Manidens condorensis

Sereno, Paul C., 2012, Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs, ZooKeys 226, pp. 1-225 : 108-111

Manidens condorensis Figs 881Tables 13

Manidens condorensis Pol et al. (2011; Figs 1, 2)

Holotype.

MPEF-PV 3211, partial skull and postcranial skeleton lacking the forelimbs, hindlimbs, and caudal vertebrae (Figs 8, 81B).

Referred material.

MPEF-PV 1718, 1719, 1786, 3810, and 3811, isolated teeth.

Type locality.

Queso Rallado, 2.3 km west of Cerro Cóndor, Chubut Province, Argentina ( Pol et al. 2011).

Horizon.

Cañadón Asfalto Formation ( Stipanicic et al. 1968; Rougier et al. 2007); Middle Jurassic, Aalenian-Bathonian, ca. 176-165 Ma ( Gradstein and Ogg 2009; Cabaleri et al. 2010).

Revised diagnosis.

Heterodontosaurid ornithischian characterized by the following four autapomorphies: (1) external mandibular fenestra absent; (2) denticules on the margins of individual denticles; (3) mesially divergent basal denticle on mesial margin in some dentary crowns; (4) mesial denticulate margin approximately 60% the length of the distal margin.

Description.

The revised diagnosis above restricts cited features to those interpreted as potential autapomorphies for Manidens condorensis . Several features listed in the initial diagnosis ( Pol et al. 2011: 370) have broader distributions and therefore were omitted. Besides the unusual features of the dentition, closure of the external mandibular fenestra is the only nondental autapomorphy listed, although more will surely be identified with additional preparation and description. The following descriptive comments are based on Pol et al. (2011) as well as stereophotographs of the holotypic specimen (courtesy of D. Pol).

Cranium.

Only a portion of theskull roof and braincase are preserved and figured ( Pol et al. 2011). Judging from the length of the dentary, the snout is likely to be proportionately shorter than in Heterodontosaurus (Figs 8A, 59, 81B). An inset, arched diastema was probably present between the premaxilla and maxilla, given the presence of a dentary caniniform tooth (Figs 8A, 81B). The form of the premaxilla and predentary are currently unknown.

As noted by Pol et al. (2011), aspects of the cranium are reminiscent of derived features in Tianyulong and Heterodontosaurus such as the arched profile of the upper temporal bar and the spacious laterotemporal fossa (Fig. 81B). The form of the postorbital, jugal, quadratojugal and quadrate exhibit features present in Heterodontosaurus , most of which are poorly known in other heterodontosaurids. The lateral aspect of the postorbital is excavated by a fossa, a laterally projecting crest and posteroventrally directed flange are present on the jugal, an embayment ventral to the lower temporal bar results in a T-shaped quadratojugal, and the ventral articular surface of the quadrate condyles angles ventrolaterally. The shaft of the quadrate dorsal to the condyles appears to be considerably more robust than in Heterodontosaurus ( Pol et al. 2011: fig. 1e).

The maxilla has a laterally protruding rim along the ventral margin of the antorbital fossa as in other heterodontosaurids. Pol et al. (2011: 371) suggested that an arched diastema may not have been present. The anterior margin of the maxilla, however, is not well preserved (Fig. 81B). The presence of a caniniform tooth in the dentary (Fig. 8A) strongly suggests that an arched diastema would have been present as in other heterodontosaurids.

The prominent laterally projecting jugal horn is very similar in form and location to that in Heterodontosaurus (Figs 59, 81B). The dorsoventrally compressed horn, which is located just ventral to the orbital margin, is connected by a ridge to the everted ventral rim of the antorbital fenestra. The jugal flange differs in its position from that in Heterodontosaurus (Figs 59, 81B). It projects posteriorly rather than posteroventrally. As a result, the flange has a more elevated position relative to the lower jaw than in Heterodontosaurus .

The postorbital has a particularly deep posterior ramus compared to Heterodontosaurus as seen in lateral view (Figs 59, 81B). In this regard, the postorbital is most similar to that in Pegomastax africanus gen. n. sp. n.asdescribed below. The postorbital fossa is well developed as in Heterodontosaurus .

Lower jaw.

The lower jaw is proportionately short with a deep dentary similar to that in Pegomastax africanus gen. n. sp. n.asdescribed below. A number of features in the lower jaw are present in several other heterodontosaurids including a deep buccal emargination, prominent coronoid process, an external mandibular fossa, and an enlarged anterior surangular foramen and associated neurovascular groove (Fig. 81B). The retroarticular process appears to be proportionately shorter than in Heterodontosaurus , and the external mandibular fenestra is closed (Figs 8A, 81B).

Pol et al. (2011) have depicted the proportions of the angular and surangular in lateral view in two ways, the former deeper as well as shallower than the latter (Figs 8A, 81A). The deeper angular (Fig. 8A) is their intended interpretation (D. Pol pers. comm.), which was recorded as a derived character in their matrix for Manidens and Heterodontosaurus . As noted above, however, the deep proportions of the angular in Heterodontosaurus (Fig. 58) are regarded here as erroneous (Fig. 59). In the reconstruction given here of Manidens , we have followed their drawing of the lower jaw, in which the angular is somewhat deeper than the surangular (Figs 8A, 81B).

The jaw joint is offset ventral to the maxillary tooth row as in Heterodontosaurus and probably also Lycorhinus (Figs 8A, 81B). Pol et al. (2011: 373) suggested that the articular cup for the quadrate condyles is "considerably longer anteroposteriorly", allowing some fore-aft movement of the quadrate. This cannot be verified in currently available images. If that is an accurate assessment of the jaw joint, then it would differ from the tight fit of the quadrate condyles to the articular cotylus in Heterodontosaurus (Fig. 61C).

Dentition.

There appears to be approximately 11 teeth in maxillary and dentary tooth rows and a diastema between the caniniform and postcaniniform teeth, judging from the preserved portions of the tooth row in the right dentary (Fig. 81B). The relatively low tooth count, marked disparity in crown size along the tooth row, straight maxillary and dentary alveolar margins, and robustly proportioned dentary are comparable to the condition in Pegomastax africanus gen. n. sp. n.as described below.

The dentary crowns also resemble the new African species in the mesial bowing of the central axis of the crown. The mesial carina, in addition, is shorter than the distal carina in both species, although this asymmetry is more strongly expressed in Manidens ( Pol et al. 2011).

Skull reconstruction.

The skull reconstruction presented here (Fig. 81B) differs in several regards from the preliminary reconstruction presented in Pol et al. (2011) (Fig. 81A). The most important differences involve the addition of an arched diastema to accommodate the dentary caniniform tooth, the alignment of maxillary teeth over the dentary cheek tooth row (the former was displaced anteriorly), the addition of braincase elements posteroventral to the quadrate head, and the lowering of the jaw joint relative to the tooth rows to match the geometry preserved in the right dentary (Fig. 8A).

Postcranial skeleton.

Portions of the axial column and pelvic girdle are preserved (Fig. 8B). The short trapezoidal centra and epipophyseal processes in mid cervical vertebrae ( Pol et al. 2011: fig. 1d) are similar to that in Heterodontosaurus (Fig. 62) and suggest that the cervical series was arched as reconstructed ( Pol et al. 2011: fig. 1). Mid and posterior dorsal vertebrae have neural spines that are longer anteroposteriorly than deep, which more closely resembles Tianyulong (Fig. 20) than Heterodontosaurus (Fig. 68).

The pelvic girdle exhibits a fully open acetabulum and a laterally prominent ischial peduncle on the ilium (Fig. 8B) similar to that in Tianyulong , the Kayenta heterodontosaurid, Abrictosaurus , Heterodontosaurus , and more advanced ornithischians. The pelvis is more primitive in two regards than some other heterodontosaurids. The iliac postacetabular process is deeper dorsoventrally than in Abrictosaurus and Heterodontosaurus (Figs 37, 68), and the postpubic process does not appear to be shortened as in Tianyulong (Fig. 30).