To kick of this discussion I'm going to write a breath summary of a post I made still in my Deviant Art with the title "Are ornithischians filaments feathers?"
Instead of actually tackling the subject of the post heads on I usually dodged the main point, doing it right now, and I did it there as well in that post, instead of talking if ornithischians filaments were or not feathers I focused on the evolution of Avemetatarsalia.
In there I treated the LCA of both lineages as being a "cold blooded" animal that later evolved "warm bloodedness" somewhere around the base of the ornithodiran node. Starting from this premise I connected the evolution of "warm bloodedness" with the smaller size of basal ornithodirans (compared to aphanosaurians and pseudosuchians); but this reduction in size together with an increase in metabolic rates would be contradictory since it is easier for smaller animals to lose their body heat. So this condition seen in basal ornithodirans would be strange and nonsense, unless those animals had a way to insulate their bodies and prevent this head from escaping.
In there I treated the LCA of both lineages as being a "cold blooded" animal that later evolved "warm bloodedness" somewhere around the base of the ornithodiran node. Starting from this premise I connected the evolution of "warm bloodedness" with the smaller size of basal ornithodirans (compared to aphanosaurians and pseudosuchians); but this reduction in size together with an increase in metabolic rates would be contradictory since it is easier for smaller animals to lose their body heat. So this condition seen in basal ornithodirans would be strange and nonsense, unless those animals had a way to insulate their bodies and prevent this head from escaping.
Therefore I concluded that feather-like filaments (stem-feathers) were an ancestral trait for Ornithodira evolving together with "warm bloodedness", while "cold blooded" was the most likely the ancestral condition of Archosauria.
02-New Data:
02-New Data:
However I missed some stuff there, at the moment I was not aware we had histology analysis of Teleocrater, the results showing an animal with a high metabolism comparable to those of silesaurids, though slower than pterosaurs and traditional dinosaurs. If I knew that in the moment, proposing an answer for the ancestor metabolism of archosaurians would be harder and we would have had a scenario with many possible alternative answers.
In addition to this SVP-2018 brought us some new information on the metabolism of basal archosaurians:
Into Lovelace now, the most relevant part of his work for this discussion is not what he presents in the abstract but rather some thing he said in his SVP lecture*. They made a modeling analysis of Chinle Formation and focused on how Coelophysis and Plateosaurus would react to the environment, results found out that Coelophysis could not survive without insulation, partially "feathered" Coelophysis would have a better chance to survive, with the only way the animal could be healthy was if it was fully "feathered".
*Information obtained from tweets by Paleontologist Robert Gay (Link 01)
03-Discussion:
Now that we know the metabolism of a good number of lineages of both sides of Archosauria, we can say that almost surly the LCA of Archosauria was indeed homoeothermic, all the lineages studied so far were shown to have been homoeothermic giving a strong support to this idea. By consequence this refutes my old hypothesis that homeothermia evolved together with filamentous integument in the base of Ornithodira.
Even though the prat about homeothermy has fallen I think more than ever we have support for stem-feathers being ancestral trait of at least Ornithodira. Lovelace et al. suggest that even larger animals like Coelophysis could die from hypothermia without insulation, so it is reasonable to assume* the even smaller basal ornithodirans like Scleromochlus, Lagerpetids and Marasuchus would die from hypothermia as well if not insulated. This supports my idea that stem-feathers would need to show up before these animals could suffer the size reduction we see at the base of Ornithodira without dying from heat loss.
*Obviously this is more complex since Ornithodira origin seems to have occurred in the Tropical Pangaea Belt, while the study was conducted for Chinle that was located further north in a (probably) temperate region. But I still thing the hypothermia idea would be valid since even if living in a hotter environment and having a lower metabolism then Coelophysis those guys would have a much inferior mass.
04-Concluding:
- The first one being "High variations in growth duration and growth rates in the early ancestors of Crocodylia" by Werning and Turner (page 238 of the abstract book)
- The second one being "Deep-time application of linked microclimate and biophysical models constrains the thermal ecology of two Late Triassic dinosaurs (Coelophysis, Plateosaurus)" by Lovelace et al. (page 172)
Into Lovelace now, the most relevant part of his work for this discussion is not what he presents in the abstract but rather some thing he said in his SVP lecture*. They made a modeling analysis of Chinle Formation and focused on how Coelophysis and Plateosaurus would react to the environment, results found out that Coelophysis could not survive without insulation, partially "feathered" Coelophysis would have a better chance to survive, with the only way the animal could be healthy was if it was fully "feathered".
*Information obtained from tweets by Paleontologist Robert Gay (Link 01)
03-Discussion:
Now that we know the metabolism of a good number of lineages of both sides of Archosauria, we can say that almost surly the LCA of Archosauria was indeed homoeothermic, all the lineages studied so far were shown to have been homoeothermic giving a strong support to this idea. By consequence this refutes my old hypothesis that homeothermia evolved together with filamentous integument in the base of Ornithodira.
Resumed phylogenetic tree of Archosauria: underlined in red means the clade was "warm blooded", underlined in gray/silver means we are not sure about the clade metabolism. (We will have information on Aetosauria when the paper comes out).
Even though the prat about homeothermy has fallen I think more than ever we have support for stem-feathers being ancestral trait of at least Ornithodira. Lovelace et al. suggest that even larger animals like Coelophysis could die from hypothermia without insulation, so it is reasonable to assume* the even smaller basal ornithodirans like Scleromochlus, Lagerpetids and Marasuchus would die from hypothermia as well if not insulated. This supports my idea that stem-feathers would need to show up before these animals could suffer the size reduction we see at the base of Ornithodira without dying from heat loss.
*Obviously this is more complex since Ornithodira origin seems to have occurred in the Tropical Pangaea Belt, while the study was conducted for Chinle that was located further north in a (probably) temperate region. But I still thing the hypothermia idea would be valid since even if living in a hotter environment and having a lower metabolism then Coelophysis those guys would have a much inferior mass.
04-Concluding:
Combining all this new information with previous knowledge show us that basal archosaurs were more active and had higher metabolic rates then we did expect; being more comparable to mammals than modern reptiles (Linnaean sensu, minus birds) only latter being reverted to pecilothermy in modern crocodiles. The highly derived ornithodirans would probably need some form of stem-feathers for insulation otherwise they would die from heat-loss, hence "feathers" would probably be an ancestral trait of Dinosauria (fanboys gonna crie).
I also wanna note that I was not present at SVP and did not attended the lectures/presentations of these works, and all this information used in here is "outsourced" so there may have been some confusion and misinterpretation of my part at some part of this. We will still have to wait for the final paper to come out to be 100% sure that this here is
Note: I used the terms "warm blooded" and "cold blooded" in here because I don't know if the metabolism of these animals fits into endothermy and/or homeothermy; so not to spread missinformation I opted to use the popular name in quotation marks cause those cover the general idea.
Read the erratum post: https://apaleontologystudentblog.blogspot.com/2018/12/erratum-of-post-svp-2018-and-evolution.html
References:
Link 01: https://twitter.com/paleorob/status/1052668072195047424
Link 02: https://twitter.com/paleorob/status/1052585584907059202
SVP-2018 abstract book
Nesbitt, Sterling J., et al. "The anatomy of Teleocrater rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic)." Journal of Vertebrate Paleontology 37.sup1 (2017): 142-177.
Note: I used the terms "warm blooded" and "cold blooded" in here because I don't know if the metabolism of these animals fits into endothermy and/or homeothermy; so not to spread missinformation I opted to use the popular name in quotation marks cause those cover the general idea.
Read the erratum post: https://apaleontologystudentblog.blogspot.com/2018/12/erratum-of-post-svp-2018-and-evolution.html
References:
Link 01: https://twitter.com/paleorob/status/1052668072195047424
Link 02: https://twitter.com/paleorob/status/1052585584907059202
SVP-2018 abstract book
Nesbitt, Sterling J., et al. "The anatomy of Teleocrater rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic)." Journal of Vertebrate Paleontology 37.sup1 (2017): 142-177.
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