Embrithosaurus, WATSON, 1914

Brandt, Marc Johan Van Den, Abdala, Fernando & Rubidge, Bruce Sidney, 2020, Cranial morphology and phylogenetic relationships of the Middle Permian pareiasaur Embrithosaurus schwarzi from the Karoo Basin of South Africa, Zoological Journal of the Linnean Society 188, pp. 202-241 : 208-209

GENUS EMBRITHOSAURUS WATSON, 1914

( FIGS 1–17, 19)

Type species: Embrithosaurus schwarzi Watson, 1914 (SAM-PK-8034).

Locality, stratigraphy and age: SAM-PK-8034 was collected by Mr A. W. Rogers and Mr E. H. L. Schwarz in 1902 on the farm Hoogeveld Lot A (Hoogeveld 270), in the Gouph region, near Knoflock’s Fontein, Van der Byl’s Kraal, Prince Albert district of the Western Cape Province of South Africa ( Broom, 1903). Kitching (1977) assigned the farm Hoogeveld Lot A to the Low Horizon of the Tapinocephalus AZ, Abrahamskraal Formation, Beaufort Group. According to Day (2013; Day et al., 2015) this locality is high in the Tapinocephalus AZ and can be constrained to the stratigraphic interval of 2150–2250 m above the base of the Abrahamskraal Formation, occurring in the lower part of the Moordenaars Member of the Abrahamskraal Formation and represents the earliest stratigraphic occurrence of Embrithosaurus . End Capitanian (Guadalupian– Middle Permian ).

Revised diagnosis: Large-sized pareiasaur with body length up to 3 m. No cranial autapomorphies were identified. Embrithosaurus is distinguished from the other co-occurring Tapinocephalus AZ pareiasaurs by nine marginal cusps on all maxillary and mandibular teeth; wider, dorsoventrally shorter maxillary teeth; marginal cusps of the maxillary teeth arranged more regularly around the tooth crown; apex of the crown of the maxillary teeth lacking an elongated, central, three-cusped trident; symmetrical mesial and distal marginal cusp arrangement on all maxillary and mandibular teeth; lingual surface of mandibular teeth with a low, smooth, triangular bulge; prefrontal forms a wide, shallow, distinct, bowl-shaped depression between the three lateral bosses and the medial prefrontal–frontal suture; mediolaterally elongated postfrontal; presence of a small, distinct, maxillary boss; presence of a moderately swollen posterodorsal maxillary-lacrimal ridge outlining the external naris, formed by the maxillary boss and the lacrimal boss complex.

Embrithosaurus shares with Nochelesaurus : Vertically oriented, mediolaterally narrow, premaxilla and maxilla, only slightly wider (by <5 mm) than the tooth row, resulting in downward pointing, vertically oriented maxillary teeth; lateral surface of the quadratojugal cheek flange flat, with distinct bosses arranged posterodorsally; distal portion of the paroccipital process of the opisthotic anteroposteriorly expanded to 55 mm.

Embrithosaurus shares with Bradysaurus baini : Large, wide, low, bulbous bosses on the posterior edge of the quadratojugal; a transversely narrow postparietal; posteriorly projecting knob-like process, on the medial edge of the posterodorsal corner of the paroccipital process of the opisthotic, larger in Bradysaurus baini .

Embrithosaurus shares with Nochelesaurus and Bradysaurus baini : Relatively small cheek flanges that extend only up to about 30° below the maxillary tooth row.

Comments: Lee (1997a) did not identify any cranial autapomorphies for Embrithosaurus schwarzi , but noted a few cranial differences compared to other co-occurring taxa (see Discussion). Lee (1997a) defined three pelvic autapomorphies. (1) Anterior expansion of the iliac blade is large and the entire blade is vertically oriented, such that the bone presents a thin edge when viewed dorsally. In all other pareiasaurs, the ventral portion of the sacral blade is not vertically oriented, but is slightly too greatly laterally bent (everted), which presents a wide surface when viewed dorsally. (2) Iliac blades diverge anteriorly, making an angle of about 40° with the sagittal plane when viewed dorsally, and are not parallel. In all other pareiasaurs the iliac blades are almost parallel, diverging only slightly anteriorly. (3) Pelvic symphysis extremely thick, being almost half as deep as long. In all other pareiasaurs the pelvic symphysis is much thinner.

CRANIAL DESCRIPTION