Dinosaur origin followed by burst of skeletal evolution + first neosuchian fossils from Missão Velha Formation of Brazil

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New papers:

Free pdf:

Chase Doran Brownstein & Christopher Thomas Griffin (2026)
An early burst of skeletal evolution at the origin of dinosaurs
Proceedings of the Royal Society B: Biological Sciences 293(2069): 20260102 .
doi: https://doi.org/10.1098/rspb.2026.0102
https://royalsocietypublishing.org/rspb/article/293/2069/20260102/481427/An-early-burst-of-skeletal-evolution-at-the-origin


Over 230 million years of Earth’s history, dinosaurs became a major terrestrial animal clade and produced one of the most species-rich living tetrapod lineages: birds. Yet, largely because of uncertainty surrounding the phylogeny of early dinosaurs, the tempo and mode of their emergence and initial radiation remain poorly constrained. Here, we reconstruct the initial diversification of dinosaurs through Bayesian tip-dating analyses. Using nine morphological datasets, we estimate that dinosaurs emerged between 250 and 240 Ma, 10 million years before the earliest unambiguous dinosaur fossils. The emergence of the dinosaurs was followed by the rapid appearance and diversification of all major lineages, coinciding with a burst of morphological evolution that peaked in the early Late Triassic. The patterns that we infer are consistent with the expectations under a scenario of evolutionary radiation, in which ecologically disparate lineages rapidly diversify from a single common ancestor. In turn, our results provide a biological explanation for the instability surrounding early dinosaur phylogeny and suggest that the diversity of dinosaurs has been sculpted by multiple rapid radiations following successive mass extinctions in deep time.

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Athirson de Souza Albuquerque, Paulo Victor Luiz Gomes da Costa Pereira, Theo Baptista Ribeiro, Diogo de Mayrinck, Paulo M. Brito & Camila Cupello (2026)
First record of neosuchian crocodyliforms from Missão Velha Formation (Upper Jurassic-Lower Cretaceous), Araripe Basin
Cretaceous Research 106414
doi: https://doi.org/10.1016/j.cretres.2026.106414
https://www.sciencedirect.com/science/article/abs/pii/S0195667126001035

Highlights

First formal description of crocodyliformes material from the Missão Velha Formation.
First Neosuchia specimens identified for the Missão Velha Formation.
Tooth material comparable to crocodyliformes from Late Jurassic and Early Cretaceous.

Abstract

Crocodyliformes are relatively scarce in Jurassic and Lower Cretaceous outcrops from Brazil, with most of this record being from fragmentary specimens and isolated teeth. Among the prospected groups, Neosuchia is the only one described for the Jurassic. The Missão Velha Formation (Upper Jurassic-Lower Cretaceous) of the Araripe Basin is the only known litostratigraphic unit of the Cariri Group with prospected vertebrates, which includes a diversity composed of fishes (actinopterygians and sarcopterygians) and tetrapods (turtles, crocodyliforms and theropod dinosaurs). In this study we provide the first formal description of crocodyliform specimens, assigning them as Neosuchia and discuss the paleoecological implications of those animals for the area. The teeth share an overall conical to triangular crown morphology, with well-developed apicobasal ridges and crenulated carinae, features commonly found in aquatic to semiaquatic archosaurians such spinosaurids, notosuchians and neosuchians. Based on careful investigation, we found that the crowns described here share many characteristics specifically to neosuchian clades such as: thalattosuchians of the genus Machimosaurus, pholidosaurids and goniopholidids. Among the features, they can show multicrenulated crowns, including both false ziphodont carinae and apicobasal crenulated ridges, as well as an anastomosed enamel pattern at their apex and circular to subcircular cross section. Thus, the specimens were identified as Neosuchia, the first ever described for the Missão Velha Formation.
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[Sean McKelvey]

I'm probably just way out of my depth here, but does Diagram 1 in the Brownstein and Griffin paper seem a bit odd to anyone else?

I could just be totally misinterpreting this, but it appears to suggest at least one analysis proposed a Permian origin for Sauropodomorpha?

Again, I'm probably wrong, but I just wanted to get some clarification if possible.

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[Jerry Harris]

That's just the statistical error bar, which is an important (and often misunderstood) part of any statistical analysis. For the Otero & Pol dataset (the tan one, and the only one with a bar extending into the Permian), the dot is the median age (looks to be in the Middle Triassic); the bars that extend on either side of the dot show the ranges of where, in the analysis, 95% of the probability values fell. That means that, statistically, sauropodomorphs could have originated in the Permian, but it's not readily distinguishable from the graph how many probability values fell toward the Permian end of that line—might not have been many, suggesting that the probability was low, although still within the realm of possibility (which would, of course, indicate that the fossil record of archosauromorphs in the Permian and Early Triassic is woefully misunderstood at present!).

[Sean McKelvey]

Ah, ok. That makes more sense. Thanks for clarifying.

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