Advances in the Reconstruction of Ungulate Ecomorphology with Application to Early Fossil Equids

Abstract

A new and greatly simplified methodology for the assessment of the dietary adaptations of living and fossil taxa has been developed which allows for microwear scar topography to be accurately analyzed at low magnification (35ϫ) using a standard stereomicroscope. In addition to the traditional scratch and pit numbers, we introduce four qualitative variables: scratch texture, cross scratches, large pits, and gouges, which provide finer subdivisions within the basic dietary categories. A large extant comparative ungulate microwear database (809 individuals; 50 species) is presented and interpreted to elucidate the diets of extant ungulates. We distinguish three major trophic phases in extant ungulates: traditional browsers and grazers, two phases represented by only a few species, and a browsing-grazing transitional phase where most species fall, including all mixed feeders. There are two types of mixed feeders: seasonal or regional mixed feeders and meal-by-meal mixed feeders. Some species have results that separate them from traditional members of their trophic group; i.e., browsers, grazers, and mixed feeders. Duikers are unique in spanning almost the entire dietary spectrum. Okapia, Tapirus, Tragulus, and Moschus species have wear similar to duikers. Proboscideans fall in the browsing-grazing transitional phase, as do the two suids studied. The latter differ from each other by their degree of rooting.Archaic fossil equids spanning the supposed browsing-grazing transition were compared to extant ungulates. Two major clusters are discerned: (1) Hyracotherium has microwear most similar to that of the duiker Cephalopus silvicultor and was a fruit/seed eating browser. (2) diets shows a dietary change in the expected direction (toward the incorporation of more grass in the diet) and follows the expected evolutionary transition from the Eocene to the Oligocene and early Miocene. Consequently, these equid taxa are reconstructed here as mixed feeders grazing on forest C3 grasses. The finer dietary differentiation shows a progressive decrease in the number of scratches and pits. Mesohippus has the most pits and scratches, followed by Parahippus, and then Merychippus (which has the least). The taxon incorporating the most grass into its dietary regime in this array is Merychippus. In Mesohippus-Parahippus versus Merychippus, differences in tooth morphology are major but microwear differences are slight.

New Data on the Miocene Stem LagomorphEurolagus fontannesi, and Its Northernmost Record

“…The relatively high number of fine scratches and very low number of coarse scratches points to a diet dominated by deli− cate vegetation, such as C3 grass−like plants frequently found in sylvan environments, and soft fruits with edible pericarps or arils. A similar pattern of microwear has been observed in Tragelaphus scriptus, which inhabits rainforests, as well as Cervus canadensis and Cavia, although the latter two taxa dis− play a higher number of scratches in general (Solounias and Semprebon 2002;Townsend and Croft 2008). Compared to modern squirrels, the most similar pits−to−scratches ratio is ex− pressed in Notocitellus (= Spermophilus) annulatus (Fig.…”

“…However, the results should be treated as preliminary, as microwear has not been studied in lagomorphs previously, thus the comparisons are limited to rodents and ungulates. The striae on the grinding surfaces are generally shallow and delicate compared to those found in most ungulates (Solounias and Semprebon 2002) and some rodent groups, such as Caviidae or Muridae (Townsend and Croft 2008;Gomes Rodrigues et al 2009).…”

“…From an environmental standpoint, we can narrow the di− etary preferences of Eurolagus fontannesi to leafs, grass, and fruits, and test the preliminary dental microwear data against results known for a few rodent and ungulate groups (Solounias and Semprebon 2002;Meng et al 2003;Nelson et al 2005;Gomes Rodrigues et al 2009). Such a comparison, based on the ratio of the average number of pits versus scratches, places Eurolagus fontannesi in the morphospace of a typical browser close to fruit−leaf and fruit−seed groups in the Townsend and Croft (2008) classification for the living Caviidae (Fig.…”

“…Such a comparison, based on the ratio of the average number of pits versus scratches, places Eurolagus fontannesi in the morphospace of a typical browser close to fruit−leaf and fruit−seed groups in the Townsend and Croft (2008) classification for the living Caviidae (Fig. 10A), or that of a seasonal−regional mixed−feeder according to the Solounias and Semprebon (2002) classification of ungulates. The relatively high number of fine scratches and very low number of coarse scratches points to a diet dominated by deli− cate vegetation, such as C3 grass−like plants frequently found in sylvan environments, and soft fruits with edible pericarps or arils.…”

Use of tusks in feeding by dugongid sirenians: Observations and tests of hypotheses

“…Casts were examined under a stereo light microscope at 335 and 370 magnification using the Solounias and Semprebon (2002) technique. A 0.3 mm 3 0.3 mm area was examined in several locations along the perimeter of the tusk tip (Fig.…”