Dicynodonts are endearingly ugly therapsids, that group sometimes called the mammal-like reptiles. These barrel-shaped, stoutly built critters had a good run between the Permian and Triassic periods; in the late Triassic they were the main competitors that early dinosaur herbivores would have to deal with. A couple of new papers look at the other side of dicynodont life in the late Triassic. Feeding traces in the form of bite marks on dicynodont bones from Poland were described in the journal Palaios last month. Another new study in the journal Lethaia, also examining Polish fossils, finds that early theropods weren't above a nice dicynodont fillet for dinner. Matching the dentition of local theropods, these are some of the earliest carnivorous dinosaur feeding traces yet.
Lystrosaurus georgi by Dimitri Bogdanov. From wikimedia commons.
Dicynodonts survived the massive extinction event at the end of the Permian, but just barely, with only two families continuing on into the Triassic. One group, the lystrosaurs, became extremely successful, dominating much of the southern hemisphere. There have been many theories seeking to explain why these few lucky dicynodonts were able to survive, and another recent paper - there have been several on dicynodonts this year - has determined that this could be because the survivors had much faster growth rates than their P-T boundary contemporaries. The Lethaia feeding traces paper mentioned above proposes that the general increase in size of dicynodonts during the Triassic was likely due to the intensifying threat of predatory dinosaurs. Had the mysterious extinction event that ended the Jurassic not happened, dicynodont competition may have constricted the evolution of the sauropod giants.
There's one pesky asterisk attached to the dicynodont timeline: Australia, that evergreen bastion of biological misfits, seems to have been home to a tenacious dicynodont that hung on until the early Cretaceous period. That's more an a hundred million years after the dicynodonts were supposed to have died. The authors of the 2003 Royal Society paper describing it invoke a famous modern analog, writing that it's "an example of a Lazarus taxon even more impressive than the extant coelacanth Latimeria, which was discovered only ca. 65 Myr after the supposed Late Cretaceous extinction of crossopterygian fishes."