Thursday, March 5, 2015

Triassic Thursday I: An Introduction, and Coelophysis

Because I’m pleased as punch to be making progress on my microfossil research, I hereby declare that, henceforth, Thursdays shall be Triassic Thursdays!

The Triassic period was one of the most bizarre periods in Earth’s history. The world was recovering from the most catastrophic mass extinction which has ever occurred: at the end of the Permian, over 90% of the planet’s species had gone extinct due mass volcanism which was covering basically all of Russia. A strange cast of characters, most of them synapsid amniotes, disappeared in this cataclysm. But the tragic end of the Paleozoic Era was the glorious dawn of a planet dominated by reptiles: the Mesozoic.

The Triassic was just plain awesome, and the fossils prove it. With the planet essentially a giant blank slate, evolution let loose the reigns of predictability and spun a ridiculous world of diapsids. The beginnings of all modern groups of reptiles can all be found in the mid-late Triassic: lizards, turtles, crocodiles, and dinosaurs all had their roots during this time, as well as other reptiles which have left no living descendants, including sauropterygians (ichthyosaurs and their kin), placodonts (which I have previously written about), and pterosaurs, the first flying vertebrates. Also thrown into the mix are reptiles which still puzzle us with their bizarre anatomy: monkey-lizards and their leaf-mimicking relatives, creatures with necks twice the length of their entire bodies, and dragon-like reptilian otters have all been discovered in Triassic localities, and are still contested over where they belong among other reptiles.

How awesome was the Triassic? This awesome. A couple of pseudosuchians (an aetosaur on left and a rauisuchian on right) square off. You can see a small theropod dinosaur in the background, biding his time before his kind throws the largest biological coup in history. Illustration by Julius Csotonyi.

This is why I am happy to be conducting research on the Triassic. I’ve been a paleo-nerd for my entire life, and anyone with a passion for paleo knows how cool the Triassic is. Not everyone agrees that it is the best (but we won’t judge them for that), but in terms of biological and evolutionary significance, it’s easily in the Top 5.

So, what exactly am I doing? Why, I’m glad you asked! So thoughtful, you.

Over the past year, I have been looking through what appears to be dirt and gravel in search of microfossils. These are 1-2mm size chunks and fragments of bone, teeth, scales, and whatever else happens to be fossilized. And there are lots of them! While a sizable chunk of matrix might only contain a couple dozen vertebrate microfossils, it is a challenge to properly identify them, just because of the condition they’re in. Trust me, when all you have of a small animal is a small chunk of a small bone, it gets tricky. But therein lies the fun!

My ultimate goal is to identify specimens of juvenile archosaurs (that is, dinosaurs and crocodylomorphs, which I have also written about) from the samples I and others have collected, and to identify characteristics of these fossils which can be used to identify other juvenile archosaurs from other places and periods. These samples, which are professionally stored in gallon plastic bags, hail from the Hayden Quarry of the Ghost Ranch locality in Abiquiu, New Mexico, which I had the pleasure of visiting and the honor of working with a group of Triassic paleontologists from around the country. 

It’s a bit ambitious, I’ll give you that. A grant reviewer even called this effort too much for a “questionable gain in knowledge.” But hey, I won’t complain. I’ve always wanted to conduct paleontological research and I’m really enjoying it. Plus, I’ve already found some fossils which may fit the criteria I’m looking for. 

Well, now that you know a bit about why I love the Triassic and why I so enjoy this project, let me introduce this week’s Triassic beastie.

Coelophysis bauri

A Coelophysis family about to chow down on an unfortunate drepanosaur. Illustration by Asparavis, from deviantArt.

Coelophysis is one of the best-known dinosaurs, largely due to the enormous quantity of specimens that have been recovered from the American southwest. Hundreds of individuals are known from several quarries in New Mexico and Arizona, and range in age from juveniles to adults. Such abundance is really awesome for paleontologists, as it is so rare to have even one individual of one species preserve in the fossil record. Coelophysis provides a unique opportunity for studies of ontogeny, or growth, from a young to mature animal. 

Like most dinosaurs of its day, Coelophysis was no heavyweight. Only a couple of meters long, it was dwarfed by an array of crocodile-line predators. However, its descendants were some of the largest predators of the Early Jurassic, soon after the crocodilian competition had gone extinct at the end of the Triassic. It probably hunted insects and small reptiles. In fact, it is one of the dinosaurs known to be preserved with stomach contents. 

Coelophysis stomach contents (in yellow). From Nesbitt et al. 2006.

It was thought for a while that this Coelophysis was a cannibal which had eaten a younger member of its species. However, it was found that the bones preserved in this guy’s torso did not belong to Coelophysis, but an early crocodylomorph. 

Coelophysis was a gracile animal with birdlike bones, a trait which is reflected in its name, which means “hollow form.” It is a classic example of the anatomical advantages that dinosaurs had over most other reptiles of the Triassic: legs held directly below the body, bipedal locomotion which freed up the hands for manipulating prey, and a long tail for anchoring leg muscles. While it wasn’t the first dinosaur, it is a good example of the general role of dinosaurs during a time when they weren’t dominant.

Oh, and Coelophysis was the second dinosaur to go to space. Don’t ask me why. 

Thanks for hanging with me, everyone. I know I haven’t written in a long while, but I do appreciate the views and support you give me. Stick around for more updates!

1 comment:

  1. Many of the trackways here in Massachusetts are by Coelophysis. I have collected a few nice prints from the Mt. Tom area. Good article.