''Indosaurus'' () is a

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 dubious carnivorous

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

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 ...

that lived in what is now

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, about 69 to 66 million years ago during 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 ...

division of the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Discovery and naming

The now-lost

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

was discovered between 1917 and 1919 in

Jabalpur Jabalpur, formerly Jubbulpore, is a city situated on the banks of Narmada River in the state of Madhya Pradesh, India. It is the 3rd-largest urban agglomeration of the state and the 38th-largest of the country. Jabalpur is the administrative h ...

, India (GSI K27/565), by Charles Alfred Matley.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 ...

, ''Indosaurus matleyi'', was named by Huene and Matley in 1933 making ''Indosaurus'' the first majungasaurine to be discovered. The generic name refers to India and the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honours Matley. This species now also includes ''

Megalosaurus ''Megalosaurus'' (meaning "great lizard", from Ancient Greek, Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic Epoch (Bathonian stage, 166 ...

matleyi''. Some

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

s have speculated that '' Indosuchus,'' '' Lametasaurus'' and ''Indosaurus'' should be considered as nomina dubia.

Description

The parietal of the frontal-parietal region is broad whereas the lower surface of the frontal is wide, the transverse crest lies above and behind the

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

. The frontals are concave and decline in to the front of the

cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

. The supratemporal fossa is short and broad as in ''

Antrodemus ''Antrodemus'' ("chamber bodied") is a dubious genus of theropod dinosaur from the Upper Jurassic, probably the Morrison Formation, of Middle Park, Colorado. It contains one species, ''Antrodemus valens'', first described and named as a species ...

''. The incomplete skull is of unusual thickness, although it lacked a dome on frontal bones as seen in '' Majungasaurus''. It would have also lacked the paired frontal horns seen in ''

Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...

''. Both '' Indosuchus'' and ''Indosaurus'' had a conservative skull roof which was dorsoventrally thickened but did not process prominences above the skull roof, similar to the condition seen in '' Abelisaurus''. The species ''I. matleyi'' weighed roughly .

Classification

Originally assigned by Huene to the

Allosauridae Allosauridae is an extinct family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Cha ...

, ''Indosaurus'' is today considered a member of the

Abelisauridae Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are fou ...

family. It shows similarities to the other Abelisaurids from India, such as '' Rajasaurus'' and '' Rahiolisaurus'', and is hence usually placed within Abelisauridae, though the fragmentary nature for this taxon makes it difficult to recognize its exact taxonomic validity.https://www.researchgate.net/publication/373144530_Review_of_the_Cretaceous_dinosaurs_from_India_and_their_paleobiogeographic_significance In 2014 Thierry Tortosa erected the subfamily Majungasaurinae. This was to separate '' Arcovenator'', '' Majungasaurus'', ''Indosaurus'', '' Rahiolisaurus'', and '' Rajasaurus'' from South American abelisaurids based on physical characteristics such as elongated

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

e in front of the eye sockets, and a sagittal crest that widens into a triangular surface towards the front of the head. It was suggested that the abelisaurids migrated between Africa, Europe, India and Madagascar, which would isolate the South American abelisaurids. It is possible that migration occurred between Europe and India across Africa given its proximity to both, and the volcanic Dras-Kohistan island arc may have allowed

island hopping Leapfrogging was an amphibious military strategy employed by the Allies in the Pacific War against the Empire of Japan during World War II. The key idea was to bypass heavily fortified enemy islands instead of trying to capture every island i ...

and an indirect path to Asia, though these are still questionable explanations. The following cladogram was recovered by Tortosa (2014):

Paleoecology

''Indosaurus'' lived in the

Lameta Formation The Lameta Formation, also known as the Infratrappean Beds (not to be confused with the contemporaneous Intertrappean Beds), is a sedimentary geological formation found in Madhya Pradesh, Gujarat, Maharashtra, Telangana, and Andhra Pradesh, Indi ...

during the

age of the

period. It is known to have lived alongside

sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

like '' Isisaurus'', '' Jainosaurus'' and the dubious ''

Titanosaurus ''Titanosaurus'' (; ) is a dubious genus of sauropod dinosaurs, first described by Richard Lydekker in 1877.R. Lydekker. (1877). Notices of new and other Vertebrata from Indian Tertiary and Secondary rocks. ''Records of the Geological Survey of ...

'', which it may have preyed upon. Other ceratosaurs such as the abelisaurid ''Rajasaurus'', ''Rahiolisaurus'' and ''Indosuchus'' are known from the formation, along with the noasaurid ''

Laevisuchus ''Laevisuchus'' (, "light crocodile") is a genus of Theropoda, theropod dinosaur from the Late Cretaceous. Its remains were discovered by Charles Alfred Matley near Jabalpur in Maastrichtian "Carnosaur Bed" deposits in the Lameta Formation in M ...

''. The

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxon'' comes from the Ancient Greek (''íchnos'') meaning "track" and English , itself derived from ...

'' Deltapodus'' is also known from the formation, which may belong to the youngest know

stegosaurid Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere (North America, Europe and Asia), Africa and South A ...

. The madtsoiid snake '' Sanajeh'' was also contemporaneous to ''Indosaurus''. The rocks of the Lameta formation appear to have been deposited in

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

conditions. The environment at the time of deposition has alternatively been considered

semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a aridity, dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as l ...

, or tropical humid. The dinosaurs in India probably all went extinct due to volcanic activity around 350,000 years before the

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end o ...

. Dinosaurs probably avoided areas with volcanic

fissure vent A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilo ...

s and

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

References

Abelisauridae Dinosaur genera Maastrichtian dinosaurs Fossil taxa described in 1933 Taxa named by Charles Alfred Matley Taxa named by Friedrich von Huene Dinosaurs of India {{theropod-stub

Discovery and naming

Description

Classification

Paleoecology

See also

References