Ancient diet of the Pleistocene gomphothere Notiomastodon platensis (Mammalia, Proboscidea, Gomphotheriidae) from lowland mid-latitudes of South America: Stereomicrowear and tooth calculus analyses combined

摘要

The gomphothere assemblage from the Pleistocene of Aguas de Araxa (Minas Gerais State, Brazil) is composed of several isolated teeth, cranial and postcranial fragments assigned to a single population of Notiomastodon platensis. The age profile suggests decline of the population, due to the large amount of senile and mature adult individuals. The mortality event probably occurred during a long period of low humidity, which could cause a mass death of the proboscideans around water refuges. The ancient feeding ecology of these gomphotheres was reconstructed through stereomicrowear and plant microfossils from teeth calculi, using molars from four age classes. The enamel microwear patterns were recognized according to published studies, whereas the average scratch and pit values were compared to an extant ungulates database. The plant microfossils were chemically recovered and microscopically analyzed. Isotopic analyses of the South American gomphotheres suggest a wide dietary range for N. platensis, except for two localities: Santiago del Estero (Argentina) and La Carolina (Ecuador). For these, isotope analyses suggested an exclusive C4 diet, whereas all other South American localities studied so far indicate an exclusive C3 diet or a mixed C3 and C4 diet. The results also support the apparent latitudinal gradient of C3/ C4 grasses. The stereomicrowear analyses for N. platensis exhibited average scratch and pit values, which places it within the extant mixed-feeder morphospace. The higher frequency of fine scratches indicated the ingestion of C3 grasses. Alternatively, the presence of coarse and hypercoarse scratches along with gouges and large pits suggested the ingestion of foliage and lignified portions. The plant microfossil analysis recovered fragments of a conifer tracheid and vessel elements with a ray of parenchyma cells, which corroborates the consumption of wood plants. Also, pollen grains (Polygonaceae), spores (Polypodiaceae) and fibers were found in the samples. According to the results, the Aguas de Araxa gomphotheres were feeding generalists and consumed wood elements, leaves and C3 grasses.