''Tetrapodophis'' (

greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

meaning "four-footed snake") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...

from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

. ''Tetrapodophis'' was previously thought to be one of the oldest members of

Ophidia __FORCETOC__ Ophidia (also known as Pan-Serpentes) is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards. Ophidia was defined as the "most recent common ancest ...

(Snakes and their extinct relatives). However, this classification has been disputed by Caldwell ''et al.'' (2016), Paparella ''et al.'' (2018) and Caldwell ''et al.'' (2021), who identify ''Tetrapodophis'' as a dolichosaurid (more closely related to the Ophidia than to mosasaurs, but lie in the greater clade,

Ophidiomorpha Ophidiomorpha is a clade composed of snakes and their primitive and early relatives proposed by Palci and Caldwell (2007)Palci, A., & Caldwell, M. W. (2007). Vestigial forelimbs and axial elongation in a 95 million-year-old non-snake squamate. Jou ...

). This species existed in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period about 120 million years ago, located in modern day Brazil. This four legged animal is around 12 inches long, weighing around 15–17 ounces.

Description

''Tetrapodophis'' possesses small yet well-developed fore- and

Hindlimb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hin ...

s like a lizard and a long body similar to a snake. Nevertheless, it shares many characteristics with modern Snakes, including an elongate body, short tail, broad belly scales, a skull with a short snout and long

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

, curved jaws, and sharp hooked teeth. BMMS BK 2-2 contains bones of another animal in its gut, indicating that ''Tetrapodophis'' was

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

like most snakes but it turns out to be a lizard. Other features such as short

neural spine The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

s suggest that ''Tetrapodophis'' was adapted to burrowing, lending support to the hypothesis that snakes evolved in terrestrial environments (another hypothesis posits that they evolved in aquatic environments). The high number of vertebrae (upwards of 150) in ''Tetrapodophis'' and snakes is not seen in other burrowing reptiles with elongate bodies and reduced or absent limbs, meaning that it is most likely not an adaptation for a serpentine form of movement. Dolichosaurids are thought to be phylogenetically close to snakes as members of

, which explains some of the morphological similarities.

Discovery and controversy

The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

, ''Tetrapodophis amplectus'', was named in 2015 on the basis of a complete skeleton (BMMS BK 2-2) preserved on a

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

slab in the

Bürgermeister Müller Museum Burgomaster (alternatively spelled burgermeister, literally "master of the town, master of the borough, master of the fortress, master of the citizens") is the English form of various terms in or derived from Germanic languages for the chief m ...

Solnhofen Solnhofen is a municipality in the district of Weißenburg-Gunzenhausen in the region of Middle Franconia in the ' of Bavaria in Germany. It is in the Altmühl valley. The local area is famous in geology and palaeontology for Solnhofen limes ...

, Germany, which was labeled as "unknown

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

" until its importance was recognized by

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

David Martill {{Short pages monitor