Episode 417: Thescelosaurus had spikes coming out of its forearms. Plus more news from SVP including why tyrannosaurs had small arms; how raptors were like cheetahs; and potential theropod embryos with palatal teeth, osteoderms, and skin.

News:

• Presentations from the Dinosaur Macroevolution/Macroecology session of SVP 2022 source
• The Soft Tissues and Taphonomy talks from SVP 2022 source

Sponsors:

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The dinosaur of the day: Caenagnathus

• Caenagnathid oviraptorosaur that lived in the Late Cretaceous in what is now Alberta, Canada (Dinosaur Park Formation)
• Large, and may have been about as big as Anzu
• Looked similar to Anzu
• Looked bird like, with feathers and long legs
• Also had a long tail, and s-shaped neck, and probably had a crest on its head
• Thought to be around the same size as Anzu because of the known specimens of Anzu and Caenagnathus, the pubes are about the same size
• Anzu was about 11 ft (3.5 m) long
• Anzu may still have been larger (known specimens may not represent its max body size, and the specimens found may have still been growing)
• Estimated to weigh up to 212 lb (96 kg)
• Had a long, flattened, toothless lower jaw
• Had a shallow jaw, which is different from other oviraptorosaurs that are more like an upturned beak. May mean it ate more plants
• Caenagnathids probably were generalist feeders that ate plants, small animals, and maybe eggs
• Fossils found include lower jaws, tail vertebra, bones from the hand and limbs
• Type species is Caenagnathus collinsi
• Genus name means “recent jaw”
• Species name “in honor of the late Dr. W. H. Collins, for many years director of the Geological Survey of Canada”
• Described by R. M. Sternberg in 1940
• At first thought to be a toothless bird
• Jaws were found in 1936 and it was named Caenagnathus
• Sternberg wrote that “The holotype is an admirably preserved lower jaw, complete except for the ventral border of the right ramus”
• Holotype was found in the summer of 1936, a field party from the National Museum of Canada, under the direction of C.M. Sternberg
• In 1988, a different specimen that had been in storage since 1923 was rediscovered and studied, and it helped link several fragments of an oviraptorosaur into one dinosaur: Chirostenotes (covered in episode 404)
• Lots of debate and subsequent studies finding Chirostenotes and Caenagnathus to be separate
• In 2010, Phil Senter did a phylogenetic analysis of Coelurosauria and found Caenagnathus and Chirostenotes to be separate, “casting doubt on their synonymy”
• More complete caenagnathid specimens found in 2014 and 2015, like the discovery of Anzu, helped show more differences in the fragmentary specimens
• In 2015, Funston and others re-examined caenagnathid fossils from Dinosaur Park Formation, and found more Caenagnathus collinsi fossils, including a tail vertebra, femur, and parts of the feet
• Funston and Currie in 2020 described another Chirostenotes specimen with a lower jaw, that supported Chirostenotes and Caenagnathus being separate
• Differences in the feet and toes, between Caenagnathus and Chirostenotes
• In 2020, Gregory Funston re-examined caegnagthid material and redescribed Caegnathus collinsi (some disagreement over the diversity of caenagnathids)
• One of the specimens was at least 12 years old and nearly done growing
• Probably grew quickly at first, then slowed down
• In 1993, Phil Currie and others named “Caenagnathus” sternbergi, based on new specimens found in the Judith River Formation, but in a 2014 analysis it was found to be a sister taxon
• Other dinosaurs that lived around the same time and place include ankylosaurs, ceratopsians, ornithopods, pachycephalosaurs, ornithomimids, oviraptorosaurs, paravians, tyrannosaurs
• Other animals that lived around the same time and place include amphibians, crocodylians, lizards, plesiosaurs, pterosaurs, turtles, mammals, fish

Fun Fact:

Sometimes you can find growth marks in ribs to calculate a dinosaur’s age when the legs don’t have growth marks.

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