troodont

anonymous asked:

So is Troodon still a thing or did Stenonychosaurus and Latenivenatrix completely replace it?

Troodon “proper” is based on a tooth. The new paper showed that troodonts can’t be distinguished from one another purely based on their teeth, so while Troodon isn’t gone, it’s a dubious taxon ala Monoclonius or Trachodon.

mage-lochlyn  asked:

Ignorant teen here- do you think that there could have been an evolutionary branch, where some raptors began to show more bird like traits while others remained raptors? Like how there are both humans and chimpanzees today, from a common ancestor?

Yep, that’s basically what we think happened!

Here’s the family tree of Eumaniraptora, the group that contains “raptors” and modern-day birds (It might be a little different from this; Deinonychosauria may actually be two distinct groups. But that doesn’t really have much impact on this.).  The earliest eumaniraptorans were animals like Archaeopteryx, the famous “first bird”.

As you can see, it has the raised “sickle claw” on the second toe that has come to be associated with “raptors”. 

Early deinonychosaurs were similar to Microraptor. There are a lot of anatomical differences, including the elongated bone struts in the tail to stiffen it, but it’s very similar to Archaeopteryx.

The earliest “true birds” (Birds is a very loosely defined term. Meg Dickson of @a-dinosaur-a-day gave a rundown of it here) were very similar to Jeholornis. It retains the sickle claw as well.

Then there’s Jinfengopteryx, a troodont (probably). It’s another early deinonychosaur*, but you can see that while it retains the sickle claw, its arms are much shorter.

Later deinonychosaurs continued this. The “sickle claws” enlarged, and they kept fairly short arms.

Later avialans, however, lost their raised sickle claws and instead kept all four toes on the ground.

*Taxonomic rant: We’re not sure where the group that we call “troodontidae” fits in taxonomically. One widely accepted position states that it is a sister taxon to dromaeosauriade, forming the deinonychosauria. However, there’s also evidence suggesting that this group may be closer to modern birds. This causes a little issue on what to call these groups, as troodontidae is defined as (Troodon>Dromaeosaurus)(i.e., all individuals closer to Troodon than to Dromaeosaurus), but Avialae is defined as (Passer>Deinonychus). Thus, if “troodontids” were closer to modern birds than to dromaeosaurs, modern birds would be troodontids and “troodontids” would be avialans. Additionally, Deinonychosauria is defined as (Deinonychus+Troodon)(i.e., the most recent common ancester of those two genera and all of that ancestor’s descendants). This would mean that if “troodonts” were closer to modern birds, modern birds would be deinonychosaurs. Clade definitions are tricky like that. And that’s not even getting into synonymous clade names.

All skeletals by Scott Hartman ( @skeletaldrawing ), taken from his website.