Wednesday, July 27, 2016

[Paleontology • 2011] Manidens condorensis • A Middle Jurassic Heterodontosaurid Dinosaur from Patagonia and the Evolution of Heterodontosaurids

Manidens condorensis  
Pol, Rauhut & Becerra, 2011
 DOI:  10.1007/s00114-011-0780-5 

Heterodontosauridae is a morphologically divergent group of dinosaurs that has recently been interpreted as one of the most basal clades of Ornithischia. Heterodontosaurid remains were previously known from the Early Jurassic of southern Africa, but recent discoveries and studies have significantly increased the geographical and temporal range for this clade. Here, we report a new ornithischian dinosaur from the Middle Jurassic Cañadón Asfalto Formation in central Patagonia, Argentina. This new taxon, Manidens condorensis gen. et sp. nov., includes well-preserved craniomandibular and postcranial remains and represents the only diagnostic ornithischian specimen yet discovered in the Jurassic of South America so far. Derived features of its anatomy indicate that Manidens belongs to Heterodontosauridae, as the sister taxon of Heterodontosaurus and other South African heterodontosaurids. The presence of posterior dentary teeth with high crowns but lacking extensive wear facets in Manidens suggests that this form represents an intermediate stage in the development of the remarkable adaptations to herbivory described for Heterodontosaurus. The dentition of Manidens condorensis also has autapomorphies, such as asymmetrically arranged denticles in posterior teeth and a mesially projected denticle in the posteriormost teeth. At an estimated total length of 60–75 cm, Manidens furthermore confirms the small size of basal heterodontosaurids.

Keywords: Ornithschia; Gondwana; Jurassic; Cañadón Asfalto Formation; Heterodontosauridae

Systematic palaeontology

Dinosauria Owen, 1842
Ornithischia Seeley, 1887

Heterodontosauridae Kuhn, 1966

Manidens condorensis gen. et sp. nov.

Etymology: The genus name Manidens, from manus (Latin, hand) and dens (Latin, tooth), refers to the similarity of the posteriormost tooth to the human hand. The specific epithet condorensis refers to the nearby village of Cerro Cóndor, Chubut Province, Argentina.

Fig. 2 Anatomical details of the craniomandibular and dental remains of  Manidens condorensis gen. et sp. nov. 
a Photographs of preserved cranial and mandibular elements of the holotype (MPEF-PV 3211) superimposed on a skull reconstruction in lateral view. b Reconstruction of the skull and mandible in lateral view. c Photograph of right lower jaw and associated elements of the holotype (MPEF-PV 3211). d Interpretative drawing of right lower jaw in lateral view (right maxilla, left lower jaw and other bones shaded in grey); dashed areas represent broken surfaces and dotted areas represent sediment. e – h SEM images of posterior mandibular tooth in mesial (e) and bucal (f – i) views corresponding to MPEF-PV 3810 (e), MPEF-PV 3811 (f) and holotype MPEF-PV 3211 (g – i). ad anteriormost denticle mesially offset, afo antorbital fossa, an angular, at anterior teeth of left dentary, ca caniniform, cr crenulations, d dentary, dc denticles, dv dorsal vertebra, f frontal, g glenoid fossa, jb jugal boss, m maxilla, mc mesial cavity, n nasal, po postorbital q quadrate, qj quadratojugal, sq squamosal, sa surangular, saf anterior surangular foramen. Scale bars indicate 10 mm (a – d), 1 mm (e – g), 0.5 mm (h) and 0.1 mm (i)

Holotype: MPEF-PV 3211 (Museo Paleontológico Egidio Feruglio, Trelew, Argentina), partial associated skeleton, including most elements of the skull and lower jaws, cervical, dorsal and sacral vertebrae, left scapula and coracoids, and almost complete pelvic girdles.
Referred material: MPEF-PV 1719, 1786, 1718, 3810, 3811 isolated posterior teeth, from the same locality and horizon as the holotype.

Locality and horizon: Queso Rallado locality within the Cañadón Asfalto Formation, 2.3 km west of the village of Cerro Cóndor, Chubut Province, Argentina. The bone-bearing layer is a silicified mudstone within a series of lacustrine mudstones and limestones (Rougier et al. 2007b). Further locality information is given in the Electronic supplementary material (ESM) and stratigraphic information can be found in Rougier et al. (2007b). GPS coordinates of this locality are deposited in the MPEF collections and are available upon request. The age of the Cañadón Asfalto Formation is usually given as Callovian–Oxfordian (e.g. Silva Nieto et al. 2002), but recent U–Pb radioisotopic age determinations (Cabaleri et al. 2010) and palynological research (Volkheimer et al. 2008) indicates that it is probably considerably older, with dates ranging from 171 ± 5 to 167 ± 4 Ma (Aalenian–Early Bathonian; Salani 2007; Cabaleri et al. 2010).

Diagnosis: Small heterodontosaurid (estimated body length of approximately 50–60 cm) with the following autapomorphies: jugal with strongly developed, dorsally placed lateral boss; dorsal part of the postorbital process of the jugal very slender and flexes abruptly posteriorly at the beginning of the articular facet for the postorbital; forebrain facet on the ventral surface of the frontal enlarged and with significantly raised margins; posterior teeth with asymmetric arrangement of denticles and with a mesial concavity in which the distal margin of the preceding tooth is lodged; posteriormost dentary tooth “hand-shaped”, with only one or two mesial denticles, the most anterior of which diverges mesially from the mesial margin of the crown; presence of small crenulations along the cutting margin of each denticle.

Fig. 1 Preserved elements of Manidens condorensis gen. et sp. nov.
Outline reconstruction of the skeleton, indicating preserved elements, with photographs of selected skeletal elements of the type specimen (MPEF PV 3211). a Pelvic girdle, lateral. b Schematic drawing of pelvic girdle. c Dorsal vertebrae, lateral. d Cervical vertebrae, lateral. e Quadrate, anterior. f Temporal (lateral) and occipital (posterior) skull elements. f Schematic drawing of temporal and occipital region. il illium, is ischia, j jugal, or occipital region of the braincase, pb pubis, po postorbital, pod postorbital depression, pp preacetabular process, sq lateral shelf of the squamosal. Dashed areas represent broken surfaces and dotted areas represent sediment. Scale bars indicate 10 mm (a, b, f, g), 2 mm (c, d) and 1 mm (e) 

Diego Pol, Oliver W. M. Rauhut and Marcos Becerra. 2011. A Middle Jurassic Heterodontosaurid Dinosaur from Patagonia and the Evolution of Heterodontosaurids.
 Naturwissenschaften. 98 (5): 369–379. DOI:  10.1007/s00114-011-0780-5