Bohra paulae Flannery & Szalay, 1982

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 : 21-26

Bohra paulae Flannery & Szalay, 1982

Bohra pauli: Dawson (2004a) , p. 271, table 1; lapsus calami.

Holotype. AM F62099 / AM F62100 , right adult calcaneus and talus. The holotype was originally based solely on the calcaneus ( AM F62099 ); the talus was listed and described separately as a referred specimen ( AM F62100 ). However, given their precise anatomical fit and similar preservation, it is beyond reasonable doubt that these two elements belong to the same individual.

Type locality. Wellington Caves (site not specified), New South Wales. No specific locality or collection details are associated with the holotype of B. paulae . However, the type locality is very likely a Pleistocene deposit (see ‘Locality information’) .

Referred specimens. Cathedral Cave, Wellington Caves. AM F62101, left tibia. AM F62102, left tibia (proximal half). Collected by Henry Barnes of the Australian Museum in 1881 ( Ramsay 1882). The stratigraphic origins of the tibiae are unknown, but Ramsay’s Shaft No. 2, positioned in the alcove south of the ‘Altar’ formation in the main chamber, evidently produced much of the larger fossil material collected from Cathedral Cave in 1881 ( Ramsay 1882).

Wellington Caves (site not specified). AM F103802 , adult right metatarsal V. AM F104075 , left juvenile metatarsal IV. AM F104092 , adult right metatarsal V. AM F104550 , juvenile left metatarsal IV. These specimens are part of the ‘Old Collection’ of the Australian Museum ( Dawson 1985), and probably originate from a Pleistocene deposit based on the same line of reasoning as for the holotype .

Etymology. Named in honour of Flannery & Szalay’s draftsperson Paula Kendall.

Revised diagnosis. A large species of Bohra , closest in size to B. wilkinsonorum in calcaneal dimensions. The species is distinguished by the following combination of calcaneal features: dorsal half of tuber calcanei barrel-shaped; plantar aspect less flared posteriorly, particularly laterally, than in the similarly large B. wilkinsonorum ; medial and lateral talar facets of calcaneus continuous anteriorly but with facet contours distinct; calcaneocuboid articulation transversely broad, with step between dorsal facets smoothed, and confluent with ventromedial facet; talar and cuboid articular surfaces separated by short distance. The talus is distinguished from that of other species of Bohra by having a shallow trochlear groove that is slightly deeper medially, and a very short talar neck. The tibia is relatively more robust than in B. illuminata and B. nullarbora , particularly distally. The metatarsals IV and V are more robust than those of B. illuminata and B. nullarbora , and the metatarsal IV diaphysis is proportionally deeper anteriorly than in B. nullarbora .

Description and comparisons. Tibia. The tibia of B. paulae ( Figure 11 ) is significantly larger ( Table 8 ) and more robust than that of B. illuminata and is more similar to species of Dendrolagus ( Figure 8 ) in its stockiness. Other aspects of its morphology, including the relative size of the anterior tibial crest ( Figure 8A ), the curvature of the shaft, and the length of distal fibular facet ( Figure 8B ) are similar between B. paulae and B. illuminata , although the proximal fibular facet ( Figure 8D ) is more pronounced in B. paulae . The tibial crest is shorter and the lateral fossa for m. tibialis cranialis ( Figure 8D ) is deeper in both B. paulae ( Figure 11 ) and B. illuminata than in species of Dendrolagus . Caudolaterally, the interosseous border of the tibia is more sinuous than that of B. illuminata and B. nullarbora , but less so than in species of Dendrolagus . The tibial diaphysis is more flared distally than in B. illuminata and B. nullarbora . The distal articular surface of AM F62101 has sustained significant post-mortem damage from rodent gnawing ( Figure 11F ), but the relatively short medial malleolus reflects the corresponding morphology of the talus.

Calcaneus. The plantar surface of the holotype calcaneus was evidently expanded posteromedially, but the specimen is abraded in this area ( Figure 12B ). It is also abraded on the lateral side ( Figure 12C ), but the contour of the surrounding bone allows us to infer that it was flared to a lesser degree than in B. wilkinsonorum ( Figure 20A–B ). Indeed, the tuber calcanei of B. paulae is distinctly barrel-shaped in dorsal view ( Figure 12A ), and not as constricted anteriorly as in other tree-kangaroo species. Otherwise, the calcaneus is similar in general proportions and size to that of B. wilkinsonorum ( Table 8 ). The distance between the talar and cuboid facets is even shorter in B. paulae than in other tree-kangaroos, e.g., D. bennettianus ( Figure 9A ). Although extended medially, the sustentaculum tali is relatively short, not extending as far posteriorly as in other tree-kangaroo species ( Figure 9A–B ). The plantar surface is flat, only slightly rugose, and very broad anteriorly ( Figure 12B ). The non-rugose flexor groove is shallow and wide, but not as wide as in D. lumholtzi ( Figure 9B ).

The medial and lateral talar facets in B. paulae are broadly continuous ( Figure 12B, E ) and more smoothed than in D. bennettianus ( Figure 9A ), D. lumholtzi , B. illuminata and B. nullarbora . The lateral facet is only slightly tapered mesially, and the medial facet is large, ovoid and almost transverse in alignment ( Figure 12A ). The calcaneocuboid articulation is relatively shallow, and the characteristic macropodid ‘step’ between the medial and lateral facets is not much more than an undulation ( Figure 12B, E, H ; cf. Figure 9A ). The ventromedial facet is broad and completely continuous with the medial and lateral facets (cf. Figure 9D ). Overall, the cranial end of the calcaneus closely resembles that of D. lumholtzi . The sulcus for the m. flexor digitorum longus is short and narrow compared with all other species (cf. Figure 9B ).

Talus. The talus of B. paulae is short and wide, but the medial crest is moderately high and steep, and the lateral crest is low and broad, resulting in a moderately shallow but asymmetrical trochlear groove ( Figure 12H, J ). This marked asymmetry in crest contour is similar to that observed in D. lumholtzi , but less so in D. bennettianus ( Figure 9H, K ) and other species of Bohra , where the crests are more equally pronounced. The talar neck is very short ( Figure 12K, N, L ), shorter in fact than in all other tree-kangaroos for which the talus is known (e.g., Figure 9H ). The navicular facet is slightly deeper relatively than that of D. lumholtzi , and most similar to that of D. bennettianus ( Figure 9K ). The malleolar fossa is broad and shallow in comparison to the conditions observed in B. nullarbora , D. bennettianus and the species of Dorcopsulus , Petrogale Gray, 1837 , Setonix Lesson, 1842 and Thylogale Gray, 1837 . The posteroventral process is similar in its posterior extension to the condition observed in B. illuminata , B. nullarbora , D. lumholtzi and D. bennettianus ( Figure 9G ), but more extended than in B. planei ( Figure 33J ).

Metatarsals. Two juvenile metatarsal IV specimens are referred to B. paulae ( Figure 13A–J ) on the basis of their overall proportions and relative robustness, and the transversely wide, conjoined articular facet for metatarsal V, as in species of Dendrolagus ( Figure 10B ). AM F104075 is more robust and slightly shorter, and has a broader, more posteriorly restricted plantar ridge compared with AM F104550. Otherwise, they are very alike and morphologically distinct from the B. illuminata holotype metatarsal IV, which is also not fully grown and missing the distal epiphysis, and from the B. nullarbora holotype metatarsal IV, which is fully grown and has a fused distal epiphysis. The proximal articular facet for the cuboid is convex dorsally, while the peninsula of the cuboid facet that extends ventrally onto the posterior face of the plantar tuberosity is concave ( Figure 13E, J ). In comparison, the dorsolateral corner of the cuboid facet is more pointed in B. illuminata , while the ventral peninsula of the facet is much broader in B. nullarbora . In B. paulae , the plantar sesamoid facet on the anteroventral face of the plantar tuberosity abuts the conjoined metatarsal V facets (AM F104550) or is separated from them by a 1-mm gap (AM F104075), as in the B. illuminata holotype, while the gap is closer to 2 mm in the B. nullarbora holotype and D. bennettianus ( Figure 10B ). The metatarsal IV of B. paulae is more robust (broader relative to length) than that of the B. illuminata holotype. AM F104550 and the B. nullarbora holotype are very similar in size and general proportions, despite the ontogenetic difference between the specimens. However, the diaphysis of AM F104550 is comparatively deeper cranially (less concave ventrally).

Two metatarsal V specimens are referred to B. paulae ( Figure 13K–R ) on the basis of their absolute size, proportions and distinctive robustness. Both are complete and fully grown with fused distal epiphyses. The proximal articular facet for the lateral facet of the cuboid is roughly triangular and concave, sweeping up onto the broad proximolateral process. The proximomedial surface has a single broad articular facet for metatarsal IV. There only noteworthy differences between them are that AM F103802 is 11% larger than AM F104092. AM F103802 and AM F104092 are 25% and 15% larger, respectively, than the B. nullarbora holotype metatarsal V ( Table 8 ), and slightly broader posteriorly (evident primarily in the plantar rugosity). Other points of morphological distinction in metatarsal V morphology between B. paulae and B. nullarbora include a relatively larger surface area of the metatarsal IV facet, shorter proximolateral process and commensurately less deeply flexed cuboid facet in B. paulae . From the smaller, ontogenetically younger B. illuminata holotype, B. paulae differs by having a more rounded medial end of the metatarsal IV facet and a more rugose interosseous ligament attachment ( Figure 13M, Q ).

Remarks. We are confident that the only known calcaneus and talus of Bohra paulae once articulated with each other and, as Flannery & Szalay (1982) originally suggested, that the two referred left tibiae belong to the same species as the tarsal bones. Both tibiae were collected from Cathedral Cave within the Wellington Caves complex ( Figure 1 ), likely from Ramsay’s Shaft No. 2. Subsequent excavations within this area of the cave led by Lyndall Dawson & others in 1982–1986 ( Dawson & Augee 1997) and by Diana Fusco and GJP since 2016 have revealed close spatial associations between limb elements of large macropodid individuals. It is conceivable that the holotype not only came from Shaft No. 2, but also belongs to the same individual as one of the referred tibiae.

By contrast, ‘ Wellington Caves’ is the only provenance information associated with the four metatarsals. Their larger size and morphological distinction from the metatarsals of B. illuminata and B. nullarbora prompt us to refer them to B. paulae rather than B. bandharr . Basic metrics ( Table 8 ) reinforce this: the holotype calcaneus of B. paulae is 23% longer than that of B. nullarbora , while metatarsal V length (mean of AM F103802 and AM F104092) is also 23% greater than that of B. nullarbora . Similarly, calcaneus length to metatarsal V length ( B. paulae holotype against mean of AM F103802 and AM F104092) is 0.72, as it is for the B. nullarbora holotype.

Figures

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

FIGURE 8. Tibia (right, adult) of Dendrolagus bennettianus (QM JM19863). A: cranial view. B: caudal view. C: medial view. D: lateral view. E: proximal view. F: distal view. DFF, distal fibular facet; ICE, intercondylar eminence; IOB, interosseous border; LCO, lateral condyle; LFO, lateral fossa; MCO, medial condyle; MMA, medial malleolus; PFF, proximal fibular facet; TAS, talar articular surface; TCR, tibial crest.

FIGURE 9. Calcaneus and talus (right, adult) of Dendrolagus bennettianus (QM JM19863). Calcaneus (A–E). A: dorsal view. B: plantar view. C: medial view. D: cranial view. E: lateral view. Talus (F–K). F. plantar view. G: medial view. H: dorsal view. I: caudal view. J: lateral view. K: cranial view. AHN, head of talus (articular facet for navicular); APT, anterior plantar tuberosity; ATF, anteromedial facet for head of talus; CFA, articular facet for cuboid; CPS, calcaneal plantar surface; DMF, dorsomedial facet of calcaneal-cuboid articulation; DLF, dorsolateral facet of calcaneal-cuboid articulation; FGS, flexor groove of sustentaculum tali; FIB, fibular articular surface; FIL, tubercles for fibular ligaments; LCS, lateral calcaneal facet; LTF, lateral facet for talus; LTC, lateral trochlear crest; MCF, medial calcaneal facet; MFO, malleolar fossa; MMA, medial malleolus; MTC, medial trochlear crest; MTF, medial facet for talus; PVP, posteroventral process; STA, sustentaculum tali; TCA, tuber calcanei; TCE, epiphysis of tuber calcanei; TPS, transverse plantar sulcus; TRO, trochlea (talo-crural joint); VMF, ventromedial facet of calcaneal-cuboid articulation.

FIGURE 10. Metatarsals (right, adult) of Dendrolagus bennettianus (QM JM19863). Metatarsal IV (A–D). A: dorsal view. B: plantar view. C: medial view. D: lateral view. Metatarsal V (E–H). E: dorsal view. F: plantar view. G: medial view. H: lateral view. CUB, articular facet for cuboid; FCL, fossa for collateral ligaments; HMT, head of metatarsal; MIIIF, articular facet for metatarsal III; MIVF, facet for metatarsal IV; MVF, articular facet for metatarsal V; PLP, proximolateral process; PSF, facet for plantar sesamoid (proximal plantar process); IOC, crest for interosseous ligaments; IOS, sulcus for interosseous ligaments.

FIGURE 11. Tibia of Bohra paulae. AM F62102, left adult tibia (A–F). A: cranial view. B: caudal view. C: medial view. D: lateral view. E: proximal view. F: distal view. AM F62101, partial left adult tibia (G–J). G: cranial view. H: caudal view. I: medial view. J: lateral view.

FIGURE 12. Calcaneus and talus (right, adult) of the holotype of Bohra paulae (AM F62099–F62100). Calcaneus (A–E). A: dorsal view. B: plantar view. C: medial view. D: lateral view. E: cranial view. Calcaneus and talus in articulation (F–I). F: dorsal view. G: medial view. H: cranial view. I: lateral view. Talus (J–O). J: cranial view. K: dorsal view. L: medial view. M: caudal view. N: plantar view. O: lateral view.

FIGURE 13. Metatarsals IV and V of Bohra paulae. AM F104075, left juvenile metatarsal IV (A–E).A: dorsal view. B: plantar view. C: lateral view. D: medial view. E: proximal (caudal) view.AM F104550, left juvenile metatarsal IV (F–J). F: dorsal view. G: plantar view. H: lateral view. I: medial view. J: proximal (caudal) view. AM F104092, right adult metatarsal V (K–N). K: dorsal view. L: plantar view. M: medial view. N: lateral view. AM F103802, right adult metatarsal V (O–R). O: dorsal view. P: plantar view. Q: medial view. R: lateral view.

FIGURE 20. Calcaneus (right, adult) of Bohra wilkinsonorum (QM F675). A: plantar view. B: dorsal view. C: medial view. D: lateral view. E: cranial view.

FIGURE 33. Calcaneus and talus (right, adult) of the holotype of Bohra planei sp. nov. UCMP 70128, holotype calcaneus (A–E). A: plantar view. B: dorsal view. C: cranial view. D: medial view. E: lateral view. NHMD 193283, partial right calcaneus (F–G). F: dorsal view. G: medial view. UCMP 70128, holotype talus (J–M). H: plantar view. I: dorsal view. J: medial view. K: lateral view. L: caudal view. M: cranial view.