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"Now we have a mammal as a starting point for further study of the lineage of all mammals, humans included," Rougier said. These fossils present the first time scientists could reconstruct the whole shape of a dryolestoid skull - they have features previously seen in primitive mammals that paved the way for the evolution of marsupials and placentals, such as the development of certain key networks of blood vessels. The first specimen, unearthed in 2002, was discovered by the expedition's mechanic. The scientists have found two partial skulls and jaws so far. Dryolestoid remains have been found before, mainly in the northern continents - this new discovery, which is significantly different from past findings, reveals this group of animals reached unsuspected levels of variety. "The amount of information we have about mammals that lived during this time in South America is extremely meager - the new finds represent by far the best specimens known from that time and place," Rougier told LiveScience.Ĭronopio belonged to a group of primitive, extinct beasts known as dryolestoids, which once were part of the lineage leading to marsupials and mammals with placentas such as humans. Cronopio is now the only other mammal known from this time, helping fill in an enigmatic 60-million-year gap in the continent's prehistory of mammals. Until now, researchers had only found one mammal skull in South America that dated back to the Age of Dinosaurs, a 130-million-year-old creature the size of a small opossum named Vincelestes neuquenianus. The mammals that lived in South America during the Age of Dinosaurs remain largely a mystery. " Cronopio's skull was not designed to support large forces, so it could not use its saber-teeth to wrestle down prey like lions can with their canines," Rougier observed. In turn, it probably ate insects, grubs, other kinds of invertebrates and perhaps some small vertebrates. Rougier suggested Cronopio was likely prey for crocodiles and carnivorous dinosaurs. "This is probably what originally buried the animals." "The area had periodic floods," he added. "We do not know much about the flora, but there were at least some tall conifers." In contrast, when Cronopio was alive, "the area was a river floodplain with numerous other animals, including large carnivorous dinosaurs, large herbivores, terrestrial crocodiles, turtles, lizardlike sphenodontians and snakes," Rougier said. "The white bones are quite visible against the bright red sandstone we find here." "It looks like another planet," Rougier said of the site in Argentina.
![squirrel from ice age squirrel from ice age](https://i.pinimg.com/736x/ce/53/da/ce53dace16b3f2b58b1c16b2438f03a1--ice-age.jpg)
The scientists discovered the previously unknown 100-million-year-old species in a very arid, remote part of southwestern Argentina, which has yielded abundant skeletons of dinosaurs and small vertebrates in the past. "Still, we don't have living parallels with any canines quite as long as seen in Cronopio - it's just beyond the scales we know." "Modern-day insectivores use long canines mostly to just grab and hold prey," Rougier said. It remains uncertain what Cronopio might have used its oversized fangs for, but long canine teeth in mammals nowadays are found mostly in insect-eaters.