''Tikitherium'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

mammaliaform Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recent com ...

s from the Late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

. It is thought to be an insectivore and a close relative to

Docodonta Docodonta is an Order (biology), order of extinct Mammaliaformes, mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early Mammaliaformes, mammaliaforms by their relativel ...

. ''Tikitherium'' refers to Tiki, the village located near the

Tiki Formation The Tiki Formation is a Late Triassic (Carnian to Norian) geologic formation in Madhya Pradesh, northern India.Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...

for his pioneering discoveries towards understanding mammalian molars.Datta, P.M. 2005. Earliest Mammal with Transversely Expanded Upper Molar from the Late Triassic (

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

) Tiki Formation, South Rewa Gondwana Basin, India. Journal of Vertebrate Paleontology. 25(1):200-207.

History and discovery

''Tikitherium copei'' was first described by Datta in 2005. The first and only specimen is an upper left molar that was discovered in the lower part of the Tiki Formation, located in the South Rewa Gondwana Basin,

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

. Both the genus ''Tikitherium'' and the species ''copei'' were named by Datta in 2005. The currently only known specimen was deposited in the Paleontology Division of the Geological Survey of India, Calcutta. Although only a single tooth was found, it showed several derived features that are similar to other early mammalian dentitions, but further detailed comparisons showed the various differences that allowed this tooth to specifically stand out on its own.

Geological and paleoenvironment

The Tiki Formation is located in the South Rewa Gondwana Basin,

Madhya Pradesh, India Madhya Pradesh (, ; meaning 'central province') is a state in central India. Its capital is Bhopal, and the largest city is Indore, with Jabalpur, Ujjain, Gwalior, Sagar, and Rewa being the other major cities. Madhya Pradesh is the second la ...

. It is known for many vertebrate fossils being found there. The area can be described as having red mudstones with greenish grey mottling, calcareous sandstones, cross-bedding feldspathic sandstones, and lime-pellet conglomerate horizon. The upper triassic Tiki Formation is a mud-dominated fluvial followed by coarse to fine grained quartzo-feldspathic sandstone.Bhat, Mohd Shafi, Sanghamitra Ray, and PM DATTA. 2017 A New Hybodont Shark (Chondricthyes, Elasmbocranchii) from the Upper Triassic Tiki Formation of India with Remarks on its Dental Histology and Biostratigraphy. Journal of Paleontology, 92(2):221-239 It is overlain by the Parsoria Formation and is composed of pink, red, and lavender colors and interbeds of sandstone that contain clay clasts of varying size. The Tiki Formation is underlain by the Pali Formation with local erosional contact to the area of study. The beginning of the Triassic is indicated by arid climate in most of the Gondwana Basins. In particular in the Tiki Formation the sandstone in the Valley turns clay dominant indicating the Middle Triassic. The Tiki Formation contains well preserved and varied vertebrate assemblages including fish, amphibians, reptilian, and mammalian amniotes.Mukherjee, Debarati and Ray Sanghamitra. 2012. Taphonomy of an Upper Triassic Vertebrate Bonebed: a New Rhynchosaur (Reptilia; Archosauromorpha) Accumulation from India. Paleogeography, Paleoclimatology, Paleoecology. 333-334:75-91. The mudstone has also been home to many teeth specimen, skull fragments, and post-crania. It also hosts partial and complete skeletons of

temnospondyls Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...

phytosaur Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...

s, and

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

s. The faunal and floral assemblages of the Tiki Formation are comparable to the Late Triassic assemblage of the German Keuper. Because of its faunal and floral assemblages, the Tiki Formation is also comparable to the lower part of the Maleri Formation of the Pranhita-Godavari Basin and the Camp Springs Member of the Dockum Group, USA, and thus was assigned the Late Triassic Age. The tooth was discovered in a bed of calcareous mudstone exposed 4 kilometers Southwest of the Tiki Village, which has the same stratigraphic horizon from a tooth of the Late Triassic Morganucodontid mammal ''Gonwanadon Tapani'' was recovered.

Description

Dentition

There has only been a single left molar found and all of the characters have been based on this sole specimen. It has several derived traits that resemble those of Docodonta and

Holotheria Mammalia is a class of animal within the phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson ...

n molars. The tooth is supported by three large roots unlike in ''

Woutersia ''Woutersia'' was a Triassic genus of 'symmetrodont' and the only representative of the family Woutersiidae. It was originally classified as a kuehneotheriid, but it has been suggested that it may be related to Docodonta. Remains of ''W. mirabili ...

'', which only has two large roots. The smallest root supports the small lingual half while in Docodonta the largest root supports the small lingual half. It is tricuspid with three buccally placed cusps forming an obtuse triangle contrasting the cusp pattern in Docodonts where they are in a linear fashion. It is thought that Woutersia's upper molar teeth to be comparable to ''Tikitherium'' in regards to cusp pattern and crown dimensions. The principal buccal cusp is the tallest measured at a height of 1.08mm and the tooth has a broad base occupying the entire length of the crown. There are prominent cusps with two associated shearing crests. There is also a talon-like platform anterior to the prominent cusps. The tooth also has a strong and wide lingual and buccal cingula. There are wear facets on the molar to suggest occlusion with the lower molars. In ''Tikitherium,'' the wear facets are found on the lingual side unlike with ''Woutersia'' where the wear facets are found only on the anterior face. The wear facets can also be described to be located in the narrow valley between the lingual face of two cusps while in Docodonts the wear facts are confined to the central basins.

Skull

It has been suggested that the angular process is a present and homologous feature across Mammaliaformes. ''Tikitherium'' could possibly have one present based on this conclusion although no conclusion can be made without the discovery of a skull specimen.

Paleobiology

Feeding

The wear facets on the upper molar suggest a probable occlusal relationship with the lower dentition. However no conclusion can be made about occlusion without a lower dentition specimen. There is also a posterolingual cusp with two shearing crests and basins to indicate mastication via grinding. This molar is the earliest representative of several independent evolutionary developments found in later mammalian groups such as

Boreosphenida Tribosphenida is a group (infralegion) of mammals that includes the ancestor of ''Hypomylos'', Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants). Its current definition is more or less sy ...

Australosphenida The Australosphenida are a clade of mammals, containing mammals with tribosphenic molars, known from the Jurassic to Mid-Cretaceous of Gondwana. They are thought to have acquired their tribosphenic molars independently from those of Tribosphenida ...

, Shuotheriids, and

. It is also the earliest mammal representative to possess this advanced dental specialization and is the evidence towards the hypothesis of homoplastic evolution of dental grinding features. Before the finding of the ''Tikitherium'' specimen, it was hypothesized that the origin of the crushing mastication in docodonts was from ''

Morganucodon ''Morganucodon'' (" Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represe ...

's'', shearing nature via the shearing crests and cusps and occlusion. It was later found that ''

'' also had the crushing molar action that would be later found in Docodonta.Sigogneau-Russel, Denise and Renate Hahn. 1995. Reassessment of the late Triassic Symmetrodont Mammal Woutersia. Acta Palaeontologica Polonica. 40(3):245-260.

Classification

''Tikitherium'' is considered to be mammal based on Datta (2005). However, the phylogeny based on Luo and Martin (2007) places ''Tikitherium'' and Docodonta as sister taxa, which are Mammaliformes, based on the shared traits of wear facets and platform on the lingual side of the molars. Although Luo and Martin conclude that ''Tikitherium'' and Docodonta are the most closely related, it is debated that ''Woutersia'' instead may be the sister taxa to Docodonta due to the similarity of their prominent lingual cusps.

References

{{Taxonbar, from=Q6146887 Prehistoric mammaliaforms Prehistoric cynodont genera Carnian genera Late Triassic synapsids Triassic synapsids of Asia Triassic India Fossils of India Fossil taxa described in 2005