Stubbs et al. 2021
looked at 241 croc taxa (some firsthand, some photos, some diagrams), all skulls and jaws, no post-crania in order to “show that crocodylomorph ecomorphological variation peaked in the Cretaceous, before declining in the Cenozoic, and the rise and fall of disparity was associated with great heterogeneity in evolutionary rates.”
241 taxa should be enough
to touch all aspects of a clade, but co-author and professor Mike Benton skipped several basal bipedal crocodylomorphs (list below and see Fig. 2) recovered by the large reptile tree (LRT, 1820+ taxa; subset Fig. 3), including a favorite Benton subject, Scleromochlus (Fig. 1). Benton 1999 and others keep hoping that Scleromochlus is a pterosaur sister. That’s been a mistake since… forever. Keeping it out of the data matrix is one trick you can use if you are Mike Benton trying to keep Scleromochlus out of the Crocodylomorpha. He likewise purposely omitted taxa in Hone and Benton (2007, 2009),
The authors note,
“Missing species either lacked skull or jaw material, or the specimens were too damaged or distorted.” True in some cases, not others. But that brings up another issue… this study was based on skull landmarks, nothing from the informative post-crania, and that’s where at least half the attention ought to be, especially in crocs (Fig. 2). Maybe there was a burst of disparity in the Late Triassic, too, but they’ll never know just looking at skulls and omitting taxa.
Stubbs et al. report,
“A composite crocodylomorph supertree was assembled following other recent macroevolutionary studies. The supertree topology is largely based on Godoy et al.
and modified from the formal supertree of Bronzati et al. We manually added more taxa, guided by published taxonomic and phylogenetic evidence, to maximize coverage and match the landmark data (see detailed description in the electronic supplementary material). The full supertree includes 373 crocodylomorphs and three pseudosuchian outgroup taxa.”
The LRT found that the traditional clade,
Pseudosuchia is paraphyletic. Even so, the three outgroup taxa cherry-picked by the Stubbs team are hard to determine since their .xls file is alphabetical and Stubbs et al. do not list them outright. Worse yet, their published cladograms (their Fig. 3) list no taxa. No taxa at all. The first time I’ve seen this. They show the topology of the tree and a few silhouettes, but their trees lack any taxa. Benton keeps on rolling his own way!
A thorough examination
of the Stubbs et al. .xls file of 241 taxa revealed no obvious or traditional non-crocodylomorph taxa listed there. If someone wants to point them out, please send that list of three.
The following are crocodylomorph taxa in the LRT
omitted or ignored by Stubbs et al.:
- PVL 4597 the Tucuman specimen, the proximal outgroup to the Crocodylomorpha
- MCZ 4116, a juvenile Trialestes
Most of these are basal bipedal crocodylomorphs.
Dyoplax is a basal marine croc in the LRT.
The authors were seeking
disparity and semblance and to turn that data into evolutionary rate (rapid or slow) results. They conclude, “Our work highlights the importance of ecological opportunity in driving innovation, even in a once diverse clade with now diminished biodiversity.”
The croc post-crania documents more diversit in the Triassic.
One wonders if this study had any need to be done other than to keep Benton’s students occupied during their expensive education. Some other of Benton’s students have a good story to tell about how they got their PhD under his tutelage and guidance.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Stubbs TL et al. (5 co-authors) 2021. Ecologicial opportunity and the rise and fall of crocodylomorpha evolutionary innovation. Proc. R. Soc. B 288: 20210069.
Note in passing: WordPress has changed from Classic Editor, which was simple, intuitive and great for 3400 posts. Now the OS, called Block Editor, is frustrating and time consuming by comparison. They got rid of the good stuff and added crap.