Wednesday, August 17, 2016

[PaleoMammalogy • 2016] Microleo attenboroughi • A Tiny New Marsupial Lion (Marsupialia, Thylacoleonidae) from the early Miocene of Australia

Microleo attenboroughi 
Gillespie, Archer & Hand, 2016  

Illustration: Peter Schouten


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

 Keywords: Thylacoleonidae; marsupial lion; new genus; new species; early Miocene; Riversleigh


Class MAMMALIA Linnaeus, 1758
Superorder MARSUPIALIA Illiger, 1811

Order DIPROTODONTIA Owen, 1866
Suborder VOMBATIFORMES Woodburne, 1984


Genus MICROLEO gen. nov.

Type Species. Microleo attenboroughi new genus and species

Etymology. From micro meaning small (Greek) and leo meaning lion (Latin). The species name honours Sir David Attenborough for his dedication and enthusiasm in promoting the natural history of the world and the palaeontological treasures of the Riversleigh World Heritage Area in particular.

Microleo attenboroughi new genus and species

Microleo attenboroughi n. gen. et sp., Holotype QM F41143: 

 FIGURE 1. 1) right maxilla and 2) left maxilla in occlusal view, stereo images; 3) interpretive drawing of right maxilla; 4) interpretive drawing of left maxilla. 5) Paratype QM F42676, occlusal views of m3 (stereophotos). 
FIGURE 2.  right maxilla. 1) buccal view; 2) interpretive drawing in buccal view; 3) lingual view; 4 ) interpretive drawing in lingual view.

Abbreviations: aabc, accessory anterobuccal cusp; abc, anterobuccal blade; ac, anterior cusp; alc, anterolingual crest; lb, longitudinal blade; mcl, metaconule; mcus, medial cusp; me, metacone; pa, paracone; pbb, posterobuccal basin; pbc, posterobuccal crest; pc, posterior cusp; plc, posterolingual crest; pr, protocone. Scale bar equals 5 mm.

 Holotype. QM F41143, an incomplete palate consisting of partial left and right maxillae (Figure 1.1-4, Figure 2). The left maxilla preserves M2-3, roots for P3-M1, alveoli for M4, and the maxillary root of the zygomatic arch. The right maxilla preserves P3-M2, alveoli for P1-2 and M1. QM F42676, paratype, is a left m3 (Figure 1.5).

Type Locality and Horizon. The Type Locality is Neville’s Garden Site, D Site Plateau, Riversleigh World Heritage Area, Boodjamulla National Park, northwestern Queensland. Neville’s Garden Site is early Miocene in age (radiometrically dated at 18.24±0.29 Ma and 17.85±0.13 Ma: Archer et al., 1997; Arena, 2004; Travouillon et al., 2006; Woodhead et al., 2016).

Diagnosis. Microleo attenboroughi is attributed to Thylacoleonidae on the basis of its bicuspid, blade-like P3 and its weakly-crenulated, subtriangular bunodont molars. Microleo attenboroughi is smaller than all other thylacoleonids (see below). Generic distinction is based primarily on its unique P3 morphology.

FIGURE 3. Cladistic relationships of Microleo attenboroughi within Thylacoleonidae and Vombatiformes: 1) strict consensus tree of nine most parsimonious trees obtained in the phylogenetic analysis (tree length = 272 steps; see Appendices 1, 2); 2) time-tree of thylacoleonid phylogeny. 

Anna K. Gillespie, Michael Archer and Suzanne J. Hand. 2016. A Tiny New Marsupial Lion (Marsupialia, Thylacoleonidae) from the early Miocene of Australia. Palaeontologia Electronica 19.2.29A: 1-25.