Zhaoqun Zhang

Replaying evolutionary transitions from the dental fossil record

The evolutionary relationships of extinct species are ascertained primarily through the analysis of morphological characters. Character inter-dependencies can have a substantial effect on evolutionary interpretations, but the developmental underpinnings of character inter-dependence remain obscure because experiments frequently do not provide detailed resolution of morphological characters. Here we show experimentally and computationally how gradual modification of development differentially affects characters in the mouse dentition. We found that intermediate phenotypes could be produced by gradually adding ectodysplasin A (EDA) protein in culture to tooth explants carrying a null mutation in the tooth-patterning gene Eda. By identifying development-based character inter-dependencies, we show how to predict morphological patterns of teeth among mammalian species. Finally, in vivo inhibition of sonic hedgehog signalling in Eda null teeth enabled us to reproduce characters deep in the rodent ancestry. Taken together, evolutionarily informative transitions can be experimentally reproduced, thereby providing development-based expectations for character-state transitions used in evolutionary studies.

Late Miocene large mammals from Ivand (Northwestern Iran)

ABSTRACT Large mammalian fossil fauna of the Ivand locality in northwestern Iran is reported for the first time. This new locality is situated north of the city of Tabriz in the geographical proximity of the famous Maragheh fossil sites. A large hipparion, represented by an almost complete skull and mandibles, is recorded from this locality. The skull, most likely of Hipparion giganteum-Hipparion brachypus lineage, represents significant evidence of the presence of large hipparionine horses in northwestern Iran in the Late Miocene. A small number of horn-cores attributed to Oioceros atropatenes Rodler & Weithofer, 1890 and Gazella sp., in addition to some indeterminate dentition, represent the bovid material in the Ivand fossil assemblage. Postcranial evidence also points to the presence of Deinotherium giganteum Kaup, 1829 and Rhinocerotinae indet., while other material adds carnivorans, giraffes and large porcupine rodents to the list of the fauna. Based on the occurrence of these taxa, the Ivand locality can be correlated with the Middle and Upper Maragheh biostratigraphical intervals, thus demonstrating a middle Turolian age (c. 8–7 Ma).

The palaeoenvironment of the middle Miocene pliopithecid locality in Damiao, Inner Mongolia, China

Damiao, Inner Mongolia, has three main fossil horizons representing the early, middle, and late Miocene. The middle Miocene locality DM01 is the only primate locality from the region and also represents the latest occurrence of pliopithecoids in northern China. The presence of pliopithecoid primates in central Asia after the middle Miocene climatic optimum seems to contradict the general trend of strengthening climatic zonality and increasing aridity. To investigate this enigma, we employ faunal similarity, ecometrics, and stable isotope analysis. Our results support previous inferences concerning the presence of locally humid environments within the increasingly arid surroundings that characterized central Asia. Hypsodonty, estimated mean annual precipitation (MAP), local sedimentology, and large mammal fossils suggest more humid and possibly more forested and wooded environments for the DM01 locality. We compared our results with the adjacent fossil-rich middle Miocene Tunggur localities. However, the small mammal fauna and isotope data are consistent with a mosaic of forest and grassland environment for all Damiao localities. Based on our results, Tunggur may have been too seasonal or not sufficiently humid for pliopithecids. This is supported by the higher mean hypsodonty and lower estimated MAP estimates, as well as slightly higher δ13C values. We suggest that DM01, the driest known Asian pliopithecid locality, may have been a more humid refugium within a generally drier regional context.