Pachyrhachis problematicus (Haas 1979) Early Cenomian, Late Cretaceous, ~100 mya, ~1.5 m in length was a primitive snake that retained vestigial hind limbs. It was derived from a sister to Adriosaurus, Dinilysia and Tetrapodophis (see below).

Distinct from Adriosaurus, the skull of Pachyrhachis had a tiny loose premaxilla, not bound to the maxillae. The nares covered most of the dorsal surface of the rostrum. The orbit was smaller. The jugal was virtually absent and the postfrontal fused to the jugal. The postorbital and squamosal disappearted. The supratemporal was larger and took over the duty of anchoring the quadrate. The teeth were longer and more recurved. The pterygoids and palatines produced similar teeth, all in a line. The mandible was more robust. The posterior dentary descended.

More cervicals, dorsals and caudals were present. No pectoral girdle or forelimbs were present. The hind limb and pelvis were vestiges.

See an animation demonstrating the crushing of the Pachyrhachis skull here.

Boa Constrictor (Linneaus 1758) is an extant snake with a popular name the same as its Latin name. It is one of the largest extant snakes.

Distinct from Dinilysia, the rear of the skull is wider than the trans-orbit width. The maxilla ventral margin is straight. The teeth angle posteriorly. The jaw joint is higher than the maxilla, and the quadrate leans medially and loosely. It can create a huge gape for swallowing prey larger than its head. The nasals wrap around the nares. The prefrontals are robust and extend to the nares.

Sanajeh indicuis (Wilson et al. 2010, Late Cretaceous, 3.5m, GSI/GC/2901-2906) is a large boa found in a nest of sauropod dinosaur eggs. Too little is known to nest in the LRT, but a restoration seems to locate this taxon between boas and rattlesnakes.

Aipysurus laevis (Lacépede 1804) is the extant olive sea snake, provided with venom and a paddle-like tail. Here it nests between the boa (Boa) and rattlesnake (Crotalus).

Crotalus horridus (Linneaus 1758) is the extant timber rattlesnake. The maxilla is reduced to a single hollow fang anterior to the orbit. The dentary teeth are likewise reduced to just anterior teeth. The former parietal crest is here a slight depression. The jugal is a tiny fused vestige.

Atractaspis irregularis (Smith 1849) is the tiny, extant burrowing viper, mole viper, stilleto snake or side-stabbing snake. This burrowing snake converges with other burrowing snakes, but is more closely related to the rattlesnake.

Haas G 1979. On a new snakelike reptile from the Lower Cenomanian of Ein Jabrud, near Jerusalem. Bulletin du Muséum national d'Histoire Naturelle de Paris Ser. 4 (1):51-64.

Lacépede BG 1804. Mémoire sur plusieurs animaux de la Nouvelle-Hollande dont la description n'a pas encore été publiée. Annales du Muséum d'histoire naturelle. 4: 184–211.

Lee MSY and Caldwell MW 1998. Anatomy and relationships of Pachyrhachis problematicus, a primitive snake with hindlimbs. Philosophical Transactions of the Royal Society London B 353:1521-1552.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Palci A, Hutchinson MN, Caldwell MW, Scanlon JD and Lee MSY 2018. Palaeoecological inferences for the fossil Australian snakes Yurlunggur and Wonambi (Serpentes, Madtsoiidae). R. Soc. open sci 5: 172012. http://dx.doi.org/10.1098/rsos.172012

Scanlon JD 1992. A new large madtsoiid snake from the Miocene of the Northern Territory. The Beagle, Records of the Northern Territory Museum of Arts and Sciences 9(1):49-60

Smith A 1849. Illustrations of the Zoology of South Africa; Consisting Chiefly of Figures and Descriptions of the Objects of Natural History Collected during an Expedition into the Interior of South Africa, in the Years 1834, 1835, and 1836; Fitted out by "The Cape of Good Hope Association for Exploring Central Africa:" Together with a Summary of African Zoology, and an Inquiry into the Geographical Ranges of Species in that Quarter of the Globe. [Volume III. Reptilia]. London: Lords Commissioners of her Majesty's Treasury. (Smith, Elder and Co., printers). 48 plates + unnumbered pages of text. (Atractaspis, new genus).

Wilson JA, Mohabey DM, Peters SE, Head JJ 2010. Benton MJ ed. Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India. PLoS Biology. 8 (3): e1000322. doi:10.1371/journal.pbio.1000322

wiki/Sanajeh
wiki/Pachyrhachis
wiki/Crotalus
wiki/Boa_constrictor
wiki/Atractaspis
wiki/Yurlunggur
wiki/Aipysurus_laevis