| Eupodophis | |
|---|---|
 | |
| Holotype ofEupodophis descouensi | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Serpentes |
| Family: | †Simoliophiidae |
| Genus: | †Eupodophis Rage and Escuillié,2000 |
| Species | |
Eupodophis is anextinctgenus ofsnake from theLate Cretaceous period. It has two small hind legs and is considered atransitional form between Cretaceouslizards and limbless snakes. The feature, described as vestigial, was most likely useless toEupodophis.[1] Thetype speciesEupodophis descouensi was named in 2000 and resides now in the paleontology section of theMim Museum in Beirut, Lebanon. The specific name is dedicated to the French naturalistDidier Descouens.[2]
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 inCenomanian-agelimestone near the al-Nammoura village inLebanon[2][3] belonging to theSannine Formation.[4]
Eupodophis was a marine snake that lived in theMediterraneanTethys Ocean. It had a laterally compressed body and short, paddle-like tail. Thevertebrae andribs ofEupodophis arepachyostotic, 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. Themetatarsals andphalanges of the foot are absent.
The fossil skeleton ofEupodophis was analyzed usingsynchrotronx-rays at theEuropean Synchrotron Radiation Facility inGrenoble,France.[1][5] The researchers determined that the hind limb on one skeleton was 0.8 inches long, with an "unmistakable"fibula,tibia andfemur.[1] 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 theGila monster,green iguana, and several species ofmonitor lizard.[6]
While they are very small in comparison to limbed reptiles, the hind limbs ofEupodophis possess much of the same anatomy as modern lizards. This suggests that the bones ofEupodophis 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 ofEupodophis are pachyostotic and osteosclerotic (meaning that theouter andinner 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.[6]
The loss of limbs inEupodophis may have been the result of changes inHox 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 inEupodophis 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 thelimb bud during embryonic development.[6]
The loss of forelimbs and reduction of hind limbs inEupodophis 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 ofEupodophis and other early snakes may have become vestigial to save energy and make movement more efficient. No vestigial limbs whatsoever are present in the modern species, which lack transitional species remnants. What few species have them protrude as tiny spurs. Most herpetologists agree snakes diverged from lizard forms by discarding impediments to effective sheltering in subterrestrial environments. Most modern snakes live above the surface.[6][7]
Other known fossil snakes with legs:
Fossilsnakes | |
|---|---|
| |
| Genera with hindlimbs and asacrum | |
| Simoliophiidae | |
| Madtsoiidae | |
| Dinilysiidae | |
| Boidae | |
| Pythonidae | |
| Palaeophiidae | |
| Viperidae | |
| Elapidae | |
| Psammophiidae | |
