Madtsoiidae


Madtsoiidae is an extinct family of mostly Gondwanan snakes with a fossil record extending from early Cenomanian to late Pleistocene strata located in South America, Africa, India, Australia and Southern Europe. Madtsoiid snakes include very primitive snakes, which like extant boas and pythons would likely dispatch their prey by constriction, such as Gigantophis, one of the longest snakes known at an estimated, and the Australian Wonambi and Yurlunggur.
As a grouping of basal forms the composition and even the validity of Madtsoiidae is in a state of flux as new pertinent finds are described.

Description

Madtsoiidae was first classified as a subfamily of Boidae, Madtsoiinae, in Hoffstetter. Further study and new finds allowed ranking the group as a distinct family in Linnaean systems. With the recent use of cladistics to unravel phylogeny, various analyses have posited Madtsoiidae as a likely clade within Serpentes, or possible paraphyletic stem group outside Serpentes and within a more inclusive Ophidia.
Madtsoiid snakes ranged in size from less than to over, and are thought to have been constrictors analogous to modern pythons and boas, but with more primitive jaw structures less highly adapted for swallowing large prey. There are specific anatomical features that diagnose members of this family, such as the presence of hypapophyses only in anterior trunk, that the middle and posterior trunk vertebrae possess a moderately or well-developed haemal keel, except for a few near the cloacal region, often with short laterally paired projections on the posterior part of the keel. Also, all trunk and caudal vertebrae have at least a parazygantral foramen, sometimes several of them, located in a more or less distinct fossa that is lateral to each zygantral facet. Additional features are the prezygapophyseal processes' absence while the paracotylar foramina are present and that the diapophyses are relatively wide, exceeding width across prezygapophyses at least in the posterior trunk vertebrae.
Like most fossil snakes the majority of madtsoiids are known only from isolated vertebrae, but several have associated or articulated parts of skeletons. Of the genera listed below, all have been referred to Madtsoiidae in all recent classifications except Najash rionegrina, which is included here based on diagnostic vertebral characters described by Apesteguía and Zaher. These authors didn't include Najash among madtsoiids because they consider that madtsoiids are a paraphyletic assemblage of basal macrostomatans related to Madtsoia bai and consequently, not related to the Cretaceous alethinophidians from southern continents.

Rieppel et al. classified Wonambi naracoortensis within the extant radiation,, of snakes as Macrostomata incertae sedis, but many of their character state attributions for this species have been criticised or refuted by Scanlon and the better-preserved skulls of Yurlunggur sp./spp. have numerous characters apparently more plesiomorphic than any macrostomatans. The partial skull attributed to Najash rionegrina resembles that of the non-madtsoiid Dinilysia patagonica, and vertebrae support that they are related. The type material of Najash is the only possible madtsoiid specimen retaining evidence of pelvic and hindlimb elements, which are claimed to be more plesiomorphic than other Cretaceous limbed snakes, such as Pachyrhachis, Haasiophis or Eupodophis, in retaining a sacro-iliac contact and well-developed limbs, with a huge and well-defined trochanter. The sacro iliac contact is perhaps misleadingly described by Apesteguía and Zaher as unique possession of a sacrum, whereas it has rarely been questioned that the cloacal vertebrae in snakes are homologous to the sacrals of limbed squamates. It would be unsurprising if other madtsoiids also possessed hindlimbs as complete as those of Najash.
Several madtsoiid genera have been named using indigenous words for legendary Rainbow Serpents or dragons, including Wonambi, Yurlunggur and Nanowana in Australia, and Herensugea in Europe. G.G. Simpson apparently started this trend by compounding Madtsoia from indigenous roots. In this particular case these originated from the Tehuelche language, although the reference made was geographic rather than mythological, the derivation being from that language's terms mad, "valley" and tsoi'', "cow" as a rough translation from Spanish name of the type locality, Cañadón Vaca.

Classification

According to a cladistic analysis by Scanlon, Wonambi and Yurlunggur as representative genera of Madtsoiidae form a monophyletic assembly. However, as Madtsoia is not included, its grouping in the same family is questionable.