Thylacoleonidae Gill, 1872

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 227

† Thylacoleonidae Gill, 1872

CONTENTS: † Priscileo , † Thylacoleo , and † Wakaleo .

STEM AGE: 39.8 Mya (95% HPD: 35.5–45.2 Mya).

CROWN AGE: 29.4 Mya (95% HPD: 21.0–37.7 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: Presphenoid exposed in roof of nasopharyngeal fossa above posterior palate (char. 43: 1→0; ci = 0.091); neomorphic labial cingulum present on M1–3 (char. 133: 0→1; ci = 0.200); metaconid absent on m1 only (char. 163: 0→1; ci = 0.250); and additional cuspid labial to m1 protoconid present, forming a vertically directed crest (char. 165: 0→2; ci = 0.286).

COMMENTS: Monophyly of † Thylacoleonidae was recovered in all of our morphological (figs. 30, 31) and total-evidence (figs. 32, 33) analyses. In our dated total-evidence analysis ( fig. 33), four craniodental features optimize as synapomorphies for the family, three of which are dental. However, the position of † Thylacoleonidae within Vombatiformes is unstable in our analyses, placed as sister to the remainder of Vombatiformes (sensu Beck et al., 2020) in our undated total analysis (fig. 32)—as also found by Gillespie et al. (2016) and Beck et al. (2020) —but forming a trichotomy with Phalangerida and Vombatiformes at the base of Diprotodontia in our dated total-evidence analysis ( fig. 33). We suspect the reason is that early thylacoleonids, such as † Lekanoleo roskellyae (see Gillespie, 1997; Gillespie et al., 2020), preserve a plesiomorphic craniodental morphology relative to other diprotodontians. If so, the basicranial features identified by previous authors ( Aplin and Archer, 1987; Aplin, 1987) as placing thylacoleonids within Vombatiformes may, in fact, be retained plesiomorphies, in contrast to the more derived basicranial morphologies of phalangeridans (see also Murray et al., 1987).

Postcranial evidence also presents an ambiguous picture: Szalay (1994: 276) suggested that tarsal features present in thylacoleonids and diprotodontoids (e.g., † Ngapakaldia ) may be synapomorphic, but Munson’s (1992) phylogenetic analysis of vombatiforms using postcranial characters placed † Thylacoleonidae as sister to a clade comprising † Diprotodontidae , † Palorchestidae , † Ilariidae , and Vombatidae . On current evidence, we argue that thylacoleonids should be considered Diprotodontia incertae sedis. Ultimately, given that † Thylacoleo survived into the late Pleistocene, it may be possible to obtain ancient DNA or ancient protein sequences (e.g., collagen) that might clarify thylacoleonid relationships.

Like most other diprotodontian families, the first record of thylacoleonids is from late Oligocene deposits in central Australia and at Riversleigh ( Rauscher, 1987; Archer et al., 1999; Archer and Hand, 2006; Gillespie, 2007; Black et al., 2012b; Gillespie et al., 2017; 2020), so their origin must predate this. Our dated total-evidence analysis estimates that † Thylacoleonidae diverged from other diprotodontians during the middle to late Eocene.