The early Pliocene fossil bovids from Langebaanweg are of interest, as they represent among the earliest well-defined members of modern tribes, such as Reduncini, Bovini and Alcelaphini (Gentry 1980; Vrba 1997). In these fossils typical tribal morphology appears to be in an early stage of evolution, which on the one hand hinders diagnosis, but on the other hand offers a unique opportunity to investigate ancestral morphological states and adaptations. In this study, we focussed on the two alcelaphine species from Langebaanweg, Damalacra neanica and D. acalla, They were of the size of the blesbok, Damaliscus pygargus, but their skulls and dental morphologies are underived representing an early stage in the appearance of distinctive alcelaphine characteristics (Gentry 1980). The dentitions of the two species are very similar and difficult to distinguish, especially when dealing with individual teeth (Gentry 1980). The aim of this study was to define the morphological characters that differentiate the dentitions of the two species and to use this distinction as the basis for assessing their trophic niches.
Figure 1: A plot of toothrow/premolar ratios against the depth of the lower jaw at the M2-M3 junction of Damalcra neanica and D. acalla.
Figure 2: A plot of the occlusal length of the M3 against its bucco-lingual (mesial) depth of Damalcra neanica and D. acalla.
The dental characteristics of the two species of Damalacra agree broadly with Gentry's assessment of the skull morphologies. It appears that D. neanica was more derived and caprine-like in its morphology than D. acalla. If mandibular depth may be taken as a proxy for hypsodonty, then it appears that D. acalla (37.9mm - 44.5mm) is only marginal less hypsodont than D. neanica (40.0mm - 47.4mm) (Fig. 1), while both are very similar to the extant blesbok, D. pygargus (38.9 - 43.9). This is somewhat unexpected, given the partly fused state of the metaconid and paraconid of the P4, and suggests the need to test hypsodonty further by means of direct measurements on unworn M3's.
If the mandibular depth data reflect hypsodonty then one would expect the trophic niches of both species of Damalacra to have tended towards grazing, as in the case of the blesbok. However, a mesowear analysis of the upper molars of Damalacra spp. suggests that this was not the case (Fig. 3). D. acalla clusters with the sample of known mixed feeders and is closest to the bushbuck (T. scriptus) in mesowear pattern. D. neanica, on the other hand, clusters with the sample of known browsers and is closest to the mule deer (O. hemionus) in mesowear pattern. Unlike modern alcelaphines then, grass appears to have been a less important component in the diets of these two early alcelaphine species. The mesowear results are in good agreement with a microwear study of an undifferentiated sample of Damalacra teeth (Ungar et al. 2007), which suggested feeding niches ranging from browsers to mixed feeders. The apparent lack of agreement between the morphological analysis and the mesowear and microwear results is of interest and will be the focus of further research.
Figure 3: Hierarchical cluster diagram of the two Damalacra species compared to a set of 27 'typical' extant species from Fortelius and Solounias (2000). Mesowear variables
Figures after J.S. Brink & D.D. Stynder. In press. Morphological and trophic distinction in the dentitions of two early alcelaphine bovids from Langebaanweg (genus Damalacra). Palaeontologia Africana.
GENTRY, A. W. 2000. Caprinae and Hippotragini (Bovidae,Mammalia) in the Upper Miocene. In: VRBA, E. S. & SCHALLER, G. B. (eds.) Yale University press, New Haven.
UNGAR, P.S., G. MERCERON & R. S. SCOTT. 2007. Dental Microwear Texture Analysis of Varswater Bovids and Early Pliocene Paleoenvironments of Langebaanweg, Western Cape Province, South Africa. J. Mammal. Evol. 14: 163–181.
VRBA, E. S. 1997. New fossils of Alcelaphini and Caprinae (Bovidae, Mammalia) from Awash, Ethiopia, and phylogenetic analysis of Alcelaphini. Palaeontol. Afr. 34: 127-198.
Morphological and trophic distinction in the dentitions of two early alcelaphine bovids
Roger Smith (Head):
Phone: 021 481 3879
Phone: 022 766 1606
Phone: 021 481 3877
Phone: 021 481 3984