Eilenodon: herbivorous Late Jurassic sphenodont

Monday, June 22, 2026 10:41

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Preface: according to Google AI
“During the 1980s and 1990s, the overall number of academic paleontologists in the U.S. remained stable at around 480 individuals in surveyed geoscience departments.”

Presently“There are approximately 1,000 to 3,000 professional paleontologists in the United States, with about 18,435 identified active researchers globally.”

That’s a 2x to 6x increase in the USA alone… so it wasn’t just a vague feeling.
No wonder so many academic papers are now authored by 4, 8 or 12 authors.

With that bit of AI news out of the way…

Figure 3. Priosphenodon nests closer to rhynchosaurs than Mesosuchus does, yet it was not included in the Ezcurra et al. 2016 study.

Haridy et al 2026
described the partial skull of the sphenodontid Eilenodon from the Late Jurassic Morrison Formation, which compares well with the more complete South American Cretaceous skull of Priosphenodon (Fig 1). “The large-bodied species is easily distinguished from other sphenodontians from the Jurassic of North America based on its unique dentition seemingly adapted for an herbivorous lifestyle.”

And yet the authors STILL don’t make the phylogenetic connection to Late Triassic rhynchosaurs, trilophosaurs and azhdenosaurs
– ALL lepidosaurs in the large reptile tree (LRT, 2340 taxa, Figs 1,2).

Here we can blame Benton 1983. Good grief! that’s 43 years of unchallenged myth.

Figure 1. Rhynchocephalian and Rhynchosaur palates. That’s Priosphenodon in the middle leading to Mesosuchus and Howesia, to Trilophosaurus and Azendohsaurus and rhynchosaurs. That’s where the palatine grows as large as and alongside the maxilla. In derived taxa these two bones fuse creating the illusion that the maxilla has the entire tooth pad. Look at those palatine stems on Priospbenodon, which really come out on rhynchosaurs.

According to Wikipedia – Rhynchosauria
“Historically, rhynchosaurs were considered to be closely related to Rhynchocephalia, the clade that includes the living tuatara and its extinct relatives. Today however the two groups are considered to be unrelated: rhynchosaurs are considered to be archosauromorphs (more closely related to modern crocodilians and birds), while rhynchocephalians are lepidosauromorphs (closer to lizards).

If you want to pass Professor Benton’s class with Benton’s textbook, this has to be your answer, even though you have studied the situation and know better.

Benton (1983) reported,
“Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”

As I reported 15 years ago,
“These nits and picks are important, but taken as a whole (which is what we must do) currently there are no taxa more closely related to rhynchosaurs than rhynchocephalians (sphenodontians) and the trilophosaurs. Granted, all other rhynchocephalians had fused ankle bones, but having an unfused ankle is simply a matter of not fusing those bones, which develop separately in embryos. Acrodont teeth also form with fusion. Again, this would be a simple matter of switching off a gene.”

Figure 2. Priosphenodon, Rhynchosaurus and Betonyx skulls compared to scale. Academics say these taxa are not related, are not lepidosaurs, but the LRT unites them.

Summary from 2011
“Romer was right. Rhynchosaurs are closer to rhynchocephalians (sphenodontians). The differences noted by Benton (1983) are insufficient to outweigh a larger suite of characters that nest these taxa together.”

As long as Benton holds the reins, students must follow his lash.
That’s why it’s sometimes good to have an independent voice in your other ear.
Run the numbers. Find out for yourself. This is science.

References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Ezcurra MD, Montefeltro, F and Butler R J 2016. The Early Evolution of Rhynchosaurs. Frontiers in Ecology and Evolution. 3. doi:10.3389/fevo.2015.00142
Haridy Y et al (7 co-authors 2026. New material of the Late Jurassic sphenodontid Eilenodon robustus reveals transitionary adaptations to herbivory. From Foster et al 206. New developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation, New Mexico Museum of Natural History and Science Bulletin 102:171–184,