Protemnodon, Owen, 1874
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publication ID |
https://doi.org/ 10.11646/megataxa.11.1.1 |
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publication LSID |
lsid:zoobank.org:pub:5F42E7FE-C154-4979-9691-E6F74BBBBC10 |
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DOI |
https://doi.org/10.5281/zenodo.10993702 |
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persistent identifier |
https://treatment.plazi.org/id/03E587FD-FF50-D58B-FCA2-728CFA47FA09 |
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treatment provided by |
Felipe |
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scientific name |
Protemnodon |
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Status of other species previously referred to Protemnodon
Australian Pleistocene species
Protemnodon brehus ( Owen, 1874) : Phil. Trans. Roy. Soc. 164, p. 272— nomen dubium.
Protemnodon mimas Owen, 1874 : Phil. Trans. Roy. Soc. 164, p. 278— nomen dubium.
Protemnodon roechus Owen, 1874 : Phil. Trans. Roy. Soc. 164, p. 281— nomen dubium.
Protemnodon antaeus Owen, 1877 : Researches on the fossil remains of the extinct mammals of Australia; with a notice of the extinct marsupials of England. 1, p. 448— nomen dubium.
This section discusses the taxonomic history and status of the remaining species of Protemnodon described by Owen (1874, 1877), including justification for the designation of Protemnodon roechus and P. brehus as nomina dubia and for the erection of two species novae from the Australian Pleistocene. For reference, all of the holotypes and lectotypes for Owen’s (1874, 1877) six species of Protemnodon are figured here ( Fig. 108 View FIGURE 108 ). Note that, as per ICZN Article 61, the holotype specimen (i.e. the name-bearing type) is the sole specimen that provides the diagnostic features of the nomen —the type (not the type series, i.e. paratypes, nor referred specimens) provides the objective standard of reference for the application of the name it bears (ICZN 1999).A loss of the utility of a nomen is the criterion for status as nomen dubium, although the nomen remains valid and available.
The following is an extract from the redescription of P. roechus from Bartholomai (1973), where the dental morphology of the species was contrasted with that of P. anak and P. brehus : ‘[ Protemnodon ] roechus is distinguished from other known species of Protemnodon by both its extreme size and generally distinct morphology. In particular, the relatively less ornamented nature of its permanent lower premolar, the broadly rounded, swollen condition of the posterior crown bases of the lower molars, the non-vertical transecting ridges of the permanent upper premolars, the crescentic shape of this tooth in occlusal view and the generally marked tuberculation of the lingual extremity of the median valley in the upper molars are all useful in the morphological separation of the species. Overlap in size does occur with P. brehus , but by applying a combination of the characters available separation of the species is achieved’ ( Bartholomai 1973, p. 346).
Nevertheless, the distinction as made by Bartholomai (1973) is in fact not so clear. For a variety of reasons, P. brehus and P. roechus have never been clearly delimited. The lectotype specimen for P. brehus, NHMUK PVOR 43303a, is a partial palate containing left M3–M4 and right M2–M4. However, the holotype specimen for P. roechus, NHMUK PVOR 35968, is a left dentary fragment containing heavily worn p3–m3, and as such the holotypes have no shared features for direct comparison. Three of the five characteristics stated by Bartholomai (1973) as distinguishing P. roechus from other species of Protemnodon are in the upper cheek teeth, which are not preserved in the holotype of P. roechus , and the holotype of neither species preserves a P3. The results of our analyses and the morphological comparisons of the material of Protemnodon from across Australia indicate that the characteristics described above do not distinguish two distinct morphotypes, but instead describe features that vary continuously within the sample.
The statement by Bartholomai (1973, p. 346) that specimens of P. roechus are characterised by “extreme size” that differentiates them from those of P. brehus is not well-supported by the data presented in that paper ( Bartholomai 1973, fig. 9), which show almost identical mean dimensions for the lower dentition, nor by the data presented here (See Figs 116–122 View FIGURE 116 View FIGURE 117 View FIGURE 118 View FIGURE 119 View FIGURE 120 View FIGURE 121 View FIGURE 122 ). The ‘crescentic shape’ of the P3 varies greatly within the sample of Pleistocene P3s not attributable to P. anak ( Fig. 109 View FIGURE 109 ). The description of the ‘relatively less-ornamented nature of its [p3]’ most probably refers to the narrow, roughly dorsoventrally orientated ridgelets on the lingual and buccal faces of the p3. These ridgelets, when numerous and thin but distinct, are diagnostic of P. anak , and are less numerous and less distinct in other Pleistocene Australian material of species of Protemnodon . No discrete difference in the number or size of these ridgelets is discernible in the sample of Pleistocene Australian material when excluding that of P. anak . These ridgelets disappear almost completely with a moderate degree of wear, and so in older and thus often skeletally larger individuals with a greater degree of dental wear, the premolar appears increasingly less ornamented. It is possible that this biased Bartholomai’s (1973) morphological analysis by causing larger individuals, i.e. those more likely to be assigned to P. roechus , to seemingly possess p3s with fewer, less raised vertical ridgelets.
The condition of rounded, swollen posterior lophid bases is present in various lower molar specimens of Protemnodon from the Pleistocene, including individuals of P. anak , rather than solely individuals allocated to P. roechus . This condition is seen in molars with residual postcingulids and very occasionally in large molars with fully developed postcingulids (as in the holotype of P. mimas, NHMUKPV OR 43351).
Our extensive survey of fossils of species of Protemnodon from the Australian Pleistocene has revealed that there are indeed two Australian Pleistocene morphotypes of Protemnodon aside from P. anak ( P. mamkurra sp. nov. and P. viator sp. nov.); however, they are primarily distinguishable on postcranial features. Neither can be delimited based on either the upper or lower cheek dentition and they have similar size ranges. As illustrated in Figs 116–120 View FIGURE 116 View FIGURE 117 View FIGURE 118 View FIGURE 119 View FIGURE 120 , any divide in terms of dental dimensions between the type material of P. mamkurra sp. nov. and P. viator sp. nov. is filled by isolated dental or craniodental specimens allocated to P. mamkurra sp. nov. or viator sp. nov. These specimens do not cluster in any distinct groups, but rather are spread between and around the groupings of P. mamkurra sp. nov. and P. viator sp. nov. specimens. This demonstrates the inefficacy of diagnosing these two taxa based on the few small differences in dental dimension groupings, as these do not serve to delimit with any confidence the many remaining fragmentary specimens.
Because the holotypes of neither P. brehus nor P. roechus can be unambiguously associated with either one of the two Pleistocene forms identifiable on the basis of partial and complete skeletons, neither nomina can be used to describe the taxa observed. We therefore recognise P. brehus ( Owen, 1874) and P. roechus Owen, 1874 as nomina dubia.
This leaves P. mimas Owen, 1874 , previously synonymised with P. brehus , and P. antaeus Owen, 1877 , previously synonymised with P. roechus . Owen (1874) observed that P. antaeus differed from P. mimas in its lack of a postcingulid and in having a larger p3 relative to its molars, and from P. roechus in being smaller. However, because these traits and proportions vary within species ( Fig. 121 View FIGURE 121 ) (see also Bartholomai 1973, p. 346) to a much greater degree than separates the holotypes of P. antaeus , P. mimas and P. roechus , and because the holotypes of P. mimas and P. antaeus , both partial left dentaries with p3–m4 with moderate wear (NHMUK PVOR43351 and NHMUK PVM2258, respectively), cannot be unambiguously associated with either P. mamkurra sp. nov. or P. viator sp. nov., P. mimas Owen, 1874 and P. antaeus Owen, 1877 are also considered nomina dubia.
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