Wikipedia
Kollikodon ritchiei is a fossil monotreme species. It is known only from an opalised dentary fragment, with one premolar and two molars in situ. The fossil was found at Lightning Ridge, New South Wales, Australia, as was Steropodon.
Kollikodon lived in the lower Cretaceous period, during the middle Albian age (113-101 million years ago).
Like Steropodon, Kollikodon was a relatively large mammal for the Mesozoic. The molars have a length of around 5.5 mm and a width of between about 4 and 6 mm (Clemens et al., 2003). Based upon these data, the potential body length could be up to a metre. Assuming the accuracy of such a guess, Kollikodon would be a contender for the largest Mesozoic mammal known, along with other possible giants such as Repenomamus, Schowalteria, and Bubodens.
Aside from its size, it is difficult to say what Kollikodon looked like. However, it may have been at least partly aquatic, as its strange teeth would work well for crushing shellfish.
Both Kollikodon and Steropodon can be found at the Australian Museum in Sydney, along with Eric, the opalised pliosaur.