As grasses grew more common in Africa, most major mammal groups tried grazing on them at times during the past 4 million years, but some of the animals went extinct or switched back to browsing on trees and shrubs, according to a study led by the University of Utah.
"It's as if in a city, there was a whole new genre of restaurant to try," says geochemist Thure Cerling, first and senior author of the study published today by the journal Proceedings of the National Academy of Sciences. "This is a record of how different mammals responded. And almost all of the mammals did an experiment in eating this new resource: grass."
The experiment peaked about 2 million years ago, says Cerling, a distinguished professor of geology and geophysics. The only major group that still mostly grazes grass is the bovids: cattle, buffalo, sheep, wildebeest, hartebeest and some antelopes such as oryx and waterbucks.
The study also revealed that the present isn't necessarily the key to the past in terms of what animals eat. Today, elephants and spiral-horned antelope (elands, kudus and bushbuck) browse on trees and shrubs, but the study showed that 2 million years ago, African elephants grazed on grass and the antelopes had mixed diets with a lot of grass. Asian elephants, which ate grass and were abundant in Africa 2 million years ago, went extinct in Africa but survive in Asia, where they graze but also browse trees and shrubs.
"That the diet of some of these animals is different from that of the present was a surprise, and shows the importance of challenging one's assumptions when making ecological reconstructions," says study co-author and geologist Frank Brown, dean of the University of Utah's College of Mines and Earth Sciences.
Overall, Cerling and colleagues wrote that the assemblages of grazing, browsing and mixed-diet animals during the past 4 million years "are different from any modern ecosystem in East or Central Africa."
A perfectly preserved amber fossil from Myanmar has been found that provides evidence of the earliest grass specimen ever discovered - about 100 million years old - and even then it was topped by a fungus similar to ergot, which for eons has been intertwined with animals and humans.
Ergot has played roles as a medicine, a toxin, and a hallucinogen; been implicated in everything from disease epidemics to the Salem witch trials; and more recently provided the hallucinogenic drug LSD.
Apparently both ergot and the grasses that now form most of the diet for the human race evolved together.
And if they already seemed a little scary, imagine a huge sauropod dinosaur that just ate a large portion of this psychotropic fungus, which in other animal species can cause anything from hallucinations to delirium, gangrene, convulsions or the staggers. The fungus, the grasses it lived on and dinosaurs that ate grass co-existed for millions of years.
The findings and analysis of this remarkable fossil were just published online in the journal Palaeodiversity, by researchers from Oregon State University, the USDA Agricultural Research Service and Germany.
"It seems like ergot has been involved with animals and humans almost forever, and now we know that this fungus literally dates back to the earliest evolution of grasses," said George Poinar, Jr., an internationally recognized expert on the life forms found in amber and a faculty member in the OSU College of Science.
"This is an important discovery that helps us understand the timeline of grass development, which now forms the basis of the human food supply in such crops as corn, rice or wheat," Poinar said. "But it also shows that this parasitic fungus may have been around almost as long as the grasses themselves, as both a toxin and natural hallucinogen.
"There's no doubt in my mind that it would have been eaten by sauropod dinosaurs, although we can't know what exact effect it had on them."
A new stable isotope record of Neogene paleoenvironments and mammalian paleoecologies in the western Great Plains during the expansion of C4 grasslands
Authors:
Kita et al
Abstract:
Stable isotopes in horse teeth from the North American Great Plains show that equids began to incorporate C4 plants in their diets about 6.5 million years ago as C4 grasslands expanded. However, the ecological response of many other ungulates to this expansion is poorly documented. We use stable carbon isotopes in mammalian tooth enamel to test whether other ungulates adapted by incorporating C4 vegetation in their diets. The openness of habitats before the expansion of C4 grasslands is uncertain, with plant phytolith studies suggesting a patchy environment with open-habitat grasses and forest, and pollen and macrofloral studies suggesting more forested habitats. To address this problem we use a model that predicts carbon isotope values for tooth enamel for a variety of environments, based on values in modern plants. Carbon and oxygen isotopes were analyzed in medium to large herbivores from three late Miocene and three Pliocene local faunas comprising a total of 13 and 7 genera, respectively, and 59 and 42 individuals. Results indicate that before the expansion of C4 grasslands, taxa with high-crowned teeth were consuming predominantly C3 vegetation. In contrast, by the late Pliocene most taxa studied were consuming a component of C4 vegetation and only the peccary Platygonus sp. had a pure C3 diet. C4 consumption increased in the late Pliocene (~ 3.0 Ma) Big Springs local fauna probably in response to increased C4 biomass. Most landscapes in the late Miocene of Nebraska were open, such as woodland-savanna or C3 grassland, although low carbon values from the Pratt Slide local fauna suggest a denser, presumably forested area. This general pattern suggests an expansion of open-habitats no later than 12 Ma (early Clarendonian). Through the Miocene-Pliocene transition there was an overall shift to lower δ18O enamel values, which parallels the long-term decrease in global mean annual temperature inferred from the marine record. Our results indicate that major changes in the diets of medium and large herbivores broadly corresponded with increased C4 biomass and cooling climate from the latest Miocene to the late Pliocene.
Spatiotemporal variation in the origin of C4 grasses: δ13C analysis of grass pollen from the southeastern United States
Authors:
Nelson et al
Abstract:
The C4-plant functional type is a major evolutionary and ecological success. However, the relative importance of environmental factors, such as climatic conditions and atmospheric CO2 concentrations, in driving the origin of C4 grasses in different parts of the world remains poorly understood. We determined the carbon-isotope composition of 612 individual grains of grass pollen in seven sediment samples from the southeastern United States from the middle/late Eocene. By applying a Bayesian model to these data, we determined the probability of rejecting (at p < 0.05) the null model that each sample contained pollen from only C3 grasses. We could not reject the null hypothesis for any sample when using a range of potential values of δ13C of atmospheric CO2. These results suggest that C4 grasses were not present on the landscape during the middle/late Eocene, a conclusion consistent with a limited number of studies from more northern and western regions of North America. In contrast, prior studies indicate that C4 grasses existed during this time in parts of Europe and South America. Together these results imply variations in the location, time, and environmental conditions associated with the origin of C4 grasses.
