Since the Late Miocene (about 11 million years), the global climate has undergone large-scale and sustained changes, with forest ecosystems dominated by warm and humid climates withering away and eventually confined to parts of the tropics; instead, grassland ecosystems dominated by grasses eventually occupy most of the ecological space on land.
Grasses can be understood as what is commonly referred to as grass, and it is not accidental that they can stand out in harsh living environments, one of the reasons is that they have a secret weapon - phytosilicate. Phytosilicas are aqueous amorphous silica particles that precipitate inside plants after absorbing soluble silica. Although phytosilicates can exist in various types of plants, in grasses, the number of phytosilic bodies is unusually large, because the phytosilic bodies have a very high hardness, so that plant-eating animals in the eating of grasses to pay a large price for excessive wear and tear of teeth, plants can effectively save themselves through this method.
However, the evolution of life is a game of cat and mouse. Plant-eaters are by no means helpless, and many have evolved more effective teeth to deal with herbs that are increasingly hardened by phytosomes. For example, the elephants we are familiar with have evolved extraordinary teeth, their molar crowns are very high, made up of many very densely arranged enamel tooth plates, this structure makes the molars of elephants like large and wear-resistant grinding discs, which can fully and efficiently process hard grasses. As a result, elephants became a very prosperous species in the late Cenozoic. They can adapt to a variety of harsh environmental climates, and even the northern savannahs during the Ice Age are full of elephants (mammoths).
The paradox of chickens or eggs is common in biological evolution. An interesting question is, did elephants advance teeth suitable for grazing, or did they choose grass as their food first? A 2013 study of elephant fossils in East Africa showed that elephant teeth evolved to look like about 5 million years ago, however, by analyzing the composition of carbon isotopes in tooth enamel, it can be inferred that elephants may have generally eaten herbs by about 10 million years. Herbivorous behavior is about 5 million years earlier than that of herbivorous teeth, which has greatly refreshed the researchers' three views.
However, 10 million years is by no means the upper limit of the time it takes for elephants to graze. In the Junggar Basin of Xinjiang, deep in asia, researchers at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences have found fossils of the gomphotherium steinheimense molars, the elephant-like ancestor of the early Miocene, about 16 million years ago.
How researchers uncovered the privacy of the Steinheim indigodge's 16-million-year-old prelude is thanks to the previously mentioned phytosil. Researchers have found the presence of phytosilic bodies in the calculus of the molars of the Steinheim indigodontis, which are the remnants of the plants that have become fossilized by the ancient elephant ancestors. Phytosilicas are very hard, and although they are a serious test for the animals that eat them, they are stable in form and easy to preserve. What's more, researchers were able to infer their parent plants from their morphology. Through microscopic observation, the researchers found that all the phytocitos in the Steinheim molar calculus molars were actually from grasses, and none of the phytosilicas belonged to non-grassy plants, so the Steinheim molars were already a strict herbivores, and this result was also consistent with the method of stabilizing isotopes and the method of microgrining of teeth. This is more than 10 million years ahead of its descendants evolving herbivorous molars, and even during this period, the earth was dominated by warm and humid forest environments, and large-scale grasslands had not yet emerged. The researchers further studied the climate and environmental evolution of the Junggar Basin in Xinjiang in the Miocene, and by analyzing the pollen data in the strata, they found that in the Junggar Basin of Xinjiang in the Miocene, the climate appeared to be dried earlier than other regions, and perhaps some small grasslands have appeared here, which may have become a prerequisite for Steinheim indigodges to feed on grass.
It should be pointed out that the Steinheim intarsia was not the only elephant class in the Junggar Basin of Xinjiang at that time, and at the same time there was another type of intermodal intarsia (gomphotherium connexum), and the presence of phytosilic bodies was also found in the calculus of the intermodal intarsula, however, most of these phytocillites belonged to non-grassy plants such as young shoots and young leaves, and the phytosilic bodies belonging to grass plants accounted for only a small part. Therefore, it can be inferred that although the intermodal intarsia and the Steinheim incarcerated elephant are in the same large ecological space, it is still a tradition inherited from its ancestors by the retainers, feeding on young branches and young leaves, and for the newly emerging steppe habitats, at most, it is shallow and does not dare to go deeper. But they did not know that the fates of each other had taken place at that moment.
Academia has long determined that the genus of incision elephants is the ancestor of our living elephants, but there are nearly twenty species found in the intarsia, and which kind of intumens eventually evolved into modern elephants, the academic community has not been conclusive. In order to solve the profound connotation of elephant feeding habits and their evolution, researchers at the Institute of Paleovertebrates used the method of branch order analysis to establish the phylogenetic relationship between 17 species of inlaid toothed elephants and later modern elephants. It turns out unsurprisingly that the Steinheim intarget is the closest species of thrombotic to modern elephants in terms of phylogeny, and it is the Steinheim intarget that has evolved several elephants that still live in our world today. And in their bumpy evolutionary path, the choice of diet may have played a key role. At the time of the initial grassland ecology, perhaps the Steinheim incarcerated elephant actively expanded its own physical space, choosing to feed on uncomfortable grasses, and its molar morphology also underwent gradual changes, and finally it could fully adapt to grass as food, thus being able to continue to this day; and its close relatives at the same time, the intermodal incarcerated elephant, due to staying in the food ecological space of young shoots and young leaves that have been adapted, can not respond to environmental changes in a timely manner, when the large-scale arid environment of the late Miocene comes, Helplessly, it went to extinction. It can be said that the choice of feeding is the ultimate choice of future destiny, and the study of the feeding habits of two Miocene mosaics in the Junggar Basin of Xinjiang provides excellent evidence for the new idea of animal behavior evolution leading morphological evolution.
On May 16, the results of the study were published online in the scientific reports. The study was funded by the National Natural Science Foundation of China, the Strategic Pioneering Science and Technology Project of the Chinese Academy of Sciences, the National Key Basic Research and Development Program, and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.
Figure 1 Geographical location, stratigraphic background and phylogenetic tree of the genus Edophora (courtesy of Wu Yan)
Fig. 2 Phytosilicate types and sponge bone needles extracted from dental calculus of the genus Incarcerated elephant and their percentage of their number (courtesy of Wu Yan)
Fig. 3 Analysis results of micro-abrasion marks of the genus Incarcerated Elephant (courtesy of Wu Yan)
Fig. 4 Analysis results of carbon and oxygen isotopes of the genus Incarcerated Elephant (courtesy of Wu Yan)