Bohra bandharr ( Dawson, Muirhead & Wroe, 1999 ) 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 : 26-31

Bohra bandharr ( Dawson, Muirhead & Wroe, 1999) comb. nov.

Protemnodon bandharr Dawson, Muirhead & Wroe, 1999 . Long et al. (2002), p. 1050.

Silvaroo bandharr: Dawson (2004b) , pp. 275, 284–288, table 1. Dawson (2006), p. 114. Eldridge et al. (2019), p. 822.

Holotype. AM F69830 , partial right adult dentary (preserving m4).

Type locality. Big Sink doline, Wellington Caves, New South Wales. Big Sink unit. Pliocene.

Paratypes. AM F69828, left adult maxilla fragment (preserving M3–4); AM F69829, right adult maxilla fragment (preserving P3, M1). Big Sink doline (Big Sink unit). A third paratype ( AM F69827, left i1) of this species was identified from the Big Sink LF ( Dawson et al. 1999), but it is deemed here to belong to a species of Congruus McNamara, 1994 .

Referred specimens. BC1 site, Bone Cave, Wellington Caves , New South Wales. AM F146754 , left P3. Collected by Michael Augee and others in the 1990s or 2000s .

Bone Cave / Phosphate Mine (probable), Wellington Caves. FMNH PM1586 , right adult maxilla (preserving M1–4). This specimen was collected by Wendell B. Swanson in 1953 and donated to the Field Museum, Chicago, in 1956, along with numerous other specimens from the Wellington Caves. An origin within Bone Cave / Phosphate Mine system seems likely, given that this is where Leslie Marcus made a collection in 1954 of fossils now deposited in the University of California Museum of Paleontology , Berkeley, and was the main focus of palaeontological attention at Wellington in the mid-20 th century ( Dawson 1985).

Etymology. In the Wiradjuri language of central New South Wales bandharr means ‘kangaroo’.

Revised diagnosis. A large species of Bohra with upper molars intermediate in size between those of the larger B. wilkinsonorum and smaller B. bila and B. illuminata . The upper molars are slightly more rectangular in occlusal outline than in other species of Bohra , while all secondary crests, including the postparacrista, are very weakly developed. The P3 is most similar in size and morphology to that of B. wilkinsonorum , but lacks the large posterobuccal eminence of that species. The postalveolar shelf of the dentary is longer and more rounded than in all other species of Bohra for which the dentary is known. The lophid sides of m3–4 are markedly convex.

Description and comparisons. Maxilla and palatine. Despite being the most complete of the three maxillary specimens, very little is preserved of the maxilla of FMNH PM1586 ( Figure 14A–C ). However, there is sufficient to suggest that, although broken off, the base of the masseteric process was positioned above the anterior root of M 3 in lateral view. A portion of the palatine bone is attached to the maxilla adjacent to M3–4. It is orientated anteroposteriorly before inflecting anterolingually mesial to the M3 metaloph ( Figure 14C ).

The position of the masseteric process relative to M3 matches that observed in adult specimens of B. nullarbora , B. bila and B. planei . The process is slightly more anteriorly located in the holotype of B. illuminata , but this is very likely because of its ontogenetically slightly younger age, the M4 having only just come into occlusion. The fusion to the maxilla of a solid portion of palatine points to the presence of an entirely bony (non-fenestrate) secondary palate in B. bandharr , which is an attribute of dendrolaginans within the Dendrolagini .

Upper dentition. Two specimens preserve P3: the paratype AM F69829 ( Figure 15G ) and the referred specimen AM F146754 ( Figure 14D–H ). Crown posterior width is similar ( Table 1 ), and crown length may be inferred to have been (enamel is missing from the anterior end of AM F69829 ). AM F146754 is narrower anteriorly than in AM F69829 , and its posterobuccal eminence is slightly better developed. The following description is primarily based on AM F146754 because it is much less worn. The main crest is straight for its length, except for the anterior- and posterior-most cuspules, which are slightly buccally offset. The main crest is composed of five cuspules ( Figure 14D ). No ridgelets ascend from them on the lingual side, but a coarse buccal ridgelet is associated with the anteriormost cuspule, while a fine ridgelet ascends from the second cuspule and a very fine ridgelet ascends from the third cuspule ( Figure 14D–E ). Each of the latter two ridgelets terminates at a small cingular cuspule, while a third cuspule is located posterior to them. The lingual cingulum is low but distinct, and inflects toward the tooth midline midway along the crown. It continues anteriorly to a position adjacent to the anterior cusp of the main crest, before again inflecting buccally and terminating at the anterior end of the crown. A very small, triangular posterior basin is present at the posterior end of the crown, separated by a coarse ridge that represents a continuation of the lingual cingulum from the expanded posterolingual portion of the crown .

The P3 is most similar to that of B. wilkinsonorum in size and morphology, but is distinguished by being relatively narrower anteriorly, and by having a much less pronounced posterobuccal eminence and three buccal cingular cuspules.Although B. nullarbora also has an anteriorly broad P3, the crown is slightly narrower posteriorly and much smaller overall.

The M1 of AM F69829 is so worn that it consists of little more than a dentine basin surrounded by a thin border of enamel ( Figure 15G ), but the molars of FMNH PM1586 are only slightly worn, with dentine breached only slightly on the loph crests of M1–2, and the lingual cusps of M3 ( Figure 14C ). The molars are low crowned, with very fine, low secondary crests, including the postparacrista and postprotocrista. The protoloph of M1 is slightly narrower than the metaloph, but is slightly wider on M2 and increasingly wider on M3 and M4 ( Figures 14C , 15H ). M1–2 are distinctly flat-sided, producing an overall quite rectangular crown shape in occlusal view. M3–4 are similar, but very slightly more convex adjacent to the interloph valley. The more posterior portion of the postmetaconulecrista forms a small but distinct shelf on the M4 posterior face. The interloph valley of M4 is bordered by a fine, low, lingual cingulum on the metaloph anterior face.

The upper molars of B. bandharr are smaller than those of B. wilkinsonorum , but larger than those of B. bila and B. illuminata ( Tables 1 , 3–5 ). They are distinguishable from other species of Bohra by being more rectangular in occlusal outline (flat-sided). Even taking into account the wear sustained by FMNH PM1586, the secondary crests, most notably the postparacrista, postprotocrista and premetacrista, are very weakly developed, which is also characteristic of B. nullarbora and B. planei .

Dentary. The holotype (AM F69830) and only known dentary ( Figure 15A–F ) has been adequately described previously ( Dawson et al. 1999). The specimen is missing much of the ascending ramus and anterior end of the dentary, and has been slightly distorted by crushing. It is shallower relative to its width than in B. bila , a trait more reminiscent of B. illuminata . The ventral profile of the dentary and the highly reduced nature of the digastric eminence and sulcus are shared with B. bila , which also has a similarly proportioned and rugose anterior insertion area for the internal superficial masseter muscle. The form of the postalveolar shelf of the dentary differs from that of all other species of Bohra for which the dentary is known. It is longer than in B. bila and B. illuminata , and has a more rounded mesial border than in B. bila and B. nullarbora , lacking any sign of a mesial process.

Lower dentition. The holotype preserves only the m4 and even that is missing the posterobuccal portion of the crown ( Figure 15A–F ). The m4 is intermediate in size between those of the smaller B. nullarbora and the larger B. bila and B. illuminata ( Tables 1 , 4–5 ). The convexity of the lophid sides, effectively the manner in which they are “bowed strongly outwards” ( Dawson et al. 1999, p. 280), is greater than that in all other species of Bohra . It is worth noting that two points of difference between B. bandharr and B. bila identified previously – “ Silvaroo bandharr …differs from S. bila in lacking a posterior cingulum or basal swelling on the posterior hypolophid of m4, [and] in having a much narrower (buccally curtailed) anterior cingulum on m4” ( Dawson 2004b, p. 285) – do not hold on closer examination. There is a low, narrow postcingulid on the m4 of B. bandharr ( Figure 15E ), and the apparently greater buccal extent of the m4 precingulid in the holotype of B. bila is an artefact of the greater wear it has sustained by comparison.

Remarks. Among the seven named species of Bohra , B. bandharr and B. bila are founded on holotypes that preserve the fewest diagnostic attributes, with B. bandharr the closest to being a nomen dubium. The holotype of B. bandharr , from the Pliocene Big Sink LF, is a partial, distorted dentary preserving one incomplete molar encompassing three diagnostic traits. These are also manifested in a partial dentary from the Pliocene Chinchilla LF (‘bowed’ buccal lophid sides, broad molars, long, rounded postalveolar shelf) herein referred to B. sp. cf. B. bandharr . Maxillary fragments from the Big Sink LF and Pleistocene Bone Cave deposit within the same cave complex in the Wellington Caves system ( Figure 1 ) are referred to B. bandharr on the grounds of commensurate size and Bohra morphology. Among the species of Bohra , the cheek teeth of B. bandharr are second only to B. wilkinsonorum in size, and it may be significant that the holotype calcaneus of B. paulae , also from the Wellington Caves, is second only in size to the calcaneus referred to B. wilkinsonorum in the Chinchilla LF. As further specimens of fossil tree-kangaroos are collected from the Wellington Caves and analysed, the prospect of B. bandharr being a junior synonym of B. paulae , which has been described to date only from hindlimb elements, will need to be considered.

The isolated left i1 (AM F69827) from the Big Sink LF listed as a paratype of B. bandharr ( Dawson et al. 1999) is deemed here to be referable to a species of Congruus (see Warburton & Prideaux 2021), as is the paratype left i1 (QM F43292) referred to by Dawson (2004b) to Silvaroo bila (herein, B. bila ).

Figures

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

FIGURE 14. Maxilla and upper cheek teeth of Bohra bandharr. FMNH PM1586, partial right adult maxilla (A–C). A: lateral view. B: mesial view. C: stereo occlusal view. AM F146754, left P3 (D–H). D: stereo occlusal view. E: buccal view. F: anterior view. G: lingual view. H: posterior view.

FIGURE 15. Craniodental specimens of Bohra bandharr. AM F69830 (holotype) right, adult dentary (A–F). A: lateral view. B: mesial view. C: occlusal view. D: stereo occlusal view of m4 and postalveolar shelf. E: posterior view. F: anterior view of m4. G: AM F69829, partial right adult maxilla (P3–M1) in stereo occlusal view. H: AM F69828, partial left adult maxilla (M3–4), stereo occlusal view.