''Raranimus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

s of the

Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...

. It was described in 2009 from a partial skull found in 1998 from the Dashankou locality of the

Xidagou Formation The Qingtoushan Formation is a Middle Permian-age geologic formation in the Qilian Mountains of Gansu, China. It is known for its diverse tetrapod fauna known as the Dashankou fauna, which likely dates to the Roadian, and includes some of the ol ...

, outcropping in the

Qilian Mountains The Qilian Mountains (, also romanized as Tsilien; Mongghul: Chileb), together with the Altyn-Tagh (Altun Shan) also known as Nan Shan (, literally "Southern Mountains"), as it is to the south of Hexi Corridor, is a northern outlier of the Kunlu ...

of Gansu, China. The genus is the most basal known member of the clade Therapsida, to which the later

Mammalia Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...

belong.

Description

''Raranimus'' shares a number of features with later therapsids and ancestral

Sphenacodontia Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes '' Haptodus baylei'', '' Haptodus garnettensis'' and '' Sphenacodon ferox'', but not '' Edaphosaurus pogoni ...

. The skull consists of a well preserved

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

. The teeth suggest a carnivorous lifestyle for ''Raranimus'', as the incisors are recurved and the second canines are serrated on their posterior edges. The incisors are morphologically similar to those seen in more derived

theriodont The theriodonts (clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, Ric ...

s. The presence of two linguo−labially compressed canines is a diagnostic feature of ''Raranimus''. The presence of two functional canines is characteristic of sphenacodontids, and this condition is seen in no other therapsid other than ''Rananimus''. However, the slender, compressed shape of these canines is a derived characteristic of therapsids, with the canines of similarly sized sphenacodontids being more massively built. The precanines are small and anteriorly serrated, similar to what is seen in the synapsids '' Dimetrodon'' and ''

Tetraceratops ''Tetraceratops insignis'' ("four-horned face emblem") is an extinct synapsid from the Early Permian that was formerly considered the earliest known representative of Therapsida, a group that includes mammals and their close extinct relatives. It ...

''. In the palate region of the skull, the anterior process of the

vomer The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right max ...

ventrally overlies the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

at the anterior margin of the

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

. This overlap is also seen in

dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinocephal ...

ns. However, unlike any other therapsid, the choanae are short and extend only from the level of the fourth incisor back to the first canine.

Phylogenetics

According to a phylogenetic analysis conducted along with its initial description, ''Raranimus'' is considered to be the basalmost therapsid. There has been some controversy as to whether ''Tetraceratops'' is a therapsid or a more basal

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...

. If ''Tetraceratops'' is a therapsid, as has recently been proposed, it would be the oldest and most basal one known, surpassing ''Raranimus'' in age by several million years. However, later studies have questioned the placement of ''Tetraceratops'' within Therapsida, and the 2009 phylogenetic analysis using ''Raranimus'' places the genus outside of the clade. ''Raranimus'' occurs in strata that were deposited during the early

Roadian In the geologic timescale, the Roadian is an age or stage of the Permian. It is the earliest or lower of three subdivisions of the Guadalupian Epoch or Series. The Roadian lasted between and million years ago (Ma). It was preceded by the ...

stage of the

.The hypothesized age for this locality is supported by the presence of the

dissorophoid Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...

temnospondyl 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 Carbo ...

Anakamacops ''Anakamacops'' (meaning "similar to ''Kamacops''" in Greek) is a genus of dissorophid temnospondyl from the early Middle Permian of China. It is known from the right side of a snout that was described in 1999 from the Dashankou locality of the ...

'', the

bolosaurid Bolosauridae is an extinct family of ankyramorph parareptiles known from the latest Carboniferous (Gzhelian) or earliest Permian (Asselian) to the early Guadalupian epoch (latest Roadian stage) of North America, China, Germany, Russia and France. ...

Belebey Belebey (russian: Белебе́й; ba, Бәләбәй) is a town in the Republic of Bashkortostan, Russia, located on the bank of the Usen River, from Ufa. Population: History Belebey was established in 1715 and granted town status in 1781. ...

'', and the basal therapsids ''

Biseridens ''Biseridens'' ("two rows of teeth") is an extinct genus of anomodont therapsid, and one of the most basal anomodont genera known. Originally known from a partial skull misidentified as an eotitanosuchian in 1997, another well-preserved skull w ...

'', ''Sinophoneus'', and ''Stenocybus''. The sphenacodontids were most diverse before the Roadian in the Early Permian, yet therapsids did not appear as a diverse group until near the Roadian-Wordian boundary. This has left a morphological and temporal gap in the fossil record during which the origin of therapsids must have occurred called

Olson’s Extinction Olson's Extinction was a mass extinction that occurred in the late Cisuralian or early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event. It is named after Everett C. Olson. There was a sudden change bet ...

. With the general absence of therapsid remains from Olson's Extinction, different hypotheses have developed in order to explain the group's origins and initial diversification. One theory suggests that therapsids diversified quickly through rapid apomorphy accumulation sometime during the gap, while the other proposes that therapsids evolved gradually over the course of up to 35 Ma. Only recently have remains of basal therapsids such as ''Raranimus'' been found from China that occur during Olson's Extinction. Other therapsids that are known to have existed during the gap include '' Sinophoneus'' and '' Stenocybus''. Raranimus skull

Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

modified from Liu ''et al.'', 2009 depicting the phylogenetic relationships of ''Raranimus'' with therapsids that occur in Olson's Gap highlighted:

References

{{Taxonbar, from=Q2044958 Permian synapsids of Asia Guadalupian synapsids Prehistoric therapsid genera Fossil taxa described in 2009 Guadalupian genus first appearances Guadalupian genus extinctions