Sanajeh
Encyclopedia
Sanajeh is a genus
of late Cretaceous
madtsoiid
snake
from western India
. A recently described fossil from the Lameta Formation
has been found coiled around an egg and an adjacent skeleton of a 50 cm long sauropod dinosaur
hatchling. This suggests that the snake preyed on hatchling sauropods at nesting sites.
specimen, known as GSI/GC/2901–2906, consists of a nearly complete skull and lower jaws, and 72 precloacal vertebrae and ribs preserved in five articulated sections. It was found from Maastrichtian
-age calcareous
sandstone
s outcropping in the village of Dholi Dungri in Gujarat.
Sanajeh was around 3.5 metres (11.5 ft) in length based on the length of the skull, which is 95 millimetres (3.7 in). On the side of the skull there is an opening called the juxtastapedial recess, which is characteristically rectangular. The juxtastapedial recess would have contained cranial nerves
associated with the ear, while another opening located in front of the recess, the trigeminal foramen, housed cranial nerves associated with the jaws. The jaw joint of Sanajeh is located to the side of the posterior margin of the braincase, which is characteristic of basal
snakes. A sagittal crest
runs along the ventral surface of the braincase and served as an attachment for m. protractor pterygoidei muscles that moved the toothed bones of the palate
.
Articulations between the vertebrae are well developed in Sanajeh in a similar way to other madtsoiids and the genus Najash. The neural spines are thin and angled posteriorly. In Sanajeh, the synapophyses, or rib articulations, extend outward past the margins of the prezygapophyses. This is a characteristic of all madtsoiids.
of snakes that includes the Australia
n genera Wonambi
and Yurlunggur. Below is a cladogram
showing the phylogenetic relations of Sanajeh:
. Therefore, it could not consume prey as large as that which many modern snakes can. Living snakes that have narrow gapes, including uropeltids, Anomochilus
, Cylindrophis, and Anilius, have diets that are limited to smaller animals such as ant
s, termite
larvae, annelid
s, and amphisbaenians and caecilian
s. The short supratemporal and broad, short quadrate indicate that the oral gape of Sanajeh was narrow. The gape is thought to have been similar to that of the extant genus Xenopeltis. However, the presence of strong m. protractor pterygoidei muscles inferred from the sagittal crest of Sanajeh indicates that it was able to manipulate prey in its mouth like modern macrostomatans. The intramandibular joint was able to flex greatly, which would allow for the consumption of larger prey. The presence of these features in Sanajeh shows that increased oral kinesis (movement of the mouth) and intraoral mobility (the ability to move the bones of the palate) preceded the development of wide gapes in snakes. Therefore, reduced cranial kinesis in basal living snakes may be a fossorial
adaptation rather than the retention of a plesiomorphic trait.
The holotype of Sanajeh was found in association with sauropod eggs belonging to the oospecies Megaloolithus dhoridungriensis
and one incompletely preserved sauropod hatchling, likely a titanosaur
. The snake was coiled around a crushed egg, which the hatchling may have exited from. The eggs were laid in a nest structure that was not preserved, but was likely covered in loose sediment or vegetation based on the porosity of the eggs. The rigid eggs were probably too large for Sanajeh to consume, but the snake would have been able to break an egg open and consume its contents in a way similar to the living Loxocemus. Sanajeh is likely to have had a nest-plundering feeding strategy, and it is possible that the snake consumed a large variety of prey items including the eggs of theropods and smaller reptiles, which are common in the Lameta Formation.
Accelerated growth rates and large numbers of hatchlings would have enabled titanosaurs such as Isisaurus
and Jainosaurus
to overcome the losses of predation by animals such as Sanajeh. Titanosaurs would have been free of the risk of predation by their first year as a result of their rapid growth rate. The size of adult titanosaurs, which could be 20–25 m (65.6–82 ft) in length, would have deterred nearly all predators.
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 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...
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...
from western India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. A recently described fossil from the Lameta Formation
Lameta Formation
The Lameta Formation is a sedimentary rock formation found in Madhya Pradesh, Gujarat, and Maharashtra, India. It is of Maastrichtian age , and is notable for its dinosaur fossils...
has been found coiled around an egg and an adjacent skeleton of a 50 cm long sauropod 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...
hatchling. This suggests that the snake preyed on hatchling sauropods at nesting sites.
Description
The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen, known as GSI/GC/2901–2906, consists of a nearly complete skull and lower jaws, and 72 precloacal vertebrae and ribs preserved in five articulated sections. It was found from 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 calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s outcropping in the village of Dholi Dungri in Gujarat.
Sanajeh was around 3.5 metres (11.5 ft) in length based on the length of the skull, which is 95 millimetres (3.7 in). On the side of the skull there is an opening called the juxtastapedial recess, which is characteristically rectangular. The juxtastapedial recess would have contained cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
associated with the ear, while another opening located in front of the recess, the trigeminal foramen, housed cranial nerves associated with the jaws. The jaw joint of Sanajeh is located to the side of the posterior margin of the braincase, which is characteristic of basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
snakes. A sagittal crest
Sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull of many mammalian and reptilian skulls, among others....
runs along the ventral surface of the braincase and served as an attachment for m. protractor pterygoidei muscles that moved the toothed bones of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
.
Articulations between the vertebrae are well developed in Sanajeh in a similar way to other madtsoiids and the genus Najash. The neural spines are thin and angled posteriorly. In Sanajeh, the synapophyses, or rib articulations, extend outward past the margins of the prezygapophyses. This is a characteristic of all madtsoiids.
Classification
Sanajeh is a member of the Madtsoiidae, an extinct familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of snakes that includes the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n genera Wonambi
Wonambi
Wonambi is a genus that consisted of two species of very large snakes. These species were not pythons, like Australia's other large constrictors of the genus Morelia, and are now a member of an extinct family Madtsoiidae...
and Yurlunggur. Below is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
showing the phylogenetic relations of Sanajeh:
Feeding
Like many early snakes, Sanajeh did not have the wide gape seen in boids, pythons, and caenophidiansXenophidia
Xenophidia is a superfamily of the suborder Serpentes that contains cobras, vipers, sea snakes and the majority of snake species. Almost all venomous snakes belong to this superfamily...
. Therefore, it could not consume prey as large as that which many modern snakes can. Living snakes that have narrow gapes, including uropeltids, Anomochilus
Anomochilus
The Anomochilidae, or anomochilids, are a monotypic family created for the genus Anomochilus, which currently contains 3 monotypic species.-Description:...
, Cylindrophis, and Anilius, have diets that are limited to smaller animals such as ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s, termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
larvae, annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
s, and amphisbaenians and caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s. The short supratemporal and broad, short quadrate indicate that the oral gape of Sanajeh was narrow. The gape is thought to have been similar to that of the extant genus Xenopeltis. However, the presence of strong m. protractor pterygoidei muscles inferred from the sagittal crest of Sanajeh indicates that it was able to manipulate prey in its mouth like modern macrostomatans. The intramandibular joint was able to flex greatly, which would allow for the consumption of larger prey. The presence of these features in Sanajeh shows that increased oral kinesis (movement of the mouth) and intraoral mobility (the ability to move the bones of the palate) preceded the development of wide gapes in snakes. Therefore, reduced cranial kinesis in basal living snakes may be a fossorial
Fossorial
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...
adaptation rather than the retention of a plesiomorphic trait.
The holotype of Sanajeh was found in association with sauropod eggs belonging to the oospecies Megaloolithus dhoridungriensis
Megaloolithus
Megaloolithus is an oogenus of dinosaur egg.-References:* Carpenter, K. 1999. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction . Indiana University Press, Bloomington, Indiana....
and one incompletely preserved sauropod hatchling, likely a titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
. The snake was coiled around a crushed egg, which the hatchling may have exited from. The eggs were laid in a nest structure that was not preserved, but was likely covered in loose sediment or vegetation based on the porosity of the eggs. The rigid eggs were probably too large for Sanajeh to consume, but the snake would have been able to break an egg open and consume its contents in a way similar to the living Loxocemus. Sanajeh is likely to have had a nest-plundering feeding strategy, and it is possible that the snake consumed a large variety of prey items including the eggs of theropods and smaller reptiles, which are common in the Lameta Formation.
Accelerated growth rates and large numbers of hatchlings would have enabled titanosaurs such as Isisaurus
Isisaurus
Isisaurus is a genus of dinosaur from the Late Cretaceous Period. Isisaurus was a sauropod , which lived in what is now India....
and Jainosaurus
Jainosaurus
Jainosaurus is a large titanosaurian dinosaur of India and wider Asia, which lived in the Maastrichtian ....
to overcome the losses of predation by animals such as Sanajeh. Titanosaurs would have been free of the risk of predation by their first year as a result of their rapid growth rate. The size of adult titanosaurs, which could be 20–25 m (65.6–82 ft) in length, would have deterred nearly all predators.