New skulls and skeletons of the Cretaceous legged snake Najash , and the evolution of the modern snake body plan

Abstract

Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes. Here, we shed light on the acquisition of the snake body plan using micro–computed tomography scans of the first three-dimensionally preserved skulls of the legged snake Najash and a new phylogenetic hypothesis. These findings elucidate the initial sequence of bone loss that gave origin to the modern snake skull. Morphological and molecular analyses including the new cranial data provide robust support for an extensive basal radiation of early snakes with hindlimbs and pelves, demonstrating that this intermediate morphology was not merely a transient phase between limbed and limbless body plans.

Megaevolutionary dynamics and the timing of evolutionary innovation in reptiles

“…However, our current knowledge of the squamate fossil record in the Jurassic is still limited to a few well-preserved articulated specimens 44,45 , and most early snakes are known only from highly fragmentary remains 45 , thus limiting our ability to understand their ecological roles and interactions with other clades. As our understanding of the deployment of the snake body plan and habitat occupation has recently been advancing based on new fossil evidence 46,47 , we predict that future findings will soon be able to reveal fundamental clues on the potential factors enabling phenotypic innovation decoupled from taxonomic radiation during early snake evolution.…”

Sphenodontian phylogeny and the impact of model choice in Bayesian morphological clock estimates of divergence times and evolutionary rates

“…In contrast, their sister clade, squamates (lizards and snakes), is currently represented by~10,650 extant species [36], indicating both lineages had very different evolutionary histories after their split from a common ancestor at about 260-270 Mya [13,37]. Despite considerable efforts to understand broad scale phylogenetic relationships, divergence times and evolutionary patterns among the various families of squamates (e.g., [13,[38][39][40][41]), there has been comparatively less effort to understand the species level relationships and macroevolutionary patterns in sphenodontians. For instance, Sphenodon punctatus has long been characterized as a "living fossil" [42], implying a relatively conserved morphology and low rates of evolution of its lineage for several million years [43].…”

The making of calibration sausage exemplified by recalibrating the transcriptomic timetree of jawed vertebrates

“…data fig. 5, 6; also, after a few changes to the dataset, Garberoglio et al, 2019: fig. S2; Sobral et al, 2020: fig.…”

“…27, 28), while both are strongly contradicted by the molecular consensus (e.g. Irisarri et al, 2017;Garberoglio et al, 2019;Sobral et al, 2020: fig. S10;Simões et al, 2020: supp.…”