A Cretaceous terrestrial snake with robust hindlimbs and a sacrum

Abstract

It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.

The skull of the round Island boa, Casarea dussumieri Schlegel, based on high‐resolution X‐ray computed tomography

“…2;Tchernov et al, 2000;Apesteguia and Zaher, 2006). These phylogenetic hypotheses stand in stark contrast to the recent findings based on molecular data, which place bolyeriids as sister-taxon to a clade that includes the uropeltines (traditionally considered non-macrostomatan), Acrochordus and colubroids, whereas the tropidophiids were found to be the sister-taxon of the non-macrostomatan genus Anilius (Vidal and Hedges, 2004; see also Vidal and David, 2004).…”

“…The Round Island boas Casarea dussumieri and Bolyeria multicarinata are of relatively small size compared to most other booids, yet they are nested deeply inside the latter (Underwood, 1976;Tchernov et al, 2000;Lee and Scanlon, 2002;Apesteguia and Zaher, 2006;Scanlon, 2006). Thus, some degree of paedomorphosis may be expected, as was indeed noted by Anthony and Guibé (1952).…”

Snake Venomics and Antivenomics of the Arboreal Neotropical Pitvipers Bothriechis lateralis and Bothriechis schlegelii

“…Panels A and B show, respectively, reverse-phase separations of soluble B. lateralis venom proteins recovered after incubation of the venom with rabbit anti-horse IgG antiserum (control sample), and with polyvalent (Crotalinae) antivenom followed by rabbit anti-horse IgG antiserum and immunoprecipitation. HPLC fractions labelled with asterisks in panel A were quantitatively immunodepleted from the venom sample incubated with the polyvalent antivenom, whereas fractions labelled in panel B with numbers (following the same numbering as in Figure 1) were not affected at all (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)20), or were only partially recognized (13)(14)(15)(16)(17)22), by the antivenom (see Figure 7). The insert in panel B shows an SDS-PAGE analysis of -mercaptoethanol-reduced fractions a-g. CID-MS/MS of tryptic peptide ions from these fractions (601.7 2+ : LSVPTSEWQR; 545.6 2+ : VVSTLPI-AHQDWLR; 621.6 3+ : TTPAVLDSDGSYFLYSK) identified them as rabbit IgGs.…”

“…However, preliminary results from our laboratories indicate that these venoms, like the B. schlegelii venom, contain a large amount of bradykinin-potentiating peptides (BPPs, Table 3). BPPs have been described as snake venom inhibitors of angiotensin-converting enzyme, a dipeptidylcarboxypeptidase expressed in endothelial, epithelial and neuroepithelial cells, which converts inactive angiotensin I into the potent vasoconstrictor angiotensin II, and degrades bradykinin into bradykinin (1-7) or bradykinin (1)(2)(3)(4)(5). 82 BPPs prevent the hypertensive effect of the angiotensin II and potentiate the hypotensive effect of the circulating bradykinin.…”

“…The most generalized phylogenetic view is that the group evolved from a family of terrestrial lizards during the time of the dinosaurs in the Jurassic period, about 200 million years (Myr) ago. [1][2][3] Advanced snakes (Caenophidia) arose in the Oligocene epoch Myr ago, but remained a small taxon until the tectonic plates drifted apart from the equator and the cool climate pushed boids to disappear from many ecological niches. 4 Nowadays, snakes are present worldwide except in the far north (Alaska and northern Canada in North America, Greenland, Iceland, Ireland, extreme northern Scandinavia and northern Russia in Eurasia), in the far south (Antarctica and New Zealand) and some small oceanic islands, 5 where they have adapted to a diverse array of habitat types, including terrestrial, arboreal, and aquatic ecosystems.…”