Protemnodon roechus Owen, 1874

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 : 238-241

Protemnodon roechus Owen, 1874

Referred material. NMV P215986 , left P3, M 1–4 in maxilla fragment, and associated premaxilla fragment with alveoli for I1–3 ; NMV P173645 , right dP2 ; NMV P173643 , left P3 ; NMV P173644 , right P3 ; NMV P173628 *, left P3 ; NMV P215999 , anterior half left P3 ; NMV P173682 , posterior half right P3 ; NMV P173687 , incomplete right P3 ; NMV P200648 /P200657, right M1 and P3 fragment ; NMV P173685 / P200654*, left M2 ; NMV P200649 /P200653*, left M3 ; NMV P173681 , right M3 ; NMV P216003 , right M3 ; NMV P173686 , left M4 and associated right anterior cingulum of M4 ; NMV P173683 , right i1 ; NMV P215988 , worn left i1 ; NMV P216041 , left i1 tip ; NMV P165457 , partial right dentary containing p3, m1–4 ; NMV P173640 , dentary fragment containing right p3, m1–2, and associated partial i1 and m3 ; NMV P173641 , associated right p3, dp3, m1, m2 ; NMV P173642 , dentary fragments containing p3, m1–2, m4 and associated m3 ; NMV P216014 , trigonid right m1 ; NMV P216016 , trigonid right m2 ; NMV P173684 , partial right m3 (missing trigonid) ; NMV P216017 , hypolophid right m3 ; NMV P216007 , hypolophid left m4. (* NMV P173685 / P200654 and NMV P200653 /P200649 are probably from the same individual as they were collected from the same location, share similar stages of wear and type of preservation, and occlusal and interstitial wear patterns align. Each tooth bears two catalogue numbers as the anterior and posterior portions of the teeth were found separately during collecting carried out in the 1970s and 80s, which were later matched up by the author.They are also thought to be associated with a P3 (P173628) from the same location (note with specimen, C. Hann, 1983).

Remarks. The specimens referred here to Protemnodon roechus Owen, 1874 are very similar in morphology, but are towards the lower end of the size range of the type population of P. roechus from the Darling Downs, Queensland ( fig. 6 ) ( Bartholomai, 1973).

NMV P165457 is the best-preserved and most complete dentary of Protemnodon from Nelson Bay ( figs. 6A–C ). It is broken at the symphysis, just anterior of the mental foramen, and lacks the ascending ramus. It is relatively robust, and is deeper dorso-ventrally than P. anak . It is slightly deeper below m1 than below m4. Although difficult to compare, the diastema is possibly slightly shorter and is more robust relative to the length of the molar row than in P. anak . The large oval mental foramen is close to p3, and the buccinator fossa extends from p3 posteriorly to below the anterior root of m3.

Although no unworn i1s are preserved for P. roechus from Nelson Bay, the i1 root associated with NMV P173640, and the isolated extremely worn left i1 ( NMV P215988) ( fig. 6E ), are considerably more robust than the i1s referred to P. sp. cf. brehus from Nelson Bay, and are more within the expected size range for the species.

In NMV P173642, a poorly developed posterior cingulid is present on all molars but is obscured by interstitial wear in the anterior molars. It is less shelf-like when compared with the posterior cingulid of P. sp. cf. brehus from Nelson Bay, and is positioned higher on the hypolophid. A horizontal groove is sometimes developed around the posterior swollen base of the hypolophid. The poor preservation of the enamel in NMV P173642 possibly artificially accentuates such a groove making it appear more shelf-like. The presence of a posterior cingulid on these specimens does not rule out their referral to P. roechus , as although the absence of a posterior cingulid on the lower molars is a defining characteristic of P. roechus , it does occur very rarely within the species, particularly on dp3 ( Bartholomai, 1973, 1977). This pattern of variable development of a posterior cingulid is similar to that seen in P. anak , where it is less well developed than in P. brehus , and is not always present on all molars within the same individual ( Bartholomai, 1973).

dP2 of P. roechus has not been reported or described in the literature. NMV P173645 ( fig. 6H–J ) is tentatively referred to P. roechus as it does not fit the descriptions of dP2 for P. anak or P. brehus given by Bartholomai (1973) and Tedford (1967), and differs from NMV P215995 (from Nelson Bay) here assigned to P. sp. cf. brehus . It is sub-triangular in occlusal outline, but is broader and more rounded than NMV P215995. It is composed of a main blade, a very low posterolingual cusp and a wide lingual cingulum. The main blade is positioned more centrally than in NMV P215995. It consists of a prominent anterior and posterior cusp, and two lower intermediate cuspules. An anterior ridge descends from the anterior cusp, curving near the base of the crown towards the lingual cingulum, but does not join it. A second strong, sharp ridge descends labially, terminating approximately two-thirds of the way down the crown in a small tubercle. Sharp non-vertical labial ridges also descend from the two intermediate cuspules, the posterior one being slightly shorter. They are linked at the bottom by a well-defined cingulum, forming a small pocket. A pocket is also formed by a cingulum that extends from the base of the anterior-most labial ridge towards the first intermediate ridge, the two separated by a tiny tubercle. A short ridge descends labially from the posterior cusp, but remains unconnected by a labial cingulum. The non-tuberculate lingual cingulum runs from the posterolingual cusp to just posterior of the anterior-most tip of the crown, delineating a wide lingual basin. Well-defined ridges in line with the intermediate cuspules cross the basin to join to the lingual cingulum, dividing the basin into three sections. A broad ridge descends lingually from the anterior cusp but does not cross to the lingual cingulum, instead forming a constriction in the width of the basin. A strong low ridge descends from the posterior cusp to the very low, poorly defined posterolingual cusp, and a second ridge descends posteriorly then curves lingually to the base of the posterolingual cusp, defining a large posterior fossette. The dP2 ( NMV P215995) referred to P. sp. cf. brehus from Nelson Bay differs from NMV P 173645 in having less well-defined labial and lingual ridges and labial ‘pockets’, a narrower lingual basin and a higher, better defined posterolingual cusp, connected to the posterior cusp by a higher ridge.

The P3s here referred to P. roechus are all similar morphologically, varying mainly in the continuity of the lingual cingulum. They are very similar to a P3 figured for P. roechus from the Darling Downs ( Bartholomai, 1973; fig 7 (6), p. 335). They possess a labially concave crown characteristic of P. roechus , the lingual cingulum does not extend beyond the prominent anterior cusp and the anterolingual fossette is often poorly defined ( Bartholomai, 1973); however, the three well-defined ridges on the labial side of the crest are more vertical than those described for P. roechus from the Darling Downs ( Bartholomai, 1973).

The upper molars are very similar in both size and morphology in P. brehus and P. roechus , and are therefore very difficult to distinguish in isolated specimens. However, the specimens here referred to P. roechus are done so based on the straight anterior edge of the anterior cingulum and the presence of a variably developed tubercle in the lingual extremity of the median valley, both characteristics of P. roechus ( Bartholomai, 1973) . Other more variable differences noted include: a slightly narrower anterior cingulum, lacking an anterolingual fossette and possessing fewer, less well-developed ridgelets; a less well-developed preparacrista; and a slightly stronger developed postparacrista.

As seen in P. sp. cf. brehus from Nelson Bay, the posterior lower molars of the Nelson Bay P. roechus are relatively smaller in comparison to other examples of the species from other sites. The Nelson Bay P. roechus is smaller overall compared to the type population from the Darling Downs, Queensland, but is similar in size to a single specimen from Cement Mills, Gore ( Bartholomai, 1977). Although it bears some similarities to P. anak , the proportions of the dentary and some features of the dentition clearly place it closer to P. roechus . To date, there has been no study into whether Protemnodon was sexually dimorphic, and the small sample size, plus the absence of any larger specimens at Nelson Bay does not allow any further speculation on this matter.

Few P. roechus specimens have been described in the literature, and some have been included within descriptions of P. brehus , e.g. Bingara and Menindee LFs ( Marcus, 1976; Tedford, 1967), causing further confusion. Some authors have suggested that P. roechus is synonymous with P. brehus (e.g. Hann, 1983; Marshall, 1973; Stirton, 1963), as specimens can possess combinations of the characteristic features of both species, which in themselves are often highly variable. The fact that both species often occur together within the same faunas may offer further support for this theory. The Nelson Bay specimens are here tentatively separated into P. sp. cf. brehus and P. roechus following Bartholomai (1973) pending a much-needed revision of the Pleistocene species.

Figures

Figure 6. Protemnodon roechus: a–c, NMV P165457, right partial dentary with p3, m1–4, occlusal, lingual and labial views; d, NMV P173641, right juvenile tooth row with unerupted p3, dp3, m1–2, occlusal view; e, NMV P215988, left i1, lingual and labial views; f, g, NMV P215986, left partial maxilla with P3, M1–4, labial and occlusal views; h–j, NMV P173645, right dP2, occlusal, labial and lingual views. Scale bars = 10 mm.

Figure 7. Protemnodon sp. postcranial material: a, b, NMV P216160, right cuboid; c, NMV P216155, right astragalus, dorsal view; d, NMV P215118, right partial calcaneum, dorsal view; e, NMV P216071, crushed distal end of left tibia, lateral view; f, NMV P216148, right fifth metatarsal, lateral view; g, NMV P216152, left fourth metatarsal, medial view; h, i, NMV P173675, partial left innominate (illium), dorsomedial and medial views; j, NMV P216158, proximal end of right fibula; k, NMV P215909, left ulna, lateral view; l, NMV P173669, ungual, dorsal and lateral views; m, NMV P200451, distal phalanx, dorsal view. Scale bars = 10 mm.