Episode 436: How dinosaurs became birds update. Plus dinosaurs of the day Ornithomimus

News:

• An update on how dinosaurs became birds, by looking for the evolution of the front of their wing source
• Sauropod expert Michael Taylor et. al have an excellent paper about the concrete Diplodocus of Vernal, Utah source
• Mattel is relaunching Barney as an animated series in 2024 source
• The Chickenosaurus project—creating a non-avian-looking dinosaur from chicken embryos—is stuck at growing a tail source

Sponsors:

You can dig up real dinosaur bones this summer with Colorado Northwestern Community College! Join them for a two week immersive field paleontology experience digging up dinosaur bones from the Jurassic period in Northwest Colorado. There are two scheduled digs: May 27–June 11 and July 1–July 16. There are also two concurrent immersive lab techniques programs available. Get all the details and register online at cncc.edu/dinodig

The dinosaur of the day: Ornithomimus

• Ornithomimid theropod that lived in the Late Cretaceous in what is now North America (Canada and the U.S.)
• Looked somewhat like an ostrich
• Walked on two feet
• Had a small head
• Had a relatively short torso
• Body covered in feathers, and had a small, toothless beak
• May have been an omnivore
• Had three toes on each foot, long arms, and a long s-curved neck
• Had hollow bones, and was a fast runner
• Had large eyes and a large brain
• Probably had good vision
• Large brain may have helped it move fast
• Had straight hand and foot claws
• Fingers were about the same in length
• Hands looked sloth-like, and Henry Osborn thought they may have used their hands to hook branches when eating
• As for size, there are two species of Ornithomimus and they vary in size
• Gregory Paul estimated in 2010 Ornithomimus edmontonicus was about 12 ft (3.8 m) long and weighed 370 lb (170 kg)
• Ornithomimus velox was about 20% smaller
• Two species: Ornithomimus velox (type species) and Ornithomimus edmontonicus
• Genus name means “bird mimic”
• Genus name refers to its bird-like foot
• Charles Marsh named Ornithomimus velox in 1890, based on a foot and part of a hand found in Colorado, US
• Species name velox means “swift”
• When Marsh first described Ornithomimus, he compared it to ostriches and turkeys
• Fossils first found in 1889 by George Lynman Cannon
• Fossils found near a small white school house with chicken coops around it
• Seventeen species were named Ornithomimus, but most of them have been reassigned to another genera or they’re considered to be dubious
• Marsh, in the same paper he named the type species, named Ornithomimus tenuis and Ornithomimus grandis, based on fragmentary fossils John Bell Hatcher found in Montana (grandis now thought to be tyrannosauroid fossils)
• Marsh also named Ornithomimus sedens in 1892 based on part of foot (now thought to be alvarezsaurid material)
• Lawrence Lambe named Ornithomimus altus in 1902 based on hindlimbs found in Alberta, but this became Struthiomimus in 1916 (talked about Struthiomimus in episode 270)
• Other Ornithomimus species that are no longer valid include O. minutus, O. affinis, O. brevitertius, O. samueli, O. mirandus, O. elegans, O. asiaticus. O. lonzeenis, O. currellii, and O. ingens
• Charles M. Sternberg named the second valid species, Ornithomimus edmontonicus in 1933, based on a nearly complete skeleton found in the Horseshoe Canyon Formation of Alberta, Canada
• For years, it was hard to distinguish Ornithomimus from Struthiomimus
• In 1972, Dale Russell did a study that found the differences between the two, and also found Ornithomimus velox and Ornithomimus edmontonicus to be valid, and then reassigned the other species and created new genera, including Dromiceiomimus (“emu mimic”)
• Struthiomimus had a longer torso and longer arms
• Russell also said it was hard to tell the difference between Ornithomimus velox and Ornithomimus edmontonicus
• Donald Baird and Jack Horner in 1979 thought that two tibiae (leg bones) found in New Jersey by Joseph Leidy in 1865 were Ornithomimus, and they named it Ornithomimus antiquus
• Originally the bones were named Coelosaurus antiquus, but Baird and Horner found the name Coelosaurus was already in use for a dubious animal (named based on one vertebra). That animal was named by an anonymous author in 1854, and we now know the author was Richard Owen
• Baird referred more specimens found in New Jersey and Maryland to Ornithomimus antiquus
• In 1997, Robert Sullivan found Ornithomimus velox and Ornithomimus edmontonicus to be junior synonyms of Ornithomimus antiquus (found velox and edmontonicus to be difficult to tell apart, and they both shared features with antiquus)
• In 2004, David Weishampel found Ornithomimus antiquus (Coelosaurus antiquus) to be a nomen dubium
• Since then there has been more lumping and splitting, including between Ornithomimus and Dromiceiomimus
• In 2015 Leon Claessens and Mark Loewen redescribed Ornithomimus velox
• Fully prepared the holotype (they weren’t fully prepared before), and 3D scanned and did photogrammetry
• “Interestingly, many of Marsh’s published drawings of O. velox illustrate anatomical detail that was not visible until its recent preparation, and several of the details of these obscured parts in his illustrations are misleading and incorrect”
• Holotype is likely skeletally mature
• Found that the Marsh’s referred specimen was also part of the holotype (same individual)
• Ornithomimus velox foot was more robust than Ornithomimus edmontonicus
• Because of its small size, especially compared to other ornithomimosaurs, said “O. velox may represent the first instance of nanism in this group”
• Four Ornithomimus edmontonicus specimens have been found with feathers
• Feather imprints were found in sandstone
• Two of them are adults with traces of feathers on the arms, and one is a juvenile with feather impressions covering the lower back, legs, and neck
• Two of the adults more complex feathers on the arms, which means the feathers changed as Ornithomimus grew up
• Juvenile was covered in filamentous type feathers
• The fourth specimen had feathers along the tail that were crushed and distorted, but looked very similar to the feathers of an ostrich. Also had skin impressions, which showed no scales on the mid-thigh to the feet, and a flap of skin connecting the torso to the upper thigh (also similar to ostriches)
• A 2012 study found Ornithomimus edmontonicus to be covered in feathers at all ages (growth stages)
• Found the patterns on the feathers to be similar to ostriches
• Based on the feather patterns and the bare skin on the legs being similar to ostriches, probably used both for thermoregulation

Fun Fact:

Not all “tyrant” dinosaurs were huge, the family Tyrannidae includes dinosaurs one millionth the size of T. rex.

Thank you Patrons!

Your support means so much to us and keeps us going! If you’re a dinosaur enthusiast, join our growing community on Patreon at patreon.com/iknowdino