| Tonomochota Temporal range: LatePleistocene | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Lagomorpha |
| Family: | Ochotonidae |
| Genus: | †Tonomochota Tiunov & Gusec, 2021 |
| Type species | |
| †Tonomochota khasanensis Tiunov & Gusec, 2021 | |
| Other species | |
| |
Tonomochota is an extinct genus ofochotonid endemic to theRussian Far East region that is known currently from the LatePleistocene and possibly the EarlyHolocene. Dental remains belonging to the genus were uncovered from fossil deposits in multiple eastern Russian caves and later formally described by Russian researchers starting in 2021. The genus name is an anagram of the extinct ochotonid genusOchotonoma. There are four species assigned toTonomochota in total.
Tonomochota is one of two ochotonid genera known from the Pleistocene, the other being the extantOchotona, which contains pikas. It would have coexisted with a few extinct small mammals along with plenty of extant small mammal species in a blend of forested and open habitats.
From 2012 to 2016, paleontologists excavated dental fossils belonging to theOchotonidae from two eastern Russian limestone caves: Sukhaya Cave and Tetyukhinskaya Cave. The fossils found in both caves date to the LatePleistocene and may have accumulated because of predatory animal and bird activities. Excavators recovered 17 teeth of undescribed ochotonid species from Tetyukhinskaya Cave from 2012 to 2015; they later uncovered 27 additional ochotonid teeth from Sukhaya Cave in 2016.[1]
In 2021, the Russian paleontologists Mikhail P. Tiunov and Alexander E. Gusev erected the genusTonomochota, describing its naming origin as an anagram of the fossil ochotonid genusOchotonoma. The type and first newly recognized species isTonomochota khasanensis, thus making the genus type locality Sukhaya Cave; the species name derives from theKhasansky District where the cave is found. The second species that the two researchers erected wasT. sikhotana from Tetyukhinskaya Cave, whose name derives from theSikhote-Alin mountain range inPrimorsky Krai where the cave is located. The third species they named wasT. major from Sukhaya Cave, its name being in reference to its large size.[1]
Another series of ochotonid dental fossil excavations were done at Korydornaya Cave at theJewish Autonomous Oblast at Russia from 2017 to 2018. In 2023, Russian paleontologists Alexander E. Gusev and Mikhail P. Tiunov studied the ochotonid teeth and erectedT. khinganica, named after theGreater Khingan mountain range in China.[2]
Tonomochota belongs to the Ochotonidae, of which the only extant genus isOchotona (which contains pikas). The family is divided into two subfamilies, theOchotoninae andSinolagomyinae.[1] The earliest fossil record of the Ochotonidae is recorded in the early LateOligocene of Mongolia. The Sinolagomyinae was the earlier-appearing family known initially from Mongolia and China that later dispersed to Europe, Africa, and North America and lasted up to the MiddleMiocene. The Ochotoninae made its first appearance in the Eurasian landmass during the Early Miocene and was especially diverse during the Middle Miocene. During the Late Miocene, newer ochotonine genera appeared in response to drier and cooler climates that led to more open environments. The evolutionary diversity of the Ochotoninae declined beginning in thePliocene likely due to competition with thecricetid subfamilyArvicolinae, leading to the eventual extinction of most ochotonid genera by the late Pliocene.[3]Ochotona andTonomochota are the only two ochotonid genera known from the Pleistocene.[1]
The Ochotoninae is defined based on specific dental traits of P3 (third lowerpremolar), namely a prominentanteroconid cusp that is either round or triangular in shape and opposite shallow front and back folds (paraflexid andprotoflexid).Tonomochota is diagnosed solely based on dental traits. The P3 tooth has a triangular anteroconid containing acementum-filled front fold and a back fold that may or may not have cementum. The inward-facing anteroconid folds lean towards the sides. It differs fromOchotona based on the typical presence of cementum-filled side folds. It can also be distinguished fromOchotonoma andOchotonoides by the deeper side folds that frontwards on both the front and back sides. It additionally differs fromPliolagomys by its smaller size, the presence of cementum-filled folds, and the specific connection of the paraflexid and protoflexid that results in the former being deep and the latter being shallow.[1]
Tonomochota is described as ranging from small to large sizes relative to other members of its family.T. khasanensis is a small-sized species as well as the smallest species of its genus.T. khasanensis andT. khinganica are both medium-sized species, although the latter is larger than both the former and thenorthern pika (Ochotona hyperborea).T. major is a large-sized ochotonid and the largest of its genus.[1][2]
Tonomochota is exclusively known from mountain ranges of theRussian Far East during the Late Pleistocene, the fossil deposits containing it dating back to MIS 3 of themarine isotope stages. During MIS 3, climates were warmer than the modern day and allowed for forested and rocky landscape habitats to co-occur with more open habitats. Dental records ofT. khasanensis suggest that it could have lived up to the earlyHolocene.[1][2]
Within the Tetyukhinskaya Cave, fossils of various other small mammals have been recovered such as those of the extinct squirrel speciesPetaurista tetyukhensis along with those of various extant species like theAmur hedgehog,Ussuri mole,Asian lesser white-toothed shrew, northern pika,Siberian flying squirrel,red squirrel,long-tailed ground squirrel,brown rat,northern red-backed vole, andwood lemming.[4] The Korydornaya Cave contains similar small mammal fauna fossils in addition to the extinct shrew genusBeremendia but additionally contains those of large mammal fossils like thesable,red fox,gray wolf,brown bear,Siberian musk deer,moose, andwild boar.[2]