. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRANIAL MORPHOLOGY OF THE DICYNODONT GENUS LYSTROSAURUS 247 Lystrosaurus declivis (Owen) (Figs 22, 23, 24, 26, 72, 73) Ptychognathus declivis Owen, i860. Ptjchognathus latirostris Owen, 1862. Ptychognathus depressus Owen, 1876. Ptjchognathus al/redi Owen, 1876. Lystrosaurus ivagneri Van Hoepen, 1916. Lystrosaurus primitivus Toerien, 1954. Type specimen: 36221. Locality: Rhenosterberg. The skull in this species resembles that of Lystrosaurus murrayi, described later, and seems to form a morph
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRANIAL MORPHOLOGY OF THE DICYNODONT GENUS LYSTROSAURUS 247 Lystrosaurus declivis (Owen) (Figs 22, 23, 24, 26, 72, 73) Ptychognathus declivis Owen, i860. Ptjchognathus latirostris Owen, 1862. Ptychognathus depressus Owen, 1876. Ptjchognathus al/redi Owen, 1876. Lystrosaurus ivagneri Van Hoepen, 1916. Lystrosaurus primitivus Toerien, 1954. Type specimen: 36221. Locality: Rhenosterberg. The skull in this species resembles that of Lystrosaurus murrayi, described later, and seems to form a morphological link between it and L. oviceps. As in oviceps, the snout is directed forward as well as down, but the smoothly curved snout is lost and the anterior premaxillary facial surface in declivis is a perfectly flat plane, broken only by a sometimes very prominent longitudinal median ridge. There is a strongly developed frontonasal ridge and prominent frontal tuberosities. The lateral snout surface lies at a sharp angle to the anterior snout surface, so that in ventral view the premaxillary portion of the palate is rect- angular. A feature of this species, as also of L. murrayi, is the division of the skull roof and snout surfaces into three planes: a parieto-preparietal plane which extends over the intertemporal region up to the frontal bosses, a frontal plane which slopes forward and down from the frontal bosses to the frontonasal ridge, and a premaxillary plane, generally referred to as the facial plane, which drops down steeply from the frontonasal ridge. The anterior two-thirds of each nasal is generally included in the plane of the anterior premaxillary Fig. 72. Lystrosaurus declivis. Nat. Mus. No. Skull in lateral Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original South African
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
