Fossil of Gondwanan 'Crazy Beast' From 66 Million Years Ago Discovered in Madagascar

Researchers have identified a bizarre, previously unknown mammal that lived 66 million years ago in what is now Madagascar, casting new light on the evolution of this animal group.

The badger-like creature—which has been dubbed Adalatherium hui, from the Malagasy word for "crazy" and the Greek word for "beast"—belongs to an extinct group of mostly small herbivorous mammals known as Gondwanatheria that have been documented in Madagascar, Africa, Antarctica and South America.

The name of this group derives from the fact that all of these regions were once part of the southern supercontinent Gondwana, which existed between around 550 million and 180 million years ago.

An international team led by David Krause, senior curator of vertebrate paleontology at the Denver Museum of Nature & Science, found a near-complete skeleton of the creature, according to a study published in the journal Nature.

Krause and colleagues say the find is the most complete known skeleton of an animal from the group Gondwanatheria, as well as the most complete of a fossil mammal from the Mesozoic era (252 million to 65 million years ago) in the regions that once formed Gondwana.

This is significant because the Mesozoic fossil record from the regions that made up Gondwana—essentially, the southern hemisphere—is very small compared to its northerly supercontinent neighbor Laurasia.

Furthermore, gondwanatherians have remained quite poorly known, and were only previously represented by isolated teeth and jaws, and a single skull. The earliest members of this group appeared just a few million years before non-avian dinosaurs were wiped out by the giant asteroid impact that occurred around 66 million years ago.

"[The discovery allows us], for the first time, to gain good insight into what gondwanatherians looked like, how they lived, and what other mammals they are related to," Krause told Newsweek. "We estimate that Adalatherium was over 20 inches long and had a body mass of 6.8 pounds, but the skeleton is of a subadult, so it was probably slightly longer and heavier when fully grown."

In fact, the Adalatherium hui specimen is among the largest Mesozoic mammals—which were, on average, mouse-sized—despite not being fully grown, according to Krause.

"In body form, it probably resembled a badger, although its trunk was probably longer. Its teeth are bizarre. The molar teeth have a construction dramatically different from those of any known mammal, extant or extinct," he said. "The front teeth were also unique in that both upper incisors were very large and had enamel on only one side. We believe the front teeth were used for gnawing and that the back teeth were used for slicing up vegetation of some kind; in other words, Adalatherium was likely an herbivore."

According to Krause, the animal's skull is also, odd featuring a large hole, or foramen, between its nasal bones for which there is no parallel in any known mammal, living or extinct. Furthermore, it had several more smaller holes, or foramina.

"It had more foramina on its snout than other mammals, indicating rich innervation to a sensitive snout, one that probably had a spray of whiskers," Krause said. "Various features of the nasal cavity and inner ear are also unique among mammals. The bony composition of its snout is also unusual in a number of ways.

"The skeleton behind the head was also weird—for example, more trunk vertebrae than any Mesozoic mammal and strangely bowed tibia bone Based on the skeleton, we think that Adalatherium was probably a digger, and that it possibly made burrows. This is indicated by some badger-like features––powerful hind limbs and a short, stubby tail," he said.

The researchers say the mammal's unusual size for its time and bizarre set of features could be explained, in part, by the fact that it evolved on an isolated island—in an environment with very particular food sources, competitors and predators. While Madagascar once formed part of Gondwana, the supercontinent began breaking up around 180 million years ago.

The island, with the Indian subcontinent attached to its east, first separated from Africa. Then, about 88 million years ago, Madagascar became fully isolated after breaking apart from the Indian subcontinent. This means that the lineage of animals that eventually resulted in Adalatherium was able to evolve in isolation from other related gondwanatherians for more than 20 million years, sufficient time to develop its strange features.

"It is the first well-documented example of evolution in isolation of a Mesozoic mammal, as evidenced by a litany of features that are unique among mammals that evolved over the course of more than 20 million years," Krause said.

Adalatherium hui
Life-like reconstruction of Adalatherium hui. Andrey Atuchin/Nature Research

The specimen was first uncovered by a Malagasy graduate student, Augustin Rabarison, in July 1999 during one of Krause's expeditions in northwestern Madagascar, although the significance of the find was not immediately apparent.

"He saw some crocodile bones that appeared to belong together and so he and a colleague encased them in a plaster jacket," Krause said. "We didn't think the crocodile specimen was particularly significant and therefore didn't open up the jacket until 2002, first attending to the preparation of other fossil jackets that we felt were more promising."

"When this particular plaster jacket was opened, I immediately recognized a mammalian elbow joint further down in the encased block of rock. The elbow joint was part of the nearly complete skeleton that we have ascribed to Adalatherium," he said.

There were several reasons why it took so long after the initial discovery for the latest study to appear, but perhaps the main one, according to Krause, was that the bones were so bizarre that he and his colleagues had "no clue" what it was.

"I can honestly say that this is the discovery of my career!" he said. "The specimen is extraordinarily complete, preserving almost all of the bones, including the tiniest foot bones, and even costal cartilages—the cartilages that connect the breast bone to the ribs—which are rarely preserved, especially in the Mesozoic."

Krause says that Adalatherium likely lived in a harsh environment, which it shared with dangerous predators, such as dinosaurs massive crocodiles and 100-pound constrictor snakes. Independent lines of evidence indicate that at the time, this part of Madagascar had a semi-arid climate with pronounced dry seasons and intense rainy season.

"The rainy seasons caused debris flows from the highlands that extended across the flood plains and buried everything in sight," Krause said. "This resulted in the burial of the skeleton of Adalatherium soon after it had died or perhaps even while still alive, as indicated by the tight articulation and exquisite preservation of the skeleton."

The latest findings shed new light on the history of gondwanatherians, which were once thought to be related to today's sloths, anteaters and armadillos. However, more recent research has indicated that they were "part of a grand evolutionary experiment, doing their own thing, an experiment that failed and was snuffed out in the Eocene, about 45 million years ago," Krause said in a statement.

While Adalatherium is a significant breakthrough in our understanding of gondwanatherians, there is still much that scientists don't know about the early evolution of mammals—a group which first appeared around 200 million years ago—in the southern hemisphere.

"Adalatherium is just one piece, but an important piece, in a very large puzzle on early mammalian evolution in the Southern Hemisphere," Krause said in a statement. "Unfortunately, most of the pieces are still missing."

Patrick O'Connor, a professor of anatomy and neuroscience from the Ohio Center for Ecology and Evolutionary Studies at Ohio University, who was not involved in the study, said the latest discovery was "remarkable" for a number of reasons.

"This truly is the 'discovery of a career,' represented by a virtually complete skeleton that preserves details from the tip of the nose to the tip of the tail, including the spectacular examples of soft tissues such as cartilage," O'Connor told Newsweek. "This one specimen provides more insight into one of the most poorly known Mesozoic mammal groups (gondwanatherians) than all other gondwanatherian fossils combined."

"Until this study, most gondwanatherian species have been based on isolated teeth and jaws—which does limit how much scientists can even say about their biology, not to mention limiting our understanding of how gondwanatherians are even related to other groups of mammals. This specimen allows for a refined understanding of Mesozoic mammal relationships" he said. "[It] sets a new standard for the type of information waiting to be discovered in southern hemisphere locales—and its discovery will no doubt cause us to revise concepts around vertebrate evolution history and to alter textbooks for years to come."

O'Connor adds that Adalatherium is convincing evidence for evolution in isolation, in this case, what was possible for animals and plants on Madagascar after it separated from other landmasses.

The island, the fourth largest in the world, located around 250 miles off the coast of East Africa, is today filled with animals and plants that are found nowhere else on Earth. In fact, Adalatherium is not the only strange, ancient vertebrate that Krause and his team have discovered on Madagascar over the last two decades or so. Previous finds include a giant, armored predatory frog known as Beelzebufo, and a pug-nosed, vegetarian crocodile called Simosuchus.

This article has been updated to include additional information from David Krause and comments from Patrick O'Connor.