Another short one today
just to dash off a progress report as I wrestle with metatherian data. Like everyone else, I’m learning as I go. Toxodon and Eurygenium (Fig. 1) were always close to Interatherium, which was recently nested at the base of all kangaroos with the addition of the short-faced kangaroo, Procoptodon to the large reptile tree (LRT, 1258 taxa). Bulky, quadrupedal Toxodon and Eurgenium previously nested with quadrupedal wombats.
The loss of pedal digit 1
found in kangaroos, interatheres and Toxodon + Eurygenium turns out to be not a convergence, but a homoplasy as the Toxodon + Eurygenium node shifts over to the Interatherium node. All three are quadrupeds.
Now basal wombats with five pedal digits,
like the koala, no longer have four-toed taxa, like Eurygenium and Toxodon, separating them from their five-toed ancestors.
Interatheres are getting to be more interesting.
loss of pedal digit 1 also occurs alone in the wolf-like marsupial carnivore, the Tasmanian wolf, Thylacinus, by convergence. By convergence, pedal digit 1 also shrinks in the bandicoot (Perameles) clade.
western Gondwana (Africa + South America) separated from eastern Gondwana (Madagascar, India, Australia, Antartica) about 180 mya (Jurassic). That’s when the ancestors of South American Interatherium and Toxodon separated from the Australian ancestors of kangaroos. This is one way to estimate the antiquity of mammal clades.
Final thought for paleontologists and soon-to-be-paleontologists:
Reexamining data, like this, is good science. Making mistakes. like this, goes with the territory. Naiveté and enthusiasm go hand-in-hand. Apologies often follow. Gaining experience is a slog, but worthwhile when the puzzle pieces fit better in the end. More work often brings new insight.