This Semi-Aquatic Mammal Lived Alongside Dinosaurs 168 Million Years Ago

A study of a strange Jurassic-era fossil sheds light on the diversity of mammal relatives and offers clues to the early evolution of certain traits.

Zomite: A study of a strange animal fossil from the Jurassic period reveals both the diversity of mammal relatives and provides clues to the early evolution of some features.

About 168 million years ago, when dinosaurs ruled the land, a strange animal hunted salamanders in the lakes and rivers of today's China. The animal's body was covered with hair, its tail was wide and flat, and its legs were suitable for swimming, but its large fangs indicated that we were dealing with a serious predator. Combining features of a platypus and an otter, this extinct animal was one of the strangest known mammal relatives of the Jurassic period.

The researchers named the mentioned species Megacauda sungei. The discovered fossil shows that this animal, weighing about one to two kilograms, was the largest known mammal relative throughout the Jurassic period; Although his weight was not more than a chihuahua dog. The name Megacauda means "big tail" and refers to one of the most prominent features of this animal's body.

Researchers discovered the delicate and detailed Megacauda Songei fossil in 2016. The results of the fossil examination, which was recently published, show that this animal lived in the Middle Jurassic period, that is, between 168 and 163 million years ago, in an area that is now a part of Inner Mongolia, China. It seems that Megacauda Songei was one of the first land mammals that had a semi-aquatic life.

Zhe Shi Luo, a paleontologist at the University of Chicago and one of the authors of the study, compared the appearance of this animal to a composite creature in an interview with Live Science and added: "It's like we're dealing with a chimera." Chimera or ratfish is a creature that has the characteristics of several different animals.

According to Luo, the back half of Megacauda's body was very similar to Platypus. Its limbs were also probably suitable for swimming and digging tunnels on the banks of rivers. However, his teeth tell a different story. This animal had powerful fangs that were adapted to cut and chew meat; These features are not seen in today's platypus.

Thomas Martin, a paleontologist at the University of Bonn in Germany and one of the authors of the study, says Megacauda songae apparently had the structures necessary for these processes. Luo also considers this ability as one of the important innovations of mammalian evolution; A capability that helped them use more diverse food sources and eventually diversify into groups with carnivorous, insectivorous, herbivorous, and omnivorous diets.

The presence of the mentioned structures in the Megacauda fossil shows that the mechanisms necessary for sucking milk and swallowing food had evolved until the Middle Jurassic, that is, about 174 to 164 million years ago. This time period precedes the separation of today's marsupials, such as kangaroos, from paired mammals, such as primates and bears. According to the estimates, this event happened about 160 million years ago. Both groups have branched from a common egg-laying ancestor approximately 180 million years old.

Luo says the new discovery suggests that the history of this feature goes back to a time before the split between today's lineages of marsupials and placental mammals. Sue Hand, a vertebrate paleontologist at the University of New South Wales in Australia, explains: "Infant sucking was once thought to be a more advanced mammalian trait, but it now appears that this ability evolved much earlier, at least 165 million years ago, in the common ancestor of mammals and their extinct relatives."

Megacauda Songae belonged to an extinct lineage of dacodonts, extinct relatives of mammals; A group of mammal relatives that lived about 200 to 120 million years ago, in the Jurassic and Cretaceous periods. The members of this group were adapted to live in diverse habitats.

Luo previously also participated in a research about Castorocauda lutrasimilis; A semi-aquatic animal that lived about 164 million years ago and is known as the "Jurassic Blue Dog".

Tim Flannery, a mammalogist at the Australian Museum's Research Institute, believes that the aquatic lifestyle probably evolved many times among early mammal species. India also considers this fossil as an impressive example of the diversity of similar animals in the age of dinosaurs. According to him, the new findings add to the growing evidence that mammals lived in diverse habitats and ecological niches long before the appearance of today's mammals.