Fossil Friday: Stokesosaurus and Tanycolagreus

Tanycolagreus chases after a tasty looking lizard without any regard for fellow dinosaurs on their morning walk. Stokesosaurus is annoyed by such inconsiderate behavior.
Tanycolagreus rushes past Stokesosaurus without even saying hello. How rude!

Species: Stokesosaurus clevelandi (Stoke-so-sore-us kleev-land-eye)

Tanycolagreus topwilsoni (Ta-nee-koe-la-grr-eh-us top-will-son-eye)

What it means: Stokesosaurus = Stokes’ lizard

Tanycolagreus = Long-limbed hunter

Other Species: None

Where I live: Western U.S.A.- The Morrison Formation

When to find me: The Late Jurassic period, about 152 million years ago.

My favorite food: Meat! We’re carnivores.

My neighborhood: The Morrison Formation covers a huge expanse of land with a variety of different habitats teaming with life. Most of it was very much like the Serengeti of modern day Africa, only with prairies of drought-tolerant ferns and cycad relatives instead of grass. Dense woodlands of tall conifers like the modern araucaria, ginkgoes, and tree ferns would only lie in places of plentiful water such as the few permanent rivers. Other areas had far more sparse and shrubbier vegetation like the open woodlands of acacia trees in the Serengetti.

Life in this environment would’ve adapted to long months of harsh drought, followed by a few months of monsoon that flooded the rivers. Many of the larger herbivores may have migrated like the herds in Africa do today, while most carnivores stayed behind to feast on the dead and dying, or else become opportunistic hunters of less traditional diets for lean times, such as fish or turtles in the rivers.

A few of my neighbors: First let me share the plant-eating giants and smaller friends who sometimes join us for lunch…

  • Long-necked sauropods like Apatosaurus, Brachiosaurus, Camarasaurus, Diplodocus, Barosaurus, Suuwassea, Supersaurus, Haplocanthosaurus, and Dystrophaeus.
  • Armored dinosaurs like Stegosaurus, Hesperosaurus, Mymoorapelta, and Gargoyleosaurus.
  • Two-legged ornithopods like Dryosaurus, Camptosaurus, and Nanosaurus

Fellow predators in the neighborhood include dinosaurs like Allosaurus, Torvosaurus, Ceratosaurus, Saurophaganax, Marshosaurus, Ornitholestes, Coelurus, Elaphrosaurus, and Koparion.

Plus there are all the small snacks scurrying around…countless lizards, crocodile relatives on land and water, mammals, frogs, turtles, fish. Pterosaurs fly in the sky after bugs.

Fun Facts:

  • Stokesosaurus is named after Utah geologist William Lee Stokes, who excavated thousands of Allosaurus bones with his assistant James H. Madsen. When Madsen catalogued these bones in the early 1970s, he discovered that some of the remains were of species new to science. He named it Sokesosaurus. The town of Cleveland, Utah gives the animal its species name.
  • Tanycolagreus is named so because its arms are longer than those of Coelurus, a similar animal from the same formation. It is from the Greek- tany (long/stretched out) + kolon (limb. Not to be confused with colon) + agreus (hunter. The r has a slight roll to it) = long-limbed hunter. The species name honors George Eugene “Top” Wilson, retired, United States Marine Corps.
  • It’s been suggested that Tanycolagreus and Stokesosaurus are synonymous. They are of similar estimated size, come from the same time and place, and all fossils known for Tanycolagreus are indistinguishable from fragmentary remains attributed to Stokesosaurus. Stokesosaurus only has a single hip bone confirmed to be identifiable from that genus, and Tanycolagreus does not have any fossil ilium preserved thus far, so it is impossible to know for sure. It’s a classic case of “we need more fossils.”
  • If more complete remains of Stokesosaurus of Tanycolagreus are discovered and confirm they are the same genus, then the older name of Stokesosaurus will be used.

Fossil Finds:

Stokesosaurus- A single left ilium, or hip bone, from a young individual. Other fragmentary remains have been assigned to Stokesosaurus, but not confirmed.

Tanycolagreus- Fragmentary and/or partial remains of several individuals. These fossils preserved most of the post-cranial bones (anything behind the head), but two preserve some fragmentary remains of the skull. No ilium preserved thus far, which causes controversy concerning Stokesosaurus.


Foster, John. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press, 2007

Carpenter, Kenneth & Miles, C. & Cloward, K.. (2005). New small theropod from the Upper Jurassic Morrison Formation of Wyoming. The Carnivorous Dinosaurs. 23-48.

“Stokesosaurus.” Wikipedia,

“Tanycolagreus.” Wikipedia,

2 thoughts on “Fossil Friday: Stokesosaurus and Tanycolagreus

  1. At first I wondered why both of them were put together, until I read that they could possibly be the same animal. I don’t think that is possible, since I often view Stokesosaurus as a tyrannosauroid and Tanycolagreus as just a coelurosaur. But I never realized that the latter could simply just be a junior synonym of the former. If you had to pick between those two, which would you go for? I would definitely look forward for Stokesosaurus to join, since it was named first.
    And two thing left to mention:
    First my birthday will be in two days (I will be turning 15 years old).
    Second, some new and upcoming CollectA figures have been revealed. I want to know what you think about those three.


    1. When we only have a single fossil from one, and mostly complete fossils from the other (but still missing the one from the first) I find it pretty easy to believe they are the same animal until we find fossils to prove otherwise. The idea that Stokesosaurus is a tyrannosaurid is almost pure conjecture, since we only have a single fossil from a juvenile, and a partial one at that. Obviously the illium is a bone that is easily distinguishable between animals or it would not be a holotype, but to say we know anything about this animal aside from it being a theropod…I think is a little presumptious. As I understand it, part of the idea of it being a basal tyrannosaurid are some limb and hand fragments, which are not confirmed to be from Stokesosaurus at all.

      Of course it would be awesome if they were two different animals, because that means there are more dinosaurs, and who doesn’t want more dinosaurs? 😀 But if they are the same, Stokesosaurus would keep the name, or perhaps they’d merge the two names, as has been done in the past. Then perhaps reassign the holotype to be the holotype of Tanycolagreus, since that is the far more complete specimen. Tanycolagreus is the cooler name, but also the name far more difficult to pronounce, so I won’t be too sad to see it absorbed by Stokesosaurus.

      As for CollectAs new figures, it’s always exciting! It’s cool to see Mamenchisaurus represented, and it’s always good to see a new hadrosaur. It doesn’t look like they gave Kamuysaurus the updated look on its front feet.

      I’m always most excited for what Safari Ltd. and Papo puts out. 😀 Safari Ltd. has hints of a tyrannosaurid and two spinosaurids next year. 🙂

      Happy birthday 🙂


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