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.html02638nas a2200217 4500008004100000245013100041210006900172300001200241490000800253520196600261653001702227653002202244653001202266653001302278653001102291653001002302100001902312700002002331700001802351856005102369 2013 eng d00aOcclusal Enamel Complexity and Its Implications for Lophodonty, Hypsodony, Body Mass, and Diet in Extinct and Extant Ungulates0 aOcclusal Enamel Complexity and Its Implications for Lophodonty H a211-2160 v3873 a

Tooth morphology and rates of wear have strong controls on how well mammals survive in their habitats. Herbivorous mammals, specifically ungulates, combat the effects of wear through a combination of changing the occlusal (chewing surface) enamel length, and changing hypsodonty (relative height of tooth). Changes in these two attributes are most notably seen in the fossil record of ungulates as they adapted to living in cooler, drier, and more open habitats. We expect enamel length and hypsodonty to be greater in ungulate taxa that feed on grasses than in non-grass feeders. We tested this hypothesis by digitally photographing 213 maxillary tooth rows from 84 species of extinct and extant ungulates (n = 1083 teeth) and measuring their occlusal enamel length and true occlusal area. We then statistically compared the influences of taxonomy, feeding strategy, tooth position, and tooth area on both hypsodonty and occlusal enamel length using principal components analysis (PCA) and a nested multivariate analysis of variance (MANOVA). The results of our PCA indicated a strong correlation between enamel length and tooth area, but little correlation of either with hypsodonty. Our nested MANOVA showed that tooth position had no significant relationship with hypsodonty (p = 0.1539), while all other factors were significant for both hypsodonty and occlusal enamel length. Our results suggest that the occlusal enamel length in ungulate teeth is constrained by both the size of the tooth (and, by proxy, the mass of the individual) and diet. Absolute tooth crown height is similarly affected by a combination of body size and diet, leading to the use of a ratio, hypsodonty index, to characterize the diet component. We propose a similar ratio, the occlusal enamel index (OEI) which reduces the effect of body mass to clearly indicate the component of enamel length determined by abrasiveness of ingested material.

10aArtiodactyla10aEnamel complexity10aEquidae10aIsometry10aMammal10aTeeth1 aFamoso, N., A.1 aFeranec, R., S.1 aDavis, E., B. uhttp://dx.doi.org/10.1016/j.palaeo.2013.07.00602875nas a2200205 4500008004100000245011100041210006900152300001000221490000800231520224900239653002202488653001502510653002002525653001202545653001202557653001402569100002002583700001502603856005102618 2013 eng d00aStable Carbon Isotope Evidence for the Abundance of C4 Plants in the Middle Miocene of Southern California0 aStable Carbon Isotope Evidence for the Abundance of C4 Plants in a42-470 v3883 a

The abrupt spread of grasslands using C4 photosynthesis, sometimes referred to as the rapid increase in C4 ecosystems (RICE), occurred in the late Miocene in North America. While fossil plant specimens from the Miocene Dove Spring Formation of California as well as data from phylogenetic studies and molecular clocks show that C4 grasses evolved prior to the RICE, most isotopic data from paleosols and mammal tooth enamel suggest that its abundance on the landscape was minimal. However, a few recent studies from the Great Plains suggest that C4 grasslands may have been more prominent prior to the RICE event. Here we examine stable carbon isotope values from ungulate tooth enamel from the Barstow Formation of southern California, which is geographically and temporally close to the Dove Spring Formation, and records a diverse and abundant paleofauna of medial Miocene age. Tooth enamel δ13C values were examined in seven ungulate genera including the hypsodont equids; Acritohippus sp. and Scaphohippus sp.; the camelids, Aepycamelus sp., Hesperocamelus sp., and Procamelus sp.; the antilocaprid, Merycodus sp.; and the proboscidean, Gomphotherium sp. More positive δ13C values observed within the equids, camelids, and antilocaprids are suggestive of C4 grasses being included in the diets of these taxa. The equids exhibited the most positive mean δ13C values, which indicate a higher component of dietary C4 grasses (up to 18%) when compared to the other sampled ungulate taxa. The tooth enamel isotope values presented in this study show the presence of C4 grasses as a significant component of ungulate diets millions of years before the RICE. The abundance of C4 plants earlier in the Miocene may imply a more significant role in the major ungulate diversification events than previously suspected. The few pre-RICE localities showing evidence of C4 abundance suggests that these grasslands were geographically restricted which limits, but may not exclude, the possibility that a world-wide mechanism controlled its spread.

10aBarstow Formation10aC4 grasses10aCarbon isotopes10aEquidae10aMiocene10aUngulates1 aFeranec, R., S.1 aPagnac, D. uhttp://dx.doi.org/10.1016/j.palaeo.2013.07.022