Microleo: another possible sister to Thylacoleo

Microleo is a small fossil
marsupial taxon known from teeth and jaw fragments. So it will not enter the LRT— unless more of it becomes known someday. Microleo gathers minor fame by being related to a large, carnivorous marsupial, Thylacoleo (Fig. 1), featured in the video below.

Like the video, a recent Microleo paper
(Gillespie, Archer and Hand 2018) failed to include a number of taxa related to Thylacoleo, including Petaurus (Figs. 1, 2), the extant sugar glider. Petaurus nests as a sister to Thylacoleo whenever the two are tested in the same analysis (Fig. 3).

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.
Figure 1. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Turns out
the sugar glider is the only living omnivore in an otherwise herbivorous clade, as noted in the video. Thylacoleo was not only larger, but less herbivorous (= more carnivorous). Which wraps up this matter rather neatly.

Figure 1. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.
Figure 2. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.

The authors report,
“Marsupial lions are the only carnivorous vombatiform marsupials as well as the only vombatiforms that have bunodont molars.”

These taxa are not wombats, as confirmed by the authors of the Microleo paper, who did not test any taxa related to sugar gliders.

Taxon exclusion mars this otherwise complete study.
As we learned earlier (in 2018) marsupial lions (Thylacoleo) are sugar gliders (Petaurus) and members of a marsupial clade apart from wombats. This clade includes all the weird-o taxa: Adalatherium, Paedotherium, Groberia, Vintana, along with some wonderful, but more ordinary extant taxa, including Balbaroo, Phalanger and Dactylopsia, all herbivores.

Figure 7. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium.
Figure 3. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium.

From the abstract
“Microleo attenboroughi, a new genus and species of diminutive marsupial lion
(Marsupialia: Thylacoleonidae), is described from early Miocene freshwater limestones
in the Riversleigh World Heritage Area, northwestern Queensland, Australia. A broken
palate that retains incomplete cheektooth rows demonstrates that this new, very small
marsupial lion possessed the elongate, trenchant P3 and predominantly subtriangular
upper molars characteristic of thylacoleonids, while other features of the premolar support
its placement in a new genus.”

Step 1. Understand the complete taxa. Step 2. Slowly sprinkle in the incomplete taxa.

“Phylogenetic analysis suggests that Microleo attenboroughi is the sister taxon to all other thylacoleonids, and that Thylacoleonidae may lie outside Vombatomorphia as the sister taxon of all other wombat-like marsupials including koalas.”

Just add taxa to find out.

“However, given limited data about the cranial morphology of M. attenboroughi, Thylacoleonidae is concluded here, conservatively, to be part of the vombatomorphian clade.”

No. Don’t do that! Don’t blame Microleo. Don’t just guess and don’t guess wrong. Don’t give up. Test more complete taxa. Then add incomplete taxa, like Microleo, more confidently.

“This new thylacoleonid brings to three the number of marsupial lion species that have been recovered from early Miocene deposits at Riversleigh and indicates a level of diversity previously not seen for this group. It is likely that the different size and morphology of the three sympatric taxa reflects niche partitioning and hence reduced competition. Thylacoleonids may have been the dominant arboreal predators of Cenozoic Australia.”

Figure 5. Dactylopsila skull and in vivo. This taxon bears a strong resemblance to Apatemys by convergence.
Figure 5. Dactylopsila skull and in vivo. This taxon bears a strong resemblance to Apatemys by convergence, but nests basal to Petaurus and Thylacoleo.
Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider.
Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider.

References
Gillespie AK, Archer M and Hand SJ 2018. A tiny new marsupial lion (Marsupialia, Thylacoleonidae) from the early Miocene of Australia. Palaeontologia Electronica 19.2.26A: 1-26.

wiki/Microleo

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