dinosaurs were active during the night or day will be weak. “[I]t is not yet possible to reconstruct the activity patterns of most fossil archosaurs with a high degree of confidence,” Hall and colleagues concluded.

Schmitz and Motani issued a rebuttal in the same issue of Science. In defense of their paper, Schmitz and Motani reject the criticisms as based on what they consider to be “unscreened data, untenable assumptions, and inappropriate methods” and affirm that their methodology properly categorized dinosaur behavior on the basis of what is known about modern animals. Regarding anatomical minutiae such as the axial length of the eye, Schmitz and Motani suggest that the outside border of the scleral ring is correlated with axial length and therefore can be used as a proxy to reconstruct an animal’s visual capabilities. Altogether, Schmitz and Motani affirm that “the inference of nocturnality in dinosaurs from scleral ring and orbit morphology is sound.”

A good deal of this disagreement deals with methods of statistical comparison and analysis that, I must admit, are over my head. Still, there remain important questions about the way skeletal anatomy relates to soft tissue anatomy. When dealing with animals that have been extinct for millions and millions of years, can we accurately reconstruct the shape and important features of their eyes? Some skeletal features definitely correspond to soft-tissue structures, but interpreting the capabilities of those reconstructed eyes is a more difficult task and the central point of contention. I have little doubt that there were dinosaurs that were active at night, in the heat of the day, and at dawn and dusk, but the trick lies in accurately figuring out which ones were which.

References:

Schmitz, L., & Motani, R. (2011). Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology Science, 332 (6030), 705-708 DOI: 10.1126/science.1200043

Hall, M., Kirk, E., Kamilar, J., & Carrano, M. (2011). Comment on “Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology” Science, 334 (6063), 1641-1641 DOI: 10.1126/science.1208442

Schmitz, L., & Motani, R. (2011). Response to Comment on “Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology” Science, 334 (6063), 1641-1641 DOI: 10.1126/science.1208489

A restoration of the island hadrosauroid Tethyshadros by Nobu Tamura. Image from Wikipedia.

Everyone knows what a “duck-billed” dinosaur was. This bit of shorthand has been permanently grafted onto the hadrosaurs—the widespread group of herbivorous dinosaurs with elongated skulls and what appear to be duck-like beaks.

The title made perfect sense during the early 20th century when these dinosaurs, such as Edmontosaurus and Parasaurolophus, were thought to be amphibious creatures that dabbled in the water for soft plants and escaped into Cretaceous lakes when predators came near. If the dinosaurs looked like monstrous ducks, then they must have acted like ducks. But that vision of paddling hadrosaurs was discarded decades ago. These dinosaurs were terrestrial animals, and discoveries of well-preserved hadrosaur beaks have indicated that the mouths of these dinosaurs were not so duck-like, after all. One beautifully preserved Edmontosaurus skull on display at the Natural History Museum of Los Angeles shows that the tough beak of this dinosaur ended in squared-off, almost vertical croppers and not a duck-like, spoon-shaped bill. The so-called duck-billed dinosaurs didn’t look like mallards at all. And one of the strangest variations in beak shape was found in a small, island-dwelling hadrosauroid described in 2009.

On the basis of a nearly complete and articulated skeleton, paleontologist Fabio Dalla Vecchia named the dinosaur Tethyshadros insularis. The name is a testament to where the dinosaur lived. During the time of Tethyshadros, around 71 million years ago, an ancient sea called Tethys covered most of southern Europe. This oceanic incursion created chains of islands, and it was on one of these islands—where Italy sits today—that Tethyshadros lived. More than that, the isolation of the dinosaur on the island might have been responsible for the dinosaur’s relatively small size (about 13 feet long) compared to its distant, North American cousins such as Edmontosaurus—it’s an example of a phenomenon called insular dwarfism that has been documented for other prehistoric herbivores, including dinosaurs.

But one of the most peculiar aspects of Tethyshadros was its beak. Instead of a long, low duck bill, the upper beak of this dinosaur was a ridged structure jutting out in a shape roughly reminiscent of a snowplow. And rather than being smooth, the margin of the upper beak was pointed, with the middle point being the largest. This general type of serrated beak has been seen before in iguanodontian dinosaurs—the stock from which hadrosaurs evolved, with Tethyshadros being closer to hadrosaurs than to the iguanodontians—but never before in such an extreme shape. Why Tethyshadros had such a strange beak is a mystery. As paleontologist Darren Naish wrote in his detailed summary of this new dinosaur, “Did [the beak spikes] help Tethyshadros to bite at specific food items? Were they for grooming? For display? The mind boggles.”

References:

Dalla Vecchia, F. (2009). Tethyshadros insularis, a new hadrosauroid dinosaur (Ornithischia) from the Upper Cretaceous of Italy Journal of Vertebrate Paleontology, 29 (4), 1100-1116 DOI: 10.1671/039.029.0428

About 110 million years ago, an ankylosaur settled on the bottom of a Cretaceous sea. This was no place for a dinosaur. No dinosaurs were adapted to a marine lifestyle, and the heavily armored ankylosaurs were probably the least suited to paddling around in the water. Yet, almost a year ago, shovel operator Shawn Funk found an ankylosaur in the marine, Early Cretaceous sediments at a Suncor mine in northern Alberta. How did the dinosaur get there?

Donald Henderson, curator of dinosaurs at the Royal Tyrrell Museum, explained how this dinosaur died, was preserved and was discovered in a recent lecture for the Royal Tyrrell Museum Speaker Series. Almost everything about the discovery was lucky. The dinosaur just happened to settle in a place where sediment quickly covered its body; the carcass was not torn apart by scavengers; the shovel operator who stumbled across the ankylosaur recognized that he found something potentially significant and the discovery of the dinosaur in the mine meant that paleontologists had lots of heavy machinery on hand to help excavate the skeleton.

But the strangest aspect of the find is the ecological context of the dinosaur. This ankylosaur must have lived along the coastline of the great Western Interior Seaway which once split North America into two. But that was many, many miles away from where the skeleton was found. Exactly how the dinosaur died is unknown, but as Henderson notes, the carcass undoubtedly floated upside-down through the sea. The gases from decomposition gave the body enough buoyancy to travel—what paleontologists commonly refer to as a “bloat and float” scenario.

A parent Massospondylus attends to its hatchlings. Art by Julius Csotonyi.

Two years ago, paleontologist Robert Reisz and colleagues revealed that the Early Jurassic dinosaur Massospondylus started off life as an awkward little thing. An exceptional set of eggs recovered from South Africa in 1976 contained the well-preserved skeletons of these baby dinosaurs, and the infants did not look very much like their parents. A roughly 20-foot-long adult Massospondylus had an extended neck and a long, low skull and it walked on two legs. But a baby of the same dinosaur had a short neck, a big head for its body, and it walked on all fours. The change between baby and adult was fantastic, and now, in a new PNAS paper, Reisz and colleagues provide an even more detailed look at how Massospondylus started life.

In 2006, Reisz and collaborators located the site where the Massospondylus eggs had been discovered in South Africa’s Golden Gate Highlands National Park. They found more eggs and baby dinosaurs, but not just that. About 190 million years ago, this place was a nesting ground that multiple Massospondylus used from one season to the next.

The paleontologists have discovered bones, eggshell fragments and ten egg clutches—the largest has 34 eggs—within a six-and-a-half-foot swath of siltstone. These nest sites were not all found in the same level, demonstrating that this particular place was used multiple times by Massospondylus moms. Despite the fact that this place was a nesting ground, however, there does not appear to be any evidence that the parent dinosaurs made special accommodations for the eggs—no clear sign of bowl-shaped depressions or other hints of nest construction were found.

Exactly how much parental care adult Massospondylus offered their babies is unknown. Crocodylians and many birds—the closest living relatives of dinosaurs—often attend their nests from the time the eggs are laid and guard their offspring for at least a short interval after their babies hatch. Massospondylus may have done the same, and small tracks found in siltstone blocks indicate that hatchling dinosaurs remained in the nesting site after emerging from their eggs. The tiny hind- and fore-foot tracks are about twice the size of what would be expected for a newly-hatched Massospondylus, and so it seems that the babies stayed at the site until they doubled in size, at least.

The setting of the nesting site allowed all these intricate details to be preserved. In the time of Massospondylus, the site was a relatively dry habitat near the margin of a prehistoric lake. Relatively gentle flooding events covered up the nest site with fine-grained sediment, and afterwards the area dried out. This was a regular, seasonal cycle, and the bad timing of some expectant dinosaur parents resulted in the good fortune of the paleontologists.

With this new data point, Reisz, Evans, and co-authors looked at the big picture of dinosaur reproduction to see which traits might be widely shared and which might be specializations. It seems that communal nesting sites that were used over and over again was an old, common aspect of dinosaur behavior. And, regarding sauropodomorphs specifically, the Massospondylus site may provide some insight into the evolution of different reproductive behavior among its larger sauropod cousins. Evidence from some sauropod nesting sites has been taken to suggest that exceptionally large long-necked dinosaurs did little more than lay eggs and leave their offspring to fend for themselves. What the Massospondylus site might indicate is that the “lay ‘em and leave ‘em” strategy was not the ancestral state for these dinosaurs, but instead was a reproductive specialization related to increasing body size.

So far, this is the oldest known dinosaur group nesting site. Similar sites created by hadrosaurs and sauropods are about 100 million years younger—a vast expanse of time. Potentially earlier nest site finds have not been well studied. One such Late Triassic site in Argentina has yielded multiple infant and juvenile specimens of the sauropodomorph Mussaurus. I asked David Evans, a paleontologist at the Royal Ontario Museum and one of the co-authors of the new study, about the possibility that the Mussaurus locality is an even older nesting ground. “[E]vidence of any form of extensive nesting site [at the Mussaurus localities] is very scant,” he said, but noted that “given our luck in South Africa, I would not at all be surprised if there are a bunch of nests similar to what we have [found] at the Mussaurus localities too—someone just needs to look and document.”

References:

Pol, D., & Powell, J. (2007). Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia Historical Biology, 19 (1), 125-144 DOI: 10.1080/08912960601140085

Reisz, R., Evans, D., Roberts, E., Sues, H., & Yates, A. (2012). Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1109385109

The reconstructed shoulder and arm of Majungasaurus. From Burch and Carrano, 2012.

A few months ago, I wrote about a big, carnivorous dinosaur with what may have been the wimpiest arms of all time. No, not Tyrannosaurus, but a very distantly related predatory dinosaur from Cretaceous South America called Carnotaurus. Despite this dinosaur’s massive, beefy shoulderblade, the arm of Carnotaurus was little more than a nub that would have barely stuck out from the body. And, according to a recent fossil find from Madagascar, Carnotaurus wasn’t alone in having ridiculously tiny forelimbs.

Carnotaurus belonged to a group of theropods called abelisaurids. Among them were large predators that spread through the southern portion of the Cretaceous world, including Majungasaurus from Madagascar. (This dinosaur got a brief publicity boost thanks to the first episode of the sensationalistic show Jurassic Fight Club.) This was another hefty carnivore with bizarre head ornamentation. As demonstrated in a new Journal of Vertebrate Paleontology paper by researchers Sara Burch and Matthew Carrano, Majungasaurus also had truly vestigial arms.

Tiny arms are a common abelisaurid feature. Majungasaurus was expected to share this feature with other closely related dinosaurs, but a lack of fossil evidence prevented paleontologists from seeing what the forelimb of this animal really looked like. That changed in 2005, when paleontologists discovered a nearly complete and mostly articulated skeleton of Majungasaurus, including elements from the entire forelimb and shoulder girdle. (Among the lot was a furcula, or the equivalent of a wishbone, which is the first time this bone has been found in an abelisaurid.)

When viewed together, the forelimbs of this animal look like an evolutionary joke. A large humerus connects to a broad shoulder girdle, but the lower part of the arm—from the radius and ulna down to the dinosaur’s four fingers—is composed of short, stout bones that altogether make up less than a third of the length of the upper arm bone. And the fingers were short, stubby, and lacked sharp claws.

But what may be even stranger is that the arms of Majungasaurus were probably capable of a relatively wide range of motion. The connection between the humerus and the shoulder girdle was more flexible than in many other theropod dinosaurs, and Burch and Carrano suggest that the wrist of Majungasaurus, too, could probably be extended quite far. Conversely, though, the paleontologists note that the fingers were probably relatively stiff and the dinosaur lacked the ability to move them very much, so perhaps the dinosaur used its hand as a single unit—like a dinosaurian mitten. That’s assuming that Majungasaurus was doing anything with its arms at all. This dinosaur’s arms and hands had become so reduced that it is difficult to imagine what they could have possibly done with them other than impotently flap them around. We may never know for sure.

References:

Burch, S., & Carrano, M. (2012). An articulated pectoral girdle and forelimb of the abelisaurid theropod Majungasaurus crenatissimus from the Late Cretaceous of Madagascar Journal of Vertebrate Paleontology, 32 (1), 1-16 DOI: 10.1080/02724634.2012.622027

A clutch of sauropod eggs at the geothermal nesting site in Argentina. Eggs are outlined by black dashes. From Fiorelli et al., in press.

Imagine a dinosaur as massive as Apatosaurus sitting on a nest. It doesn’t really work, does it? We know without a doubt that these large sauropod dinosaurs laid eggs, but there is no conceivable way that the gargantuan dinosaurs could have sat on their grapefruit-sized eggs without crushing them all. There must have been some other way that the eggs could have been kept safe and warm enough to develop properly. One special site in Argentina suggests that some sauropods had a geological solution to the problem.

Two years ago, paleontologists Lucas Fiorelli and Gerald Grellet-Tinner announced the discovery of a unique nesting site that sauropods returned to multiple times. During a stretch between 134 million and 110 million years ago, expectant mother sauropods came to this site to deposit clutches of up to 35 eggs within a few feet of geysers, vents and other geothermal features. This basin held naturally heated dinosaur nurseries.

A new, in-press paper about the site by Fiorelli, Grellet-Tinner and colleagues Pablo Alasino and Eloisa Argañaraz reports additional details of this site. To date, more than 70 clutches of eggs have been found across an area spanning more than 3,200,00 square feet in a section of rock about four feet thick. Rather than focusing on the habits of the dinosaurs, however, the new study fills out the geological context of the place as a possible explanation for why the dinosaurs came here.

On the basis of geological features and minerals, the authors suggest that the site may have resembled the Norris Geyser Basin of present-day Yellowstone National Park. A series of underground pipes and tubes fed geysers, hot springs and mud pots scattered across an ancient terrain crossed by rivers. The fact that the egg clutches are consistently found near the heat-releasing features is taken by Fiorelli and co-authors as an indication that parent dinosaurs were seeking out these spots to lay their eggs. And this site isn’t the only one. Fiorelli and collaborators also point out that similar sauropod egg sites have been found in South Korea.

Exactly what happened to preserve so many nests is not immediately clear, but the eggs were buried in sediments at least partly produced by the surrounding geothermal features. The eggs were eroded and thinned by the acidic nature of the entombing sediment. Some eggs were destroyed by these and other processes, but others held out and became preserved in place.

Not all sauropod dinosaurs selected such sites for nests. Particular populations near geothermal features may have received a benefit from the natural heat, but how did other populations and species far removed from these hot spots lay and protect their nests? We still have much to learn about how baby sauropods came into the world.

References:

Fiorelli, L., Grellet-Tinner, G., Alasino, P., & Argañaraz, E. (2011). The geology and palaeoecology of the newly discovered Cretaceous neosauropod hydrothermal nesting site in Sanagasta (Los Llanos Formation), La Rioja, northwest Argentina Cretaceous Research DOI: 10.1016/j.cretres.2011.12.002

Another year, another fantastic spate of dinosaur discoveries. Even as 2011 draws to a close, the findings keep rolling in—from the way Deinonychus used its killer cutlery to the first record of sauropod dinosaurs from Antarctica and sexual selection among dinosaurs. There has been such a glut of interesting papers that it would be impossible to mention every bit of dinosauriana from this year, but here is a partial listing of some of the stories that caught my eye.

Dinosaur Growth

Everyone knows that there are lots of unknown dinosaur species left to be discovered. What has become increasingly contentious is the question of how many species can be counted among what has already been collected. This year saw a continuation of the 2010 “Toroceratops” debate with a paper on the enigmatic Nedoceratops by Andrew Farke early in the year, followed by a response to his paper by John Scannella and Jack Horner this month. Likewise, paleontologists suggested that the hadrosaur Anatotitan and the tyrannosaur Raptorex were really just growth stages of other known dinosaurs (the latter being similar to Tarbosaurus, a juvenile of which was also described this year).

Dinosaur senses

How did dinosaurs perceive their world? Two significant papers approached this question—one focused on smell (see the video above), and the other vision. As with studies of dinosaur growth, though, investigations of dinosaur senses can be controversial. Last week’s issue of Science included a comment and reply about the idea that the bony rings preserved in the eyes of some dinosaurs might be used to reconstruct the time of day when the animals were most active.

Archaeopteryx

This year marked the 150th anniversary of the discovery of Archaeopteryx. But 2011 has been full of ups and downs for the Urvogel. Even though an 11th specimen of the feathered dinosaur was announced, a controversial paper proposed that the creature was not an early bird but rather a non-avian dinosaur more distantly related to the first birds. Exactly what Archaeopteryx is and what that interpretation means for our understanding of bird evolution will continue to be debated.

New species

New dinosaurs are named just about every week, but two in particular caught my eye: Brontomerus, a sauropod whose name translates to “thunder thighs,” and Teratophoneus, a short-snouted tyrannosaur. (I just realized that both were found in Utah, though, so perhaps I have a bias for my adoptive state!)

That is just a smattering of findings from 2011. Shout out your favorite 2011 dinosaur discoveries in the comments. And, if you want to see how 2011 compares to previous years, see my lists from 2010 and 2009.

A reconstruction of Patagonykus. The newly-described Bonapartenykus was a close relative of this dinosaur. Image from Wikipedia.

Alvarezsaurs are Cretaceous mysteries. These small dinosaurs, a feathered subgroup of coelurosaurs, had long jaws studded with tiny teeth, and their arms were short, stout appendages that some researchers hypothesize were used to tear into anthills or termite mounds. But no one knows for sure. We understand very little about the biology of these dinosaurs, but even as we puzzle over their natural history, more previously unknown genera are being found. The latest is Bonapartenykus ultimus from the Late Cretaceous of Patagonia, and what makes this dinosaur so special is what was found with its bones.

Paleontologists Federico Agnolin, Jaime Powell, Fernando Novas and Martin Kundrát describe the new dinosaur in an in-press Cretaceous Research paper. The alvarezsaur was not in good shape when the researchers found it. While some of the bones, particularly those of the leg, were close to their original articulation, Bonapartenykus is represented by an incomplete set of partially damaged bones, without a skull. In life, the dinosaur is estimated to have been about eight and a half feet long. (Subtle characteristics of the preserved vertebra, shoulder girdle, and hips are what led Agnolin and co-authors to identify this animal as an alvarezsaur despite the paucity of bones.) But there was also something else. Next to the bones were the battered remnants of at least two dinosaur eggs. Could these be fossil evidence of a Bonapartenykus that was protecting its nest?

Determining who laid those eggs is a difficult task. No evidence of embryos has been found inside the egg, so we can’t entirely be sure of what kind of dinosaur was growing inside. The close association between the fossils is the primary line of evidence that the eggs might be attributable to Bonapartenykus. This is the hypothesis favored by Agnolin and co-authors, but they doubt that the small site represents parental care. There is no evidence of a nest. Instead the scientists suggest that the two eggs may still have been inside the dinosaur when it died—a hypothesis based on the previous discovery of an oviraptorosaur from China with a pair of eggs preserved where the dinosaur’s birth canal would have been. When the alvarezsaur perished, the eggs may have fallen out of the body and been preserved with the bones.

Yet I wonder if there might be alternative explanations. Just because fossils are found together does not necessarily mean that the organisms those fossils represent interacted in life. Making connections between organisms found at the same site requires a detailed understanding of taphonomy—what happened to those organisms from the time of death to discovery. In this case, the bones of  Bonapartenykus are scattered and poorly preserved, and the eggs were also partially broken. Did the animal simply fall apart, as the authors seem to suggest, or were the bones and eggs brought together through rushing water? Perhaps the body of Bonapartenykus was carried by a water flow to the location of the eggs, fell apart after the water receded and then was buried again. This is a bit of armchair speculation on my part, and the hypothesis proposed by Agnolin and co-authors is a reasonable one, but we need a detailed understanding of how this little fossil pocket formed if we are to understand the relationship between the eggs and the bones. The geological and taphonomic details of the fossil site are important for framing hypothesis about what happened so many millions of years ago. We may have to wait for more intricately preserved fossils to be sure. A Bonapartenykus preserved on a nest, or a female dinosaur with eggs preserved within her hips, would do nicely.

References:

Agnolin, F., Powell, J., Novas, F., & Kundrát, M. (2011). New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs Cretaceous Research DOI: 10.1016/j.cretres.2011.11.014

A comparison of Triceratops (left) and Nedoceratops (right). From Scannella and Horner, 2011.

When the “Toroceratops” controversy broke in the summer of last year, I felt sorry for Nedoceratops. Hardly anyone said a word about this unusual horned dinosaur. Fans of Triceratops wept, wailed, and gnashed their teeth at their misapprehension that Museum of the Rockies paleontologists John Scannella and Jack Horner had exterminated the beloved horned dinosaur while paleontologists wondered if this dinosaurian mainstay of the Late Cretaceous could have grown into what had previously been called Torosaurus. But no one shed a tear at the proposition that Nedoceratops, too, might have been just a growth stage of Triceratops.

Known from a solitary skull on display at Smithsonian’s National Museum of Natural History, Nedoceratops has perplexed paleontologists since it was first described more than 100 years ago. The skull was found from the same end-Cretaceous strata that yielded Triceratops and Torosaurus, yet the dinosaur eventually labeled Nedoceratops was different from both. The skull had the general Triceratops-Torosaurus shape, but was distinguished by the lack of a nasal horn, a small opening in the preserved parietal portion of the frill, and two asymmetrical holes in the wing-shaped squamosal bones which made up the border of the frill. (These holes were thought to be old battle scars from some Cretaceous clash, but later studies showed these unusual perforations to be natural parts of the animal’s bone growth.) Scannella and Horner disagreed. Some of the unusual features, such as the apparent absence of a nasal horn, fell within the expected variation of Triceratops, and they interpreted the small hole in the parietal to be an early stage of the larger, rounded openings seen in the elongated frills of Torosaurus. Therefore, Scannella and Horner proposed, the Nedoceratops skull was a dinosaur virtually caught in the act of transitioning between the traditional Triceratops and Torosaurus forms, linking all three animals together into a single, late-life growth series.

Andrew Farke, a ceratopsian expert at the Raymond M. Alf Museum of Paleontology, came to a different conclusion when he published a reanalysis of the Nedoceratops skull earlier this year. The mix of features exhibited by Nedoceratops distinguished the dinosaur from both Triceratops and Torosaurus, Farke argued, which would remove the form with transitional features from the growth series. More than that, Farke offered up additional criticisms of the growth series Scannella and Horner proposed—Torosaurus might not be sunk, after all.

Now Scannella and Horner have published a response to Farke’s response. To an outsider, this might look like an echo of the 19th century “Bone Wars,” when the cantankerous naturalists Edward Drinker Cope and Othniel Charles Marsh battled each other in print over the proper identification and interpretation of dinosaurian remains. The headline for LiveScience’s report on the new paper states that the “debate rages,” though the argument is probably better cast of a difference of opinion that has generated some friendly competition. Farke and Scannella are close colleagues, and as Farke mentioned in a behind-the-scenes post on his Nedoceratops work, the paleontologists have helped critique and strengthen each other’s arguments prior to publication. The paleontologists are not about to assault each other at the next Society of Vertebrate Paleontology meeting, either.

Despite the collegiality between the parties, however, Scannella and Horner object to Farke’s critique. For one thing, the Montana-based researchers argue, each of the seemingly unique features of Nedoceratops can be found within the variation of Triceratops (which they count as including Torosaurus-type animals). Though Triceratops is classically portrayed as being a “three-horned face,” when I asked about the apparently absent horn of Nedoceratops, Scannella pointed out that “there are many Triceratops specimens which show similar low, subtle nasal ornamentation—not quite to the degree seen in ‘Nedoceratops’ but certainly approaching that state.” Alternatively, the nasal horn of Nedoceratops might have been broken off or lost after death since the horn does not actually fuse to the nasal bones until late in life. At the moment no one knows for sure whether the horn was lost or was simply never there, but Scannella emphasizes that none of these scenarios hinders the idea that Nedoceratops might be better categorized as a Triceratops.

And that’s not all. Some of the features thought to mark the Nedoceratops skull as an old individual that had finished growing are ambiguous, Scannella and Horner say. The rough bone texture and fusion between certain skull bones—thought to be indicators of maturity, and even old age—are variable in Triceratops and don’t necessarily represent the age range of the animal accurately. They uphold their original interpretation of the dinosaur as a Triceratops, and I have to admit that I was amused that Scannella and Horner pointed out that Nedoceratops translates to “insufficient horned face” in their paper. Though this refers to the apparent lack of a nasal horn, there is a certain poetic justice to it in a paper which seeks to sink the name. “I think ‘insufficient horned face’ is a very appropriate name given that the genus likely represents variation within Triceratops,” Scannella said.

Scannella and Horner offer an explanation for the slit-like opening on one side of the specimen’s frill. (The completed Nedoceratops skull on display was partially reconstructed, so we don’t know for sure if there was a matching hole on the other half.) The projected sequence of transformation from Triceratops to a Torosaurus-type form predicts that there would be a stage in which the solid frill of Triceratops would develop depressions or holes that would eventually open to create large, circular fenestrae. Scannella explains the transformation happening like this:

As Triceratops matured, the parietal developed increasingly thin areas which eventually formed the holes previously thought to be characteristic of “Torosaurus.” If you take a typical Triceratops with a thick, solid frill and have it undergo this transformation to “Torosaurus,” there’s going to come a point where the parietal is going to begin to develop openings. These openings will likely start off rather small and continue to grow as resorption continues and the parietal expands. This is what we see in “Nedoceratops“—it’s a fairly mature specimen, the squamosals are slightly elongate (approaching the morphology observed in “Torosaurus“), and the parietal has a small opening in the same place where in Triceratops we see thinning occurring and in “Torosaurus” we see holes. So—one possibility is that this is a distinct genus of dinosaur that has tiny holes in its parietal. Another is that this is simply a Triceratops caught in the act of becoming “Torosaurus.” Jack and I favor the hypothesis that “Nedoceratops” is actually a transitional morphology, between Triceratops and “Torosaurus.”

One of the areas of debate has been the number of triangular, bony ornaments called epiossifications around the border of the Triceratops frill, which is composed of the parietal and squamosal bones. Previous studies have established that these bones start off being prominent, pointed ornaments, but as Triceratops aged these bones flattened out until they were barely visible. The question is whether the number of some of these epiossifications could change during growth, thus bridging the gap between the different number of these ornaments on the parietals of Triceratops and Torosaurus.

While Triceratops typically has five or six of these bones, called epiparietals, Torosaurus have been found with spots for 10 to 12, requiring the number to double if Scannella and Horner are right. This kind of addition has not been seen in well-sampled populations of horned dinosaurs before, but Scannella and Horner propose that such changes were indeed possible. As evidence, they cite a single epiossification marked by two peaks, which they hypothesize is an ornament in the process of splitting into two. Additional specimens will be needed to determine whether this double-peaked adornment truly was splitting during a transformative growth stage or is an unusual and unique variant. While Farke cautions that he hasn’t seen the specimen in question himself, he does offer an alternative interpretation. The double-peak shape “could also just be resorption of the tip without splitting a single element into two,” he says. “This is relatively common in ceratopsids—many of them tend to resorb the tips of the ‘high points’ on the skull, and that may be what is happening here.” If this is the case, then the epiossification would be part of the typical transformation into flatter adornments and not indicative of splitting.

This aspect of debate brings up the question of how useful epiossification counts might be for identifying distinct ceratopsids in the Hell Creek Formation. Individual variation, changes in growth and possibly even variation from one slice of time to the next might complicate matters. “As we are finding more and more Triceratops in the Hell Creek Formation of Montana,” Scannella says, “we are seeing specimens with quite a bit of variation in both the number and position of frill epiossifications–a finding which urges caution before considering epiossification number and position a set in stone indicator of taxonomic identity, at least in taxa closely related to Triceratops.” Farke takes a different view. “[Scannella and Horner are] almost certainly correct that there is stratigraphic variation in epiossification count (presumably related to evolutionary change in a lineage),” he says, but points out that “This would strengthen the argument that epiossification count has phylogenetic significance … [I]f early Torosaurus have one count and late Torosaurus have another count, this would suggest that this trait changes through time and we can use epiossification count to distinguish different species.” Though all this argument over ceratopsid ornaments might seem esoteric, it is a key part of the discussion over what Nedoceratops and Torosaurus truly were. Did some ceratopsid dinosaurs add—and even double— frill ornaments as they matured? The answer to that question will have a major influence on the future of this debate.

What was Nedoceratops? That still depends on who you ask, and there is more than one possible answer. Farke, while noting that “Scannella and Horner raise some valid critiques of my diagnosis of Nedoceratops” in the new paper, still doesn’t see the dinosaur as an intermediate growth stage. “[W]e do still disagree on the taxonomic relevance of things like the parietal fenestrae,” Farke says. “[T]hey cite [the fenestrae] as transitional morphology between the Triceratops-morph and the Torosaurus morph of a single animal’s growth trajectory, whereas I would posit it as the end-member morphology for whatever Nedoceratops is.” And these aren’t the only options. “Of course, Nedoceratops might be an unusual or pathological individual of Triceratops. I’m not particularly married to any hypothesis at this point,” Farke says.

If Nedoceratops is an intermediate growth stage between the classic Triceratops and Torosaurus body types, further sampling of the Hell Creek and Lance Formations should eventually turn up still-growing Triceratops with similar features. Then again, if Nedoceratops is a distinct genus we would expect to eventually find juvenile individuals which share specific features with the single known skull to the exclusion of Triceratops and Torosaurus. Or maybe Nedoceratops is just a weirdo Triceratops.

This isn’t just a bit of paleontological arcana. The scientific conversation about Triceratops growth emphasizes the difficulties of recognizing prehistoric species and understanding their biology. What were once considered to be different species may just be growth stages or variants of one dinosaur, and these revisions affect our understanding of dinosaur evolution, biology, and ecology. I asked Scannella for his thoughts on the implications for his hypotheses, particularly given the fact that many dinosaurs are known from single, and often partial, specimens:

Increasingly, we are learning that many skeletal features in a wide variety of dinosaurs change throughout development.  There is also individual variation to consider. If all the differences between specimens are considered taxonomically informative, then it is easy to see how 16 species of Triceratops were named based on small differences in cranial morphology. Dinosaurs changed as they grew—and so, we need to evaluate which features are the most taxonomically informative. This can be hard to do if there is only one specimen of a particular dinosaur. We can start by examining developmental trends in dinosaurs thought to be closely related to that one specimen – as we’ve done with “Nedoceratops.” Examination of the bone microstructure is also important, in order to get an idea of relative maturity.

Paleontologists have recognized the problems of identifying slightly different specimens as new species before, but the debate over Triceratops—as well as Tyrannosaurus, Pachycephalosaurus, and other Hell Creek dinosaurs—has helped reinvigorate interest in how little dinosaurs grew up. Paleontologists are still in the relatively early phases of this investigation, and there are far more questions than there are definitive answers. The clues that will resolve the question of whether Triceratops was the lone ceratopsid of the Hell Creek still wait in museum collections and the expansive fossil graveyard that is the badlands.

References:

Farke, A. (2011). Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0016196

Scannella, J., & Horner, J. (2010). Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny Journal of Vertebrate Paleontology, 30 (4), 1157-1168 DOI: 10.1080/02724634.2010.483632

Scannella, J., & Horner, J. (2011). ‘Nedoceratops’: An Example of a Transitional Morphology PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028705

Tail vertebrae from a previously known Alamosaurus specimen (A), compared with a newly-discovered Alamosaurus tail vertebra (B) and a tail vertebra from the large titanosaur Futalognkosaurus (C). From Fowler and Sullivan, 2011.

Alamosaurus was an unusual sauropod. What makes it so remarkable is not so much its appearance—the dinosaur seems to be a fairly typical member of a group called titanosaurs—but when and where it lived. Even though North America once hosted multiple, coexisting genera of sauropods during the Late Jurassic, that diversity was eventually lost until, about 100 million years ago, there were none left on the continent. By this time the horned dinosaurs and hadrosaurs were the primary herbivores on the landscape. Then, after a 30 million year absence, sauropods returned to what is now the southwestern United States in the form of Alamosaurus. A new study suggests this dinosaur may have been one of the biggest ever.

Among the various dinosaur superlatives, the title of “biggest dinosaur” is always the most hotly contested. It’s also among the most difficult to assign. Despite their size, many of the contenders for biggest dinosaur, whether they’re going for the all-time title or just in a particular slice of prehistory, are known from only partial remains. Some degree of estimation is often required to envision the whole animal. Then there’s the problem of what characteristics make a dinosaur the largest of its kind—is it just length? Or do weight and height also get figured in? Many of the contenders for largest sauropod ever are estimated to have been about 90 to to 110 feet long, and so far, no dinosaurs have exceedingly outstripped that range. (I am not counting the supposed giant Amphicoelias since the original material was lost long ago and no additional remains have been confirmed.) This range may represent some kind of upper limit for sauropod body size due to constraints of structure or biology.

According to the new paper by paleontologists Denver Fowler from the Museum of the Rockies and Robert Sullivan of the State Museum of Pennsylvania, newly-discovered fossils from the latest Cretaceous of New Mexico may indicate that Alamosaurus reached the top tier of titanosaur size. The material in question consists of two partial vertebrae and a partial femur found at different field sites, and the assignment of these bones to Alamosaurus is based upon the fact that this sauropod is the only one presently known from the Late Cretaceous deposits where the remains were found. (Though it should be noted that the fragmentary nature of this specimen and others from around the same time makes comparisons between dinosaurs and estimates of actual diversity difficult.) The fact that the bones were found at different field sites means that the three bones came from different individuals of different sizes and ages, but comparison of these bones with those of other sauropods can provide a rough idea of how large Alamosaurus grew to be.

The two vertebrae described by Fowler and Sullivan appear to indicate that Alamosaurus could reach roughly the same size as the titanosaurs Futalognkosaurus and Puertasaurus. Both of these dinosaurs from South America are estimated to have been within the roughly 90 to 110 foot size range that many other big sauropods fall into, although the fact that paleontologists have not yet found complete skeletons of either dinosaur means we can’t be really sure just how big they got. This makes estimating the actually upper size range of Alamosaurus problematic. The vertebrae Fowler and Sullivan describe are certainly larger than those previously assigned to Alamosaurus, but accurately estimating the size of the dinosaur requires reliance on previous estimates of other partially known specimens. Alamosaurus appears to have been in the upper sauropod size class—and was probably among the biggest ever to have lived in North America—but additional fossil material from this dinosaur and other giants will be needed to figure out exactly how enormous they became.

There was one other wrinkle to this story that caught my attention. A Montana State University press release about the study stated that a tyrannosaur tooth was found near another Alamosaurus vertebrae that was being excavated by the same team. Whether this is an indication of predation or scavenging by the tyrannosaur remains to be seen—teeth are resilient and easy to transport—but the association is a further confirmation that Alamosaurus shared its habitat with Tyrannosaurus rex. The two dinosaurs have been found in the same deposits before, such as Utah’s North Horn Formation, and the occurrence of the two dinosaurs in New Mexico makes me wonder exactly how a large tyrannosaur would go about hunting an enormous sauropod. Clashes of titanic dinosaurs were not restricted to the Late Jurassic of North America or the Cretaceous of South America. At the close of the Cretaceous, prehistoric New Mexico may have been the setting for confrontations between the largest herbivore and carnivore ever to live in North America.

References:

Fowler, D., & Sullivan, R. (2011). The first giant titanosaurian sauropod from the Upper Cretaceous of North America Acta Palaeontologica Polonica DOI: 10.4202/app.2010.0105

A life restoration of Spinops sternbergorum. Copyright Dmitry Bogdanov, courtesy of Raymond M. Alf Museum of Paleontology

Almost a century ago, skilled fossil collectors Charles H. Sternberg and his son Levi excavated a previously unknown horned dinosaur. Paleontologists didn’t realize the importance of the discovery until now.

The long-lost dinosaur was sitting right underneath paleontologist’s noses for decades. In 1916, while under commission to find exhibit-quality dinosaurs for what is now London’s Natural History Museum, the Sternbergs discovered and exhumed a dinosaur bonebed in the northwestern part of what is now Dinosaur Provincial Park in Canada. Among the haul were several portions of a ceratopsid skull. Some parts, such as the upper and lower jaws, were missing, but portions of the frill and a piece preserving the nasal horn, eye sockets and small brow horns were recovered. Although there was apparently not much to go on, the Sternbergs thought this dinosaur might be a new species closely related to the many-horned Styracosaurus.

Authorities at the London museum were unimpressed with what the Sternbergs sent over. Museum paleontologist Arthur Smith Woodward wrote to the Sternbergs that their shipment from the ceratopsid site was “nothing but rubbish.” As a result, the fossil collection was shelved and left mostly unprepared for 90 years. The museum had no idea there was a new dinosaur collecting dust. It wasn’t until 2004, when Raymond M. Alf Museum of Paleontology scientist Andrew Farke was rummaging through the museum’s collections during a visit, that the long-lost dinosaur was rediscovered.

We hear plenty about the struggles and adventure of digging up dinosaurs in the field. We hear far less about those finds that had been hidden away in museum collections—important specimens of already-known dinosaurs or previously-unknown species. I asked Farke how he rediscovered what the Sternbergs had found so long ago:

I first saw the specimen back in 2004, when I was over in the U.K. filming for “The Truth About Killer Dinosaurs.” I had a few hours to myself, so I arranged for access to the collections at the Natural History Museum. In browsing the shelves, I ran across these partially prepared ceratopsian bones. The thing that really caught my eye was this piece of the frill—the parietal bone. It was upside down and embedded in rock and plaster, but I saw what looked like two spikes sticking out the back of it. My first thought was that it was Styracosaurus, but something just didn’t look right. Could it possibly be a new dinosaur?! I spent a long time trying to convince myself that it was just a funky Styracosaurus, or that I was misinterpreting the bones. When I got back home, I chatted with Michael Ryan about it, and he was very surprised to hear about it too. Apparently it was this legendary specimen—Phil Currie had snapped a photo of it back in the 1980s, and Michael hadn’t been able to relocate it when he visited London himself. One way or another, I was the first person to relocate and recognize the fossil. So, we contacted Paul Barrett (dinosaur curator at the NHM), and Paul was able to arrange to get the specimen fully prepared.

When the dinosaur was fully prepped and studied by Farke, Ryan and Barrett with colleagues Darren Tanke, Dennis Braman, Mark Loewen and Mark Graham, it turned out that the Sternbergs had been on the right track. This Late Cretaceous dinosaur truly was a previously unknown animal closely related to Styracosaurus. The paleontologists named the animal Spinops sternbergorum as a reference to the dinosaur’s spiny-looking face and as a tribute to the Sternbergs.

A reconstruction of the Spinops skull, with grey areas representing the bones known to date. Copyright Lukas Panzarin, courtesy of Raymond M. Alf Museum of Paleontology

Rather than being something wildly different, Spinops looks rather familiar. As Farke put it, this centrosaurine dinosaur “is like the love child of Styracosaurus and Centrosaurus,” the latter being a common horned dinosaur with a deep snout, large nasal horn, small brow horns and distinctive frill ornamentation. Whereas Spinops is like Centrosaurus in having two, forward-curving hooks near the middle of the frill, Farke notes, the two large spikes sticking out of the back of the frill in Spinops are more like the ornaments of Styracosaurus. Given these similarities, it might be tempting to think that the dinosaur just named Spinops was really just an aberrant Centrosaurus or Styracosaurus, but this doesn’t seem likely. “[W]e have two specimens of Spinops that show the same frill anatomy,” Farke says, “so we can be confident that this is a genuine feature and not just a freak example of Styracosaurus or Centrosaurus.”

Nor does Spinops appear to be just a growth stage of a previously known dinosaur. Over the past few years there has been a growing debate among paleontologists about the possibility that some dinosaurs thought to be distinct species were really just older or younger individuals of species that were previously named. (The idea that Torosaurus represents the skeletally mature form of Triceratops is the best-known example.) Horned dinosaurs, especially, have come under scrutiny in this lumping/splitting argument, but Spinops seems to be the real deal. Farke explains, “We have excellent growth series for Styracosaurus and Centrosaurus (the two closest relatives of Spinops), and nothing in their life history looks like Spinops—young or old. There’s no way to “age” Spinops into an old or young individual of another known horned dinosaur.”

This has significant implications for our understanding of how many dinosaurs were running around in the Late Cretaceous of what is now Canada. According to Farke, there are now five known species of centrosaurine dinosaurs within the series of rocks containing the Oldman Formation and Dinosaur Park Formation (spanning about 77.5 million to 75 million years ago). Not all of these dinosaurs lived beside each other at the same time, though, and determining exactly where Spinops fits is difficult because paleontologists have been unable to relocate the Sternberg quarry. Paleontologists are still trying to do so. A combination of fossil pollen from the rock Spinops was preserved in and historical documentation have allowed paleontologists to narrow down the area where Spinops was probably excavated, and Farke says he’s “cautiously optimistic that [the quarry] will be relocated—maybe not tomorrow, but hopefully in the next few decades.”

Pinning down where Spinops came from and exactly when it lived will be important to understanding how horned dinosaurs evolved during the Late Cretaceous. Such geological resolution would allow paleontologists to investigate whether Spinops was close to the ancestral line of Styracosaurus or was a more distant relative, Farke said. Perhaps continued prospecting will even turn up new specimens of Spinops from other locations. “We know the general area and rock level where Spinops came from,” Farke explained. “I think it’s just a matter of time and fossil collecting to find more!” Additional fossils would certainly be welcome, especially because there are plenty of questions about what Spinops means for our understanding of centrosaurine evolution. As Farke and co-authors lay out at the conclusion of the new paper, questions such as “Do the ceratopsians preserved here document anagenesis or cladogenesis [changes within a lineage or between lineages]? How are the taxa of Alberta related to those from elsewhere? Was Spinops a rare element of the Campanian fauna, or will more remains be recognized?” remain to be answered.

For me, at least, the discovery of a new ceratopsid dinosaur is always cause for celebration. Sadly, though, some of the media coverage of this well-ornamented dinosaur has been less than stellar. Gawker led in with “Moron paleontologists find new species of dinosaur in their own museum.” At least when they decide to miss the point, they really commit to that approach. Whatever scientific content there is in the news is overwhelmed by meanspirited snark, although, as some folks pointed out when I expressed my frustration about the piece on Twitter last night, Gawker is meant to be a joke site. Fair enough. In that case, getting your science news from them is about as productive as asking your friend who lives in a symbiotic relationship with the couch and is fueled almost entirely by Mr. Pibb for dating advice.

Juvenile snark is one thing. Trotting out the old “missing link” mistake is another. The Huffington Post fell into that trap when they ran their story “Spinops Sternbergorum: New Dinosaur Species Discovered, Could Be Missing Link.” *Facepalm* First off, there is presently no way to know whether Spinops was ancestral to any other kind of dinosaur. Farke and colleagues were able to determine the relationships of the new dinosaur compared to those already known—that is, they could tell who is more closely related to whom—but dinosaur paleontologists typically draw ancestor-descendant ties only in the case of exceptional and well-constrained evidence. In this case, especially, Farke and co-authors reject the hypothesis that Spinops was an intermediate form between Centrosaurus and Styracosaurus, and the scientists emphasize caution in hypothesizing about the relationships of Spinops to these dinosaurs until more data is found. The “missing link” hook is entirely unwarranted. Furthermore, the phrase “missing link” is closely tied to a linear view of evolution that obscures the deep, branching patterns of change over time, and there’s even a basic semantic issue here. When paleontologists find what the uninformed call a “missing link,” that link is no longer missing!

Media blunders aside, Spinops surely was a funky looking dinosaur, and the centrosaurine’s discovery emphasizes the role collections can play in our growing understanding of dinosaurs. There are far more dinosaur specimens than paleontologists, and there are still plenty of field jackets and specimens that have been left unprepared. Who knows what else is out there, waiting to be rediscovered? There is certainly an air of romance about fieldwork and hunting down dinosaurs, but there are surely fascinating, unknown dinosaurs hiding in plain sight.

References:

Farke, A.A., Ryan, M.J., Barrett, P.M., Tanke, D.H., Braman, D.R., Loewen, M.A., and Graham, M.R (2011). A new centrosaurine from the Late Cretaceous of Alberta,
Canada, and the evolution of parietal ornamentation in horned dinosaurs Acta Palaeontologica Polonica : 10.4202/app.2010.0121

Bones from the foot of a hadrosaur attributed to Edmontosaurus annectens. Modified from Zheng et al., 2011.

Sometimes, hadrosaurs can be a real pain. Even though they are some of the most abundant dinosaurs among Late Cretaceous fossil sites, and are therefore an excellent resource for investigating the biology of dinosaurs, the fact is that there are far more isolated bits and pieces of them than complete skeletons. Properly identifying and cataloging these single bones can be difficult—you need a comprehensive knowledge of dinosaur anatomy to know what a lonely bone once belonged to. Now students Rachel Zheng and Gy-Su Kim from southern California’s Webb Schools and paleontologist Andy Farke have taken a step towards offering their colleagues a way to recognize isolated bones from hadrosaurine dinosaurs.

Zheng, Farke, and Kim have just published a hadrosaur atlas in PalArch’s Journal of Vertebrate Palaeontology. Their aim was to fill in a gap in the literature. Even though lots of hadrosaurs have previously been described, seemingly no one had published a detailed, illustrated guide to the hadrosaur foot. To remedy this, the researchers decided to compose a detailed description of the well-preserved foot of a specimen tentatively attributed to the common Late Cretaceous hadrosaur Edmontosaurus annectens. With this atlas to the hadrosaur foot, they propose, other researchers and collections managers may be better able to properly identify hadrosaur foot bones, especially if those researchers don’t already have a reference collection to make comparisons with.

Frustratingly, the precise identity of the dinosaur used to create the atlas is uncertain. Hadrosaurs are notoriously difficult to identify without their skulls, and the specimen in question was missing one. Nevertheless, a combination of anatomical and geological detail allow Zheng, Farke and Kim to hypothesize that the dinosaur in their atlas is an Edmontosaurus annectens. Along with the foot and other bones, part of the right hip (the ischium) of the dinosaur was found. The distal tip of this hip bone is narrow, and this feature identifies the dinosaur as belonging to the hadrosaurine lineage of hadrosaurs. (The other major hadrosaur lineage—the ornately-crested lambeosaurines—had a flared ischium tip.) Since Edmontosaurus annectens is the only hadrosaurine dinosaur known from the Hell Creek strata where this specimen was uncovered, the identification is the most reasonable one on the basis of the material at hand.

The bulk of the paper consists of labeled color photographs of the hadrosaur’s foot from different angle. This is not the super-sexy kind of research that’s going to end up in Nature or Science. That’s a good thing. Some of the biggest gaps in our understanding about dinosaurs involve relatively simple things. There is a definite need for detailed descriptions and comprehensive atlases that will allow other researchers to easily compare and identify different dinosaurs. I love paleobiology and wondering about the lives of dinosaurs as much as anybody else, but in order to generate hypotheses we need a solid foundation of descriptive analysis. I certainly hope that other researchers take the time to go through their own collections, identify well-preserved specimens, and create similar guides so that various mystery bits scattered through museums can be better identified and cataloged.

References:

Zheng, R.; Farke, A.; Kim, G. (2011). A Photographic Atlas of the Pes from a Hadrosaurine Hadrosaurid Dinosaur PalArch’s Journal of Vertebrate Palaeontology, 8 (7), 1-12

A reconstructed skeleton of Rapetosaurus on display at the Field Museum of Natural History in Chicago. Image by Lisa Andres, from Wikipedia.

Everyone knows the sauropod body plan: thin at one end, much thicker in the middle, and then thin again at the far end. Yet simply calling these dinosaurs “long necks” or focusing on their often enormous size doesn’t do justice to the diversity of forms within this group. Different sauropods had vacuum-shaped heads, whiplash tails, long bony spines jutting out of their necks, tail clubs and, among other things, armor. Regarding this latter feature, some sauropods within the titanosaur subgroup had bones embedded within their skin—called osteoderms—that would seem to have strengthened their hides against attack. According to a new Nature Communications report by paleontologist Kristina Curry Rogers and colleagues, however, an inside look at two such osteoderms yielded new evidence that these bones might have had a different function.

The pair of osteoderms that are the focus of the new study were found in association with two different specimens of Rapetosaurus, a titanosaur estimated to have reached an adult length of about 50 feet. These dinosaurs lived sometime between 70 million and 65 million years ago on what is now the island of Madagascar. One piece of armor was found next to the tail vertebrae of a juvenile individual. As seen in osteoderms of other animals, the bone had a dense outer layer surrounding spongy bone inside.

When the paleontologists used CT-scanning technology to look inside a larger, approximately 22-inch-long osteoderm found near the hips of an adult Rapetosaurus, however, they found something unusual. The inside of the osteoderm was mostly hollow. What’s more, the thickness of the outer layer of bone varied around the internal cavity, and the microscopic bone structure inside the osteoderm showed signs that bone was actually being resorbed by the body.

Maybe the osteoderms in the adult animals were not actually armor at all. A mostly hollow, relatively thin-walled bone is not exactly the sort of structure that is going to protect a sauropod from attack, especially since Curry Rogers and co-authors suggest that sauropods like Rapetosaurus were probably not fully covered in osteoderms, anyway. Instead, the paleontologists take the bone resorption within the larger osteoderm as a clue that these bones might have been mineral reservoirs for when times got tough or when egg-laying dinosaurs required extra calcium to give their a hard shell. While small Rapetosaurus might have had relatively solid osteoderms, adult individuals may have drawn upon the calcium and phosphorous in these bones to meet the demands of growing, reproducing, or living in an arid environment poor in such minerals. These dinosaur decorations may have had little to do with attack or defense.

References:

Curry Rogers, K., D’Emic, M., Rogers, R., Vickaryous, M., & Cagan, A. (2011). Sauropod dinosaur osteoderms from the Late Cretaceous of Madagascar Nature Communications, 2 DOI: 10.1038/ncomms1578

A Microraptor catches a prehistoric bird, based on bird bones found within one Microraptor specimen. Art by Brian Choo and from O'Connor et al., 2011.

In life, Microraptor gui must have been an elegant dinosaur. This small, sickle-clawed dromaeosaurid was covered in plumage, including long feathers along its arms and legs. We know this thanks to the exquisite preservation of multiple Microraptor specimens found in the roughly 120-million-year-old strata of northeastern China. But feathers aren’t the only delicate dinosaur features that remained intact during the process of death, burial and fossilization. In at least one Microraptor specimen, paleontologists have found scraps of the dinosaur’s last meal.

Attendees to the 71st annual Society of Vertebrate Paleontology meeting in Las Vegas, Nevada earlier this month got a preview of the specimen during one of the conference’s poster sessions. Now the full paper describing the fossil, written by Jingmai O’Connor, Zhonghe Zhou and Xing Xu of Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology, has been published in PNAS. There are a few notable details of the feathery dinosaur.

The skeleton of this Microraptor, like others, is arched into the classic dinosaur death pose with the head arched back and the tail angled upwards. Whether the trigger for this posture turns out to be death throes, a result of immersion, or something else, the posture may be a clue to how the dinosaurs died or were rapidly buried. This Microraptor is also of interest because the dinosaur’s skull appears to be more complete and less crushed than some of the other specimens published so far, though the authors note that this specimen is relatively poorly preserved and therefore difficult to study. As for feathers, only a few tufts were preserved along the dinosaur’s head, neck and back. But the focus in the new paper isn’t on the dinosaur’s skeleton or outside appearance. The study is about what was inside the dinosaur’s body cavity when it died. There, hidden beneath the ribs, are parts of the wing and feet of a Cretaceous bird.

Exactly what genus of bird Microraptor consumed is impossible to say at the moment. Even so, anatomical characteristics of the bird feet allowed O’Connor and colleagues to classify the unfortunate avian as an enantiornithine, a form of archaic and now extinct bird. The position of this bird’s remains within the dinosaur is as good an indication as any that the feathered, non-avian dinosaur Microraptor at least sometimes consumed its distant avian cousins. But what happened just before the Microraptor swallowed the bird?

According to O’Connor and co-authors, the position of the bird bones within the Microraptor indicate predation rather than scavenging. The fact that the feet of the bird are closer to the front end of the dinosaur indicate that the prey was swallowed head first. The paleontologists cite this hypothesis as evidence that Microraptor was an arboreal dinosaur. Since the avian prey had anatomical specializations for life in the trees, and Microraptor supposedly caught the bird while the prey was still alive, then Microraptor must have been a skilled climber if not a regular tree-dweller.

Strangely, however, the paleontologists did not explore other scenarios for what might have happened in the moments before the Microraptor consumed the bird. Scavenging is briefly mentioned and dismissed as a possibility, but otherwise the idea that Microraptor scrambled up trees to catch birds is taken as the primary hypothesis. We know the facts—that a Microraptor swallowed a bird—but there is more than one pathway to that point.

Let’s assume that Microraptor truly did capture a live bird. But there is no indication whether the prey was caught on the ground or in the trees. In fact, as I sit here writing this, my cat Teddy is sitting in front of the window watching chickadees forage on the ground on my front lawn. Anatomically, the birds in my yard are specialized for life in the trees, but they do spend a considerable amount of time on the ground, and birds are often caught by cats and other terrestrial predators when the birds come down from their perches. Perhaps early birds also foraged on the ground, and when doing so they would have been vulnerable to attack by dinosaurs such as Microraptor.

Furthermore, there is nothing that tells us whether the bird was alive or dead when the dinosaur consumed it. Perhaps the bird died, fell to the ground, and the Microraptor was the recipient of a relatively fresh, free meal. All we know is that the bird was probably intact when the dinosaur ate it, but we can’t tell whether the bird was alive or recently deceased at the time.

We don’t know exactly what happened to the little bird, and therefore the association between the dinosaur and its prey can’t be cited as supporting either a ground- or tree-dwelling lifestyle for Microraptor. Nevertheless, the discovery that Microraptor ate birds adds one more piece to our understanding of this peculiar dinosaur, and I, for one, am a little tickled by the description of an avian dinosaur within a feathered non-avian dinosaur just prior to Thanksgiving. Turducken, anyone?

References:

O’Connor, J., Zhou, Z., & Xu, X. (2011). Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1117727108