Amphicticeps

Diversité décrite (Catalogue of Life)

Distribution biogéographique

• DISTRIBUTION: Early Oligocene of northcentral Mongolia. An undescribed record was mentioned in the early Oligocene Khatan­ Khayrkhan locality of Altai Province of Mongolia by Russell and Zhai (1987: 324). GEOLOGY AND AGE: The above referred specimens of Amphicticeps shackelfordi come from three localities (some specimens lack a detailed locality record): (1) general vicinity of Loh for AMNH 19017 and 19127; (2) 2 mi southwest of Loh for AMNH 19010, AMNH 19128, MAE BU. 91.9187 – 90, and MAE M­ 217; (3) general vicinity or 2 mi west of the Ulaan Khongil (‘‘ Grand Canyon’ ’ or Tatal Gol) for AMNH 21695 and 83610. While field studies are currently pursued by the on­going joint expeditions of the MAE and formal stratigraphic revisions will have to wait for that result (see Höck et al., 1999, for a recent summary), it is relevant to note here that the above three Amphicticeps ­ producing localities fall within a more restricted concept of the Hsanda Gol Formation close to the level of a discontinuous but approximately contemporary basaltic lava (Basalt I of Höck et al., 1999). Historic collections are largely concentrated in the Ulaan Khongil fauna in the lower part of the Hsanda Gol Formation below the prominent basaltic lava and immediately above. Amphicticeps specimens from near the Loh campsite and 2 mi southwest of Loh (including the holotype) are darkly stained due to the percolation of ground water, and they all belong to the Ulaan Khongil fauna. AMNH 21695 and 83610 from near the ‘‘ Grand Canyon’ ’ area, on the other hand, are light­colored and may belong to the Zavlia fauna in the upper part of the Hsanda Gol Formation above the lava. This presumed younger age of AMNH 21695 and 83610 relative to the rest of the A. shackelfordi hypodigm is also consistent with the former’s wider m 1 and more prominent lingual cingulum on the m 1 trigonid, tendencies that indicate a slightly more advanced stage of evolution for the species. EMENDED DIAGNOSIS: Amphicticeps shackelfordi is distinguishable from the more derived A. makhchinus and A. dorog by its smaller size, smaller angle between the labial borders of P 4 and M 1, more enlarged M 1 parastyle, larger M 1 metaconule, more reduced anterior cingulum of M 1, and more lingually located M 2. In addition, the P 4 protocone of A. shackelfordi is larger than in A. dorog, but is less well developed than in A. makhchinus.1 esp.

Régions biogéographiques agrégées depuis Catalogue of Life Cross-References (distribution par espèce déclarative).

Taxons enfants directs (3)

• Espèce Amphicticeps dorog
• Espèce Amphicticeps makhchinus
• Espèce Amphicticeps shackelfordi