Stenocybus acidentatus

From Palaeos.org

"Biarmosuchia"
 `--o Dinocephalia
    |?-Stenocybus
    |?-Estemmenosuchidae
    `--+--Anteosauria
       `--o Tapinocephalia
          |--Styracocephalus
          `--+--Titanosuchidae
             `--Tapinocephalidae

Stenocybus acidentatus Cheng & Li 1997

Parent taxa: Therapsida, Dinocephalia.

Location: Xidagou Formation, Dashankou, Yumen, Gansu Province, China.

Age: Upper Permian.

Remains: One near-complete skull (IGCAGS V 361), plus the right premaxilla, maxilla and dentary of a second (IVPP V12008).

Size: Skull length 12-15 cm.

Diagnosis: (from Cheng & Li, 1997) Skull high, narrow, slender without pachyosteosis; orbit large; temporal fossa small; maxilla high, triangular-shaped, with top above canine and connecting with prefrontal; lacrimal large and extending forward; frontal with no boss and interorbital ridge; anterior border of attachment depression for lower jaw adductor on dorsal surface of postfrontal; small teeth present on palatine and transverse process of pterygoid; marginal tooth formula I 5/4, C 1/1, PC 6-8/6; incisors large, procumbent, interlocked, with labial talon pointer and lingual heel.

Comments: Stenocybus acidentatus was a relatively small dinocephalian that lacked the pachyosteosis of more derived forms. It had a very high, narrow skull, triangular in dorsal view, with a large orbit compared to other dinocephalians.

Cheng & Li (1997) assigned their new form to the Dinocephalia on the basis of the lingual heel on the incisors and the position of the lower jaw adductor, but regarded it as basal within the clade due to the small skull without pachyosteosis, small temporal fenestra, lower jaw articulation not anteriorly moved, maxilla with apex above the canine rather than posteriorly, and lacrimal extended anteriorly rather than short. While Cheng & Li (1997) placed Stenocybus outside the Anteosauria + Tapinocephalia clade, they seem to have only compared it with members of Anteosauria and not directly to members of Tapinocephalia. Rubidge & Sidor (2001) place it closer to Anteosauria than Tapinocephalia, again without much comment.

References

Cheng Z. & Li J. 1997. A new genus of primitive dinocephalian - the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]

Rubidge, B. S., & C. A. Sidor. 2001. Evolutionary patterns among Permo-Triassic therapsids. Annual Review of Ecology and Systematics 32: 449-480.

Credits

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