Protemnodon, Piper, 2016

Piper, Katarzyna J., 2016, The Macropodidae (Marsupialia) of the early Pleistocene Nelson Bay Local Fauna, Victoria, Australia, Memoirs of Museum Victoria 74, pp. 233-253 : 243-247

Protemnodon n. sp. A

cf. Protemnodon sp. Turnbull and Lundelius, 1970: 63, pl.

XXVIII.

Protemnodon sp. A Whitelaw, 1989: 625.

Protemnodon sp. Flannery, Rich, Turnbull and Lundelius, 1992: 29, figs. 14C–E, 15.

A collection of small Protemnodon teeth from Nelson Bay ( figs. 8 , 9 ; table 1) show similarities to upper molars and premolars of Protemnodon from the early Pliocene Hamilton LF (4.62–4.48 Ma) in western Victoria and the late Pliocene Dog Rocks LF, Batesford, Port Philip Basin, Victoria (2.58–1.95 Ma) ( Flannery et al., 1992; Turnbull and Lundelius, 1970; Whitelaw, 1991). They probably represent a new species of Protemnodon , but without review of the genus, or until more complete material is found, it is not possible to definitively ascertain this and it is therefore not named here.

Nelson Bay referred material. NMV P216005, associated right dP2, unerupted P3 and M3; NMV P200471, right dP2; NMV P187198, right P3; NMV P215998, right P3; NMV P200472, right M1; NMV P216013, right M1; NMV P215785, protoloph left M1; NMV P215788, protoloph left M1?; NMV P218245, left M2; NMV P216040, metaloph right M2; NMV P187192, right M3; NMV P200473, right M3; NMV P200604, left M3; NMV P216009, protoloph left M3.

Hamilton referred material. NMV P160372, left dP3; PM 4429, left M2 (described as dP 3 in Turnbull and Lundelius (1970), p. 63–64; pl. XXVII A–E, and M 1 in Flannery et al. (1992), p.29); NMV P162896, anterior fragment of left dP2.

Dog Rocks referred material. NMV P201862b, right M1, M3.

Diagnosis. Square, moderately low-crowned upper molars, unconstricted across the median valley, with gently sloping lingual loph margins and swollen loph bases; anterior cingulum square-shaped and restricted lingually, particularly in dP3 and M1. Variably developed postlink present on anterior upper molars in some specimens. Relatively and actually elongate P3 with four intermediate cuspules, of which the centre two are the most distinct.

Differs from all other known species of Protemnodon , except P. otibandus and P. chinchillaensis , in possessing a P3 that is relatively elongate compared to upper molars (see table 2), and from all species in having upper molars that are more rounded in occlusal outline (i.e. unconstricted across the median valley – base of lophs expanded lingually and swollen in the labial moiety of the transverse median valley, forming a convex labial margin in occlusal view). Differs from all species except P. otibandus and P. tumbuna in having gently sloping lingual loph margins and a variably developed postlink on anterior molars in some individuals.

Differs from P. anak , P. brehus , P. roechus and P. devisi in being smaller, in having upper molars with narrower and shorter anterior cinguli, relatively stronger premetacristae and postparacristae, and a tightly V-shaped median valley. The P3 has four intermediate cuspules and labial ridgelets, of which the centre two are most defined (in other species the anterior-most ridgelets are the most distinct) and lacks lingual ridgelets that cross the lingual basin. Differs from P. brehus , P. roechus , P. chinchillaensis and P. devisi in having only an occasional single, weak, lingually positioned ‘forelink’ instead of numerous ‘ridgelets’ on the anterior cingulum of the upper molars. Differs from P. chinchillaensis in having weaker premetacrista in M2–3 and a more square-shaped anterior cingulum.

Differs from P. otibandus in being higher crowned, having narrower and longer anterior cinguli on upper molars, and having a premolar with two distinct intermediate labial ridgelets, less distinct lingual ridgelets and a more tuberculate lingual cingulum.

Differs from P. snewini in having a stronger postparacrista, premetacrista and midlink, a narrower, more lingually restricted and more basin-like anterior cingulum on upper molars, and a more robust P3.

Differs from P. nombe and P. tumbuna in being larger, from P. tumbuna and P. hopei in having relatively narrower upper molars, and from P. tumbuna in having a P3 with a less concave buccal margin, a tuberculate lingual cingulum, four intermediate cuspules and ridgelets, and lacking a buccal fossette; and having a much stronger preparacrista on upper molars.

Description. Only the upper dentition is known from Nelson Bay ( figs. 8 , 9 ). Protemnodon n. sp. A shows many morphological similarities to both Protemnodon and Wallabia . It falls within the size range of P. chinchillaensis and P. otibandus , but is closest in morphology to P. otibandus . The following description is based primarily on the Nelson Bay specimens, supplemented by elements from the Hamilton and Dog Rocks LFs where available.

The two dP2s ( NMV P200471, P216005) from the Nelson Bay LF are complete and only slightly worn. NMV P216005 ( figs. 8A–C ) is subrectangular in occlusal outline and consists of a main blade positioned slightly labial of the midline, a posterolingual cusp and a well-developed lingual cingulum. The main blade consists of a high anterior cusp, a slightly lower posterior cusp and three lower intermediate cuspules. A strong vertical labial ridgelet ascends from the central intermediate cuspule almost to the base of the crown. Labial ridgelets from the anterior and posterior intermediate cuspules are very short and weak. A strong ridge ascends from the anterior cusp slightly posterolabially to the base of the crown. A second ridge ascends directly anteriorly, curving lingually at the base to terminate on the anterolingual base of the anterior cusp, and does not link to the lingual cingulum. A third, weaker ridge ascends directly lingually terminating at a small cuspule, which marks the start of the lingual cingulum. The lingual cingulum extends posteriorly, defining a wide lingual basin, and terminates at the large, low, rounded posterolingual cusp. The basin is divided into two pockets by a transverse ridge in line with the anterior intermediate cuspule. The anterior pocket is smaller and narrower than the posterior pocket. The posterolingual cusp is linked to the posterior cusp by a strong, moderately high ridge. A small U-shaped posterior cingulum marks a shallow posterior fossette. NMV P200741 ( figs. 8D–F ) differs in having a weaker lingual cingulum and shallower lingual basin, weaker labial ridgelets and weaker/absent lingual ridgelets.

There are three P3s present in the current Nelson Bay sample ( NMV P187198, P215998 and P216005) ( figs. 8G–O ). P3 is very long compared to the molars, as in P. chinchillaensis , and is slightly longer than those of P. roechus from Nelson Bay. The crown is subovate in occlusal outline. It is flattened anteriorly and posteriorly, does not narrow anteriorly, and has a slightly concave labial and straight lingual margin. It is composed of a main blade, a low posterolingual cusp and a wide, low lingual cingulum. The main blade is straight, curving only very slightly labially posteriorly. It consists of a high prominent anterior cusp, a lower posterior cusp and four intermediate cuspules, of which the centre two are much more prominent than the external two. Moderately strong vertical ridgelets ascend labially from the centre two intermediate cuspules almost to the base of the crown. Only very short, weak labial ridgelets ascend from the anterior and posterior intermediate cuspules. The corresponding lingual ridgelets present in other species of Protemnodon are either very weakly developed/absent in Protemnodon n. sp. A or are removed by wear. A strong ridge and deep groove ascends posterolabially from the anterior cusp, but is not as strong or as continuous as in P. roechus and P. brehus . A second ridge ascends directly anteriorly curving lingually at the base of the crown to terminate at a small anterolingual cuspule. A weaker ridge also ascends directly lingually linking to the start of the lingual cingulum. The anterolingual cuspule is separated from the lingual cingulum by a groove. The lingual cingulum extends posteriorly, terminating at the high posterolingual cusp defining a lingual basin that widens posteriorly. The lingual cingulum indents slightly opposite the space between the first and second intermediate cuspules, constricting the lingual basin into a small circular anterior pocket and a wider, elongate posterior pocket, but they are not completely divided from one another. The posterolingual cusp is slightly lower than the posterior cusp, the two connected by a moderately high anterolabially trending ridge. The posterior cingulum is low, extending across the entire posterior face of the crown, and defines a large, deep posterior fossette.

NMV P215998 is moderately worn and differs from the unerupted NMV P 216005 in that the anterolingual cuspule is absent; therefore, the anterior margin of the crown is more tapered, rather than flat, and the anterior ridge terminates on the anterolingual base of the anterior cusp. The posterolingual cusp is much shorter than the posterior cusp owing to wear. NMV P187198 is also worn and differs from both NMV P215998 and NMV P 216005 in that the lingual cingulum narrows rapidly anteriorly resulting in the loss of the small anterior basin, but the lingual ridge from the anterior cusp is retained.

dP3 ( NMV P160372) was described and figured by Flannery et al. (1992, p. 29; figs. 14C–E, 15; table 1) from the Hamilton LF. It is not known from the Nelson Bay LF. Two M1s are known from the Nelson Bay LF ( NMV P200472 and NMV P216013) ( figs. 9A–C ) and one from the Dog Rocks LF ( NMV P201862b). The lophs are moderately low crowned and taper towards the crown apices, particularly lingually, owing to the gently sloping slightly concave lingual loph margins. The bases of the lophs are extended lingually and slightly swollen labially. Lophs are strongly concave posteriorly in unworn specimens, and the metaloph is wider and higher than the protoloph. The anterior cingulum is low, short and transversely narrow, extending from the anterior base of the paracone to the anterior base of the protocone. It is truncated abruptly lingually and is near planar. A strong preparacrista closes off the labial end of the anterior cingulum. The postparacrista and premetacrista are relatively strong and meet in some specimens ( NMV P201862b) at the base of the median valley about one-half the distance from the midlink to the labial edge, and close off the labial end of the median valley. The lingual and labial moieties of the median valley are tightly V-shaped. The midlink is strong, ascending from the protocone to the centre of the median valley to meet with the weak contribution from the centre of the metaloph. The posterior cingulum consists of a strong, slightly swollen, curved postmetaconulecrista terminating labial of the midline, separated from the weaker postmetacrista by a fissure. A short, weak postlink is present on the posterior face of the metaloph in NMV P201862b and NMV P200472, positioned slightly labial of the midline, but is absent in P216013. M1 differs from dP 3 in being higher crowned, relatively more elongate and having a wider protoloph.

Two complete M2s, one from the Hamilton LF ( PM 4429) and one from Nelson Bay ( NMV P218245) ( figs. 9D–F ), plus an M2 metaloph ( NMV P216040) are known. M2 is as M1 except that it is slightly larger, the metaloph and protoloph are approximately equal width, the postparacrista and particularly the premetacrista are weaker and do not meet, the contribution from the metaloph to the midlink is slightly stronger, and the anterior cingulum is slightly broader transversely, with the lingual third sloping away steeply to the anterolingual base of the protoloph. There is a slight hint of a lingual ‘forelink’. The labial bases of the lophs are strongly swollen, giving the labial margin of the crown a convex appearance in occlusal view as in Wallabia . A low rounded crest runs parallel to the edge of the postmetaconulecrista. The Hamilton M1 differs from the Nelson Bay M 1 in being slightly lower crowned and possessing a weak postlink (only an extremely weak postlink is present on the isolated metaloph, NMV P216040, from Nelson Bay).

Four complete M3s and one M3 protoloph are known from Nelson Bay ( NMV P187192, P200473, P200604, P216005, P216009) ( figs. 9G–R ) and one complete M3 from the Dog Rocks LF ( NMV P201862b) ( figs. 9S–U ). M3 is as M2 but is slightly larger and the anterior cingulum is squarer, slightly longer and bulbous anteriorly. A weak ‘forelink’ is present near the lingual end of the anterior cingulum in NMV P187192, NMV P216009 and NMV P201862b. The crest parallel to the postmetaconulecrista is strongly swollen. A very weak hint of a postlink is present on NMV P201862b. No M4s are currently recognised in any of the assemblages.

Remarks. Within Protemnodon n. sp. A, P3 morphology appears to be quite variable, but this is common within the genus ( Bartholomai, 1978). But they are all consistently elongate compared to the molars, and are actually longer than all other species, except for some large individuals of P. brehus and P. roechus ( Bartholomai, 1978) (see table 2). Protemnodon n. sp. A is closest overall in size and morphology to P. otibandus , sharing features such as an elongate P3, sloping lingual loph margins, a narrow anterior cingulum, poor development of dP3 protoloph and a slight postlink on anterior molars ( Flannery et al., 1992; Plane, 1967). It also shares features with P. chinchillaensis in the size and relative P3 length ( Bartholomai, 1978), and with P. tumbuna in the slope of the lingual loph margins and lingually restricted anterior cingulum ( Flannery et al., 1983). P. chinchillaensis appears to be quite close in morphology to P. otibandus differing only in lacking a postlink on the anterior molars ( Flannery and Archer, 1984). The postlink is very weak and variably developed in Protemnodon n. sp. A, occurring mainly in the specimens from the Pliocene local faunas. The Hamilton specimens also appear to be slightly lower crowned than the Nelson Bay and Dog Rocks specimens. This suggests that a morphological cline exists within this species, with molars becoming higher crowned and losing the postlink with time.

Many questions remain unanswered regarding the morphology and phylogenetic position of Protemnodon n. sp. A owing to the lack of complete tooth rows and certainly associated lower dentition. As the Nelson Bay LF appears to be a mixed assemblage of relicts from the Pliocene and Pleistocene/modern species ( Piper, 2006a, b; Piper, 2007), it is likely that Protemnodon n. sp. A would be more typically found within Pliocene deposits.

Figures

Figure 8. Protemnodon n. sp. A from the Nelson Bay LF: a–c, NMV P216005, right dP2, occlusal, labial and lingual views; d–f, NMV P200471, right dP2, occlusal, labial and lingual views; g–i, NMV P187198, right P3, occlusal, labial and lingual views; j–l, NMV P215998, right P3, occlusal, labial and lingual views; m–o, NMV P216005, right unerupted P3, occlusal, labial and lingual views. Scale bar = 10 mm.

Figure 9. Protemnodon n. sp. A from the Nelson Bay LF: a–c, NMV P216013, right M1, occlusal, labial and lingual views; d–f, NMV P218245, left M2, occlusal, labial and lingual views; g–i, NMV P187192, right M3, occlusal, labial and lingual views; j–l, NMV P200473, right M3, occlusal, labial and lingual views; m–o, NMV P200604, left M3, occlusal, labial and lingual views; p–r, NMV P216005, right M3, occlusal, labial and lingual views.Protemnodon n. sp. A from the Dog Rocks LF: s–u, NMV P201862b, right M3, occlusal, labial and lingual views. Scale bar = 10 mm.