Nature Ecology & Evolution has a new paper on Mazon Creek tetrapods. This paper describes snake-like limb loss in an amniote, Nagini mazonense, found in the Mazon Creek fossil deposit. The authors are Arjan Mann of the Smithsonian Institution, Jason Pardo of the Field Museum, and Hillary Maddin of Carleton University in Ottawa, Ontario, Canada. Arjan did a great presentation on Mazon Creek tetrapods back in November 2020. There's a nice summary of the paper in "Behind the paper" here.
Abstract
Among living tetrapods, many lineages have converged on a snake-like body plan, where extreme axial elongation is accompanied by reduction or loss of paired limbs. However, when and how this adaptive body plan first evolved in amniotes remains poorly understood. Here, we provide insights into this question by reporting on a new taxon of molgophid recumbirostran, Nagini mazonense gen. et sp. nov., from the Francis Creek Shale (309–307 million years ago) of Illinois, United States, that exhibits extreme axial elongation and corresponding limb reduction. The molgophid lacks entirely the forelimb and pectoral girdle, thus representing the earliest occurrence of complete loss of a limb in a taxon recovered phylogenetically within amniotes. This forelimb-first limb reduction is consistent with the pattern of limb reduction that is seen in modern snakes and contrasts with the hindlimb-first reduction process found in many other tetrapod groups. Our findings suggest that a snake-like limb-reduction mechanism may be operating more broadly across the amniote tree.
