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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

One of the sad dinosaurs at Stewart's Petrified Wood near Petrified Forest National Park in Arizona. Photo by David Williams.

I have a fondness for roadside dinosaurs. Not because they’re accurate. Quite the contrary. Concrete and plastic dinosaurs beside America’s highways are often sad, malformed creatures that are truly terrible. Nevertheless, they are a reminder of the popularity and cultural importance of Mesozoic life, especially along roads that connect fossil-rich exposures where many authentic dinosaurs were found.

My vote for the best worst dinosaurs goes to the monstrosities at Stewart’s Petrified Wood shop near Petrified Forest National Park in Arizona. One sad, roughshod theropod is poised to chomp down on a poor mannequin, and a model in a shock wig rides a dilapidated sauropod surrounded by icicle lights (seen above in a photo by David Williams).

But I know there must be others out there. I want to hear your suggestions for the worst roadside dinosaurs. And if you have a snapshot, share the photos of the poor beasts. You can send your submissions to dinosaursightings@gmail.com. I’ll share the best of the worst later next week.

Ceratosaurus nasicornis at the Smithsonian National Museum of Natural History. Photo by the author.

Eastern Utah’s Cleveland-Lloyd dinosaur quarry is a treasure trove of predatory dinosaurs. In addition to elements from more than 46 individual Allosaurus, this fossil-rich pocket has yielded remains of rarer predators that lived in the region 150 million years ago, including the little-known Marshosaurus and the tyrannosaur Stokesosaurus. The charismatic, well-ornamented predator Ceratosaurus has been uncovered from these deposits, too, but the particular individual found in the Jurassic quarry might belong to a species that was only recently recognized.

Since the late 19th century, the Ceratosaurus genus has been best represented by one species: Ceratosaurus nasicornis. Paleontologist O.C. Marsh included a beautiful reconstruction of this dinosaur in a kangaroo-like pose in his essential 1896 tome The Dinosaurs of North America. In 2000, however, paleontologists James Madsen and Samuel Welles named two additional species in their detailed monograph on the osteology of Ceratosaurus. One, represented by an articulated skeleton found in Colorado’s Fruita Paleontological Area, was named Ceratosaurus magnicornis, and the unusual Cleveland-Lloyd specimen was dubbed Ceratosaurus dentisulcatus.

A reconstruction of Ceratosaurus at the Museum of Ancient Life. Photo by the author.

The Cleveland-Lloyd species was not found all together in a single, articulated skeleton. Work over many years turned up the scattered remains of what Madsen and Welles considered to be a single Ceratosaurus individual. When the isolated parts were viewed together, the paleontologists were struck by the size of the dinosaur. This Ceratosaurus was significantly larger than any found before. (I have seen these fossils myself in the Natural History Museum of Utah collections, and compared to the skeleton on display at the Smithsonian National Museum of Natural History, the Cleveland-Lloyd Ceratosaurus is huge.) What Masen and Welles called Ceratosaurus dentisulcatus also differed in various anatomical aspects such as larger, more recurved teeth and a nasal opening set lower down at the front of the skull. Sadly, the portions of the skull which preserved the dinosaur’s ornaments were not found, so we don’t know how this species might have differed from others in this respect.

It’s difficult to say how large this individual actually was. The Cleveland-Lloyd Ceratosaurus was much larger than the roughly 17.5-foot specimen that formed the basis of previous anatomical descriptions, and informal estimates have placed the larger species at about 28 feet. Yet, given the new interest in dinosaur growth, I have to wonder if Ceratosaurus dentisulcatus really represents a bigger, badder species than Ceratosaurus nasicornis. Ceratosaurus is a relatively rare dinosaur, so much so that we still don’t have a good idea of how individuals varied from one to another, nor do we have a solid understanding of Ceratosaurus growth. Maybe the Cleveland-Lloyd Ceratosaurus is just an older, and therefore larger, individual of Ceratosaurus nasicornis in the same way that the dinosaur often called Saurophaganax might be an older or particularly large variant of Allosaurus. Even though the dinosaurs of the Morrison Formation have been known for a long time and seem familiar, there is much we still don’t know about their biology.

References:

Madsen JH, Welles SP. Ceratosaurus (Dinosauria, Therapoda), a Revised Osteology. Miscellaneous Publication. Utah Geological Survey.

I’ve never been a “Doctor Who” fan, but any show that devotes an episode to dinosaurs is  alright in my book. In the above video, Barry Letts and Terrance Dicks talk about how the clunky, stiff dinosaurs in the 1970s episode “Invasion of the Dinosaurs” came to life (or, as it were, not).