Palaeontologists believe this would have been used to grapple its intended prey, as well as providing it with a sure footing on tree trunks and branches. The hind feet had four functional toes, the first digit being much reduced in size, but possessing a roughened pad similar to that of possums, which may have assisted with climbing. The discovery in 2005 of a specimen which included complete hind feet provided evidence that the marsupial lion exhibited syndactyly (fused second and third toes) like other diprotodonts. Its strong forelimbs and retracting claws mean that Thylacoleo possibly climbed trees and perhaps carried carcasses to keep the kill for itself (similar to the leopard today). The climbing ability would have also helped them climb out of caves, which could therefore have been used as dens to rear their young. Due to its unique predatory morphology, some scientists have claimed Thylacoleo to be the most specialised mammalian carnivore of all time. Thylacoleo had vertical shearing 'carnassial' cheek teeth that are relatively larger than in any other mammalian carnivore. Thylacoleo was clearly derived from the diprotodontian ancestry due to its incisor morphology and is distinguished by the pronounced development of upper and lower third premolars which functioned as extreme carnassials with complementary reduction in the molar teeth row. They also had canines but they served little purpose as they were stubby and not very sharp. Behaviour and diet Diet When Thylacoleo was first described by Richard Owen, he considered it to be a carnivore, based on the morphology of its skull and teeth. However other anatomists, such as William Henry Flower disagreed. Flower was the first to place Thylacoleo with the Diprotodonts, noting its skull and teeth to be laid out more like those of the koala and the wombat, and suggested that it was more likely a herbivore. Owen did not disagree with Flower's placement of Thylacoleo with the Diprotodonts, but still maintained that it was a carnivore, despite its herbivorous ancestry. Owen found little support in his lifetime, despite the pointing out of Thylacoleo'''s retractable claws, something only found in mammalian carnivores, and its lack of any ability to chew plant material. In 1911, a study by Spencer and Walcott claimed that certain marks on the bones of megafauna had been made by Thylacoleo, but according to Horton (1979) they were not sufficiently rigorous, resulting in their arguments being strongly challenged by later