Hairy Museum of Natural History

A new fossil mammaliaform has been described by researchers from the Carnegie Museum of Natural History, Nanjing University, and the Chinese Acadamy of Geological Sciences.
The new species shows several adaptations for a semiaquatic lifestyle, including strong arms, fish-eating teeth, and a flat, paddled tail. This combination of features has inspired its name: Castorocaudia lutrasimilis, a Latin mouthful meaning “Beaver-tailed and similar to otters.”

Although superficially like modern otters and beavers, Castrocaudia was a very distant relative. It belonged to a long-extinct group known as the docodonts, which diverged from the mammal family tree before any of the modern groups of mammals (monotremes, marsupials, and placentals) made their first appearance. Its otter-like teeth and beaver-like tail were the result of convergent evolution, a process whereby distantly related organisms independently evolve similar features in order to adapt to similar environments.

Perhaps the most important feature of Castrocaudia, however, was one that it truly shared with modern mammals. The exquisite preservation of the fossil clearly shows that it was covered in hair. At 164,000,000 years old (Middle Jurassic), Castrocaudia not only sports the oldest known fur coat, but is also the most primitive mammaliaform known from a furred fossil.

The pelt of Castrocaudia consisted of long guard hairs and a dense under-fur that helped keep water away from its skin. This degree of specialization suggests that hair had a long evolutionary history well before any modern (or crown-group) mammals inherited this hallmark feature.

The relatively large size (40+ cm long) and specialized lifestyle of Castrocaudia set it apart from other Jurassic mammals and mammaliaforms, which were more similar in size, appearance, and habits to tiny generalists like modern shrews. Castrocaudia shows that the story of Mesozoic mammal evolution may have many more surprises waiting to be discovered.

Castrocaudia is published in the current issue of Science (link goes to the freely available abstract).

The story is popping up around the web, but most are based on this press release from the Carnegie Museum of Natural History. Don’t miss the images, including a reconstruction and restoration from Mark A. Klinger.

—Matt Celeskey.

File under: Jurassic, Recent Discoveries, Synapsids.

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This Monday night, I’ll be giving a talk on those “Monkey-Lizards of the Triassic” at the New Mexico Friends of Paleontology meeting. NMFOP meets at 7:00pm the third Monday of each month at the New Mexico Museum of Natural History & Science. There is always a paleo-related talk or presentation and the meetings are free and open to the public. I’d encourage any readers in the vicinity of Albuquerque to attend.
I’ve just finished the above diagram showing the five species of Triassic Monkey-Lizard, their relative sizes, and completeness (excepting little “Vallesaurus”, which is known from complete, but undescribed remains). A 550KB PDF of the diagram can be downloaded by clicking on the image.

—Matt Celeskey.

File under: Reptiles, Triassic.

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In which we introduce a new feature of the HMNH: the hairball, a collection of strands found across the web, consolidated and regurgitated for your review:

It’s Darwin Day! When all celebrate the 197th birthday of that esteemed naturalist who took a good long look at life, from the grand to the humble, and developed an elegant theory to explain it all. His insights gave us a new way to interpret the world, and paved the way to a deeper understanding of natural history. Last year, Ray Troll and I worked up an Evolutionist’s Prayer as one way to celebrate the holiday—other events are advertised here.

Speaking of Ray, his Troll Art site has new artwork and photos from a new traveling exhibit from the Miami Museum of Science—Amazon Voyage: Vicious Fishes and Other Riches.

And Darwin Day seems an appropriate time to direct visitors to Darren Naish’s Tetrapod Zoology blog. A thoroughly enjoyable take on the biology, taxonomy, and miscellany of all manner of fossil and living animals.

Finally, the excellent repository of arcane book illustrations BibliOdyssey has two current posts showing little-seen work from one of the first masters of restoring extinct animals—Benjamin Waterhouse Hawkins.

—Matt Celeskey.

File under: Miscellany.

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A lovely little critter from the base of the tyrannosaur family tree has just been described. Guanlong wucaii, “the crowned dragon from the five-coloured rocks,” was discovered in Late Jurassic strata in China’s Junggar Basin. At 160,000,000 years old, it is a good 90 million years older than T. rex and about 40 million years older than the next-oldest tyrannosaurs, Dilong paradoxus from China and Eotyrannus lengi from England.

But perhaps the most unusual feature of this new tyrannosaur is its snout. All tyrannosaurs have some form of decoration on top of their noses, although they typically limit their ornamentation to a tasteful roughened texture or small row of hornlets. Guanlong, on the other hand, flaunted its family’s conventions and sported a spectacular crest, “thin as a tortilla” and riddled with holes. It is, proportionally, the largest cranial ornament known from any non-avian theropod, and it would not have looked out of place on a tapejarid pterosaur.

With a feature like that, how could I not break out the sketchbook?

The spectacularly-crowned Guanlong wucaii

Today’s Nature has the paper, which requires a subscription to read in full, but as always the most important parts are freely available. An online news story is also available for free.

National Geographic has the story, along with a beautiful restoration by Zhongda Zhang.

ScienceBloggers Afarensis and Pharyngula have it covered.

And Carl Zimmer fits Guanlong into the bigger picture over at The Loom.

Thanks to all the folks who alerted me to the story!

—Matt Celeskey.

File under: Dinosaurs, Jurassic, Recent Discoveries.

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When asked to think of a venomous animal, most people will picture spiders or snakes. But a recent paper in Acta Palaeontologica Polonica suggests that venom might be a hallmark of mammals, or at least it may have been early on in their history.

The platypus is one of the few venomous mammals alive today.* Unlike snakes and spiders, it delivers its venom using sharp spurs on the inside of its ankles; kicking at enemies or rivals like a duck-billed cowboy. The platypus’ closest living relatives, several species of spiny, ant-eating echidna, also have these extratarsal spurs, although these are non-venomous.

In their new paper, Jørn H. Hurum, Zhe-Xi Luo, and Zofia Kielan-Jaworowska review what is known of the ankles in several groups of Mesozoic mammals, and find that the ankle-spur has a much wider distribution at the base of the mammal family tree. Monotremes (the platypus and echidnas) had it, but it is also present in mammals that are more closely related to us, like eutriconodonts, multituberculates, and “symmetrodonts.”

Newly described “symmetrodont” Akidolestes is mentioned—the holotype preserves traces of the keratin that covered its spur in life. (See if you can find the spurs in this diagram.)

Plugging these groups into a (very simplified) mammal family tree shows an interesting pattern:

Distribution of ankle-spurs in early mammals. From info in Hurum, Luo, & Kielan-Jaworowska 2006.

Some sort of ankle-spur is present in most groups of early mammals. It is unknown whether any of these Mesozoic mammals armed their spurs with venom, but the paper suggests it is an intriguing possibility. Perhaps our ancestors would have found a little poison useful when fending off attacks from predatory dinosaurs.

The groups that happen to be the most successful today—marsupials and placentals—have lost the ankle-spur. But the fossils suggest that this is the exception, not the rule.

It may be that kicking venom is as fundamentally mammalian as fur or milk.

Hurum, J.H., Luo, Z−X., and Kielan−Jaworowska, Z. 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51 (1): 1–11. PDF

Tip of the toupee to Trevor Dykes for the heads-up on this one. Trevor’s Mesozoic Eucynodonts site is a good place to spend a few days if you’re interested in finding out more about the mammal groups mentioned here.

*Actually, only the males produce venom. So in all fairness to the non-poisonous females, the platypus really is only a half-venomous mammal.

—Matt Celeskey.

File under: Mammals, Mesozoic, Recent Discoveries, Synapsids.

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