Chronoperates

This possibility (that Chronoperates is a late-surviving basal holotherian mammal) has been hinted at by some other workers.

Archive 2006-05-01 Darren Naish 2006

Thirdly, the tooth enamel of Chronoperates is reportedly of pseudoprismatic type, a morphology not present in placental mammals and thus by inference expected in non-mammalian synapsids.

Archive 2006-05-01 Darren Naish 2006

Now, if Chronoperates did possess a Meckel’s cartilage, this would be a first for a post-Mesozoic synapsid, and would further support ideas that Chronoperates is actually a late-surviving basal mammal.

Archive 2006-05-01 Darren Naish 2006

If this is correct, then the geological range of non-mammalian cynodonts had just been extended by about 100 million years, and it’s for this reason that the name Chronoperates means ‘wanderer through time’ (since 1992, Upper Jurassic and Cretaceous non-mammalian cynodonts have been described, thereby shortening this gap, but I don’t want to cover them here: wait for next post).

Archive 2006-05-01 Darren Naish 2006

In their Classification of Mammal: Above the Species Level, McKenna & Bell (1997) classified Chronoperates as a basal holotherian (Holotheria = kuehneotheriids, spalacotherioids, dryolestoids, therians etc.).

Archive 2006-05-01 Darren Naish 2006

With a lower jaw that (when complete) would have been less than 30 mm long, and with tooth crowns about 2 mm tall, Chronoperates would have been shrew-sized.

Archive 2006-05-01 Darren Naish 2006

Among synapsids, this combination of features is reportedly only seen in non-mammalian cynodonts, and Fox et al. concluded that Chronoperates must have been one of these: the first of them (at the time) to come from post-Jurassic strata.

Archive 2006-05-01 Darren Naish 2006

Fox and his colleagues have stuck to their guns, and in recent publications have continued to regard Chronoperates as a non-mammalian cynodont (Scott et al. 2002).

Archive 2006-05-01 Darren Naish 2006

For now, this is all we know of Chronoperates, and it remains a controversial enigma, and possibly an exciting anachronism.

Archive 2006-05-01 Darren Naish 2006

The image above (sorry again for the poor resolution) shows the holotype jaw of Chronoperates together with a life restoration of the Jurassic docodont Haldanodon (no life restorations of Reigitherium available, unfortunately).

Archive 2006-05-01 Darren Naish 2006