Amphitherium

Amphitherium is an extinct genus of stem cladotherian mammal that lived during the Middle Jurassic of England. It was one of the first Mesozoic mammals ever described. A recent phylogenetic study found it to be the sister taxon of "Palaeoxonodon". It is found in the Forest Marble Formation and the Taynton Limestone Formation.
Etymology.
"Amphitherium" comes from the Greek "amphi" meaning 'on both sides', and "therion" meaning 'wild beast'. This was in reference to de Blainville's incorrect belief that the original fossil jaw of this animal was not a mammal, but something in between mammals and reptiles.
History.
The first jaws of mammals from the Mesozoic - including "Amphitherium" - were found in the Stonesfield Slate, part of the Taynton Limestone Formation near Stonesfield in England. These were bought by a student of William Buckland's. Although he thought the jaws were mammalian, he asked the great anatomist Georges Cuvier for his opinion. He misidentified them as being from a marsupial mammal, "Didelphis". Later they were identified as being a new genus, and named "Amphitherium". It was first mentioned in the scientific literature alongside "Megalosaurus", by the famous British paleontologist Reverend William Buckland. It came from the Stonesfield Slate of Oxfordshire, England, and Buckland described it in 1824 as "not less extraordinary" than the dinosaur, but it was the larger fossil reptile that captured public imagination. Additional remains were recovered in the late 20th century from the Kirtlington Quarry and Watton Cliff, both part of the Forest Marble Formation
Other early mammal discoveries included "Amphilestes", "Phascolotherium", and the mammal relative, "Stereognathus".