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The reconstructed skeleton of "Brontosaurus" from W.D. Matthew's 1915 book Dinosaurs.

Blog long enough, and it will happen eventually—someone else will get to that fascinating topic you had planned to write about before you do. I had intended to write about the rejected idea that sauropod dinosaurs gave live birth—a hypothesis popularized by paleontologist Robert Bakker in his 1986 book The Dinosaur Heresies—but zooblogger par excellence Darren Naish just wrote an in-depth summary of the idea and why it’s wrong.

In Bakker’s view, sauropods must have given birth to live young because the babies would have been too big to have been laid as eggs. The large size of the passageway in sauropod hips seemed in accord with the hypothesis. Without confirmed sauropod eggs, nests, or babies to test the idea, the notion was within the realm of possibility. But, as Darren points out, the subsequent discovery of scores of sauropod eggs and nests have shown that Bakker was wrong. Diplodocus and its allies started off as runts hatched from eggs in nests that also harbored about 10 siblings or so, and they quickly closed the size gap through rapid growth.

Bakker wasn’t the first paleontologist to come up with the idea that sauropods gave birth to live young. Decades earlier, when sauropods were cast as swamp-dwelling sluggards, William Diller Matthew proposed a similar notion for reasons exactly the opposite of Bakker’s. As also covered by Darren, Bakker posited his version of the idea under the theoretical architecture of sauropods as active, “hot-blooded” land dwellers, whereas Matthew saw live birth as a possible adaptation to a life spent wading through water.

Matthew tucked a brief summary of his idea into a footnote to the 1915 guidebook Dinosaurs: With Special Reference to the American Museum Collections. After casting sauropods as “spending their lives entirely in shallow water, partly immersed” and “unable to emerge entirely upon dry land,” Matthew included a note of dissent from the marine reptile expert Samuel Wendell Williston saying “I cannot agree with this view—the animals must have laid their eggs upon land—for the reason that reptile eggs cannot hatch in water.”

But Matthew disagreed. “[W]ith deference to Williston’s high authority,” Matthew replied, “I may note that there is no evidence that the Sauropoda were egg-laying reptiles. They, or some of them, may have been viviparous like the Ichthyosaurus.” What Matthew was referring to here were exquisitely preserved specimens of ichthyosaurs found in Germany preserved with near-term embryos peeking out of their mothers’ bodies. These fossils have sometimes been cast as mother ichthyosaurs that died in the act of childbirth, but it is more likely that the developing babies were pushed out of their mother’s bodies as gases built up during the process of decomposition. Either way, their presence confirmed that at least some ancient aquatic reptiles had independently evolved the ability to give live birth in the water, and with no known sauropod eggs, it was reasonable to suggest that sauropods might have evolved a similar reproductive technique.

Matthew and Bakker were both wrong about sauropod reproduction, but for very different reasons. Their views on sauropods could scarcely have been more different. That is what I find fascinating—how a simple hypothesis could so readily be accommodated into two very distinct theoretical perspectives of dinosaur lives. I wonder what other instances there might be of two paleontologists casting the same idea in very different ways.

The horns of Marsh's Bison alticornis, now recognized as those of a ceratopsian dinosaur. Image from Wikipedia.

Triceratops—the giant with a “three-horned face”—is one of the great ambassadors for dinosaurs. Everyone knows this well-ornamented Cretaceous herbivore today, but the dinosaur was originally mistaken for a very different creature. For a short time, the horns of Triceratops were thought to belong to a giant bison.

Near the close of the 19th century, relatively little was known about the dinosaurs of North America (or, in fact, dinosaurs in general). The word “dinosaur” had been coined by the English anatomist Richard Owen in 1842, and the entire group was only represented by a handful of species known from specimens of varying completeness. The extraordinary fossil-rich formations of the American West had just begun to be examined, meaning each discovery had the potential to significantly change the image of prehistoric life. The early Triceratops fossil was one such discovery.

The story of the fossil—including its changing attribution—was retold by paleontologist Ken Carpenter in a 2007 paper in the book Horns and Beaks. The tale of the specimen began in the rock around Denver, Colorado. This area was peppered with fossils from the last days of the dinosaurs and the earliest days of the post-dinosaur world, and the fossils were so accessible that many were picked up by local collectors and those in want of natural curiosities to display at home.

But the Triceratops fossil had a different fate. In the spring of 1887, a local high school teacher and geologist by the name of George Cannon found two large horns and part of a skull roof. The specimen was sent to Othniel Charles Marsh at Yale University, and after urging his contacts in the field that he wanted more of the skull, a few more fragments of the horns soon followed. Altogether, the fossil consisted of a pair of long horns attached to part of the skull roof, and it had clearly belonged to some prehistoric animal much larger than anything that roamed the West in modern times.

Anatomically speaking, the horns most closely resembled those of herbivorous, horn-bearing mammals like bison. In fact, the horns looked as if they had come from some gigantic predecessor of that iconic Western symbol, and therefore Marsh named this new creature “Bison alticornis” that same year. Those who know the rocks from which the bones came were not so sure. Cannon, who had found other dinosaur fossils in the same rock layers, found it strange that the remains of a giant bison should be found mixed in with those of dinosaurs, and he wrote to Marsh that he would devote every spare second to figuring out why such disparate organisms should be found in the same strata.

Marsh eventually recognized the Denver horns as belonging to a horned dinosaur, but his path to this conclusion was circuitous. For example, in 1888 Marsh named the dinosaur Ceratops on the basis of similar, smaller horns that had been sent to him, but the Yale paleontologist initially thought the horns were spikes akin to those anchored in the tail of Stegosaurus. (Another dinosaur that Marsh changed his mind about multiple times.) Marsh changed his stance again after receiving the partial skull of the dinosaur that he would name Triceratops horridus in 1889 —the long, pointed structures were horns peculiar to this previously unrecognized group of dinosaurs, and further discoveries of horned dinosaurs reinforced this view. (Marsh’s nemesis, Edward Drinker Cope, had studied a number of horned dinosaur specimens during the 1870s, but he was also left puzzled by the horn cores and other incomplete remains from the ceratopsians.) Still, to cover his mistake, Marsh affirmed that the structure of the Denver horns truly was similar to that of a bison. This isn’t so far-fetched. The horn structures of Triceratops and bison are somewhat similar, and paleontologist Tobin Hieronymus and colleagues recently used the horn anatomy of buffalo and musk oxen to reconstruct the facial structures of the horned dinosaur Pachyrhinosaurus.

As Carpenter cautions, though, we should not ridicule Marsh for his mistakes. No one in the late 1880s knew what a ceratopsian really looked like, especially since many of the dinosaurs that Marsh had previously studied were Jurassic creatures that lived many millions of years before. With nothing else for comparison, the Triceratops horns did show some features in common with both bison horns and Stegosaurus spikes, which led Marsh to incorrect conclusions until more complete specimens finally solved the mystery. Marsh’s mistakes are a prime example of how new dinosaurs are sometimes identified—parts of unknown creatures are compared to what is already known in an attempt to narrow down a range of possibilities for identification. Triceratops was so different from other dinosaurs Marsh studied that it is little wonder that he erred in his conclusions. Who could have imagined an animal as magnificent as Triceratops on the basis of the horns alone?

References:

Carpenter, K. 2007. “Bison” alticornis and O.C. Marsh’s early views on ceratopsians. In K. Carpenter ed.,  Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. pp. 349-364. Bloomington: Indiana University Press.

Hieronymus, T., Witmer, L., Tanke, D., & Currie, P. (2009). The Facial Integument of Centrosaurine Ceratopsids: Morphological and Histological Correlates of Novel Skin Structures The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 292 (9), 1370-1396 DOI: 10.1002/ar.20985

The cover of Doug TenNapel's Tommysaurus Rex.

According to Robert Mash, author of How to Keep Dinosaurs, Tyrannosaurus rex is the antithesis of everything a good pet should be. “Literally awful and almost certainly needing a special insurance policy” to keep, the king of the tyrant dinosaurs would be nothing more than a bloody catastrophe waiting to happen. That hasn’t stopped dinosaur fans from imagining what it might be like to keep a pet tyrannosaur, though, and that childhood fantasy was played out in Doug TenNapel’s 2005 graphic novel Tommysaurus Rex.

TenNapel’s story starts out with a sadly familiar tragedy—a young boy named Ely loses his best friend when his dog is struck and killed by a car. In an attempt to take the boy’s mind off the accident, his parents send him to stay on his grandfather’s farm for the summer. Insult is added to emotional injury when a gang of bullies assaults Ely, but he quickly finds a new friend and protector. Locked away in the recesses of a cave is a Tyrannosaurus rex—a friendly dinosaur that just happens to have the same mannerisms as Ely’s lost dog.

Naturally, the Tyrannosaurus immediately shows off why big, carnivorous dinosaurs would not make good pets. The predator gobbles up a cow, plows through fences, gives a few houses some impromptu remodeling, and leaves king-sized piles of dino scat all over the local park. Fortunately for Ely, though, the mayor and other townsfolk allow the dinosaur to stay, as long as the boy provides some better training for the prehistoric beast. Almost everyone seems mollified, save for one spiky-haired bully who has it out for Ely and his dinosaur.

But the story is not really about what it would be like to keep a Tyrannosaurus as a pet. The dinosaur is one big MacGuffin—an object that keeps the story moving along as the main characters develop. The dinosaur is there to teach Ely about loss, responsibility and, ultimately, sacrifice as his relationship with the town bully changes. There are a few cute moments specific to the dinosaur—legendary stop-motion film artist Ray Harryhausen makes a cameo to sketch the tyrannosaur—but the story is about Ely beginning to gain some emotional maturity more than a fantastical tale of a life with a dinosaur.

Drawn in black-and-white, TenNapel’s art is closer to that of Calvin and Hobbes than dinosaur-focused comics like Paleo or The Age of Reptiles. That doesn’t mean that TenNapel traded accuracy for a more distinctive personal style, though. The story’s Tyrannosaurus isn’t a plodding, Godzilla-like monster, but a lithe and agile creature that fits modern restorations of the famous dinosaur. Of course, a few embellishments were needed to make the carnivorous dinosaur a sympathetic character; for instance, the eyes and brow ridges of the dinosaur move to give the gargantuan pet emotional depth.

Tommysaurus Rex is not a detailed exploration of what it would be like to keep a pet Tyrannosaurus. It is not meant to be, and that’s a good thing. If Ely’s tyrannosaur had acted like the genuine article—one of the largest predators ever to walk the earth—the boy’s relationship with the dinosaur would have probably ended very abruptly. A flash of teeth, a crunch, and the book would have been finished. I am glad TenNapel took a different route!

A skeleton of the Late Triassic ichthyosaur Shastasaurus liangae. The head is to the right. From Sander et al., 2011.

Everybody knows that chewing your food carefully is part of good table manners. No one told that to Shastasaurus. This 27-foot marine reptile was probably a suction feeder that slurped up little cephalopods in the Late Triassic seas.

Shastasaurus was not a dinosaur. Instead, this creature was an ichthyosaur, a member of a group of fish-shaped marine reptiles that became beautifully adapted to a life spent entirely at sea. Thanks to new specimens found in the 228- to 216-million-year-old strata of China, paleontologists P. Martin Sander, Xiaohong Chen, Long Cheng and Xiaofeng Wang have discovered that Shastasaurus differed from the rest of its family in a strange way. Whereas most other ichthyosaurs had long snouts filled with small, conical teeth suited to snatching fish and cephalopods, Shastasaurus had a shortened, toothless maw.

Sander and colleagues reported their findings in the journal PLoS One earlier this week. Although several species of Shastasaurus are already known from China, British Columbia and the western United States, the new study is based on fossils previously described under the name Guanlingsaurus liangae. These fossils, it turned out, were actually another species of Shastasaurus, and the specimens illustrate that the skull anatomy of this ichthyosaur was different than previously supposed.

In Richard Hilton’s 2003 book Dinosaurs and Other Mesozoic Reptiles of California, for example, two Shastasuaurus species were reconstructed with the long, toothy snouts typical of other ichthyosaurs. Since the complete snouts of these North American species were unknown, and partial fossils assigned to Shastasaurus from Mexico and Canada seemed to indicate they were long-snouted, the ichthyosaur was given the usual, toothy profile. As Sander and co-authors point out, though, it is now thought that those long-snouted fossils don’t belong to Shastasaurus at all, and the specimens from China indicate that Shastasaurus had a short snout devoid of teeth.

Naturally, this revised skull shape has implications for the way Shastasaurus fed. Modern-day beaked whales appear to be good analogs. Much like Shastasaurus, beaked whales have short skulls which, with the exception of one or two pairs of small teeth in the lower jaw, are functionally toothless. Rather than biting down on food, these whales rapidly retract their tongue, creating a small pocket of suction that draws in small prey. Since Shastasaurus has a generally similar skull anatomy, as well as equivalent sites for muscle attachments that would have allowed them to perform similar lingual maneuvers, Sander and colleagues propose that the ichthyosaur was adapted to be a suction feeder many, many millions of years before whales.

After revising the anatomy and habits of Shastasaurus, Sander and co-authors also suggest that the existence of multiple, suction-feeding ichthyosaur species over the course of millions of years during the Late Triassic indicates some underlying environmental cause. The scientists note that levels of atmospheric oxygen dropped during the time of Shastasaurus. Fish populations, strangled by the reduced oxygen in the seas, may have declined as a result, but cephalopods like squid—which are more tolerant of low-oxygen environments—may have proliferated. Since suction-feeding appears to be an adaptation to consuming small, quick prey, and soft-bodied cephalopods are known to have been an important part of the ichthyosaur diet, the scientists hint that the evolution of Shastasaurus might be attributable to a boom in squid which was itself caused by a decrease in ocean oxygen levels. This hypothesis is not delineated in detail and relies on assumptions about large-scale evolutionary patterns, though, and testing it will require detailed studies of the prehistoric atmosphere, Triassic cephalopods, prehistoric fish and ichthyosaurs.

Regardless of the impetus for the evolution of Shastasaurus, the recognition that this animal was a suction-feeder adds to the diversity of ichthyosaur types known to have existed during the Triassic. There were crushers, cutters and squid-suckers, all filling different ecological roles when the seas were very different. Some whale species occupy some of the same ecological roles today, and in the way they swim and feed, they are fuzzy echoes of a long-lost Triassic past.

References:

Sander, P., Chen, X., Cheng, L., & Wang, X. (2011). Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019480

Are there too many dinosaurs? Paleontologist Jack Horner thinks so, and he explained his reasoning in a short TED talk last month in Vancouver, Canada.

Over the past several years, Horner has been picking over the skeletons of Late Cretaceous dinosaurs from North America in an attempt to figure out whether some of the dinosaurs labeled as distinct species are actually growth stages of a single species. In 2009, for starters, Horner and Mark Goodwin proposed that the dome-headed dinosaurs Dracorex and Stygimoloch were actually immature representatives of the larger Pachycephalosaurus. Last year, Horner and colleague John Scannella made a bigger splash when they published a Journal of Vertebrate Paleontology paper suggesting that the broad-frilled, horned dinosaur Torosaurus was the adult stage of Triceratops (though this hypothesis has been contested). In the video, Horner also suggests that the hadrosaur Edmontosaurus was the subadult stage of the larger Anatotitan.

This kind of revision isn’t new. Many dinosaurs specimens that were once thought to be pygmies or oddly-proportioned adults of new species have turned out to be juveniles, such as the diminutive sauropodomorph Mussasaurus, hadrosaur specimens previously assigned to “Procheneosaurus,” and the ever-contentious Nanotyrannus. What’s different now is that paleontologists have more powerful techniques to investigate and compare specimens from well-sampled areas. Scientists can now look into the bone itself to estimate age, for example, allowing researchers to see if a seemingly small form was truly an adult or still had a bit left to grow.

I wouldn’t say that we have too many dinosaurs, though. Many new species are coming from areas that have not been previously explored or are poorly understood. Given how little we know about the past and how few paleontologists there are,many, many dinosaurs are undoubtedly yet to be discovered. These new species will be subjected to in-depth scientific investigations and in time, paleontologists will gain a deeper understanding of how dinosaurs grew up.

For another take on the same video, check out Love in the Time of Chasmosaurs.