03526nas a2200217 4500008004100000245010200041210006900143300001400212490000700226520287500233653001403108653001403122653001203136653001503148653001503163653001203178653001903190100002003209700001903229856006003248 2017 eng d00aHypsodonty, horses, and the spread of C4 grasses during the middle Miocene in southern California0 aHypsodonty horses and the spread of C4 grasses during the middle a201–2230 v183 a
Background: C4 grasses were not abundant in North America during the middle Miocene (c. 15 Ma). They did not become abundant until around 7 Ma. One can analyse stable carbon (δ13C) and oxygen (δ18O) isotope values in the enamel of fossil horse teeth to determine the
extent to which horses were eating C4 grasses even during the period before those grasses became abundant.
Questions: In southern California, what proportion of a middle Miocene horse’s diet was made up of C4 grasses? Was the amount enough to influence the size and shape of horse teeth?
Organisms: Eighty-five specimens of five fossil horse species – Acritohippus stylodontus, Archaeohippus mourningi, Merychippus californicus, Scaphohippus intermontanus, and Scaphohippus sumani – from the middle Miocene (c. 16 Ma) of southern California (i.e. Barstow Formation, Cajon Valley Formation, and Temblor Formation).
Methods: To determine if C4 grasses were present in middle Miocene horse diets, we analysed stable carbon (δ13C) and oxygen (δ18O) isotope values from the enamel of the fossils. If the result did indicate C4 foraging at a locality, we modelled the percentage of C4 grasses in equid diets using Stable Isotope Analysis in R (SIAR) v.4.2.2.
Results: Modelled percentage C4 in equid diets was <20%. Each formation was statistically significantly different from the others in terms of δ13C values. Barstow specimens had the highest values, those from Cajon Valley the lowest, and those from Temblor were intermediate.
Those results indicate that horses ate C4 grasses within the Barstow and possibly the Temblor Formation but not the Cajon Valley Formation. Within the Barstow sample, Scaphohippus sumani had statistically significantly lower δ13C but statistically significantly higher δ18O values than Acritohippus stylodontus, suggesting a higher proportion of C3 grasses in the diet of Scaphohippus sumani versus a higher proportion of C4 grasses for Acritohippus stylodontus. The latter species also had higher tooth crowns, consistent with a diet richer in C4 grasses. There were no statistically significant differences between species at Cajon Valley for either δ13C or δ18O. The δ13C values for Merychippus californicus suggest that the habitats of the Temblor Formation had a low percentage (<6%) of C4 plants.
Conclusions: C4 grasses lived in the mid-Miocene landscape in southern California up to 8 million years before the rapid increase in C4 ecosystems that occurred worldwide about 7 to 5 Ma. Horses foraged these grasses, so hypotheses related to horse morphological evolution must take C4 plants into account.
10aC3 plants10aC4 plants10aEquidae10agrasslands10ahypsodonty10aMiocene10astable isotope1 aFeranec, R., S.1 aPagnac, D., C. uhttp://evolutionary-ecology.com/abstracts/v18/3016.html02253nas a2200265 4500008004100000022001400041245009000055210006900145260001600214300001000230490000700240520144200247653001701689653001101706653001701717653001501734653003101749653005401780100001901834700001801853700002001871700002301891700001801914856005501932 2016 eng d a1064-755400aAre Hypsodonty and Occlusal Enamel Complexity Evolutionarily Correlated in Ungulates?0 aAre Hypsodonty and Occlusal Enamel Complexity Evolutionarily Cor cJan-05-2016 a43-470 v233 aThe spread of grasslands and cooling climate in the Miocene contributed to an increasingly abrasive diet for ungulates. This increase in abrasiveness is proposed to select for both hypsodonty and increasing complexity of occlusal enamel bands. If these traits evolved in response to strong selection to resist tooth wear while feeding in grassland habitats, we might expect them to have evolved in a correlated fashion. If, on the other hand, there was a developmental or physiological constraint, or if selection was not strong on total enamel production, we would expect species to have evolved one or the other of these traits at a time, producing an uncorrelated, or even inversely correlated, pattern of trait evolution. To test these hypotheses, we examined the Occlusal Enamel Index (OEI) and Hypsodonty Index (HI) of 773 ungulate teeth. We tested the dependence of OEI on HI for the orders Artiodactyla and Perissodactyla using phylogenetic generalized least squares regression (PGLS). The two traits are not significantly correlated in the PGLS, for Artiodactyla and Perissodactyla. Despite their physical proximity, close functional utility, and conventional correlation, our results reject the hypothesis that HI and OEI are evolutionarily linked in these lineages, suggesting that selection to resist tooth wear was not so strong as to drive the overall evolutionary trajectory of both these traits at the same time.
10aArtiodactyla10aEquini10aHipparionini10ahypsodonty10aOcclusal enamel complexity10aPhylogenetic generalized least squares regression1 aFamoso, N., A.1 aDavis, E., B.1 aFeranec, R., S.1 aHopkins, S., S. B.1 aPrice, S., A. uhttp://link.springer.com/10.1007/s10914-015-9296-703285nas a2200217 4500008004100000245008700041210006900128300001200197490000600209520264800215653002302863653000902886653001202895653001502907653001902922653001102941653001802952653001302970100002002983856006403003 2007 eng d00aEcological Generalization During Adaptive Radiation: Evidence from Neogene Mammals0 aEcological Generalization During Adaptive Radiation Evidence fro a555-5770 v93 aQuestion: How does the evolution of a key adaptation affect niche breadth during an adaptive radiation?
Organisms: Cenozoic horse and camel species, as well as Pleistocene ungulates.
Predictions: Niche breadth theoretically could increase, decrease or remain the same as attainment of a key adaptation facilitates a niche shift. Simpson predicted a decrease in niche breadth (ecological specialization) when key adaptations lead to adaptive radiations. I test Simpson’s prediction by examining ecological response to attainment of high-crowned teeth (hypsodonty). The evolution of hyposdonty represents a key adaptation involved in many ungulate adaptive radiations.
Methods: To test whether hypsodont ungulates have potentially wider or narrower niche breadth in respect to their non-hypsodont, pre-adaptive radiation ancestors, I analysed δ13C values in the tooth enamel of Pleistocene ungulates as a proxy for dietary breadth. For Cenozoic horses and camels, I measured the total number of biogeographic provinces and the total number of fossil localities in which individual taxa were found to assess breadth of habitat use. I considered these two parameters (dietary breadth and habitat breadth) as two major niche axes from which I qualitatively estimated niche breadth. I also compared taxon survival between low-crowned and high-crowned taxa, reasoning that if high-crowned taxa had less broad niches, their probability of extinction should be higher and their temporal duration shorter.
Results: The δ13C values of herbivores from the Pleistocene of Florida revealed that high-crowned taxa fed on a diet of both C3 and C4 forage, while low-crowned taxa confined their feeding to C3 plants. In the Cenozoic horse and camel clades, there was no statistically significant difference between high-crowned and low-crowned taxa in the number of biogeographic provinces or localities occupied. Nor were there significant differences between high-crowned and low-crowned taxa in the duration of time a particular species survived.
Conclusions: Simpson’s prediction that key adaptations that lead to adaptive radiation also result in decreased niche breadth is not supported in the case of the evolution of hypsodonty by the ungulates. Instead, the attainment of hypsodonty in these taxa broadened niche space along one of the studied axes (dietary variety) and had no discernible effect on the other (habitat occupancy).
10aadaptive radiation10aDiet10ahabitat10ahypsodonty10akey adaptation10aMammal10aniche breadth10aUngulata1 aFeranec, R., S. uhttp://www.evolutionary-ecology.com/abstracts/v09/2114.html