Hallautherium sp.

Świło, Marlena, Niedźwiedzki, Grzegorz & Sulej, Tomasz, 2014, Mammal-like tooth from the Upper Triassic of Poland, Acta Palaeontologica Polonica 59 (4), pp. 815-820 : 817-818

publication ID	https://doi.org/ 10.4202/app.00016.2013
persistent identifier	https://treatment.plazi.org/id/2C4187AA-476B-B22E-7678-F8E4FA7EFDBF
treatment provided by	Felipe
scientific name	Hallautherium sp.
status

Treatment

Hallautherium sp.

Material.— ZPAL V.33/734 (lower molariform) from Upper Triassic , Lipie Śląskie clay-pit at Lisowice, Silesia, southern Poland .

labial

250 lingual

Description.— ZPAL V.33/734 is a very small, but nearly complete double-rooted right lower molariform with a main row of three (or even four, specimen is incomplete) cusps and additional anterior and posterior lingual cusps ( Fig. 2 View Fig ). The mesio-distal length of the crown is 1.3 mm and the maximum width is 0.48 mm ( Fig. 3 View Fig ). The height of the whole tooth, including roots is 3.19 mm. Tooth is in the size range of Morganucodon watsoni , Hallautherium schalchi , and Morganucodon peyeri . Its crown is clearly laterally compressed and primary cusps (a–c) are arranged longitudinally ( Fig. 3 View Fig ). It is lower molariform, because the principal cusps a, b, and c are in line and the cusp a, the highest, is positioned slightly mesial to the middle of the crown. Additionally, cusp c is much larger than cusp b. Typically, in low- er molariforms of Morganucodontide, cusp g is large and situated lingual to the apex of cusp a, but in described specimen supposed cusp g is very small and situated lingual to the apex of cusp c.

The central cusp (cusp a), which is slightly flattened labio-lingually, is more massive than the mesial and distal ones and is slightly inclined distally. At the apex there is a small circular wear facet ( Fig. 2 View Fig ). Crests run down from the apex, anteriorly toward cusp b and posteriorly toward the groove separating the main cusp from cusp c. The posteriorly-inclined crest is more pronounced. The distolingual part of cusp a is concave and shows wear ( Fig. 2 View Fig ). In the specimen ZPAL V.33/734 the principal cusp (a) is anterior to the midpoint of the crown length.

Cusp b is conical and much smaller and lower than cusp a. It is located on the anterior part of the tooth. Mesio-lingual to cusp b is the slightly smaller cusp e, which is visible only on the lingual side. Cusp c is larger, and set much higher than cusps b and e. It is also closer to cusp a, separated from the cusp a by a shallow groove. It is cracked at the base in its distal part. Two crests run down from the top of cusp c. Just below cusp c, on the lingual surface, a small additional cusp is visible and most likely represents a poorly developed cusp g ( Fig. 2 View Fig ). There is a small part chipped off at the distal edge of ZPAL V.33/734 ( Fig. 3 View Fig ) where another small cusp (cusp d) may originally have been present. Neither surface (labial or lingual) of the lower part of the crown possesses a clearly marked cingulum, which supports identification of the specimen as a molariform of Hallautherium . As in Hallautherium schalchi but unlike any known morganucodontids a distal labial basin is present on ZPAL V.33/734 (in the form of a small depression on the described specimen). The roots are arranged mesio-distally and are massive at the base of the crown. They are very long and well separated, with a characteristic division up to the crown base ( Fig. 3 View Fig ). Both roots are oval in outline. Pulp canals are open and the roots draw near each other at the ends.

ZPAL V.33/734 does not contain a cingulum, which is generally poorly developed in the molariforms of basal mammaliaforms, but is a characteristic feature of morganucodontid molariform teeth (e.g., Mills 1971; Kermack et al. 1973; Clemens 1980; Sigogneau-Russell 1983a, b; Hahn et al. 1991). ZPAL V.33/734 lacks a distinct system of wear facets and there is no evidence that this molariform was interlocked with an opposing tooth.