Saturday, July 13, 2013

"Porpoise Turtles" and Repenomamus

Well, this goes right up there with Sharktopus, Dinocroc, and Pizza the Hut.
(Are you catching the movie references?)
Marine reptiles are awesome. One of the "big three," as I like to call them, (the other two being Dinosaurs and Pterosaurs), marine reptiles are any group of reptiles that evolved into an aquatic niche. They include a number of unrelated groups, from giant marine squamates like Mosasaurs, to sauropterygian Plesiosaurs, to living Marine Iguanas. I get the honor of seeing some of the best extinct marine reptile specimens in the world every week, at my local museum where I recently began to volunteer. It has both the world's most complete Mosasaur as well as the only known specimen of a pregnant Plesiosaur on display. It's a nerd's paradise. Hopefully I can take some pictures of the specimens to share with you in the future.

While I would like to discuss those specimens in depth, I'll have to do that at another time. Sea turtles are going to be the topic of today's post. What few realize is that sea turtles are the only marine reptile family known to have survived the K-T extinction into modern day. You're probably all familiar with the extinct giant sea turtles like Archelon and Protostega, which are within a family called the dermochelyoidae, whose sole surviving representative is the Leatherback sea turtle (Dermochelys coriacea). However, recently on PLOS, a new member of the giant sea turtle family was announced, named Ocepechelon bouyai, which has to be one of the most awesome sea turtles I've ever seen.

A big, weird, and freaky skull.
Almost hard to believe it comes from a turtle...
Why is Ocepechelon so awesome? Because it is just plain freaky (but in a good way). When I first saw the artist's rendering above, I almost thought it was a fish-eating crocodilimorph like a Phytosaur (by the position of the nostrils), but after reading it was a turtle I was shocked. Its skull (which is sadly the only part we have from this giant) was more than two-feet long, elongated, and tubular, and a horny beak, while probably present, would've been extremely abbreviated and ineffective in capturing prey. The fact that this giant was found in late Maastrichtian rocks of Morocco makes it even more exciting, as we lack virtually any fossils from Late Cretaceous Africa.

Ocepechelon's living habits are even more amazing. The authors make a compelling case that this guy was a suction feeder, and they drew a huge number of adaptations for such a lifestyle. However, he is unique among tetrapods in apparently being a pipette-feeder, like seahorses and pipefish. While most suction feeders alive today have short, wide jaws to maximize water flowing into their mouth, these fish focus on smaller prey and pick them out of the water selectively. Apparently Ocepechelon fed in a similar way as seahorses and, to a lesser degree, beaked whales, which it shares numerous adaptations with as well. The latter features inspired the nickname I posted above: the Porpoise Turtle.

So, great job to the researchers who discovered and described Ocepechelon! He's now officially my favorite Mesozoic sea turtle, and he's just further evidence that the Mesozoic was teeming with reptile diversity. A lot of recent research into other reptile groups outside of the big three also shows that virtually every reptile during the Mesozoic was doing great. We have fossil squamates, snakes, mesosaurs, crocodilians, and sphenodonts running around during the Mesozoic, doing all sorts of things. Almost makes me feel sad for small mammals, as they were the only Mesozoic group that had virtually no diversification. As with most everything, however, there were a few exceptions.

There are a few really cool mammals that lived during the Mesozoic. Repenomamus, the dinosaur-eating mammal found in Yixian, is one of my favorites, as it has guts. These guys reached huge sizes compared to other mammals, exceeding ten pounds, which is a lot for a mammal back then. Not just that but one specimen was found to have a baby Psittacosaurus in its gut, showing that these guys ate dinosaurs. The four-episode Discovery television series "Dinosaur Revolution" had a few clips that included small mammals, such as the beaver-like Castorocauda and flying squirrel-like Volaticotherium. I understand they were also going to include a section on Repenomamus, but it got cut from the project. Nobody knows why the segment got scrapped, but my guess is because it included the now-dubious taxon Raptorex kriegsteini.

Luckily, I was able to find a storyboard sequence of the scene on YouTube. Enjoy, but be warned...I was ROTFL so much after watching this. :)

Until next time, stay sharp!

Click here for Part 2:
Nathalie Bardet, Nour-Eddine Jalil, France de Lapparent de Broin, Damien Germain, Olivier Lambert & Mbarek Amaghzaz (2013) A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods. PLoS ONE 8(7): e63586. doi:10.1371/journal.pone.0063586

No comments:

Post a Comment