A furry predator that lived 165 million years ago is offering scientists an unexpected glimpse into the evolution of mammals. Known as Megacauda sungei, this ancient hunter measured only about half a meter (20 inches) from nose to tail, yet it was remarkably large compared with most of its Jurassic relatives. It hunted in the water, using teeth with backward-curving cusps to grip slippery prey.
Its most significant feature, however, was not its size or hunting ability. Researchers discovered evidence of a sophisticated soft palate that separated the mouth from the pharynx, the passage connecting the mouth to the throat. This anatomical development helped make it possible to swallow while maintaining the ability to breathe, an essential adaptation for mammals that nurse their young. The findings, from researchers in Shenyang, Chicago, and Bonn, have been published in the journal Nature.
How an Ancient Predator Reveals the Evolution of Swallowing
Many animals lack a soft palate and instead rely on a relatively simple arrangement of hyoid bones in the throat. Without the complex swallowing mechanism found in mammals, feeding can require very different movements.
Crocodiles, for example, lift their heads and make sudden jerking motions to move unchewed food down their throats. “This is achieved with the aid of gravity,” explains paleontologist Prof. Dr. Thomas Martin from the University of Bonn.
Mammals have a more elaborate hyoid structure that allows them to swallow even when gravity is working against them. Humans, for instance, can drink through a straw while upside down and still breathe.
This ability has played an important role in mammalian evolution. It allows young mammals to consume nutrient-rich milk safely, preventing liquid from entering the nasal passages. By supporting effective nursing, this adaptation provided an important survival advantage.
“It was this adaptation that made brain development, eventually leading to humans, possible,” stresses Martin. “The soft palate and the shaping of the oral cavity and pharynx are directly linked to the evolution of mammals.”
Remarkably, Megacauda sungei already possessed evidence of this anatomical development millions of years before modern mammals appeared.
A 165-Million-Year-Old Predator Built for Swimming
With its short fur and broad, flattened tail, Megacauda sungei would have looked somewhat like a modern otter, beaver, or platypus. Its body was also well suited to moving through water.
Scientists used computed tomography scans of the fossil to create detailed three-dimensional reconstructions of its anatomy. These models suggest that the animal propelled itself through the water by paddling with its front legs and moving its tail in an undulating motion. Its hind legs likely helped it change direction.
“It is the earliest evidence of an aquatic lifestyle in mammals,” says the paleontologist from the University of Bonn.
Its teeth revealed another unusual adaptation. Along with the backward-curving cusps that helped it catch aquatic prey, the animal possessed specialized canine teeth with three roots, a distinctive feature that surprised the researchers.
By comparing the fossil with other prehistoric specimens and living animals, the team determined that Megacauda sungei belonged to the docodonts, an extinct group of early mammal relatives known as mammaliaforms. These animals were especially widespread during the Jurassic Period. The fossil itself was discovered in Xiayingzi, Inner Mongolia.
A Tiny Giant in the Age of Dinosaurs
“The new species Megacauda sungei is the largest of the mammaliaforms from the Jurassic,” says Thomas Martin.
At roughly half a meter long and weighing about two kilograms (4.4 pounds), this prehistoric “top predator” would seem insignificant beside modern giants such as elephants, rhinoceroses, and whales.
But size was relative in the Jurassic world.
The Mesozoic Era, which lasted from approximately 230 million to 66 million years ago, was dominated by dinosaurs. Early mammal relatives generally remained small, with many weighing only a few grams.
Against that backdrop, Megacauda sungei was unusually large. Although tiny by today’s standards, this aquatic hunter was a heavyweight among the early mammal relatives that shared the planet with dinosaurs.
An Extraordinary Fossil Discovery in Inner Mongolia
The scientific importance of Megacauda sungei might never have been recognized without a fortunate series of events.
Years ago, the Paleontological Museum of Liaoning in Shenyang (China) acquired the fossil, which had been unearthed in Inner Mongolia, as part of a collection of specimens. Its exceptional features became apparent when three scientists examined it together: Prof. Dr. Chang-Fu Zhou from Shandong University (China), Prof. Dr. Zhe-Xi Luo from the University of Chicago (USA), and Prof. Dr. Thomas Martin from the University of Bonn.
Recognizing that the specimen represented a previously unknown species, the researchers chose to honor Prof. Sun Ge, the Honorary Director of the Paleontological Museum of Liaoning.
They combined the name “large tail” (Megacauda) with the species designation “sungei,” creating the scientific name Megacauda sungei.
Establishing the animal’s identity required years of detailed analysis, comparisons, classification, and documentation.
“It is the result of a long period of teamwork,” says Thomas Martin.
The research has provided important new insights into the early history of mammals, particularly how rapidly their ancestors developed specialized bodies and lifestyles.
Other Jurassic docodont fossils show that members of this group were already adapting to very different environments. Some lived in trees, others burrowed underground like moles, and species such as Megacauda sungei were adapted to life in water.
“This shows how widespread docodonts were in the Northern Hemisphere and that this diverse group of animals developed very different lifestyles at an incredibly early stage,” summarizes Martin.
Together, these discoveries reveal that long before modern mammals became dominant, their ancient relatives were already experimenting with an impressive range of ways to survive.
