Saturday 7 March 2015

Kannemeyeriiforme Dicynodonts from the Middle Triassic of Shanxi Province, China.

Triassic deposits are widespread in Northern China, but Tetrapod fossil producing locations are very rare. Those that are known are restricted to the Heshanggou, Ermaying and Tongchuan formations, with the Ermaying producing the most abundant and diverse assemblages.

In a paper published in the journal Vertebrata PalAsiatica on 12 January 2015, Liu Jun of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences describes a series of Kannemeyeriiforme Dicynodont remains from two new Triassic localities in Liulin and Linxian counties in Shanxi Province.

The first set of remains comprise the front part of a skull with an associated jawbone, a cervical vertebra, a rib, a left humerus, radius, femur and tibia and an incomplete right ilium from an exposure of the Tongchuan Formation at Baidaoyu in Linxian County. These remains are placed in the genus Sinokannemeyeria, due to the wide low shape of the skull, the short anterior end of the premaxilla, a shallow depression on the anterior of the premaxilla, long dentary symphysis and a wide femur, and described as a new species, Sinokannemeyeria baidaoyuensis, meaning ‘from Baidaoyu’, due to an extension of the prefrontal bone level with the posterior margin (back) of the postnarial excavation.

Sinokannemeyeria baidaoyuensis: Skull in dorsal (A), ventral (B), anterior (C), and lateral (D) views; lower jaws in dorsal (E), lateral (F) and ventral (G) views. Abbreviations: L, lacrimal; M, maxilla; N, nasal; Pf, prefrontal; Pm, premaxilla; Sm, septomaxilla. Lui (2015).

Lui also notes that the caniniform tooth of the specimen is not completely wrapped by the caniniform process, and that this does not appear to be as a result of post-mortem damage. Since this state would weaken the tooth and has no apparent useful function it is thought to be a pathology suffered by the animal in life. The specimen also has weakly sutured skull bones and poorly ossifies ends on the humerus and femur, which may indicate it was a sub-adult.

Sinokannemeyeria baidaoyuensis: (A) A cervical vertebra in anterior view; (B) distal portion of left humerus in ventral (B1) and dorsal (B2) views; (C) left radius in anterior (C1) and posterior (C2) views; D. partially right ilium in lateral (D1) and medial (D2) views; (E) left femur in posteroventral (E1) and anterodorsal (E2) views; (F) left tibia in proximal (F1), anterior (F2) and posterior (F3) views. Abbreviations: cn.c, cnemial crest; ect, ectepicondyle; ent, entepicondyle; ent. f, entepicondyle foramen; ipp, iliac posterior process. Lui (2015).

The second set of remains comprise an occiput, a quadrate, a quadratojugal; a right caniniform process with tusk, one centrum, five neural arches, four sacral vertebrae with ribs; a right ilium, a left and right radius, a left and right tibiae and one claw, also from the Baidaoyu exposure of the Tongchuan Formation. These remains are assigned to the genus Parakannemeyeria on the basis of the caniniform process and occiput, but due to the poor preservation of the skull is not classified to species level.

Parakannemeyeria sp: (A) Right caniniform process with tusk in lateral (A1) and medial (A2) views; (B) right quadrate and quadratojugal in anterior (B1) and posterior (B2) views; (C) occiput in anterior (C1) and posterior (C2) views; (D) neural arch of axis in anterior (D1) and posterior (D2) views; (E) neural arch of a cervical in anterior (E1) and posterior (E2) views; (F) four sacral vertebrae with ribs in dorsal (F1) and ventral (F2) views; (G) ventral portion of right ilium in lateral (G1) and medial (G2) views; (H) left radius in anterior (H1) and posterior (H2) views; (I) left tibia in anterior (I1) and posterior (I2) views; (J) a claw in dorsal (J1) and ventral (J2) views.

The third set of remains comprises some vertebrae including an axis (the first vertebra, which connects to the skull), a tibia and some bone fragments, from an exposure of the Tongchuan Formation at Sanjiao in Liulin County. These remains are thought to belong to either Sinokannemeyeria or Parakannemeyeria; the axis is very similar to those of Sinokannemeyeria and a dorsal vertebra resembles that of Sinokannemeyeria yingchiaoensis, while the narrow centrum of the specimen resembles those of Parakannemeyeria and the general shape of the tibia resembles Parakannemeyeria youngi and most of the other bones could belong to members of either genus.

Unidentified Kannemeyeriid: (A) Axis in anterior (A1), lateral (A2) and posterior (A3) views; (B) a dorsal vertebra in lateral (B1) and posterior (B2) views; (C) incomplete left precoracoid in medial view; (D) proximal portion of left ulna in anterior (D1) and posterior (D2) views; (E) left tibia in anterior view. Scale bars equal 2 cm. Abbreviations: cn.c, cnemial crest; n.s, neural spine; od, odontoid; pap, parapophysis; przp, prezagapophysis; pzp, postzagapophysis; s.n, sigmoid notch; tr.p, transverse process. Lui (2015).

The final set of remains comprises an incomplete skull, an axial neural arch, a cervical, one incomplete hand and some bone fragments from Sanjiao in Liulin County. This is poorly preserved, and not assigned to any genus or species, however some observations are made. The premaxila has a smooth surface lacking the lateral extension seen in Sinokannemeyeria and Parakannemeyeria. The external naris is small, there is no postnarial excavation and the caniform process extend laterally, not ventrally, all character states seen in Rhadiodromus, Kannemeyeria and Shaanbeikannemeyeria, but not Sinokannemeyeria or Parakannemeyeria. The size of the snout suggests the living animal was considerably larger than Shaanbeikannemeyeria. Based upon this the specimen is excluded from Sinokannemeyeria and Parakannemeyeria, suggesting that at least three species are present in the total assemblage.

Unidentified Kannemeyeriid: (A) Incomplete skull in lateral (A1) and ventral (A2) views; (B) one metacarpal and two manual phalanges (possible same digit) in dorsal (B1) and ventral (B2) views; (C) a cervical in posterior (C1), lateral (C2) and anterior (C3) views; (D) left half of axial neural arch in anterior view; (E) an incomplete hand in dorsal view. Lui (2015).

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