. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. A NEW GENUS AND SPECIES OF PLIOCENE BOSELAPHINE 181 last difference appears valid. The premolar row is about as long as in M. amalthea from Pikermi (Fig. 26). Mesembriportax acrae differs from Tragoportax salmontanus by being larger, the top of the anterior keel terminating well below the tip on the horn core, the horn cores inserted more uprightly and further apart, the greater divergence of the horn cores, the expanded internal sinuses of the frontals and the orbits without a projecting dorsal rim,
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. A NEW GENUS AND SPECIES OF PLIOCENE BOSELAPHINE 181 last difference appears valid. The premolar row is about as long as in M. amalthea from Pikermi (Fig. 26). Mesembriportax acrae differs from Tragoportax salmontanus by being larger, the top of the anterior keel terminating well below the tip on the horn core, the horn cores inserted more uprightly and further apart, the greater divergence of the horn cores, the expanded internal sinuses of the frontals and the orbits without a projecting dorsal rim, the braincase more angled on the face axis, the braincase roof not curved downwards posteriorly, temporal ridges not approaching so closely posteriorly, and the central longitudinal groove on the basioccipital not extending forwards between the anterior tuberosities. Mesembriportax acrae seems to be a fairly isolated form by the huge extent of its frontals' sinuses and by other characters of the skull top and horn cores. The wide palate may also be notable. It could perhaps have descended from the Fort Ternan Protragocerus labidotus, which has horn cores with quite strong torsion, wide insertions, medio-lateral compression, and a long terminal part of small cross-section. The development of such distinctive horn core tips would be unique outside Miotragocerus, and only occurred in an area south of the known range of Miotragocerus. The main problems with such a hypothesis of descent are what could have happened to the anterior ridges of the horn pedicels and whether the premolar row could have lengthened. Mesembriportax acrae seems rather further from Miotragocerus, which has narrower skulls (with the possible exception of M. amalthea) and more closely inserted horn cores with generally less torsion. Its wide horn core insertions and the basioccipital mor- phology suggest that it is not close to Tragoportax salmontanus. A tentative phylogeny is shown in Figure 27. Pachyportax l
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
