Pregnant sloth fossil with preserved baby is revealed – 07/07/2023 – Science

An exceptional finding of a pregnant fossil sloth with the pup preserved in the womb was released this week by researchers from the Museum of Natural Sciences at PUC (Pontifical Catholic University) Minas Gerais.

The preservation of the fetus containing more than 200 bones, including the skull with teeth, is unique and unknown in the fossil record in the world. The material was excavated more than 40 years ago by the museum’s paleontologist and professor, Cástor Cartelle Guerra, but the detailed study and disclosure of the find were only made now.

“The fossil species is known from other places, but it is the first time that a pregnant female with the calf has been found with this type of exceptional preservation, much better than even the mother”, said the paleontologist to Sheet.

The fossil, which measures approximately 25 centimeters, was found in Toca da Boa Vista, near the municipality of Campo Formoso, in the interior of Bahia. The material is deposited in the Paleontology Collection of the Museum of Natural Sciences at PUC, in Belo Horizonte.

Laziness is of the kind Nothrotherium machinense, had terrestrial habits and lived at least 40 thousand years ago, at the end of the Pleistocene. The same species has already been found in other caves in the region and also in São Paulo and Minas Gerais, in addition to Uruguay.

The first to describe the species was the Danish-Brazilian paleontologist Peter Lund, considered the father of paleontology in Brazil. He found remains of the sloth in Toca de Maquiné, near the municipality of Cordisburgo, in Minas Gerais, in 1836, where today there is a museum in his honor.

According to Guerra, the article describing the morphology in detail of the fetus and the mother was sent for publication in the scientific journal Journal of Mammalian Evolution. The work should be published in the coming days. Researchers from Canada and Argentina co-signed the study.

Ground sloths lived from 2.6 million years ago to approximately 10,000 years ago, when they became extinct after the last Ice Age. Fossils of sloths are known from different locations in Brazil, Argentina, Uruguay, Chile and the United States, says Guerra. They are part of the group of mammals known as xenarthrans, which include armadillos, anteaters and arboreal sloths.

“There were two types of sloths, arboreal sloths, which include the sloth species that still exist today, and terrestrial sloths, which included species up to six meters tall, such as giant sloths. [gênero Megatherium]. This sloth from Toca da Boa Vista is considered the smallest species of ground sloths, reaching two meters in length from the tip of the snout to the tail”, he explains.

Although it is a relatively common species in the fossil record, finding an individual with the calf preserved, including the ear bones — a rare preserve — is extremely unusual, he said.

According to Guerra, it is possible that the calf weighed around 1.5 kg to 2 kg, while the mother, at around two meters, could reach 250 kg. “The meticulous study of skull bones and teeth allowed us to discover hitherto unknown ecological habits, such as the fact that the fetus already has all its teeth formed in the womb, indicating that they weaned very early after birth”, he explains.

Paleontologist Fabiana Rodrigues Costa, a professor at UFABC (Federal University of ABC), who did not participate in the research, said that the record is very important and will help clarify, for example, aspects of the development cycle of sloths.

“Until today, there were records of a maximum of four or five fossil remains of fetuses, so finding a skeleton like that is extremely rare”, he says. “Fossils so well preserved can help in studies of biomechanics and animal behavior using 3D modeling to simulate animal movement in a virtual environment, as we can’t see sloths walking around here today.”

Guerra, now 85 years old, more than 60 working as a researcher, hopes to be able to make a three-dimensional copy of the fossil for display at the PUC Minas Museum, but the project lacks financial support. “In the meantime, we do the promotion with the photo and supporting material,” he said. About the possibility of continuing to work even at an advanced age, he says that, “as long as the head is good, it will not stop”. “Here you still have material to study for over a hundred years.”