Palæos:		Unit 400: Therapsida
The Vertebrates		200: Therapsida: Raranimus

Therapsida: Raranimus

SYNAPSIDA
|
Therapsida
|--Tetraceratops
|--Raranimus
`--+-?Phthinosuchidae
   |--Biarmosuchia
   `--+--Dinocephalia
      `--+--Anomodontia
         |  |--Venyukovioidea
         |  `--Dicynodontia   
         `--Theriodontia
            |--Gorgonopsia
            `--+--Therocephalia
               `--CYNODONTIA

Taxa on This Page

1. Raranimus X

Raranimus

Raranimus - artwork by Dmitry Bogdanov - Wikipedia

Overworked author's note: the following is from Wikipedia (quoted here in toto because it is so well-written and there are so many pages to get through...) - content mostly by Smokeybjb

Raranimus is an extinct genus of therapsid of the Middle Permian. 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 of Gansu, China. The genus is the most basal known member of the paraphyletic order Therapsida, from which the class Mammalia is a descendant taxon. (Liu, Rubidge, & Li 2009)

Description

Partial skull of Raranimus dashankouensis (drawing of holotype) left lateral view. Abbreviations: c1–2, canine 1–2; ch, choana; en, external naris; i1–6, incisor 1–6; M, maxilla; N, nasal; p1–3, postcanine 1–3; Pf, prefrontal; Pl, palatine; Pm, premaxilla; Pt, pterygoid; rc, replacement canine; ri, replacement incisor; Sm, septomaxilla; sp, small precanine maxillary tooth; V, vomer. From Liu, Rubidge, & Li 2009 p.395.

Raranimus shares a number of features with later therapsids and ancestral sphenacodontids. 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 theriodonts. 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.(Romer & Price 1940, Laurin & Reisz 1996]

In the palate region of the skull, the anterior process of the vomer ventrally overlies the premaxilla at the anterior margin of the choana. This overlap is also seen in dinocephalians. However, unlike any other therapsid, the choanae are short and extend only from the level of the fourth incisor back to the first canine.Liu, Rubidge, & Li 2009

Phylogenetics

According to a phylogenetic analysis conducted along with its initial description, Raranimus is considered to be the basalmost therapsid. Liu, Rubidge, & Li 2009 There has been some controversy as to whether or not 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.Laurin & Reisz 1996. 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. (Liu, Rubidge, & Li 2009, Sidor & Hopson 1998, Conrad & Sidor 2001]

Raranimus occurs in strata that were deposited during the early Roadian stage of the Middle Permian.[The hypothesized age for this locality is supported by the presence of the dissorophoid temnospondyl Anakamacops, the bolosaurid Belebey, and the basal therapsids Biseridens, 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. (Abdala et al 2008) This gap has been called "Olson's Gap".[Lucas 2004, Ivakhnenko 2005

With the general absence of therapsid remains found from strata deposited during Olson's Gap, 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. (Abdala et al 2008, Kemp 2006] Only recently have remains of basal therapsids such as Raranimus been found from China that occur during Olson's Gap. Other therapsids that are known to have existed during the gap include Sinophoneus and Stenocybus.[Cheng & Li 1997]

Raranimus: R. dashankouensis Liu, Rubidge, & Li 2009.

Range: Roadian (Early Middle Permian) of China.  (Xidagou Formation, Dashankou, Gansu, China)

Phylogeny: Therapsida : + (Biarmosuchia + (Eotitanosuchia + Eutherapsida)))) + *. 

Characters: Plesiomorphic, short choana; long facial process of septomaxilla; one precanine and two functional linguo-labially compressed canines on maxilla; six incisors.

Size: complete skull estimated to exceed 16 cm.

Reference: Liu, Rubidge, & Li 2009

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