Fossil Friday: Coelophysis

Species: Coelophysis kayentakatae (See-loh-fy-sis Kah-yen-tah-kah-tay)

What it means: Hollow form

Other species: Coelophysis bauri (type), Coelophysis rhodesiensis

Where I live: Arizona in the U.S.A.- The Kayenta formation

When to find me: The Early Jurassic period, about 196 million years ago.

My favorite food: Meat! I’m a carnivore.

My neighborhood: The Kayenta formation used to be a tropical floodplain, a bit like African savannah today- but no grass or flowers. Ferns cover the open plains, dotted with islands of spiky cycad groves. Rivers crisscross the land with lush tree ferns, ginkgo trees, and conifers. Every year during the wet season the plains turn into a flooded marsh, but the hottest months bring no rain, and the rivers shrink until the plains are almost as dry as the great desert that lies to the north.

A few of my neighbors: Sarahsaurus (an early sauropod) and Scelidosaurus (armored dinosaur) are some tough neighbors. We don’t talk much. But if I’m lucky, little Scutellosaurus (small armored dinosaur) might join me for lunch. Dilophosaurus is the biggest carnivore around, but Kayentavenator (smaller meat-eater) are happy to share a few leftovers or join me on a quick chase after frogs, turtles, or a crocodile cousin or two. They like to stay close to the rivers. A long-tailed pterosaur patrols the skies for insects like beetles, dragonflies, an ancient cousin of the moth, and something called a snakefly.

Fun Facts:

  • My brother and sister Coelophysis have been running around here since the Triassic period! (technically different species of Coelophysis, but still, same genus)
  • I’m also known by the name Syntarsus, because it can be hard to figure out what bones are supposed to look like when they’re squashed by time, or broken before they’re fossilized. It was later determined that what appeared to make the bones unique from Coelophysis were really just distortion, so the name Syntarsus is no longer used.
  • When I was first discovered, some thought I might be a young Dilophosaurus because I have a double crest like the big guy, but they quickly determined that I was not because just like human children, young dinosaurs have bones that still have soft areas with room to grow. All my bones were ossified, and could not grow anymore.
  • The name Coelophysis comes from the Greek koilos (hollow) and physis (form). Kayentakatae is in honor of Dr. Kathleen Smith, who was often called “Kayenta Kay” for her work in the Kayenta formation, including her involvement in the discovery of the type specimen for C. kayentakatae.

Fossil Finds: Remains of at least three semi-articulated individuals that died in the same time and place, so that the bones are intertwined with each other.


Rowe, (1989). A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona. Journal of Vertebrate Paleontology. 9, 125-136.

Bristowe, A. & Raath, M.A. (2004). “A juvenile coelophysoid skull from the Early Jurassic of Zimbabwe, and the synonymy of Coelophysis and Syntarsus“. Palaeontologia Africana40: 31–41

21 thoughts on “Fossil Friday: Coelophysis

  1. Very interesting. The tropical floodplains must have been an amazing ecosystem back then with many diverse forms of life that never left fossils.


    1. Hi, thank you for stopping by! 😀

      The great thing about floodplains is that they are an ideal habitat for preserving fossils! Not as good as an anoxic lake like the Solnholfen formation in Germany, but still pretty good as far as preservation goes! Every year there is seasonal flooding when the rains come, burying everything in layers of silt and mud. Some of the things buried would be what scattered bones are still left from the dry season, while others might be creatures that drowned in the seasonal marsh, or otherwise where quickly lost and buried in the flooded plain.

      Larger animals may get partially covered in silt, but not covered enough when the dry season came and dried up the marsh, so we only have a fragmentary fossils of certain animals. Scelidosaurus is an example of one of these. The only reason we can guess that Scelidosaurus even lived in the Kayenta formation are the armor scutes found. But that’s pretty much all there is known about it. Most Scelidosaurus fossils are from Europe. Armored dinosaurs have a tendency to flip upside down in water, so perhaps a few were surprised by flashfloods while crossing a river, and only the armor scutes were buried in silt before the dry season came and left the rest of it exposed for scavengers. Or perhaps Scelidosaurus really only came to the floodplains during the dry season, and so the only bones still left when the floodwaters buried everything where the hard scutes. Who knows? It’s fun to guess though. 😀

      The seasonal marsh is great for preserving all the little stuff though, so in the Kayenta formation there are even fossils of tiny aquatic organisms. 🙂

      The tough part is finding the research papers describing the fossils! Everyone wants to publish a paper on dinosaurs, but it’s much harder to find and interpret any research on everything else in the environment. 🙂


  2. Thank you for stopping by Angel, I hope your sister had a good birthday. 🙂

    I’m trying to keep these Friday posts brief, because that is how I can publish every week while still making progress on the books. That said, many of the papers I read in researching Coelophysis k. used the name Syntarsus k., so that’s the name I mentioned. I only read about the insect on Wikipedia, so even though it was a reason not to use Syntarsus for the dinosaur anymore, the papers I came across talked more about “Syntarsus” being synonymous with Coelophysis, and didn’t mention the insect. A few referenced Megapnosaurus in passing, but I mentioned the more commonly used name Syntarsus.

    If anyone ever wants to find out more, Wikipedia is a great place to start for further research. 🙂 The purpose for this site is to be a jumping off point. Perhaps people can find out about creatures they never knew about, and do further research elsewhere if they so wish.

    Coelophysis will not be added to the shop until I get to the Triassic, which may take a while. These Friday posts are just to get a nice overview on particular formations, and are not official characters in the shop (except for the ones that actually are lol ).


    1. I’m glad you agree on one of my points. Also my sister had a good birthday, and her party was yesterday. I can see that you’ve got book progress to make, so I am okay with brief weekly blog posts. Anyway, good job with focusing on the Jurassic side of Coelophysis.


    2. Okay, so apparently as time has passed, Coelophysis has been gotten into some complications. Apparently, the genus Megapnosaurus was revived around this year and now Coelophysis has only one species, C. bauri, though it is still a bit unclear as to the validity between all this.
      And while this is a bit off-topic, I apparently read that Allkaruen, Asfaltovenator, Patagosaurus, Manidens, Volkheimeria, Condorraptor, Piatnitzkysaurus, Eoabelisaurus, and all the other biota of the Canado Asfalto Formation have been moved from the Middle Jurassic to the Early Jurassic. This is news to me, and I have no idea why this was all done. But hey, at least for Bagualia, I’ve always recognized it as from the Early Jurassic.


      1. And not only that, but is it more accurate that Mussaurus was from the Triassic, Jurassic, or both? The ages in which certain prehistoric animals lived at are becoming even more confusing, especially when I first found out that Afrovenator and Jobaria were actually from the Jurassic and not the Cretaceous as it was once believed.


        1. It’s not quite so cut and dry. We only know when and where certain animals lived because we find the fossils. And of course those fossils only show us about that particular individual at that particular place and time. It’s estimated that only about 1 in a million species gets fossilized, and then we need to be lucky enough to find it before the exposed bones are weathered away. We really only have tiny pockets that we find a decent amount of fossils, compared to huge swathes of land and time that we know absolutely nothing about.

          Take Stegosaurus for example. An animal that lived most commonly during the Late Jurassic, because that is when we find most of the fossils, but we would never know if a particular species survived into the Cretaceous unless we find the evidence for it. Platypus, aardvarks, and llamas are perfect examples of the last members of a once numerous group surviving long past the time they are supposed to be extinct. It is highly unlikely that aardvarks or llamas will fossilize due to their environment, so future paleontologists may never know about them, and may suppose that their lineages died out back when their more common ancestors went extinct.

          For animals like Mussaurus, it is more likely that it lived during both the Jurassic and Triassic periods, instead of limiting it to one or the other. Especially when it is difficult to determine the precise age of the rock the fossils were found. The Kayenta formation is another area that was under contention for some time.

          I find it a little hard to believe that there is only one species of Coelophysis. We have so many fossils! Granted, most of those are of one species in one location, but still. The primary reason that many of these animals are getting divided into different genera is because most of these fossils are fragmentary. Rather than having a “wastebasket” taxon, many paleontologists are erring on the side of caution when we don’t have enough material to compare two specimens. A good example of this is Macelognathus and Hallopus. We have bits and pieces of both, but none overlap so they cannot be compared until we find the fossils that can either confirm the separate genera or synonymize them. With computer data able to compare thousands of characters from different fossils, it’s probably easiest to be overly specific on naming a new genus, and then be able to synonymize them later once new fossils are found.

          A similar problem is not having enough fossil material to know what is individual variation, a separate species, or a separate genus altogether.

          I haven’t read the paper, since Coelophysis is generally a Triassic critter, and I won’t be getting there for a while. If a new genera is determined, then that’s great, it just means more dinosaurs to love! New research and technologies are always changing things around, so I’m just happy to learn something new whenever I come across it.


  3. Okay, a few things to mention:
    Base the PPS Coelophysis of off the type species C. bauri once added (probably under the name Cole)Yes, I know Coelophysis was known from the Jurassic, but it’s more famous for being a Triassic dinosaur. Also, Syntarsus was no longer used once it was found out that an insect had already occupied the name. Therefore, Megapnosaurus was used until it was found out to actually be a Coelophysis species. I just want to say to not do specific posts for secondary species. Also, can you please mention the type species in here?
    That was just my opinion on this. Also, two days ago was my sister’s birthday.


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