I Know Dino Podcast Show Notes: Ornitholestes (Episode 80)

Episode 80 is all about Ornitholestes, a carnivorous theropod with a small head.

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In this episode, we discuss:

First theropod discovered in the 1900s
Holotype expedited by Peter Kaisen, Paul Miller, and Frederic Brewster Loomis
Known from one partial skeleton with a crushed skull (found at the Bone Cabin Quarry in Wyoming, near Medicine Bow, in 1900)

Partial skeleton includes parts of the vertebral column, forelimbs, pelvis, and hindlimbs
Later, there was an incomplete hand thought to be Ornitholestes, but is considered Tanycolagreus
Tanycolagreus was found only a few hundred yards from Ornitholestes (that’s why the hand was assigned to it, at first)

Type species (only species) is Ornitholestes hermanni
Named after the American Museum of Natural History preparator Adam Hermann (directed the restoration and mounting of the skeleton)
Theodore Gill suggested the genus name

Charles Gilmore said Ornitholestes was identical to Coelurus (1920), and in 1934 Oliver Perry Hay said there was only a difference at the species level, and renamed Ornitholestes, Coelurus hermanni; in 1980 John Ostrom revived the genus Ornitholestes
Bipedal carnivore
Had a head proportionally smaller than most other carnivorous dinosaurs

Had a short snout and robust lower jaw
Had conical front teeth, back teeth were recurved and serrated (Henry Osborn said there were four teeth in the premaxilla, Gregory S. Paul in 1988 said the skull had only three remaining premaxillary teeth)
Had large eye sockets, that were more than 25% of the skull’s length

Big eyes may have been used to hunt at night
Small skull means it would have been difficult to catch prey with its mouth (probably used arms)
Had strong arms

Could tuck hands close to body, similar to the way a bird holds its wing
In 2006 Phil Senter did a biomechanical study using Ornitholestes casts (the right forelimb) to figure out its range of motion (found it could swing in a 95 degree range, and could bend its elbow at a 53 degree angle, which is more acute than Maniraptoriformes (can bend forearms to 90 degrees), but absent in primitive theropods like Coelophysis and Allosaurus
Forearm could not form a straight angle, so the forearm was permanently rotated upward

May have used its forearms to grasp prey (with both hands)
Osborn described Ornitholestes as having “rapid grasping power” of hands, “balancing power” of tail, and large, conical front teeth (he saw as adaptation to prey on contemporary birds); then in 1917 Osborn suggested Ornitholestes was an early transition from carnivore to herbivore, but Charles Knight drew Ornitholestes chasing Archaeopteryx (and other illustrations like this have continued to appear)
Ornitholestes came from western U.S., Archaeopteryx known from central Europe

May have eaten birds, fish, small vertebrates, mammals, lizards, frogs, salamanders, hatchling dinosaurs, or gone after other small theropods (if it hunted in packs, may have been able to prey on juvenile Camptosaurus)
Probably ate about 1.5 lb or 700 grams of food a day
May have been prey for larger theropods (Ceratosaurus and Allosaurus)

Had a short, S-shaped neck and a long, whiplike tail (over half the length of its body)
Had long forelimbs, about 2/3 the length of its hind legs
Had fairly short hind legs; Osborn calculated that the shin bone was only 70% as long as the thigh bone (shin bone was missing)

Thought to be a fast runner, but lower leg bones thought to be shorter than the femur (so probably didn’t chase after other small dinosaurs)
In 1969 John Ostrom said that the innermost toe (digit II) was larger than digits III and IV, and that digit II may have had a modified sickle claw, like Deinonychus (but digit II is in poor condition so it’s hard to know for sure)
Depicted as having a small crest on its snout (thought to be for display), but now thought there was no crest

Has a broken bone near the nostril that seems to bulge upward, which made Gregory S. Paul think it had a nasal horn “rather like a chicken’s comb in looks” according to his Predatory Dinosaurs of the World in 1988; but in 2003 Oliver W.M. Rauhut and in 2005 Kenneth Carpenter said it didn’t have a nasal horn but that the bulge was from the skull being crushed after the dinosaur died
Percy Lowe said in 1944 Ornitholestes may have had feathers
Because of Sinosauropteryx (primitive coelurosaur found in 1996) had furlike feathers, most paleontologists think all coelurosaurs probably had some type of insulating feathers; John Foster in 2007 said Ornitholestes probably had more primitive feathers than birds, used for insulation and possibly brooding eggs, and would have covered most of the body

If Ornitholestes had feathers used for insulation, probably had a fast metabolism and was pretty active
Because of its size, Ornitholestes was considered a coelurosaur, but in 1986 Jacques Gauthier redefined Coelurosauria
Friedrich von Huene named the infraorder Coelurosauria in 1914 (for a while it was a taxon wastebasket for small theropods)

But in 1986 Jacques Gauthier redefined Coelurosauria
In 1988 Gregory Paul said Ornitholestes had a similar skull to Proceratosaurus (Middle Jurassic theropod, found in England), and he put the two together in Ornitholestinae, a subfamily of Allosauridae; but Proceratosaurus is a tyrannosaur so this classification is untenable
Now Ornitholestes considered Coelurosauria, as defined by Gauthier (some think it’s the most primitive member of Maniraptora)

Coelurosauria group is thought to be closer to birds than more primitive theropods, such as Allosaurus
Coelurosauria means “hollow tailed lizards”
Clade includes theropods more closely related to birds than carnosaurs

Coelurosaurs have a sacrum (vertebrae that attaches to the hips) longer than in other dinosaurs, a tail that stiffens towards the tip, a bowed lower arm bone, and a tibia longer than the femur
Fun fact: Fossils are the perfect candidates for CT scans. Once a fossil is scanned it’s very simple to make a 3-D model, and then you can 3D print out as many copies as you want! It’s still not quite as good as traditional casting techniques because of 3-D printing resolution limits, but it’s getting better all the time!

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