''Menarana'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of madtsoiid

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

which existed in

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

. The

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

is ''Menarana nosymena''. Several

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e and

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

fragments as well as part of the

basicranium The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...

have been found from the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

-age

Maevarano Formation The Maevarano Formation is a Late Cretaceous sedimentary formation (geology), rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rive ...

in the

Mahajanga Basin Mahajangā (French: Majunga) is a city and an administrative district on the northwest coast of Madagascar. The city of Mahajanga (Mahajanga I) is the capital of the Boeny Region. The district (identical to the city) had a population of 258,068 ...

Paleobiology

''Menarana'' was around long and was probably

fossorial A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...

, burrowing with its head. Evidence of a fossorial lifestyle can be found in its braincase, as the bones of the basicranium are highly fused to withstand stresses from burrowing. This degree of fusion is otherwise only seen in

caecilia ''Caecilia'' is a genus of amphibians in the family Caeciliidae Caeciliidae is the family of common caecilians. They are found in Central and South America. Like other caecilians, they superficially resemble worms or snakes. Although they ...

ns,

amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of typically legless lizards, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. A ...

ns, and uropeltid snakes, all of which are highly specialized burrowers. The vertebrae are depressed and have very low

neural spine Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

s similar to those of living burrowing snakes. The

atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

, which is the first vertebra of the spine closest to the head, may show adaptations toward structural integrity under loads that would be encountered during tunnel excavation. The

neural arch Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

es of the atlas are fused to the intercentrum, strengthening the anterior atlantal cotyle, a cup-like depression that articulates with the

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...

of the skull. Despite these features, it is possible that ''Menarana'' was not a powerful burrower, and that the burrowing characteristics were retained from a burrowing ancestor. The related madtsoiid ''

Yurlunggur ''Yurlunggur'' is a genus of fossil snake in the extinct family Madtsoiidae containing the species ''Yurlunggur camfieldensis'' known from the Oligocene and Miocene of Australia''.'' ''Y. camfieldensis'' was a large apex predator that typical ...

'' also has a highly fused basicranium, but its snout is unspecialized and unsuitable for digging. Moreover, its large body size would have made it difficult to burrow through compact soils. This indicates that ancestral fossorial characteristics can be retained even if the snake was not fossorial. While ''Menarana'' is less than half the size of ''Yurlunggur'', it would have also encountered problems while burrowing due to its large size. Most head-first burrowers are very small, with heads that have a small diameter to allow them to push through soil more easily. While most living head-first burrowers are less than in diameter, ''Menarana'' could have exceeded in diameter, with a cross-sectional area even larger than living burrowers because of an increase in size according to a

quadratic function In mathematics, a quadratic function of a single variable (mathematics), variable is a function (mathematics), function of the form :f(x)=ax^2+bx+c,\quad a \ne 0, where is its variable, and , , and are coefficients. The mathematical expression, e ...

(the square of the diameter). Therefore, ''Menarana'' may have required significantly greater force to push through compact sediment, with the force possibly being ineffective or impossible to generate. Due to its small size, the diet of ''Menarana'' probably consisted of prey ranging in mass from to . ''Menarana'' would not have been able to consume any of the nonavian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s that are also known from the Maevarano Formation, and probably could not prey on any

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...

s with the exception of the

notosuchia Notosuchia is a clade of primarily Gondwanan mesoeucrocodylian Crocodylomorpha, crocodylomorphs that lived during the Jurassic and Cretaceous. Some phylogeny, phylogenies recover Sebecosuchia as a clade within Notosuchia, others as a sister group ...

n ''

Araripesuchus tsangatsangana ''Araripesuchus'' is a genus of extinct crocodyliform that existed during the Cretaceous period of the late Mesozoic era some 125 to 66 million years ago. ''Araripesuchus'' is generally considered to be a notosuchian (belonging to the clade Mesoe ...

''. It most likely fed on smaller snakes,

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s, and small

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

References

External links

''Menarana''
in the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

{{Taxonbar, from=Q6816464 Cretaceous snakes Fossil taxa described in 2010 Maevarano fauna