The origin of endothermy triggered by the P-Tr extinction event?

Benton 2020 reports,
“the emergence of endothermy in a stepwise manner began in the Late Permian but accelerated in the Early Triassic. The trigger was the profound destruction wrought by the Permian-Triassic mass extinction (PTME).”

Two more abbreviations found in Benton 2020 that will be making the rounds:

  1. Mesozoic Marine Revolution (MMR)
  2. Triassic Terrestrial Revolution (TTR).

According to Benton 2020:
“Among tetrapods, both synapsids and archosaurs survived into the Triassic, survivors were marked by the acquisition of endothermy, as shown by bone histology, isotopic analyses, and the acquisition of insulating pelage. Both groups before the PTME had been sprawlers; after the event they adopted parasagittal (erect) gait.”

Actually lots of other clades lacking endothermy, a pelage or a parasagittal gait also survived into the Triassic, as everyone knows.

Actually, none of these traits appeared in any of the above-named groups until the Middle Triassic and then tentatively. Even so, that was just a few million years after the extinction event.

Actually, one group of lepidosaurs also produced endotherms with insulating pelage: fenestrasaurs (including pterosaurs; Fig. 1). This has been a thorn in Benton’s side since Peters 2000–2009. Benton and his colleagues have ignored and omitted these peer-reviewed contributions to the literature for the last twenty years to preserved some sort of status quo.

As everyone knows., crocs returned to a sprawling gait and ectothermy. Hmmm…

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Figure 1. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Benton continues making classic mistakes by

  1. including pterosaurs with dinosaurs.
  2. omitting the bipedal basal crocodylomorphs that are essential to the dinosaur origins story.
  3. omitting the basal bipedal fenestrasaurs that are essential to the pterosaur origins story.
  4. omitting Repenomamus and other mammal mimics.

Benton claimed
“there is now substantial evidence that dinosaurs originated in the Early Triassic following several discoveries in 2010 and 2011. Asilisaurus, from the Manda Formation (Anisian, Middle Triassic, 247–242 Ma) of Tanzania, and postulated that this was a representative of a new group called the silesaurids, close to dinosaurs.”

Unfortunately, adding taxa reveals
the poposaur Silesaurus and Asiliisaurus are poposaurs, dinosaur mimics not close to dinosaurs.

Another Middle Triassic poposaur with erect limbs,
Lotosaurus
, would have supported Benton’s claims, but was not mentioned. The origin of the poposaurs (Turfanosuchus (Fig. 2) certainly could go back to the Early Triassic.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 2. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Benton perpetuates the myth
of the Pseudosuchia, an invalid clade in the LRT.

Benton employs too few taxa
to realize the basal dichotomy between Euarchosauriformes and Pararchosauriformes that preceded the extinction event.

Likewise, Benton employs too few taxa
to realized the basal reptile split between lepidosauromorphs (including pterosaurs and rhynchosaurs) and archosauromorphs (including synapsids, non-lepidosaur diapsids and archosauriformes) goes back to the Early Carboniferous).

Key taxa,
like Euparkeria, Youngosuchus, Decuriasuchus, Turfanosuchus, Pseudhesperosuchus, Gracilisuchus and PVL 4597 (Fig. 2), are not mentioned in the Benton text.

The Middle Triassic is when archosauriformes radiated widely,
perhaps with Early Triassic and Late Permian roots, but everyone knew this already.

In short,
there is little to nothing new here and lots of mythology. I think everyone knew animals on planet Earth essentially picked themselves up and started all over again after the end Permian extinction event which wiped out 95% of all species.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 3. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

More taxon inclusion would have saved this paper.
You may remember Benton and Hone 2007, 2009 also deleted taxa and citations to achieve the end they sought, based on Benton’s 1999 paper on pterosaur origins, featuring the tiny bipedal croc with tiny hands, Scleromochlus. Sadly, Benton’s latest cherry-picking and machinations are destroying any good reputation earlier work may have earned him.


References
Benton MJ 2020. The origin of endothermy in synapsids and archosaurs and arms races in the Triassic, Gondwana Research (2020), https://doi.org/10.1016/j.gr.2020.08.003
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330

http://reptileevolution.com/pterosaur-wings.htm

https://pterosaurheresies.wordpress.com/2012/04/13/a-supertree-of-pterosaur-origins-hone-and-benton-2007-2009/

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