Bohra bila ( Dawson 2004b ) Prideaux & Warburton, 2023

Prideaux, Gavin J. & Warburton, Natalie M., 2023, A review of the late Cenozoic genus Bohra (Diprotodontia: Macropodidae) and the evolution of tree-kangaroos, Zootaxa 5299 (1), pp. 1-95 : 38-42

Bohra bila ( Dawson 2004b) comb. nov.

Wallabia indra ( De Vis, 1895) : Bartholomai (1976b), pp. 375, 378 (partim), plate 53: figures 1–3. Not W. indra ( De Vis, 1895) .

Silvaroo bila Dawson, 2004b : Dawson (2006), p. 114. Piper & Herrmann (2006), p. 130. Louys & Price (2015), pp. 565, 567–568, figure 8M. Piper (2016), p. 238. Eldridge et al. (2019), p. 822.

Holotype. QM F43280 , partial left adult dentary (preserving p3, m1–4).

Type locality. Chinchilla Rifle Range (site not specified), north bank of the Condamine River, Chinchilla, western Darling Downs , southeastern Queensland. Chinchilla Sand. Pliocene. Collected by Doris and Cecil Wilkinson .

Paratypes. QM F43276 , partial left maxilla (preserving M1–4). Chinchilla Rifle Range (site not specified). Collected by Doris and Cecil Wilkinson. A second paratype ( QM F43292 , left i1) from Chinchilla is deemed here to be referable to a species of Congruus .

Referred specimens. Lion Hill, Chinchilla Rifle Range, Queensland. QM F58668, left m1; QM F58669, left juvenile dentary fragment (preserving m3). Collected by Doris and Cecil Wilkinson.

Chinchilla Sand, Chinchilla Rifle Range (site not specified). QM F58667, left M2. Collected by Doris and Cecil Wilkinson.

Chinchilla (presumably Chinchilla Sand). QM F4740, partial left adult maxilla (preserving M2–4). Collected by Kendall Broadbent in 1887.

Probably Darling Downs, Queensland. QM F4749, partial left juvenile dentary (preserving dp3, m1 trigonid). No locality details are associated with this specimen.

Etymology. In the Wiradjuri language of central New South Wales, bila means ‘river’, a reference to the surmised riparian habitat of this species.

Revised diagnosis. Bohra bila is distinguished from all other species of Bohra by having the palatine extend anteriorly to a position mesial to the M2 protoloph. The upper molars are similar in size to those of B. bandharr and B. illuminata , but its M4 is slightly smaller. They are most similar in morphology to those of the slightly smaller B. planei . They differ by having the cusp C region of the stylar crest diverge from the postparacrista closer to the paracone apex, and by lacking any sign of the stylar crest on M3. The ventral margin of the dentary is very smoothly curved posteriorly in lateral profile, lacking the digastric eminence of B. illuminata and B. nullarbora . It differs from that of B. bandharr by being deeper and having a shorter postalveolar shelf, which bears a small mesial process. The lower molars are similar in size and morphology to those of B. illuminata , but they lack a distinct premetacristid and the lophids are thinner in buccal view. The p3 is large and robust.

Description and comparisons. Maxilla and palatine. QM F4740 is a chunk of maxilla that retains M2–4 and the complete masseteric process, and has attached to it a thin strip of palatine ( Figure 21D–E ). QM F43276 retains M1–4, but the end of its masseteric process is abraded off. It also has a thin strip of palatine fused to it, which extends anteriorly to a position mesial to the M2 anterior root ( Figure 21B ). The masseteric process of QM F4740 is triangular in lateral view. Its tip aligns with the M3 interloph valley ( Figure 21D ), and its leading edge is slightly twisted anterolaterally. Although the tip of the masseteric process is missing in QM F43276, we can extrapolate that it would have been positioned adjacent to the M3 protoloph.

In B. bila , the maxilla–palatine suture extends anteriorly to a position adjacent to the M2 anterior root, but in B. nullarbora , B. illuminata , B. planei and B. bandharr it stops and inflects lingually at or posterior to a position mesial to the anterior edge of M3. The position of the masseteric process in B. bila is consistent with that observed in adult specimens of B. nullarbora , B. planei and B. bandharr . The form of the masseteric process is a good match for that of B. illuminata , but in the holotype of that species it is instead positioned adjacent to the M2 metaloph. This may be an artefact of its younger ontogenetic age (M4 is in the process of rotating into occlusion).

Upper dentition. Previously described in detail for QM F43276 ( Dawson 2004b). The referred unworn M2, QM F58667 ( Figure 21F–J ), is indistinguishable from the M2 of QM F 43276 in size and morphology, except for possessing a very slightly weaker cusp C region of the stylar crest.

Bohra bila is a close match for B. bandharr and B. illuminata in upper molar size, but it has a slightly smaller M4 ( Tables 1 , 4–5 ). In morphology, including general shape of the crown outline, B. bila is most similar to B. planei , and to a slightly lesser degree, B. nullarbora , both of which have smaller molars. In contrast to that of B. planei , the cusp C region of the stylar crest diverge from the postparacrista closer to the paracone apex in B. bila rather than further up the paracone. In addition, there is no manifestation of this stylar crest region on M 3 in B. bila . The upper molars of B. bila differ from those of B. nullarbora by having a cusp C region of the stylar crest on M1–2, incurved postpara- and premeta-cristae, and a broader, more open posterior metaloph face on M4.

Dentary. Previously described in detail for the holotype, QM F43280 ( Dawson 2004b). The two referred juvenile dentary fragments are too incomplete to add to the knowledge of dentary morphology, but QM F58669 does confirm the absence of a digastric eminence .

The holotype dentary of B. bila ( Figure 22A–C ) is most similar in overall form to that of B. nullarbora , but its ventral margin has a much more evenly curved profile due to the barely discernible digastric sulcus and absence of a digastric eminence ( Figure 22A–B ). It also has a larger and more rugose anterior insertion area for the internal superficial masseter muscle, and a more distinct buccinator sulcus ( Figure 22A ).The latter feature is also characteristic of the smaller B. bandharr , which is distinguished by its longer, rounded postalveolar shelf. A postalveolar shelf that bears a mesial process is shared with B. nullarbora , but the process on the latter is more pronounced.

Lower dentition. The lower cheek teeth of the holotype have been described ( Dawson 2004b), but the molars are heavily worn. Here we describe the teeth of three referred specimens, which have sustained little to no wear, one of which ( QM F4749 ) preserves the previously unknown dp3 .

The dp3 is narrow, especially anteriorly due to the compressed form of the trigonid ( Figure 22D ). The protolophid is very narrow and inflects at the protoconid into a paracristid that rises to a point anteriorly that matches the protoconid in height. From there a crest descends lingually to the anterolingual corner of the crown. If this is a continuation of the paracristid, then its terminus is likely the position of the paraconid; however, it is also conceivable that the high point on the paracristid marks the paraconid ( Figure 22H, L ). The buccal face of the crown is sheer; there is no distinct cingulum, although the crown bulges slightly near to the base. There is no parastylar crest. The metaconid is higher than the protoconid and gives rise to short, fine pre- and post-metacristids ( Figure 22D ). Although broader than protolophid, the hypolophid is quite narrow relative to the m1 protolophid, and sits substantially lower than it in buccal view. Like the protolophid, the hypolophid slopes slightly buccally, resulting in the hypoconid being noticeably lower than the metaconid. The cristid obliqua descends into the interlophid valley and smoothly ascends to the protoconid apex, such that there is no distinct postprotocristid ( Figure 22D ). The posterior face of the hypolophid is smooth and featureless.

QM F58668 is a complete, isolated, unworn m1 crown ( Figure 22F–G, J, M–N ), whereas QM F4749 is missing the m1 talonid. The only slight difference is that the most posterior portion of the paracristid is slightly inflected in QM F58668 and straight in QM F4749. The m1 protolophid is narrower than the hypolophid, and its crest is straight for much of its length, as opposed to posteriorly convex like the hypolophid. The paracristid trends anterolingually from the protoconid apex before turning lingually, forming a distinct anterior shelf with a rounded lingual border ( Figure 22F, M ). The small precingulid is at a distinctly lower level than the anterior portion of the paracristid ( Figure 22M ). A short, distinct parametacristid is directed anterobuccally from the metaconid apex, but terminates high on the protolophid anterior face. The cristid obliqua terminates low on the protolophid posterior face, buccal to the tooth midline. There is no distinct premetacristid, but the anterior face of the hypolophid is broadly convex on the lingual side. The posterior face of the hypolophid is smooth and featureless, except for a slight bulge low on the crown on the buccal side ( Figure 22F, N ).

The m3 is generally similar in form to the much smaller m1, but differs in the following ways: the lophid sides are more convex, the protolophid is not as narrow relative to the hypolophid, the precingulid is broader, and the parametacristid is very low and barely discernible ( Figure 22E–F ).

The dp3 is not known for any other species of Bohra . It is closest in overall morphology to that of the much smaller Setonix brachyurus ( Quoy & Gaimard, 1830) , with these species sharing a very similar trigonid topology. The main difference is that S. brachyurus lacks the crest that descends lingually to the anterolingual corner of the crown from the anterior high point on the paracristid. In addition, the base of the crown is not as narrow anteriorly relative to posteriorly in S. brachyurus , and the hypolophid curves more smoothly into the cristid obliqua and premetacristid than in B. bila . In species of Dendrolagus and dorcopsins, there is no distinct protolophid and paracristid, but rather a single crescentic crest (paralophid), which is met halfway along its length by the cristid obliqua. Species of Dendrolagus (e.g., D. bennettianus ) may also have a distinct parastylar crest, but this is absent from B. bila . The p3 of B. bila is large and robust relative to the molars compared with its proportions in B. illuminata and B. sp. cf. B. bandharr , which are the only other species of Bohra for which p3 is known. The lower molars of B. bila are similar in size and morphology to those of B. illuminata ( Tables 4–5 ), but the lophids are thinner in buccal view and the m3 lacks a distinct premetacristid.

Remarks. Bohra bila is known definitively only from the Pliocene Chinchilla LF of southeastern Queensland ( Figure 1 ). The referred specimen QM F4749 is from the Darling Downs, and is probably from Chinchilla, judging from the preservation of the bone, teeth and adhering sediment. This species is one of three in the Chinchilla LF, which is the most of any known assemblage.

By recognising that Silvaroo bila Dawson, 2004b belongs in Bohra Flannery & Szalay, 1982 , we render Silvaroo Dawson, 2004b a junior synonym of Bohra , because S. bila is its type species ( Dawson 2004b). Furthermore, we recognise that the species originally named Protemnodon bandharr Dawson, Muirhead & Wroe, 1999 , before it was shifted to Silvaroo by Dawson (2004b), also belongs in Bohra . Silvaroo sp. indet. 1 and Silvaroo sp. indet. 2 of Dawson (2004b) include specimens referable to B. bandharr and B. planei , respectively. The one remaining species that was allocated to Silvaroo is Protemnodon buloloensis Plane, 1967 from the Pliocene Awe LF of Papua New Guinea. Because it lacks the generic attributes of Protemnodon Owen, 1874 ( Dawson 2004b; Kerr & Prideaux 2022), and because Silvaroo is a junior synonym of Bohra , the generic allocation of this species is uncertain. Although resolving this problem is outside of the scope of this work, it is worth noting that the form of the p3 is dorcopsin-like: it is markedly elongate relative to the molars and broader anteriorly before constricting just forward of the posterior end of the tooth. It is within the size range of Watutia novaeguineae , which is likewise from the Awe LF ( Flannery et al. 1989), but it is clearly distinct from it, minimally at the species level.

Figures

FIGURE 1. Map of Australia and New Guinea showing localities that have produced fossils attributable, or potentially attributable, to species of Bohra.

FIGURE 21. Maxillary and upper dental specimens of Bohra bila. QM F43276, partial left adult maxilla (A–C).A: lateral view. B: mesio-occlusal view. C: stereo occlusal view (cast). QM F4740, partial left adult maxilla (D–E). D: lateral view. E: stereo occlusal view. QM F58667, left M2 (F–J). F: stereo occlusal view. G: lingual view. H: buccal view. I: anterior view. J: posterior view.

FIGURE 22. Dentary and lower dental specimens of Bohra bila. QM F43280 (holotype) left adult dentary (A–C). A: lateral view. B: mesial view. C: stereo occlusal view (cast). QM F4749, partial left juvenile dentary (D, H, L). D: stereo occlusal view. H: lateral view. L: mesial view. QM F58669, left juvenile dentary fragment (E, I, K, O–P). E: stereo occlusal view. I: lateral view. K: mesial view. O: anterior view. P: posterior view. QM F58668, left m1 (F–G, J, M–N). F: stereo occlusal view. G: buccal view. J: lingual view. M: anterior view. N: posterior view.