Episode 56 is all about Coelurus, the first named small theropod found in the Morrison Formation.
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In this episode, we discuss:
- The dinosaur of the day: Coelurus
- Name means “hollow tail” (has hollow tail vertebrae)
- Only one valid species; type species C. fragilis (Charles Marsh described in 1879)
- Type species was a partial skeleton (most of the arms and legs, partial pelvis); skeleton now housed in the Peabody Museum of Natural History; found in the Morrison Formation
More bones found in 1980 (in Wyoming and Utah) - First named small theropod from the Morrison formation
Charles Marsh only described the vertebrae from the back and tail, found in the same area as the type specimen of another genus/species he named, Camptonotus dispar, later renamed Camptosaurus, because the name Camptonotus was already used to describe a type of cricket - Marsh described it as an “animal about as large as a wolf, and probably carnivorous”, though he was not sure it was a dinosaur at first. He described it more in 1881 and created some illustrations, and classified it in the new order Coeluria and family Coeluridae
- Lots of confusion and different species named and moved out of the genus
- Coelurus has been grouped with compsognathids, tyrannosaurids, and even as basal maniraptorans. Sometimes it’s considered it’s own family, Coeluridae
- For a while, Coeluridae and Coelurosauria were wastebasket taxons for small theropods
- C. fragilis skeleton was scattered, and fossils found between Sept. 1879 and Sept. 1880. Some of the bones found, Marsh classified as a new species, C. agilis, based on fused pubic bones he believed were part of an animal three times larger than C. fragilis
- In 1888 Marsh named C. gracilis, based on a single claw bone from a small theropod that lived in the Early Cretaceous (found in Maryland); no longer accepted though
Cope also named some species in Coelurus (even with Bone Wars); he named C. bauri and C. longicollis (from Triassic, New Mexico),; but then put them in their own genus, Coelophysis - Henry Fairfield Osborn named Ornitholestes in 1903, based on a partial skeleton. In 1920, Charles Gilmore said Ornitholestes and Coelurus were synonyms, which scientists believed until John Ostrom’s study in 1980
- Ostrom showed the differences between Ornitholestes and Coelurus, and showed that C. fragilis and C. agilis were the same (as Gilmore had thought)
- Dale Russell thought C. agilis was a species of Elaphrosaurus, based on incomplete information, but Ostrom showed that wasn’t true. Also showed that one of the three C. fragilis vertebrae Marsh had illustrated was a composite of two vertebrae
- Also sometimes confused with Tanycolagreus (Coelurus, Ornitholestes and Tanycolagreus were best known small theropods from the Morrison Formation); but Coelurus and Ornitholestes have been better described (Coelurus had longer back and neck, and longer, more slender legs and feet than Ornitholestes)
- In 1995, a partial skeleton in the Morrison Formation was thought to be Coelurus, but a study showed it was a different genus, Tanycolagreus
- Six species have been named to Coelurus. In addition to C. bauri and C. longicollis, there was C. daviesi (Richard Lydekker named in 1888 based on a neck vertebrae from England, but later was named its own genus, Thecocoeulurus
- Also C. gracilis in 1888 (based on limb remains) but Gilmore reviewed the species in 1920 and only found a single claw (proposed it was Chirostenotes), but now considered dubious
- When Ornitholestes was considered synonymous to Coelurus, it’s type species was named C. hermanni
- Coelurus lived in Jurassic
- Small, bipedal, with long legs (fast)
Speed was defense from larger theropods - Around 29-44 lb (13-20 kg)
- About 7.9 ft (2.4 m) long
- Carnivore
- Coelurus ate small prey (insects, mammals, lizards), and was faster than Ornitholestes
- Long neck, potentially slender skull
- Not much known about the skull, except part of the lower jaw (found in same area as known Coelurus bones, and has some similarities, but is very slender, which means it’s not part of the same known Coelurus skeleton
- Long, low vertebrae; neck vertebrae had many hollow spaces (hence its name)
- Morrison Formation was semiarid with flat floodplains.
- Vegetation included conifers, ferns
- Other dinosaurs found include Ceratosaurus, Allosaurus, Apatosaurus, Diplodocus, Stegosaurus
- Coeluridae is a family of small, carnivorous dinosaurs that lived in the Jurassic
- In 2003 O.W.M. Rauhut grouped Coelurus, Compsognathus, Sinosauropteryx, and an unnamed Compsognathus-like dinosaur into Coeluridae
- In 2007 Phil Senter suggested Coelurus and Tanycolagreus were the only coelurids, and were actually tyrannosauroids(was a wastebasket taxon for a while) Dinosaurs that were in the “wastebasket taxon” and since reclassified include Laevisuchus, Microvenator (relative of oviraptorid)
- Coelurosauria includes other theropod groups now, including alvarezsaurs, ornithomimosaurs, therizinosaurs, dromaeosaurs, and tyrannosaurs (though at first only included small theropods); still a lot of questions over how Coelurus genus was related to others
- Fun fact: Out of the 188 confirmed impact craters in the Earth Impact Database, the Chicxulub crater on the Yucutan penninsula is the second largest, and the largest in the last two billion years