Protitanops

Protitanops ( , in reference to Titanops ) is an extinct genus of horned brontothere that lived in North America during the Late Eocene, in the Duchesnean land mammal age. The genus contains a single species, P. curryi, known from fossils found in California, Texas, and Chihuahua. Protitanops was a large and heavy animal, estimated to have stood about tall at the shoulder and to have weighed over two tonnes. The skull was broad and saddle-shaped, with large zygomatic arches, fused facial bones, and short and bulbous, knob-like horns. Protitanops was broadly similar to the better known Megacerops, but distinguished by its smaller size, smaller horns, and retention of several primitive features, such as its smaller incisors and canines, and the somewhat flattened upper surface of its skull.

Protitanops ( , in reference to Titanops ) is an extinct genus of horned brontothere that lived in North America during the Late Eocene, in the Duchesnean land mammal age. The genus contains a single species, P. curryi, known from fossils found in California, Texas, and Chihuahua. Protitanops was a large and heavy animal, estimated to have stood about tall at the shoulder and to have weighed over two tonnes. The skull was broad and saddle-shaped, with large zygomatic arches, fused facial bones, and short and bulbous, knob-like horns. Protitanops was broadly similar to the better known Megacerops, but distinguished by its smaller size, smaller horns, and retention of several primitive features, such as its smaller incisors and canines, and the somewhat flattened upper surface of its skull. in Texas|upright=0.8]] Protitanops had a brachycephalic (short and broad) and strongly saddle-shaped skull, though the upper surface was somewhat flattened. The zygomatic arches were wide and with large swellings, and had a somewhat curved appearance. The arches were historically erroneously interpreted as nearly straight, based on a plaster reconstruction of one of the arches in the type specimen. The outwards-pointing direction of the zygomatic arches gave the skull a somewhat bow-like shape. The bones of the facial area of adult Protitanops, i.e. the frontals, nasals, premaxillae, and maxillae, were entirely fused together to such an extent that no sutures can be seen. The nasal process was broad and angled slightly downwards at its end. The premaxillomaxillary rostrum (the part of the jaw extending below the nasal incision) of Protitanops curved slightly upwards. The nasal process and the premaxillomaxillary rostrum were about equally wide and long. Protitanops had bulbous, large, and relatively short knob-like horns that rose up from the skull slightly in front of the orbits. The horns were oval in cross-section, pointed slightly forwards and outwards, and did not rise up very far above the orbits. The horns were relatively larger and wider than in more primitive genera, such as Protitanotherium, but not as large as in Megacerops. Fossil horns have a roughened surface. Adult P. curryi horns measure between . Protitanops had a shallow nasal incision, which extended to the anterior margin (frontmost part) of the third upper premolar. The anterior rim of the orbit was directly above the first upper molar. The position of the orbit varied slightly between specimens, a common intraspecifically variable feature in brontotheres. Relative to the dentition, the orbits of Protitanops were positioned further forward on the skull than those of Eubrontotherium, further back than in Notiotitanops, and in a similar position to some specimens of Duchesneodus. The sides of the skull had prominent parasagittal ridges (ridges running lengthwise along the skull), which constricted the skull's upper surface towards the back. The degree of constriction varied somewhat between specimens. The occiput was large and robust, but not nearly as massive as in Megacerops. The nuchal crest (the posterior edge of the skull) varies in morphology between specimens; in some P. curryi, the nuchal crest was thin and smooth, and in others it was thick and rugose. of P. curryi (TMM 45805-1) from Chambers Tuff|upright=0.8]] P. curryi had the dental formula . Protitanops had two pairs of small and globular upper incisors, positioned in a straight row. The reduced number of upper incisors is a trait seen only in certain horned brontotheres, shared with Eubrontotherium, Dianotitan, Duchesneodus, Megacerops, and Notiotitanops. There was no diastema (gap) between the upper incisors and canines. Like the incisors, the canines were relatively small. There was a long diastema between the canines and upper premolars, about as long as the length of the second upper premolar. This diastema is a relatively primitive trait; among the aforementioned genera, Protitanops shares this diastema only with Eubrontotherium and Notiotitanops. The first premolar was much smaller than the other premolars, and had a complex morphology, with two labial (towards the lips) cusps (metacone and paracone). The second premolar had a distinct metacone, and the third and fourth premolars had a roughly rectangular outline, with distinct hypocones (another cusp). The upper molars were characteristically brontothere and have no diagnostic features specific only to Protitanops; they had weak labial ribs and tall ectolophs (outer ridges) with thin enamel. There were three pairs of lower incisors, which formed a subtle arch between the lower canines. The lower incisor row was similar (but slightly more arched) than in Eubrontotherium, and less arched than in Parvicornus. The second pair of lower incisors were the largest, whereas the first and third pair were small. Like in the upper dentition there was no diastema between the lower incisors and canines. Also similar to the upper dentition, there was a diastema between the lower canine and premolars slightly longer than the length of the second lower premolar. The lower cheek teeth are poorly preserved in all known specimens of P. curryi. The lower premolars and molars do not appear to be noticeably different from the lower cheek teeth of close relatives, such as Duchesneodus, Eubrontotherium, and Parvicornus.

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