Menarana
Encyclopedia
Menarana is an extinct genus
of madtsoiid
snake
which existed in Madagascar
during the Late Cretaceous
. The type species
is Menarana nosymena. Several vertebrae and rib
fragments as well as part of the basicranium have been found from the Maastrichtian
-age Maevarano Formation
in the Mahajanga Basin
.
, 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
ns, amphisbaenia
ns, and uropeltid snakes, all of which are highly specialized burrowers. The vertebrae are depressed and have very low neural spines similar to those of living burrowing snakes. The atlas
, 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 arches of the atlas are fused to the intercentrum, strengthening the anterior atlantal cotyle, a cup-like depression that articulates with the occipital condyle
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 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 1 centimetre (0.393700787401575 in) in diameter, Menarana could have exceeded 7 centimetres (2.8 in) in diameter, with a cross-sectional area even larger than living burrowers because of an increase in size according to a quadratic function
(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 5 kilograms (11 lb) to 1 kilograms (2.2 lb). Menarana would not have been able to consume any of the nonavian dinosaur
s that are also known from the Maevarano Formation, and probably could not prey on any crocodylomorphs with the exception of the notosuchia
n Araripesuchus tsangatsangana. It most likely fed on smaller snakes, lizard
s, and small mammal
s.
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 madtsoiid
Madtsoiidae
Madtsoiidae are an extinct group of mostly Gondwanan snakes with a fossil record extending from early Cenomanian to late Pleistocene strata located in South America, Africa, India, Australia and Southern Europe...
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...
which existed in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
during 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...
. 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...
is Menarana nosymena. Several 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...
fragments as well as part of the basicranium have been found from the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
-age Maevarano Formation
Maevarano Formation
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges...
in the Mahajanga Basin
Mahajanga Province
Mahajanga is a former province of Madagascar with an area of 150,023 km². It had a population of 1,896,000 . Its capital was Mahajanga.Except for Fianarantsoa, Mahajanga Province bordered all of the country's other provinces:...
.
Paleobiology
Menarana was around 2.4 metres (7.9 ft) long and was probably fossorialFossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...
, 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
Caecilia is a genus of amphibians in the family Caeciliidae.- Species :...
ns, amphisbaenia
Amphisbaenia
The Amphisbaenia are a usually legless suborder of squamates closely related to lizards and snakes. As many species possess a pink body coloration and scales arranged in rings, they have a superficial resemblance to earthworms. They are very poorly understood, due to their burrowing lifestyle...
ns, and uropeltid snakes, all of which are highly specialized burrowers. The vertebrae are depressed and have very low neural spines similar to those of living burrowing snakes. The atlas
Atlas (anatomy)
In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....
, 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 arches of the atlas are fused to the intercentrum, strengthening the anterior atlantal cotyle, a cup-like depression that articulates with the occipital condyle
Occipital condyle
The occipital condyles are undersurface facets of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra....
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 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 1 centimetre (0.393700787401575 in) in diameter, Menarana could have exceeded 7 centimetres (2.8 in) in diameter, with a cross-sectional area even larger than living burrowers because of an increase in size according to a quadratic function
Quadratic function
A quadratic function, in mathematics, is a polynomial function of the formf=ax^2+bx+c,\quad a \ne 0.The graph of a quadratic function is a parabola whose axis of symmetry is parallel to the y-axis....
(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 5 kilograms (11 lb) to 1 kilograms (2.2 lb). Menarana would not have been able to consume any of the nonavian dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s that are also known from the Maevarano Formation, and probably could not prey on any crocodylomorphs with the exception of the notosuchia
Notosuchia
Notosuchia is a suborder of primarily Gondwanan mesoeucrocodylian crocodylomorphs that lived during the Cretaceous. Fossils have been found from South America, Africa, and Asia...
n Araripesuchus tsangatsangana. It most likely fed on smaller snakes, 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 small mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s.
External links
- Menarana in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...