Ericiolacerta parva Watson, 1931

Huttenlocker, Adam K. & Sidor, Christian A., 2012, Taxonomic revision of therocephalians (Therapsida: Theriodontia) from the Lower Triassic of Antarctica, American Museum Novitates 2012 (3738), pp. 1-20 : 12-13

Ericiolacerta parva Watson, 1931

HOLOTYPE: CAMZM T 369 , skull, lower jaw and nearly complete skeleton; Harrismith , Free State, South Africa, Lystrosaurus Assemblage Zone (Lower Triassic), Balfour Formation, Beaufort Group.

REVISED DIAGNOSIS: Small baurioid with well-developed secondary palate, in which palatal processes of the maxillae meet at the midline, ventral to the anterior portion of the vomer; two highly procumbent lower incisors present the dentary; upper and lower caniniform teeth reduced or absent.

REFERRED SPECIMEN: AMNH FARB 9542 ( figs. 6 , 7 ), disarticulated cranial material including pterygoid and associated left dentary with imperfectly preserved dentition.

LOCALITY AND HORIZON: AMNH FARB 9542 is from Kitching Ridge, near the junction of the Shackleton and McGregor glaciers, central Transantarctic Mountains; lower Fremouw Formation, Victoria Group, Beacon Supergroup.

REMARKS: As Colbert and Kitching (1981) described AMNH FARB 9542 in detail, we will highlight only its most pertinent features. The pterygoids are paired, tetraradiate in structure (with anterior, transverse, quadrate, and parabasisphenoid processes), and preserved in ventral view ( fig. 6 ). The left transverse flange is damaged and missing in the specimen. Anteriorly, both the intermediate and median ventral crests (diagnostic for scylacosaurian therocephalians) are visible in the specimen ( fig. 6 ; table 1: 2.1). The intermediate ventral crest is edentulous (as in most eutherocephalians) and converges with a paired, posteriorly sweeping ventral rim of the parabasisphenoid process as in scylacosaurids and eutherocephalians ( table 1: 2.2). These paired processes border an enlarged, heart-shaped interpterygoid vacuity typical of most baurioids and juvenile eutherocephalians in general. The stout transverse flange, preserved only on the right side, borders a very large suborbital vacuity approximating the condition in the types of Ericiolacerta and Scaloposaurus ( Mendrez, 1975; Mendrez-Carroll, 1979). Colbert and Kitching (1981) noted the lateral extent of the transverse flange is unexpectedly short in AMNH FARB 9542, as it does not reach beyond that of the quadrate ramus. However, the lateral extent of the quadrate ramus is not easily distinguishable in the type of Ericiolacerta . In Scaloposaurus , the transverse flange only extends laterally to the lateral limits of the quadrate ramus.

The dentary ( fig. 7 ) is a slender element with a smooth, but slightly rounded ventral margin (lacking a sharp angular process). Along with the dentition, this element provides the most compelling evidence, albeit modest, for an assignment to Ericiolacerta parva ( Colbert and Kitching, 1981) . Although the crown of the first incisor is missing, its root is preserved in its alveolus ( fig. 7 ) and demonstrates that it was large and procumbent, as in the type ( Watson, 1931: figs. 4–6). There is likewise no indication of an enlarged lower canine. Rather, the anterior incisor is immediately followed by a smaller alveolus for another small, somewhat procumbent tooth, then a series of at least six irregularly spaced teeth. The dental patterns, including irregular spacing of the individual teeth, as well as an anterior accessory cusp and strong wear facet on the distal edge of the last dentary tooth (pc 6?), are consistent with what was described in Ericiolacerta by Crompton (1962), who reconstructed the tooth-wear and replacement patterns. Colbert and Kitching (1981) interpreted space for additional teeth between these, accommodating nine small dentary teeth behind the anterior incisiforms, with the posteriormost dentition bearing wear facets and accessory cusps, as in the type ( Watson, 1931; Crompton, 1962). However, additional alveoli are not clearly distinguishable in AMNH FARB 9542. The crowns of the anterior dentary teeth are broken, making impossible the determination of whether they had accessory cusps.

Figures

FIG. 6. AMNH FARB 9542, cf. Ericiolacerta parva, isolated pterygoid in ventral view. Numbers refer to apomorphies listed in table 1. Abbreviation: cr. v.-int. Pt, intermediate ventral crest of pterygoid. Scale bar = 5 mm.

FIG. 7. AMNH FARB 9542, cf. Ericiolacerta parva, isolated left dentary in lateral view. Numbers refer to apomorphies listed in table 1. Abbreviations: i1, root of first lower incisor; i2, root of second lower incisor; pc1?, possible first lower postcanine tooth; pc6?, possible sixth lower postcanine tooth. Scale bar = 5 mm.