Saturday, 29 November 2014

What were the gondwanatheres?

Right mandible of Sudamerica ameghinoi a gondwanathere
From Koenigswald W. Acta palaeontologica polonica 1999; 44: 263-300
Gondwanatheria is a clade of mammal-like forms once widely distributed on the southern continents that once were part of Gondwana. Until now they were known only from teeth and jaw fragments such as the one shown above. It therefore was a major breakthrough when a complete skull was found in Cretaceous deposits on Madagascar. It is described in the current issue of Nature (here) as a new genus and species Vintana sertichi.

The most exciting part of the paper is the phylogenetic analysis. Firstly, it reveals a sister group relationship between gondwanatheres (from southern continents) and multituberculates (from the northern continent Laurasia). Secondly, it shows both can be accommodated with another enigmatic group, the haramiyids, in a monophylectic clade Allotheria, i.e. all these fossil species shared a common ancestor.

Finally, Allotheria fits within Mammalia so all these mammal-like species were true mammals. The lineage that led to present day monotremes (duck-billed platypus and echidnas) is basal to Allotheria whereas that of marsupials and placentals came later.

My recent post on Extinct Madagascar concerned more recent mammals, all descendants of individuals that reached the island by rafting. But Madagascar has a more distant past, starting as part of the supercontinent Gondwana. Vintana derives from a lineage that existed on Gondwana before the breakup, evolved in isolation and went extinct, leaving Madagascar without mammals for millions of years.

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