An animal that lived before the dinosaurs looked like a rotund lizard with a very small head and had a hippo-like semiaquatic lifestyle, according to fossils that were recently excavated in France.

The amphibious animal, which represents a previously unknown genus and species of mammal ancestor, measured about 12 feet (4 meters) long, researchers reported in the October issue of the journal Palaeo Vertebrata, published online in July. They dubbed the new species Lalieudorhynchus gandi; it lived about 265 million years ago on the Pangaea supercontinent, just before the era of the dinosaurs.

Fossils of the unusual animal were first discovered in 2001 in the Lodève Basin in southern France, by study co-author and paleontologist Jörg Schneider, a professor in the Department of Paleontology and Stratigraphy at the University of Freiberg in Germany, and doctoral candidate Frank Körner. They found two large ribs, each measuring 24 inches (60 centimeters) long, in a rocky streambed. During later visits to the site, Körner found additional bones from the mystery animal: a femur measuring 14 inches (35 cm) long, and a shoulder blade measuring 20 inches (50 cm) long.

Their analysis has been 20 years in the making, largely because the fossils were encased in concrete-hard sandstone and their preparation took years to complete, the researchers reported in the study.

From this partial but well-preserved skeleton, the paleontologists deduced that the primitive creature was a type of caseid — an extinct group of fossil reptiles that possessed mammalian traits and are thought to be mammal ancestors — in the genus Lalieudorhynchus. Described in the press release as a “chubby lizard” and as a 3.5-meter-long “pile of meat”, the creature lived during the Permian, a period that began about 299 million years ago and ended about 252 million years ago with the onset of the Triassic period (and the rise of the dinosaurs).

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Caseids were mainly herbivores — perhaps some of the earliest herbivores in evolutionary history. They had small heads and barrel-shaped bodies that held large digestive tracts for breaking down plants, and despite their reptilian appearance, caseids were ancestors of mammals. .

"The highly diverse group of mammal ancestors was the dominant group before the dinosaur ages," Frederik Spindler, co-author of the study and scientific director at the Dinosaur Museum Altmühltal in Denkendorf, Germany, told Live Science. When Spindler examined the newfound fossils, he concluded that they belonged to a new species. There have been fewer than 20 species of caseids identified in the fossil record to date; most came from the United States and Russia, but some have recently been found in southern Europe, Spindler said.

However, L. gandi could be a particularly advanced species of caseid, unlike any seen before, Spindler added. "New genera are diagnosed by detailed anatomical comparisons," and the analysis on L. gandi was conducted by lead study author Ralf Werneburg, director of the Natural History Museum at Bertholdsburg Castle in Schleusingen, Germany, Spindler said. Werneburg identified five unique features "that are not known in any other caseids, and 20 more that make up a unique combination within this family," Spindler explained.

This newly identified creature is not a so-called missing link in any evolutionary lineage of the mammal family tree, but its status as one of the youngest caseids yet found may be significant for understanding mammalian evolution. "It increases the known diversity of large caseids, marking them as a very important herbivorous group," Spindler said. What's more, L. gandi could be the pinnacle of evolution for all caseids before they went extinct, meaning that the species had the most advanced features in the group, Spindler said.

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The structure of L. gandi's bones, which were spongy and flexible when viewed under a microscope, hinted to the study authors that the ancient caseid may have led a semiaquatic lifestyle, much like that of modern hippos. In life, L. gandi likely weighed hundreds of pounds, and all that body weight may have required extra support from immersion in water, according to the study.

However, L. gandi is not a hippo relative, and any similarities to modern hippos are in the ancient animal's habits and not its anatomy, Spindler said.

"Spongy bones can imply a diving lifestyle in some extinct amphibians and marine reptiles," Spindler said. By comparison, most mammals — including hippos — have denser bone tissue. "Our new caseid would swim better, whereas hippos walk closer to the ground," Spindler said.

"A low browsing semiaquatic lifestyle is what large caseids share with hippos, if we are right," Spindler said. "One could say that Lalieudorhynchus gandi 'invented' a niche that hippos repeated later."

Originally published on Live Science.