Garberoglio et al. 2019
bring us long awaited skull data and several new partial skeletons of a Late Cretaceous snake with legs, Najash rionegrina (Figs. 1, 2). It must be said, the only evidence of legs supplied by the current authors was a caption labeled tibia on a tiny straight bone near the edge of the matrix. Nevertheless, legs and hips were described earlier in other headless specimens of Najash (Apesteguía and Zaher 2006; Fig. 1).
Most of the new specimens
were found in layered sandstone related to migrating aeolian dunes, along with abundant rhizoliths (root systems encased in desiccated mineral matter) and burrows.
From the authors’ abstract:
“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.”
That’s not true.
In the large reptile tree (LRT, 1602+ taxa, subset Fig. 3) snakes have a well documented ancestry back to Cambrian lancelets. The cladogram presented by the nine co-authors was steeped in tradition and lacking in appropriate outgroup taxa. Contra Garberoglio et al. 2019, Varanus and its monitor lizard kin are not part of snake ancestry in the LRT.
Garberoglio et al. continue:
“These new Najash specimens reveal a mosaic of primitive lizard-like features such as a large triradiate jugal and absence of the crista circumfenestralis, derived snake features such as the absence of the postorbital, as well as intermediate conditions such as a vertically oriented quadrate. The new cranial data also robustly resolve the phylogenetic position of this crucial snake taxon, along with other limbed snakes.”
- The authors’ cladogram did not nest Najash with burrowing snakes, as in the LRT, but at a much more primitive node.
- Perhaps this is so because Tetrapodophis and Barlochersaurus were not mentioned in the text.
- The quadrate was sharply bent posteriorly at a right angle, a trait only found in burrowing snakes.
- I found no primitive lizard-like features here, other than legs and hips, traits found in Tetraphodophis and Barlochersaurus, the last common ancestors of all living snakes.
- Najash is a crown-group snake in the LRT until additional untested taxa move it out.
Najash rionegrina (Apesteguía and Zaher 2006; Garberoglio FF et al. 2019; Late Cretaceous) is a tiny burrowing snake that retained a pelvis and hind limbs, transitional between Tetrapodophis and Loxocemus. The premaxilla was tiny, as in terrestrial snakes. The mandible rose anteriorly, as in burrowing snakes. The jugal and vomers were retained.
Apesteguía S and Zaher H 2006.A Cretaceous terrestrial snake with robust hindlimbs and a sacrum. Nature. 440 (7087): 1037–1040.
Garberoglio FF et al. (eight co-authors) 2019. New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake plan. Science Advances 2019(5):eaax5833, 8pp.