Importantly, the results of the other team's study, which analyzed collagen protein, were consistent with the mitochondrial study. Paleoproteomics, or the use of protein evidence for taxonomic purposes, is a relatively new area, but collagen type 1 ("bone") has become an increasingly important source of information in mammalian paleontology, for two years. reasons: it degrades more slowly than DNA, and it can be found in large quantities in well-preserved fossils because it accounts for 80 to 90% of the organic fraction of the bone. The genes providing the instructions for the synthesis of bone collagen reside in the nucleus and, because of the precise relationship between the constituent elements of a given gene and the protein for which it encodes, the amino acids of the protein reflect the present information. in the gene at the level of the protein. Level of DNA. Thus, between them, the two studies sampled both parts of the genome, both nuclear and mitochondrial.

"Structural proteins such as collagen potentially last much longer after death than the relatively fragile DNA molecule," said Samantha Presslee, lead author of the publication. Nature Ecology and Evolution paper and doctoral student at York University. "This means that scientists can extract and interpret protein evidence from a wide range of extinct species far beyond the current scope of ancient DNA."

Other proteomic studies have revealed the presence of high quality collagen from specimens aged 3.8 million years old, originating from an island in the Canadian Arctic. In the case of the laziness study, the earliest recovery was obtained with a fossil aged 120,000 to 400,000 years; older specimens were tested but did not provide any useful information.

"Having before us the results of the two sources of molecular information, we knew that we were staying on solid ground and that it was time to review the evolution and classification of laziness," he said. Hendrik Poinar of the Ancient DNA Center at McMaster University. who was also a corresponding author on the mitogenomic paper.

With their long arms, crocheted claws and backward locomotion, the six living lazy species seem remarkably similar, but research has shown that they have acquired their adaptation to life in trees independently. thanks to a phenomenon called evolutionary convergence. Molecular studies also confirmed the converging origins, but most other inferences about the evolutionary relationships of laziness were unfounded. For example, the three-toed sloths have long been considered as different from the other anatomically lazy ones, so that they have been classified into a completely distinct evolutionary branch. The evidence for mitochondrial and protein proteins indicates that this view is false: Bradypus bends well in Megatherioidea, a group that also included the largest of all lazy, Megatherium, a giant elephant-sized floor. Similarly, the unaus (two-fingered lazy) belonged to another major group called the mylodontoids, although they had already been placed in Megalonychidae, a family originally defined to include the lazy North soil. American extinct Megalonyx and several islands species that lived in the West Indies until a few thousand years ago.