Eupodophis
Encyclopedia
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 lizard
s 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
.
. It had a laterally compressed body and short, paddle-like tail. The vertebrae and rib
s 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-ray
s 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.
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.
Other known fossil snakes with legs:
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
period. It has two small hind legs and is considered a transitional form
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...
between Cretaceous lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s and limbless snakes. The feature, described as vestigial, was most likely useless to Eupodophis. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the 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
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
-age limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
near the al-Nammoura village in Lebanon
Lebanon
Lebanon , officially the Republic of LebanonRepublic of Lebanon is the most common term used by Lebanese government agencies. The term Lebanese Republic, a literal translation of the official Arabic and French names that is not used in today's world. Arabic is the most common language spoken among...
.
Description
Eupodophis was a marine snake that lived in the Mediterranean Tethys OceanTethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
. It had a laterally compressed body and short, paddle-like tail. The vertebrae and rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s of Eupodophis are pachyostotic
Pachyostosis
Pachyostosis is a condition in vertebrate animals in which the bones experience a thickening, resulting in unusually solid bone structure with little to no marrow. It occurs in both terrestrial and aquatic vertebrates, such as manatees and dugongs, plesiosaurs, and members of the Dinocephalia...
, or thickened, as an adaptation to a marine lifestyle. The pelvic bones are small and weakly attached to each other. Tarsal
Tarsal
Tarsal could refer to:*tarsus *tarsus *superior tarsal muscle...
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
Synchrotron
A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...
x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s at the European synchrotron radiation facility
European Synchrotron Radiation Facility
The European Synchrotron Radiation Facility is a joint research facility supported by 19 countries situated in Grenoble, France...
in Grenoble
Grenoble
Grenoble is a city in southeastern France, at the foot of the French Alps where the river Drac joins the Isère. Located in the Rhône-Alpes region, Grenoble is the capital of the department of Isère...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. The researchers determined that the hind limb on one skeleton was 0.8 inches long, with an "unmistakable" fibula, tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
and femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
. 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
Gila monster
The Gila monster is a species of venomous lizard native to the southwestern United States and northwestern Mexican state of Sonora...
, Green Iguana
Green Iguana
The Green Iguana or Common Iguana is a large, arboreal herbivorous species of lizard of the genus Iguana native to Central and South America...
, and several species of monitor lizard
Monitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...
.
Cortical bone
Cortical bone, synonymous with compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name...
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.
Paleobiology
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 budLimb bud
In embryology, the limb bud is a structure formed by the developing limb, derived from lateral plate mesoderm. It is intimately related with the apical ectodermal ridge, which secretes factors inducing the initial differentiation of 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.
See also
Other known fossil snakes with legs:
- PachyrhachisPachyrhachisPachyrhachis 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 one of three genera of Cenomanian snakes with hindlimbs. Many of today's modern pythons and boas still have small bone spurs, where limbs...
- HaasiophisHaasiophisHaasiophis, consisting of the sole species Haasiophis terrasanctus, is an extinct genus of snakes with hind limbs. It is one of three genera of Cenomanian snakes known to have possessed hindlimbs.-Etymology:...
- Najash
External links
- The Cenomanian: stage of hindlimbed snakes
- Ancient serpent shows its leg Jonathan Amos, BBC News