Shipley et al 2024 report bipedalism in dinosaurs did NOT make them successful

Decades after dinosaur success
was attributed to their bipedal stance and the higher metabolism and uninterrupted respiration that comes with that stance, Shipley et al 2024 concluded, “Our study suggests that bipedality or cursoriality were not key and that these locomotor advances were not actively selected for. Instead, our results suggest a more stochastic pattern, with the rise of dinosaurs instead potentially attributed to their ability to exhibit greater plasticity in their locomotion.”

Keep in mind, there is a difference between the RISE of dinosaurs and their REIGN.

The authors drop a nod to Carrier 1987
who described the much greater locomotor stamina that comes as a bonus from erect limbs. Evern since 1987 that’s where the consensus on dinosaur success has been. Shipley et al want to cast an opposing vote. Do they have a point?

No. Worse yet, they undercut their study several ways.

The out-dated phylogeny employed by Shipley et al provides no confidence that they know their subject matter. Their taxon list would have benefited from adding several dozen pertinent archosauriformes while deleting several dozen lepidosaurs they mistake for archosauromorphs.

They chose to feature taxa known from scraps when more complete taxa are known.

Figure 1. Teleoctrater compared to related taxa in the LRT. ” data-image-caption=”

Figure 1. Teleoctrater compared to related taxa in the LRT.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/02/teleocrater_turfanosuchus588.jpg?w=135″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/02/teleocrater_turfanosuchus588.jpg?w=460″ src=”https://pterosaurheresies.files.wordpress.com/2024/02/teleocrater_turfanosuchus588.jpg” alt=”Figure 1. Teleoctrater compared to related taxa in the LRT. ” class=”wp-image-84217″ />

From the abstract:
“The Triassic was a time of ecological upheaval as life recovered from the Permian-Triassic mass extinction. Archosauromorphs were a key component of the recovery, diversifying substantially during the Triassic and encompassing the origins of dinosaurs, pterosaurs and crocodylomorphs.

According to the large reptile tree (LRT, 2311 taxa) pterosaurs are not archosauromorphs. They were removed from that traditional nesting 24 years ago (Peters 2000). This traditional omission likely stems from the inclusion of professor and textbook author, Michael Benton, as a co-author on Shipley et al 2024.

Here’s the history (link): In 1999 Benton promoted the tiny bipedal crocodylomorph, Scleromochlus, as a pterosaur + dinosaur relative despite the tiny hands and only four toes. Benton also introduced the invalid clade, Avemetatarsalia to replace the equally invalid clade Ornithodira.

“Here, we explore the evolution of locomotion in Archosauromorpha to test whether dinosaurs show any distinctive locomotory features that might explain their success.”

After Ostrom 1970, Bakker 1971. 1972 school children were taught that basal dinosaurs were active, speedy and bipedal.

After Carrier 1987 kids have been taught dinosaurs did not have to stop to catch their breath. They had long distance stamina because they had erect limbs and a short stiff back.

“We implement geometric morphometrics on limb bone shapes and use limb ratios to calculate bipedality and cursoriality metrics.”

Again, nothing new here. Readers should realize by now that statistics and metrics do not provide the wealth of information contained in one wide-gamut phylogenetic analysis.

“We find that the Avemetatarsalia (dinosaurs, pterosaurs and relatives) exhibit more variable limb form and limb ratios than any other group, indicating a wider range of locomotory modes”.

Any paper that lumps dinosaurs together with pterosaurs in 2024 runs the risk of appearing bogus, out-of-date or both. That’s unfortunate and unnecessary. It’s also unfortunate that the authors do not keep their focus on the high metabolism and the stiff back that bipedalism provided to basal dinosaurs and all their quadrupedal descendants. By convergence, pterosaurs also arose from bipedal lepidosaurs with a short stiff back, so they also active lifestyles and a high stamina.

“The earliest avemetatarsalians were bipedal and cursorial, and their range of form increased through the Triassic with notable diversification shifts following extinction events.

Not sure how the authors intend to square pterosaur bipedality with pterosaur workers who wrongly consider all pterosaurs quadruepds based on the quadrupedal tracks of beachcombing quadrupedal pterosaurs. Many pterosaur workers were taught by Benton or out of Benton’s textbooks.

“This is especially true of dinosaurs, even though these changes cannot be discriminated from a stochastic process. By contrast, the Pseudosuchia (crocodilians and relatives) were more restricted in limb form and locomotor mode with disparity decreasing through time, suggesting more limited locomotor adaptation and vulnerability to extinction.

In the LRT ‘Pseudosuchia‘ is paraphyletic and therefore of no use. In the LRT crocodilians and their relatives include only dinosaurs. Only these two clades comprise the Archosauria in the LRT. The archosaur outgroup is the clade Popsauria. Other archosauriform clades precede these.

“Perhaps the greater locomotor plasticity of dinosaurs gave them a competitive advantage in the changing climates of the Late Triassic.”

By the way, plasticity is also found in the clades Crocodylomorpha and Poposauria. Like dinosaurs, both had a bipedal start (Fig 1). Both clades also gave rise to a variety of quadrupeds. This was completely overlooked by Shipley et al.

Apparently the same sort of plasticity that gave us the gracile bipedal crocodylomorph, Litargosuchus (Fig 2), eventually failed, because we don’t see croc bipeds anymore, falsifying the Shipley et al hypothesis. On the same (but opposite) point, all the quadrupedal dinosaurs are also extinct. Turns out that sort of plasticity was successful, until it wasn’t.

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one. ” data-image-caption=”

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one.

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From the Introduction
“Dinosaurs are members of the clade Avemetatarsalia, which includes pterosaurs as well as two clades that originated in the Middle Triassic (Anisian), the Aphanosauria, quadrupedal forms such as Teleocrater and Dongusuchus, and the Silesauridae such as Asilisaurus.”

None of this is confirmed by the LRT. Silesaurus is a poposaur. Dongusuchus is known from only a few bones. Teleocrater (Fig 1) is known from a few more bones (Fig 1) and it nests outside the Poposauria in the LRT. It gets worse.

In the Shipley et all SuppData
the authors list several rhynchosaurs as basal archosauromorphs. They are lepidosaurs in the LRT, derived from rhynchocephalians via Mesosuchus. The authors list Pamelaria and Prolacerta as basal archosauromorphs. They are protorosaurs in the LRT, the outgroup clade to the Archosauriformes. The authors list the ‘rib glider’ Mecistotrachelos, as a basal archosauromorph. It is a pre-lepidosaur in the LRT. The authors list Sharovipteryx as a a basal archosauromorph. It is a bipedal lepidosaur in the LRT.

These authors have no idea how their taxa are related to one another. One gets the impression that their cadre has run out of things to keep them busy so they rehashed a previously resolved problem and put a spin on it.

A while back, I noticed a dearth of new paleo material. That’s why I’m sort of thankful that fish are so difficult to resolve.

As a reminder, in the LRT
all reptiles after Silvanerpeton are either Lepidosauromorpha or Archosauromorpha following traditional established definitions. The problem in Shipley et al clearly comes from taxon exclusion. The authors have not tested a sufficient number of taxa back to Silvanerpeton to discover this Lepidosauromorph-Archosauromorph split at the base of Reptilia for themselves. When they do that their cladogram is going to shift several taxa around, as in the LRT.

The problem comes from momentum: Benton would rather not update his textbooks. And at his age he is more likely to delegate phylogenetic analysis than to take it on as a personal project. We’ve seen him delegate work to an eager, but naive student earlier here.

From the Phys.org publicity,
“The researchers compared the limb proportions of a broad array of reptiles from the Triassic. They found that, from the beginning, not only were the dinosaurs and their close relatives bipedal and cursorial—which meant they had limbs adapted for running, they also showed a much wider range of running styles than some of their close competitors, called the Pseudosuchia.”

Add taxa. That seems to solve all traditional problems.
If you think that’s going to take too much time and effort, cite the LRT.

References
Bakker RT 1971. Dinosaur physiology and the origin of mammals. Evolution 25, 636-658.
Bakker RT 1972. Anatomical and ecological evidence of endothermy in dinosaurs. Nature 238, 81-85.
Carrier DR 1987. The evolution of locomotor stamina in tetrapods: circumventing a mechanical constraint. Paleobiology13, 326-341.
Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana”. Bulletin of the Peabody Museum of Natural History. 35: 1–234.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Shipley AE et al 2024. Locomotion and the early Mesozoic success of Archosauromorpha, Royal Society Open Science (2024). DOI: 10.1098/rsos.231495

Publicity
https://phys.org/news/2024-02-dinosaurs-success-specialized-stance-gait.html