Dactylopsila trivirgata (Gray 1858) is the extant striped possum (Fig. 1), closely related to the sugar glider, Petaurus and the marsupial lion, Thylacoleo (below), according to the large reptile tree (LRT, 1412 taxa). Dactylopsila is an arboreal marsupial with a prehensile tail the size and proportions of a placental squirrel. The fourth finger is elongated and used to extract beetles and caterpillars from tree bark, analogous to the extant aye-aye, Daubentonia. Dactylopsila, also eats leaves, fruit and small vertebrates.
By convergence
Dactylopsila has similar teeth and overall proportions to the extinct arboreal placental Apatemys (Fig. 2).
Figure 1. Dactylopsila skull in 3 views, plus in vivo. Comparisons to the extinct arboreal placental Apatemys (figure 2) are intriguing, showing convergence.
For comparison, we recently looked at Apatemys
here as it relates to the extant shrew opossums Caenolestes and Rhyncholestes, now nesting as apatemyid placentals in the LRT, rather than as traditional didelphid marsupials. The convergence is powerful here. Despite the phylogenetic distance, only 12 extra steps are needed to nest caenolestids with basal didelphids.
Figure 2. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth.
The nesting of Dactylopsila
close to Petaurus (Fig. 3) is not controversial.
Figure 3. Subset of the LRT showing the nesting of Dactylopsila, the striped opossum, with Petaurus the sugar glider and Thylacoleo, the marsupial lion.
The problem continues to be
the traditional nesting of the marsupial lion, Thylacoleo (Fig. 4), as a member of the wombats (Vombatiiformes), rather than the Phalangeriformes and Petauroidea, as recovered by the LRT (Fig. 3), which points to a bigger problem…
Nowhere in traditional taxon lists
will you find interatheres, toxodontids and creodonts. All these taxa need to be tested in traditional metathere trees because the LRT has tested them and they nest with metatheres. It’s a good time for a confirmation or a refutation. PhD students… are you looking for a good subject to write about for your dissertation?
Figure 4. Large Thylacoleo skeleton compared to small Petaurus skeleton to scale. Dactylopsila is similar in size to Petaurus.
Here, again,
is where tradition, opinion and bias have, so far, trumped testing. Taxon exclusion needs to be tested with taxon inclusion. The list of taxa needing testing is provided by the LRT.
References
Gray JE 1858. List of species of Mammalia sent from the Aru Islands by Mr A.R. Wallace to the British Museum. Proceedings of the Zoological Society of London. 26: 106–113.
The Pterosaur Heresies 