''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 n ...
of
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 mor ...
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, 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 Kunl ...
of
Gansu,
China. The genus is the most
basal
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
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), fu ...
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 pogonia ...
. The skull consists of a well preserved
rostrum. 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, R ...
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
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non- mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodo ...
'' 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. I ...
''.
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 maxil ...
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. Dinoceph ...
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. 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 stage 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 ...
.[The hypothesized age for this locality is supported by the presence of the dissorophoid ]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 Carb ...
'' Anakamacops'', the bolosaurid
Bolosauridae is an extinct family (biology), family of ankyramorph parareptiles known from the latest Carboniferous (Gzhelian) or earliest Permian (Asselian) to the early Guadalupian Epoch (geology), epoch (latest Roadian stage) of North America, ...
''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 ...
'', ''Sinophoneus'', and ''Stenocybus''. The sphenacodontids were most diverse before the Roadian in the Early Permian 01 or '01 may refer to:
* The year 2001, or any year ending with 01
* The month of January
* 1 (number)
Music
* 01'' (Richard Müller album), 2001
* ''01'' (Son of Dave album), 2000
* ''01'' (Urban Zakapa album), 2011
* ''O1'' (Hiroyuki Sawano ...
, 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.
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
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
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''.
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