INFERRING MESOZOIC TERRESTRIAL ENVIRONMENTS USING ECOLOGICAL STRUCTURE OF EXTANT SMALL-BODIED MAMMALIAN COMMUNITIES

Today mammalian communities show drastic ecological responses to ongoing environmental change on both temporal and spatial scales. Similarly, environmental alteration has played a vital role in shaping ecological dynamics in the past, resulting in today’s faunal associations. Mesozoic terrestrial environments, which had a great impact on the earliest mammals, have been extensively studied using isotopic, invertebrate, and flora proxies. Here we present the first study inferring Mesozoic terrestrial environments using mammalian communities themselves. To do so, we compiled ecological data for four Mesozoic mammalian communities from northeastern Asia and 98 extant small-bodied mammal communities from across the globe. Specifically, we collected three ecological parameters (body size, diet preference, and locomotor mode) and four environmental factors (temperature, precipitation, elevation, and latitude) of the extant communities. We categorized each extant community into two habitat (closed and open), four climatic (tropical, arid, temperate, and cold), and eight vegetation (tropical rain forest, tropical seasonal forest, savanna, grassland, shrubland, desert, temperate forest, and boreal forest) types. We applied discriminant function analysis (DFA) to the three ecological parameters to classify habitat, climatic, and vegetation types of the extant faunas and investigated relationships among the ecological parameters and environmental factors. The resulting relationships were used to infer the Mid-Late Jurassic and Early Cretaceous terrestrial environments in northeastern Asia. Our results indicate that environmental factors shape extant small-bodied mammalian communities by differentiating ecological structures from different environments. Distinct assembly of ecological structure of different environments is a result of ecological interactions of ecological entities rather than randomization. Environmental factors temperature and precipitation seem to play the most important roles in this process. We suggest that, during both the Mid-Late Jurassic and Early Cretaceous, arid to tropical climates prevailed in local terrestrial environments from which mammalian faunas have been described, an interpretation that is generally consistent with previous studies.