There is no dinosaur named Troodon
Alaskan Troodontid - Julio Lacerda @paleoart
A brief sorry for not writing for a while. Had a lot on my mind and also just struggled to get that jump-start on my creativity again. But after having a bit of nerd-out at a friend recently, I have a dinosaur related thing to talk about today.
For anyone knee-deep into dinosaur stuff, they'd know about the popular stereotyping around small meat eating dinosaurs. The likes of "Raptors" are often portrayed as problem solvers; coordinated, and clever. And although most modern birds have more developed brains than extinct non-bird dinosaurs, the exception of Troodon is often brought up.
Troodon - @/the_meep_lord on Twitter
Troodon is a name that dino-nerds will bring up as a notable example of smart dinosaurs. It was one of the dinosaurs most closely related to birds, it had large eyes for its head, and in fact the largest brain to body size ratio of any non-avian dinosaur. But what many dino-nerds might struggle with, is that most palaeontologists believe that the genus Troodon is not valid.
Now when I first heard this information, my reaction was likely the same to yours reader. What do mean the genus isn't valid? Ask anyone what Troodon looks like, we have a very clear picture. How can we have full skeletons of a dinosaur that didn't exist? How come we have a significant clade of dinosaurs named after it (Troodontidae)? It is a dinosaur that even had unfortunate older stereotypes in its design (pictured below: the olive green smooth skinned Troodon that inspired the ugly Dinosauroid speculative biology thing).
llustration of Troodon - De Agostini Library (unable to find artist)
The issue, as I'll try to explain, was an unfortunate game of guesswork and generalisation across the Palaeontological community.
In 1855, a single fossil teeth was found in Montana, USA. This was a particularly jagged tooth, and seemed to belong to some form of carnivorous or at least omnivorous reptile. It was named Troodon formosus meaning "wounding tooth, well formed". This tooth was originally classified as belonging to a lizard, so the genus Troodon was born.
Troodon holotype drawing, 1860
In 1901, it was decided that Troodon's tooth belonged to a dinosaur, within the group Megalosauridae. But as I've discussed previously, Megalosaurus was a wastebasket taxon, and other experts wanted to place Troodon somewhere more definitive. In 1924, Troodon was classified as a relative of dome-headed dinosaurs such as Pachycephalosaurus and Stegoceras. And since Troodon pre-dated many dinosaurs in this group, the family was at the time referred to as Troodontidae.
"Sandy", Pachycephalosaurus specimen at Royal Ontario Museum
Troodon as a Pachycephalosaur lasted until 1945, when Troodon was finally reclassified as carnivorous dinosaur, and the dome-headed dinosaurs were renamed under the title Pachycephalosauridae.
For a long time, the issue with Troodon was that because it's teeth were one of a kind, they did not know how the rest of it's body looked. The first dinosaur to be classified under Troodontidae that wasn't named just for teeth was a dinosaur called Stenonychosaurus (meaning 'narrow claw lizard").
Stenonychosaurus, Nix Illustration @alphynix
The original specimen of Stenonychosaurus did not have teeth, but it's close relative Saurornithoides did. And once both specimens had more complete specimens collected, they were classified under the group Saurornithoididae in the 1980s. But soon, scientists found similarities between the teeth of Saurornithoididae dinosaurs, and that of Troodon. The Principle of Priority states that earlier names for taxon are more valid taxonomically, so Saurornithoididae was considered synonymous with Troodontidae, and all specimens previously referred to as Stenonychosaurus were now called Troodon.
"Troodon" Specimen, Perot Museum, Texas
Most of the facts we now think of as Troodon were originally attributed to Stenonychosaurus, and many other North American Troodontids were considered as possible synonyms of Troodon, but this received some push back.
The idea that most of North America's Troodontids all belonging to one taxa was questioned. So, as had happened to other wastebasket taxon prior, Troodon was reanalysed.
In the late 2000s, a Troodontid called Pectinodon was separated from the Troodon genus and considered its own taxon. In the mid-late 2010s, some material originally classified under Stenonychosaurus, and then Troodon, was given its own genus, Latenivenatrix.
Latenivenatrix sculpture, @bookrat
Was "Troodon" really Troodon?
So the question of "What is a Troodontid?" had a very clear answer now. They were small to medium Theropod dinosaurs with narrow skulls, front facing eyes, larger braincases, and often restored with sickleclaws and feathers, similar to the Dromeosaurs. But the question came back to the Genus Troodon itself. We had sufficient material of many other Troodontids to tell what most of their body looked like, but the "holotype" of Troodon was still just one tooth.
In case you need a refresher on the terminology, a holotype is the first fossil a new species is named for. For another fossil to be named the same species, it needs to be identified as similar enough to the holotype. Holotypes are often fragmentary, it is common practice to fill in the full skeleton with details from similar relatives, but you still need enough details to identify who your relatives are.
The holotype of Troodon was so fragmentary, (again one bone), that it has been referred to as undiagnostic. Terminology lesson again, that means you CANNOT tell what it belongs to.
The fragmentary Holotype of the more recent Troodontid "Talos sampsoni", was almost complete in comparison to Troodon's. Credit: Scott Hartman
The Troodon tooth was *similar* enough to Stenonychosaurus that they were proposed to be close relatives, but there were differences enough for there to be initial scepticism at their synonymy. The original explanation proposed that the Troodon tooth came from an individual who was older, or in a different part of the mouth to teeth found from Stenonychosaurus, but this was never scientifically scrutinised, just proposed. The whole absorbing of Stenonychosaurus into Troodon was based on heresy that had never been scientifically tested.
So in 2017, almost universally, it was decided that Stenonychosaurus be separated from Troodon as its own valid dinosaur. Almost all material that had at that point been assigned to Troodon were reassigned to Stenonychosaurus or Latenivenatrix. And now the genus Troodon had a problem. If all known fossil material came down to a single, very undiagnostic tooth, then what WAS this dinosaur actually like?
Stenonychosaurus - Anuperator (deviantart)
The current take is that there was no dinosaur known as Troodon in the technical sense. The tooth may not even belong to a Troodontid. But since Troodontidae has become an established group with established diagnostic traits, we still get to keep the name, for the group at least.
Troodontidae is still a very popular mainstream group of dinosaurs, but the names Stenonychosaurus, Saurornithoides, and Latenivenatrix are not as well known as Troodon. Many recent paleoart projects, particularly animations have depicted Troodon-like dinosaurs. But for scientific accuracy, they often decide to use the catch-all term "Troodontid", so audiences know what dinosaur we're talking about without being unscientific.
The YouTube Animation series "Dinosauria" features an episode on Arctic North American Dinosaurs. The main character is referred to as an Alaskan Troodon. This dinosaur has been originally proposed as a larger subspecies of Troodon described from larger teeth found in Alaska. As of writing, this Troodontid still does not an official description or scientific name.
In the 4th episode of the Apple TV+ series, Prehistoric Planet, we again see a dinosaur probably based on the Alaskan Troodon, this time just referred to as a "Troodontid".
In both pieces of media, the Troodontids engage in intelligent problem solving, but nothing on the level of what Jurassic Park would engage in. In Dinosauria, the Troodontid uses vocal mimicry. In Prehistoric Planet, it uses burning sticks to spread a wildfire. Both behaviours that different modern birds engage in, but may have been a stretch for what non-avian dinosaurs were capable of.
If you are still a bit confused as to what this all meant, that's OK, it took me a while to get me head around it too. I encourage readers to do their own research and come to their own conclusion as to what this all means.
If you did feel my explanations helped you learn something new today, please reblog and spread the word. Of course add on your own commentary to the reblogs if you have insight that would better clarify the topic.
Thankyou for reading, and I'll hopefully have something else to post on here soon.
