Tikitherium

''Tikitherium'' is an extinct genus of mammaliaforms from India, known from a single upper tooth. Originally argued to be a primitive mammaliaform from the Late Triassic, a 2024 study argued that it actually represented the remains of a shrew from the Neogene. ''Tikitherium'' refers to Tiki, the village located near the Tiki Formation where the specimen was originally thought to have come from, and ''therium'' is Greek for “Beast”. The species was named ''copei'' in honor of Edward Drinker Cope for his pioneering discoveries towards understanding mammalian molars.Datta, P.M. 2005
Earliest Mammal with Transversely Expanded Upper Molar from the Late Triassic (Carnian) 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 tooth that was thought to have discovered in the lower part of the Late Triassic Tiki Formation, located in the South Rewa Gondwana Basin, India. 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.

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.

A 2024 study argued that the tooth was actually the upper fourth premolar of a shrew belonging to the subfamily Crocidurinae, and actually dated to the Neogene rather than the Late Triassic as had previously been supposed. The authors suggested that ''T. copei'' "likely represents a distinct taxon at least at the species level. However, as the validity of ''T. copei'' is not certain, Pal/CHQ-009, the holotype of ''T. copei'', should be currently identified as Crocidurinae gen. et sp. indet."

Description

''Tikitherium'' is only known from a single upper tooth, originally argued to be a left molar but currently thought to be a right fourth premolar. The tooth closely resembles members of the modern shrew subfamily Crocidurinae in having a "short horseshoe-shaped protocone", and the hypocone being absent. The tooth is broadly similar to those of species of '' Suncus.'' It differs from modern members of Crocidurinae by "a more massive central cusp ( paracone) and a more obtuse angle between the paracone axis and the lingual lobe.", which are likely plesiomorphic features.

Geological and paleoenvironment

''Tikitherium'' was previously thought to have originated from the Tiki Formation, which is well known for its Late Triassic vertebrates. However, it has since been argued that ''Tikitherium'' actually was found in reworked sediments derived from erosion of the Tiki Formation that formed much later during the Neogene. A similar issue was previously reported with '' Tikiguania'' which was also previously interpreted as coming from the Tiki Formation, and thus the oldest known squamate, but was later interpreted as modern agamid lizard coming from Neogene or Quaternary deposits.

References

{{Taxonbar, from=Q6146887

Prehistoric mammals of Asia
White-toothed shrews
Neogene Asia
Fossils of India
Fossil taxa described in 2005