Two ‘possums’, Phalanger and Spilocuscus, join the marsupial lions in the Didelphis clade
There has been some reader pushback
on the phylogenetic move of the marsupial lions, Thylacoleo and Wakaleo (Fig x) from diprodontids = wombats to didelphids = opossums in the large reptile tree (LRT, 2338 taxa).
Everyone gets into paleontology to discover something. No one likes it when others discover something – especially non-academics unwed to textbook doctrine.
Figure 1. Large Wakaleo and giant Thylacoleo here shown in several views and to scale with smaller omnivorous Caluromys and Chironectes, extant opossums derived from Didelphis.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg?w=111″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg?w=380″ class=”size-full wp-image-95104″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg” alt=”Figure 1. Large Wakaleo and giant Thylacoleo here shown in several views and to scale with smaller omnivorous Caluromys and Chironectes, extant opossums derived from Didelphis.” width=”584″ height=”1573″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg?w=584&h=1573 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg?w=56&h=150 56w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg?w=111&h=300 111w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/wakaleo.dorsal588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure x. Large Wakaleo and giant Thylacoleo here shown in several views and to scale with smaller omnivorous Caluromys and Chironectes, extant opossums derived from Didelphis.
The present phylogenetic confusion
only gets worse as two traditional possums from New Guinea and Australia also move over to the didelphid clade in the LRT. These two are Phalanger (Fig 1) and Spilocuscus (Fig 2). Both are traditional members of the Diprodontia = wombats and koalas.
Now there are more chips on the table.
Figure 1. A museum mount of Phalanger alongside Digimorph.org images of the skull. DGS colors applied here.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg?w=584″ class=”size-full wp-image-95147″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg” alt=”Figure 1. A museum mount of Phalanger alongside Digimorph.org images of the skull. DGS colors applied here. ” width=”584″ height=”410″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg?w=584&h=410 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg?w=150&h=105 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg?w=300&h=211 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/phalanger_orientalis588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. A museum mount of Phalanger alongside Digimorph.org images of the skull. DGS colors applied here.
Earlier the LRT recovered marsupial lions
in the didelphid clade – but just barely. The diprodontid traits are numerous.
Let’s see what the experts say.
Figure 2. Skulls of mature and immature Spilocuscus. DGS colors applied here.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg?w=227″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg?w=584″ class=”size-full wp-image-95149″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg” alt=”Figure 2. Skulls of mature and immature Spilocuscus. DGS colors applied here. ” width=”584″ height=”772″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg?w=584&h=772 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg?w=114&h=150 114w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg?w=227&h=300 227w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_wilsoni.adult_.skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Skulls of mature and immature Spilocuscus. DGS colors applied here. Note the reduction of the premaxilla in the adult specimen vs the juvenile specimen.
According to the Australian Museum website,
“There is much debate over which marsupial group gave rise to thylacoleonids. Candidates include phalangeroids (brushtail possums), vombatiforms (wombats, koalas and their extinct relatives) or possibly an unknown group of stem diprotodontians.”
“Wakaleo does not appear to have any of these wombat-like characters, unlike Thylacoleo, and does not seem to have any relationship to vombatiform marsupials. It may be that the genus Wakaleo (although not W. vanderleuri) evolved from a phalangeroid ancestor and is ancestral to Thylacoleo, and that Thylacoleo’s vombatid-like skull features evolved independently from true vombatiforms.”
Just let that sink in. The experts are not sure. Neither is the LRT.
Let’s be open to consider another possibility since the traditional answer is equivocal.
Figure 3. Spilocuscus invivo.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg?w=584″ class=”wp-image-95151 size-full” src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg” alt=”Figure 3. Spilocuscus invivo. ” width=”584″ height=”335″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg?w=584&h=335 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg?w=150&h=86 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg?w=300&h=172 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/spilocuscus_kraemeri_invivo588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Spilocuscus invivo.
All these phylogenetic problems would go away
if diprodontids were somehow derived from didelphids with marsupial lions in the middle. Presently the little canine-like tooth in diprodontids is a premolar 1, while the same essentially identical little canine-like tooth is a canine in didelphids.
Problems like this might be why mammal experts gave up attempting to build mammal cladograms from traits. Instead they started trusting genomic trees – that omit fossils and match dissimilar taxa together – without complaint!
References
Cooke BN 2000. Cranial remains of a new species of balbarine kangaroo (Marsupalia: Macropodoidea) from the Oligo-Miocene freshwater limestone deposits of Riversleigh World Heritage Area, Northern Australia. Journal of Paleontology 74(2) 317-26.
Demarest 1818. Proc. Zool. Soc. London 1861:316.
Pallas 1766. Miscellanea Zoologica.
wiki/Phalanger
wiki/Phalangeridae
wiki/Admiralty_Island_cuscus
Source: https://pterosaurheresies.wordpress.com/2025/11/12/two-possums-phalanger-and-spilocuscus-join-the-marsupial-lions-in-the-didelphis-clade/
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