Najash is an extinct basal snake from the Late Cretaceous Candeleros Formation of Patagonia. Like a number of other Cretaceous and living snakes it retained hindlimbs, but Najash is unusual in having well-developed legs that extend outside the rib cage, and a pelvis connected to the spine. Fossils of Najash were found in the terrestrial Candeleros Formation, in Rio Negro Province, Argentina, and date to roughly 90 million years ago. The skull and spine of Najash both show adaptations for a subterranean existence, consistent with the hypothesis that the long bodies and reduced limbs of snakes are an adaptation for burrowing.

 This burrowing creature had not lost its sacrum, the pelvic bone composed of several fused vertebrae, nor its pelvic girdle which are absent in modern snakes, and in all other known fossil snakes as well. Several phylogenetic analysis place Najash as either the most primitive known snake, or near the base of the snake radiation, but outside of all living snakes.

 This discovery does not support the hypothesis, first offered by the nineteenth-century paleontologist Edward Drinker Cope, that snakes share a common marine ancestry with mosasaurs. The marine origin hypothesis received new impetus with the discovery in the 1990s of basal snakes with vestigial limbs in marine sediments in Lebanon.

 The generic name comes from the biblical legged snake of Genesis, Nahash, who tempted Adam and Eve to eat from a forbidden fruit tree.

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 Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, about 1 m (3–4 ft) long. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited.

 Pachyrhachis is one of three genera of Cenomanian snakes with hindlimbs. Although many modern pythons and boas still retain remnants of legs, in the form of small spurs, the tiny legs of Pachyrhachis included a hip, knee, and ankle joint. Pachyrhachis was originally described by Haas (1979, 1980) who noted it had a puzzling melange of snake and lizard features; its status as an early snake was later confirmed (Caldwell and Lee 1997).

 The position of Pachyrhachis within snakes has been debated (e.g. Lee and Scanlon 2002; Rieppel et al. 2003). Pachyrhachis is among the oldest known snakes and retains well-developed hind limbs, suggesting it represented a transitional form linking snakes to marine lizards (Lee and Scanlon 2002), though other studies place Pachyrhachis within the modern snake radiation Macrostomata (Zaher & Rieppel, 1999).

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 Eupodophis descouensi — древняя змея из семейства Pachyophiidae, у которой сохранились ноги.

 Окаменевшие останки обнаружены в Ливане близ деревушки Аль-Наммура в 2000 году. Возраст находки — около 92 миллионов лет.

 Eupodophis is an extinct genus of snake from the Late Cretaceous period. It has two small hind legs and is considered a transitional form between Cretaceous lizards and limbless snakes. The feature, described as vestigial, was most likely useless to Eupodophis. The type species Eupodophis descouensi was named in 2000. The specific name is dedicated to the French naturalist Didier Descouens.

 The fossilized specimen from which the description of the type species was based was 85 cm (33.5 in) long and is approximately 92 million years old. It was found in Cenomanian-age limestone near the al-Nammoura village in Lebanon.

 Eupodophis was a marine snake that lived in the Mediterranean Tethys Ocean. It had a laterally compressed body and short, paddle-like tail. The vertebrae and ribs of Eupodophis are pachyostotic, or thickened, as an adaptation to a marine lifestyle. The pelvic bones are small and weakly attached to each other. Tarsal bones are present but reduced in size and form. The metatarsals and phalanges of the foot are absent.

 The fossil skeleton of Eupodophis was analyzed using synchrotron x-rays at the European synchrotron radiation facility in Grenoble, France. The researchers determined that the hind limb on one skeleton was 0.8 inches long, with an "unmistakable" fibula, tibia and femur. One limb was visible on the surface of the fossil while the other was hidden within the limestone. The scans were compared with similar ones taken of the limbs of extant lizards including the Gila monster, Green Iguana, and several species of monitor lizard.

 While they are very small in comparison to limbed reptiles, the hind limbs of Eupodophis possess much of the same anatomy as modern lizards. This suggests that the bones of Eupodophis became reduced in size through a change in the rate of bone growth, not major anatomical changes. The lack of thickening at either end of the limb bones suggests that growth had stopped occurring in the limbs at one point in the animal's lifetime. While the vertebrae and ribs of Eupodophis are pachyostotic and osteosclerotic (meaning that the outer and inner parts of the bone are compact), the limb bones remain light. This lightness is also seen in the bones of terrestrial lizards, suggesting that the limbs had not been part of the overall adaptation of the skeleton for an aquatic lifestyle.

 The loss of limbs in Eupodophis may have been the result of changes in Hox genes, genes that specify the development specific regions of the body. Because Hox genes are involved in determining specific features of the axial skeleton, the loss of limbs would also result in the loss of cervical (tail) vertebrae that are near them. This loss is seen in Eupodophis and modern snakes but not legless lizards, which may be far less common because some other factor besides Hox genes were involved in the loss of their limbs. The loss of digits on the hind limbs may be explained by a low number of cells in the limb bud during embryonic development.

 The loss of forelimbs and reduction of hind limbs in Eupodophis was likely an adaptation for swimming. While living snakes usually employ undulatory movement for moving over land, sinuous movements are also an effective means of moving through water. Large, well-developed limbs increase drag on swimming animals, so the limbs of Eupodophis and other early snakes may have become vestigial to save energy and make movement more efficient.

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 Madtsoia is an extinct genus of madtsoiid snake. It is known from the Eocene of Argentina (M. bai), the Paleocene of Brazil (M. camposi), the Late Cretaceous (Campanian) of Spain (M. laurasiae), the Late Cretaceous of India (M. pisdurensis), and the Late Cretaceous (Campanian-Maastrichtian) of Madagascar and possibly Niger (M. madagascariensis).

 As extinct snakes go, Madtsoia is less important as an individual genus than as the eponymous representative of the family of snake ancestors known as madtsoiidae, which had a worldwide distribution from the late Cretaceous period all the way up to the Pleistocene epoch, about two million years ago. However, as you can surmise from this snake's unusually wide geographic and temporal distribution (its various species span about 90 million years) not to mention the fact that it's represented in the fossil record almost exclusively by vertebrae. Paleontologists are far from sorting out the evolutionary relationships of Madtsoia and the madtsoiida and modern snakes. Other madtsoid snakes, at least provisionally, include Gigantophis, Sanajeh and most controversially the two-legged snake ancestor Najash .

 Madtsoiidae are an extinct group of mostly Gondwanan snakes with a fossil record extending from early Cenomanian (Upper Cretaceous) 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 10.7 meters, and the Australian Aboriginal mythology-named 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.

 Madtsoiidae was first classified as a subfamily of Boidae, Madtsoiinae, in Hoffstetter (1961a). 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 1 m (estimated total length) to over 9 m, 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. Addition 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. (Scanlon 2005)

 Like most fossil snakes the majority of madtsoiids are known only from isolated vertebrae, but several (Madtsoia bai, M. camposi, Wonambi naracoortensis, Nanowana spp., unnamed Yurlunggur spp., Najash rionegrina) 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 (2006). 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. (2002) classified Wonambi naracoortensis within the extant radiation, (crown group), of snakes as Macrostomata incertae sedis, but many of their character state attributions for this species have been criticised or refuted by Scanlon (2005a) and the better-preserved skulls of Yurlunggur sp./spp. have numerous characters apparently more plesiomorphic than any macrostomatans (Scanlon 2006). The partial skull attributed to Najash rionegrina  (Apesteguía and Zaher 2006) 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 (i.e. the sacrum is present but has lost contact with the reduced ilia in other taxa). 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 (Pitjantjatjara), Yurlunggur (Yolngu) and Nanowana (Ancient Greek nano-, 'dwarf' + Warlpiri Wana) in Australia, and Herensugea (Basque) in Europe. G.G. Simpson (1933) 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.

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