2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Skull of Stephanorin Stephanorhinus from Dmanisi
Researchers using a proteome have identified the place of the Stephanorin rhinoceros, which died 1.77 million years ago, on a phylogenetic tree, according to Nature. Proteins are preserved in ancient samples much longer than DNA, therefore, by determining the composition of the proteome of a particular tissue, it is possible to trace the evolution of long-extinct species. Scientists have confirmed this by conducting tests on the tooth enamel of various species of mammals.
In recent years, researchers have increasingly determined the place of an extinct species on a phylogenetic tree based on the sequencing of the genome. However, DNA is degraded relatively quickly, which limits the maximum age of samples for study. To date, paleogenetics have succeeded in sequencing DNA about 400 thousand years old from deposits (1) and 560-780 thousand years old from permafrost (2). Unlike DNA, proteins persist much longer - for example, it was possible to sequenced individual amino acid sequences and determine proteins from a fossilized ostrich shell about 3, 8 million years old.
However, when it comes to mammalian fossils that are too ancient or in hot climates, scientists, for the most part, are able to recover only type 1 collagen. The problem is that this protein is very conservative, that is, its sequence changes insignificantly during evolution, so it is not very suitable as a phylogenetic marker.
Scientists led by Eske Willerslev of the University of Copenhagen decided to use mammalian tooth enamel as samples to reconstruct ancient proteins. It is the hardest vertebrate tissue and is often found during excavations, so it could be a suitable subject for research and help scientists trace the evolution of animals that became extinct earlier than 700 thousand years ago and their DNA has already collapsed.
For research, the authors selected fossils of large mammals aged 1, 76-1, 85 million years old, found in Dmanisi in southern Georgia. They took 11 samples of bone tissue for analysis, one sample of dentin - the hard tissue of the tooth that is covered with tooth enamel - and 14 samples of tooth enamel, some of them with traces of dentin. In 15 of 23 samples, the authors found proteins and analyzed using mass spectrometry.
In particular, researchers in different samples were able to reconstruct specific structural proteins of tooth enamel: amelogenin, enamelin, amelotin and ameloblastin, enzymes specific to it, and nonspecific proteins, including serum albumin. The genes of one of the enamel proteins, amelogenin, in males and females of many mammals are located on the Y and X chromosomes and their sequence is slightly different. Moreover, the “male” isoform of amelogenin is found only in males, and the “female” isoform is found in both. This difference in protein composition can be seen using mass spectrometry and thus determine the sex of the animal. Thanks to this, the authors of the study were able to find out that the fossils of four mammals, including the extinct Pseudodama deer, two other representatives of the deer and one of the bovids, were males.
The most complete proteome (875 amino acids from six proteins) was obtained by the authors from the lower molar of Stephanorhinus. Representatives of this genus lived in Eurasia in the Pleistocene. They had two horns, weighing more than three tons, and reaching four meters in length. Stephanorins include the Merka rhinoceros (Stephanorhinus kirchbergensis) and the Etruscan rhinoceros (Stephanorhinus etruscus).
Place of Stephanorinus from Dmanisi on the phylogenetic tree
The researchers compared the obtained sequences of amino acid proteins of the tooth enamel of Stefanorin with the already known sequences of all modern rhino species, as well as the extinct Merck rhinoceros and woolly rhinoceros (Coelodonta antiquitatis). After that, they managed to determine the place of Stephanorin from Dmanisi on the phylogenetic tree. Its closest relatives turned out to be the extinct woolly and Merka rhinoceros, and from the modern species - the Sumatran rhinoceros.
Previously, researchers have already developed a technology for determining the sex of human remains by the composition of amelogenin in tooth enamel. Scientists suggest that this method is suitable for determining the sex of children and adolescents. In these cases, the osteological method used to find out the sex of adults does not always work. It will also be useful if little has survived from the remains, except for the teeth.
