A very nice paper and ‘News and Views’ on the discovery of yet another incredibly well preserved early mammal from Liaoning, China. This one preserved both ossified Meckels cartilage (OMC, already known from close relatives) AND attached to this are ALL of the middle ear bones! These are adrift of the dentary where they are thought to have moved from into the ear of mammals, yet they are still attached to it via this OMC. As the new beastie is found ‘higher’ up the phylogenetic tree than monotremes and multituberculates, both known to have the DMME, and plenty of close and distant relatives have either the OMC or a groove where it is thought the OMC lies, it indicates that the DMME, once thought to indicate the origin of mammalia, has likely evolved multiple times independently:

http://www.nature.com/nature/journal/v472/n7342/full/nature09921.html

and News and Views on the paper:

http://www.nature.com/nature/journal/v472/n7342/full/472174a.html

* This is ‘definitive’ if you accept a) the phylogeny presented and b) that this is not simply a reversal (though the presence of the ossified meckels cartilage in multiple taxa indicates this is unlikely). The phylogeny is open to discussion however, as it is partly based on the hypothesis that tribosphenic teeth also evolved independently at least twice, and there is evidence both for and against this. If you accept both of these, it’s homoplasy a go go in the two key mammalian morphological key innovations!

-Ian