Episode 448: The Dinosauroid (the human-troodontid hybrid). Troodon was a brooder, a neuroscientist’s take on if dinosaurs could become as smart as humans, and dinosaur extinction arguments

News:

• A neuroscientist’s take on whether dinosaurs could evolve to be as intelligent as humans source
• The debate on what made the dinosaurs go extinct continues, with more arguments in favor of the Chicxulub impact source
• Troodon could change its body temperature and likely brooded its eggs in nests shared with other females of the same species source

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The dinosaur of the day: Stenonychosaurus

• Troodontid theropod that lived in the Late Cretaceous in what is now Alberta, Canada (Dinosaur Park Formation)
• Possibly also found in the Two Medicine Formation
• Looked like other small theropods, with a long tail, probably covered in feathers, an s-curved neck, short arms, long legs, and as a troodontid, had sickle-shaped claws on the second toes of each foot
• Estimated to be about 8.2 ft (2.5 m) long and weigh 77 lb (35 kg)
• Had long, slender legs, so may have been a fast runner
• Tail was flexible at the base, which may have helped it turn while walking or running
• Had large eyes and binocular vision
• Able to grasp and hold objects
• Possibly reached adult size at three to five years old, based on a troodontid found in Two Medicine Formation
• Possibly was an omnivore
• Teeth were different compared to other theropods
• Had jaws similar to an iguana’s (which eats plants), and the teeth had large serrations
• In 1988 Tom Holtz and Daniel Brinkman found that troodontid teeth had larger denticles than other theropods, and that the serration scaling is what made it so confusing on how to classify Troodon when it was first described
• Stenonychosaurus and Troodon have been lumped and split in the past, and Troodon was named from a single tooth, in 1856 (part of why it’s confusing)
• Talked about Troodon in episode 36
• Suggested Troodon would have also eaten eggs and invertebrates (like worms), and others have suggested troodontids ate insects
• Type and only species is Stenonychosaurus inequalis
• Genus name means “narrow claw lizard”
• Named by Charles M. Sternberg in 1932
• Sternberg described a left foot, parts of a hand, and some tail vertebrae
• In 1932, Sternberg wrote: “Observant collectors and students of vertebrate paleontology, who have studied the Belly River and Edmonton faunas fully realize that, in spite of the many fine dinosaurian specimens which have been collected from these beds in recent years, many forms are still imperfectly known. Perhaps the light-limbed theropods are among the least known of these dinosaurs”
• Sternberg found Stenonychosaurus to closely resemble Ornitholestes, but Stenonychosaurus was bigger and had some differences in the tail and feet
• Also wrote: “The structure of both the front and hind feet of Stenonychosaurus seems to suggest that it should be regarded as a direct descendant of Ornitholestes though the difference in the caudal vertebrae might be against this suggestion” (ended with need to find more complete specimens/more fossils to learn more)
• Over the years, Stenonychosaurus has been reassigned and reclassified
• Russell had at one point synonymized Polyodontosaurus and Ornithomimus altus as Stenonychosaurus but said there wasn’t enough evidence to synonymize with Troodon
• Carpenter later synonymized Polyodontosaurus, Stenonychosaurus, Ornithomimus altus, and Troodon formosus as Saurornithoides inequalis
• Currie synonymized Stenonychosaurus and Pectinodon under Troodon formosus
• Phil Currie found that differences in the teeth and jaws of troodontids were based on age and position of the tooth in the jaw, instead of being a feature of different species. He reclassified Stenonychosaurus as Troodon, and reclassified other troodontids as Troodon formosus
• Later, other scientists, including Currie, thought there may be more troodontid species. Ended up splitting out Dinosaur Park Formation fossils that used to be Stenonychosaurus as Troodon inequalis
• In 2011, Lindsay Zanno and others analyzed how troodontids were classified, and found all the specimens assigned to Troodon formosus were probably different species, and since the holotype of Troodon is a tooth, Troodon may be a nomen dubium
• In 2017, Evans and others agreed that the holotype of Troodon was not unique enough and suggested reviving Stenonychosaurus for troodontid fossils found in Dinosaur Park Formation
• In 2017, Aaron van der Reest and Phil Currie found Troodon formosus to no longer be valid
• Studied a troodontid pelvis van der Reest had found in 2014 in Dinosaur Provincial Park, which led him to examining troodontid skull fossils
• Led to him and Phil Currie resurrecting Stenonychosaurus inequalis and naming Latenivenatrix mcmasterae
• They reassigned a lot of the Stenonychosaurus fossils to a new dinosaur, Latenivenatrix
• Covered in episode 144
• Talked about how it seemed unlikely for all those fossils to belong to Troodon, because that would mean it spanned 15 million years and has been found in what is now Mexico all the way up to Alaska
• A 2021 study by Thomas Cullen and others found that Latenivenatrix was actually a junior synonym to Stenonychosaurus (the differences in features were due to individual variation)
• In 1969 Dale Russell described a more complete Stenonychosaurus skeleton. This skeleton was the basis for a life-sized sculpture of Stenonychosaurus, and a sculpture of the famous “dinosauroid”
• In 1982, Russell & Séguin did a thought experiment on what Stenonychosaurus would look like if it had continued evolving until today
• In 1982, Russell and Séguin wrote: “Stenonychosaurus was a highly progressive animal for its day”
• Said: “It might also be entertaining to speculate in a qualitative manner on how the descendants of S. inequalis might have appeared had they survived the terminal Mesozoic extinctions” and evolved to have an EQ similar to humans
• Said that over time, the EQ (encephalization quotient), relative brain weight compared to body weight, in dinosaurs increased
• Found that while a Troodontid skull had a low EQ compared to a human, it was a lot higher compared to other dinosaurs
• Had a large brain, especially compared to other dinosaurs
• Suggested that if Stenonychosaurus evolved until today, could have an EQ similar to a human’s
• Thought the large brain would lead to a shorter face, and would eventually be toothless and have a short neck to support the larger brain, and eventually walk like a human, and have a partially opposed finger on each hand (since it could grasp)
• Being upright would also mean no more tail, or a stump of a tail
• This Dinosauroid looked very human like
• Could also argue it looked like a sci-fi alien, with large eyes
• Russell and Séguin argued that humans have the best body shape for our big brains, which is why Stenonychosaurus would potentially evolve to look more human, but also allowed that they may be biased
• Imagined this Dinosauroid would give live birth instead of lay eggs (for the brain power/larger brains and heads) and feed regurgitated food
• Ended the paper with: “The presence of this body form in Homo sapiens demonstrates that the solution exists. It may, however, not be unique. We invite our colleagues to identify alternate solutions”
• Thought experiment has had lots of criticism, for the Dinosauroid being too human-like (some scientists have said it would keep its theropod body, and be more horizontal than vertical, with a long tail)
• Possible that eggs and nests found in Two Medicine Formation in Montana belong to Stenonychosaurus (has been thought to be Orodromeus, then later Troodon, then Van der Reest and Currie said it was possibly Stenonychosaurus)
• Lived on a warm coastal floodplain covered by forests
• Other dinosaurs that lived around the same time and place include Daspletosaurus, Gorgosaurus, Lambeosaurus, Corythosaurus, Prosaurolophus, Styracosaurus, Centrosaurus, Chasmosaurus, Scolosaurus, Euoplocephalus, Edmontonia, Stegoceras, and Foraminacephale

Fun Fact:

Most dinosaurs never got the chance to see a butterfly, but some did!

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