https://doi.org/10.24199/j.mmv.1978.39.06 7 July 1978

RAEMEOTHERIUM YATKOLAI, gen. et sp. nov., A PRIMITIVE DIPROTODONTID FROM THE MEDIAL MIOCENE OF SOUTH AUSTRALIA

By Thomas H. Rich, 1 Michael Archer, 2 and Richard H. Tedford*

1 National Museum of Victoria. 2 Queensland Museum, Brisbane 3 American Museum of Natural History, New York

Abstract

A new genus and species, Raemeotherium yatkolai, from the medial Miocene Namba Formation in South. Australia, is the most primitive member of the Diprotodontidae yet des- cribed. On its most anterior lower molar is a well-developed paracristid and protocristid. This, together with a strong cristid obliqua on all lower molars suggests derivation of diprolodontids from selenodont rather than quadritubercular ancestors.

Introduction NMV National Museum of Victoria, Melbourne. SAM South Australian Museum, Adelaide. In September 1976, Mr Ian Stewart (Na- tional Museum of Victoria) discovered the di- Terminology and Measurements protodontid dentary here described as Rae- Mandibular terminology follows Stirton meotherium yatkolai (SAM P19764). It was (1967), dental terminology is modified from found at the south end of Lake Pinpa, South Archer (1976) (see fig. 1), and enumeration of Australia, in the medial Miocene Namba For- the teeth follows Archer (in press) (see fig. 1, mation. Only one or two centimetres away at 2). The system of tooth enumeration used here the same level was a mandible of a species of departs radically from all previously proposed. pseudocheirine similar generically to that Ted- In it, the permanent cheek teeth of diproto- ford et al. (1976, p. 56) characterized as dontids are P3 M2, M3, M4, M5. In contrast, ?

\ ., the most abundant mammal in the Pinpa in the two systems previously employed by

Fauna . . .', (NMV P48616, see pi. 16, fig. Twentieth Century authors, the same teeth are 10). designated P3 or P4, Ml, M2, M3, M4. Three additional isolated teeth referred to Measurements were made with a Wild Raemeotherium yatkolai were collected ten microscope equipped with a mechanical stage, kilometres to the south on the west side of enabling an accuracy of 0- 1 millimetres. Lake Namba at a site in the Namba Formation Systematics designated as South Prospect B by Woodburne and Tedford (1975). A single isolated upper The following diagnoses are not intended to incisor of R. yatkolai was found at Ericmas be exhaustive at each taxonomic level, but Quarry, four kilometres to the north on the rather are restricted to those features which can west side of the same lake, again in the Namba be observed on the type and referred specimens Formation. of Raemeotherium yatkolai. Callen and Tedford (1976, p. 135) and Ted- Class MAMMALIA Linnaeus, 1758 ford et al. (1977, pp. 56-57) discuss the basis Subclass THERIA Parker and Haswell, for assigning a medial Miocene age to the 1897 Namba Formation. Infraclass METATHERIA Huxley, 1880 Abbreviations Superorder Marsupialia Illiger, 1811 AM Australian Museum, Sydney. AMNH American Museum of Natural History, New Order Diprotodonta Owen, 1866 York. Family Diprotodontidae Gill, 1872 BMNH British Museum (Natural History), Lon- Diagnosis: Distinguished from all other Marsu- don.

85 86 THOMAS H. RICH, MICHAEL ARCHER, and RICHARD H. TEDFORD

aepd pmcd med Raemeotherium gen. nov. \ \ / Type species: Raemeotherium yatkolai sp. nov. ^rld Known distribution: Medial Miocene, Tarka- end —*C_^ rooloo Basin, South Australia.

Diagnosis: Distinguished from all other dipro- hlch todontids by the presence of a distinct crest, the ^paed protocristid, directed buccally from the proto-

conid on M2 ; a well-developed anterior ento- cristid on M2 ^; and the ascending ramus more recumbent than in other species. hycK / pcd Etymology: RAEME, acronym for the Royal CO Australian Electrical and Mechanical En-

gineers; Orjfjiov, Greek, beast. Figure 1 —Schematic diagram of diprotodontid lower molar showing terminology em- ployed. Abbreviations: aecd, anterior en- Raemeotherium yatkolai sp. nov. tocristid; co, cristid obliqua; end, ento- Plate 16, figures 1-5, 7, 8, 11) conid; hid, hypolophid; hyd, hypoconid; med, metaconid; pacd, paracristid; pcd, Hohtype: SAM PI 9764, right dentary frag- protocristid; pmcd, posterior metacristid; ment with Ii, M 2 -5, and alveoli for P3 . It lacks prd, protoconid; prld, protolophid; psd, the P,i, condyle, and angular region and has protostylid. Modified from Archer (1976). been crushed in a mediolateral direction so that traces of many structures on the medial side such as the digastric fossa have been ob- literated.

Type locality and stratigraphic position: Nam- ba Formation, southwest corner of Lake Pin- pa, grid zone 6, grid reference 317146 on the Curnamona topographic series SH 54-14, 1: 250,000 (1965, South Australia), 31° 8i'S., 140° 13'E.

Diagnosis: That of the genus until other species are described. Figure 2 Schematic diagram of a diprotodontid — Etymology: Named in honour of the late Mr mandible illustrating system of numbering Daniel A. Yatkola, a student teeth employed in this paper and method of mammalian of measuring inclination of anterior bor- palaeontology. der of ascending ramus (angle a) and elevation of condyle (angle b). Referred specimens: NMV P48537, isolated

right M 4 or M 5 . NMV P48538, isolated right

P. AMNH 102186, isolated left M4 . Collected pialia by the presence of four simultaneously from the Namba Formation, South Prospect functional bilophodont molars lacking fore B, Lake Namba, grid zone grid reference and midlinks and absence of a masseteric 6, 3201 35, Curnamona topographic series SH canal in the dentary. 54-14, 1:250,000 (1965, South Australia), 31° Subfamily Zygomaturinae Stirton, Woodburne, 14'S., 140° 14'E. They were found in the white and Plane 1967. coloured unit described by Woodburne and

'. Diagnosis: Most members, including Raemeo- Tedford (1975, p. 3) as a . . very fine

.', therium yatkolai, distinguished from all other sand . . developed as lenses within the diprotodontids by the presence of a distinct \ . . thin-bedded black claystone . . .', at paracristid on M 2 . South Prospect B. MIOCENE DIPROTODONTID RAEMEOTHERIUM 87

AMNH 102183, isolated right P. Collected the insertion of the geniohyoideus muscle, dis- from the Namba Formation, Ericmas Quarry, rupts the outline of the symphysis at its pos- Lake Namba, grid zone 6, grid reference terior end as a notch of smooth bone. The 320140, Curnamona topographic series SH mental foramen is located 1*7 mm anterior of 54-14, 1:250,000 (1965, South Australia), 31° the anterior edge of P , 8 1 ;J and mm below the 12'S., 140° 14'E. It was found in a channel de- dorsal edge of the horizontal ramus. It is ellip- posit formed of white quartzose sand contain- tical in outline with the major axis 4-2 mm in ing green limonite-cemented clayballs. length and gently inclined anteriorly; the minor axis is 2 8 mm. Above and somewhat TABLE 1 posterior to the mental foramen is a much Measurements (mm) of lower molars of smaller foramen. The ventral edge of the Raemeotherium yatkolai horizontal ramus below the molar row is Width Width gently convex downward. Posterior to that re- Anterior Posterior gion, the shape of the ventral border is un- Length Moiety Moiety certain owing to SAM P19764 crushing. M» 10 7 5-9 6-7 In the badly crushed posterior area of the M^ 110 65 7-4 mandible, part of the opening for the mandi- M 4 111 71 7-1 bular foramen is preserved M- 11-2 7-2 70 24 mm behind M 5 and about 3 mm below the level of the dorsal NMV P48537 edge of the horizontal ramus. Distortion in or 11 7-6 7-3 M 4 M 5 this area is so great that the position in life of AMNH 102186 this foramen might have been several milli- M or M 11 7-7 7-8 4 r> metres away. Despite the shattered nature of

the posterior part of the mandible, there is no TABLE 2 doubt that a masseteric canal was not present. Measurements (mm) of the mandible of The anterior edge of the ascending ramus is SAM PI 9764, type specimen of posteriorly inclined. Angle a as defined in Raemeotherium yatkolai Figure 2 is 62°. Although the condyle is not a Length, diastema l!-P : preserved this specimen, 3 I5 on because the dorsal

Depth, horizontal at anterior of : 19 ramus end P 3 part of the posterior edge of the coronoid pro- Depth, horizontal ramus at middle of M„: 25 u cess is intact, angle b as defined in Figure 2 u Depth, horizontal ramus at middle of M : 26 4 could not have been more than 34°. Length, : 2" M2_5 44 a = approximately. Lower dentition, /,; The thin layer of enamel on this tooth is confined to the buccal and ven- Description tral surfaces above the alveolar border. Along

Mandible: The mandible is remarkably delicate the dorsal border of the enamel, a well-de- compared with other diprotodontids and in this veloped wear facet extends from the tip to respect resembles those of similar-sized macro- about midway along the posterior edge of the

podids. The diastema between Ii and P is only enamel. An appression fossette is developed :J about a third the length of the lower molar on the ventromedial surface of the enamel row. In outline, the symphysis is almost ellip- where this tooth contacted the left Ii. As on tical. Its major axis is about 25 mm in length the molars behind, the enamel surface when and dips posteriorly at an angle of 35° with re- unworn is wrinkled with gentle, irregular sinu- spect to the dorsal edge of the horizontal ra- ous folds. The posterior end of the root is open

mus. Its posterior edge is below the posterior and located beneath the middle of P3 .

root of Pa- The length of the minor axis is P3 : This tooth is not preserved but its two al- 13 mm. The surface of the symphysis is rough veoli are present in the type specimen. On the and there is no indication of its having been basis of the alveoli, this tooth, although much

fused with the left mandible. The genial pit, for smaller, was similar to the P3 of Kolopsis torus 88 THOMAS H. RICH, MICHAEL ARCHER. :mt] RICHARD H. TFDFORD

in the ratio of its length to that of M,, and in width and distinctly narrower than the talonid. the markedly greater posterior than anterior Ms-S; The anterior moieties of these teeth are width- quite different from that of M.. In contrast, the Ms ; Unlike - a M 3 r„ distinct trigonid is de- posterior moieties of all molars are similar. A veloped on the anterior moiety of the Mo. A well-developed precingulum extends from the well-developed paracristid extends from the anterobuccal side of the protoconid base to protoconid anterior to the forward margin of the anterior side of the metaconid base. Un- the tooth. A paraconid is not present at the like the M2i the paracristid forms only a poorly- anterior end of the paracristid, but a cingulum defined vertical crest from the tip of the pro- begins at that point and extends posterolingu- toconid to its base, and because of this the ally along the margin of the tooth, terminating anterior moiety is not distinctly triangular in at the anterior end of the swelling at the base outline when viewed from above. Between the of the metaconid. Part of the mctaconid is protoconid and metaconid is a well-developed missing but enough remains to confirm that the protolophid that is convex posteriorly in occlu- protolophid extends from the protoconid to sal view. Projecting a short distance posterolin- the medial slightly and posteriorly positioned gually from the tip of the metaconid is a small metaconid. A short ridge or cristid, the proto- posterior metacristid. This structure is some- cristid is directed posterobuccally from the tip what weaker on M rj than on -.». If it M :{ was of the protoconid. At the buccal present end of the on M2 , damage to that area of the protocristid, there is a slight swelling to indi- tooth has removed all trace of the structure. cate the possible presence of a distinct cusp, Because of the similarity in the posterior the protostylid. moiety of all lower molars, only differences The cristid obliqua is directed anterolingu- from the condition of M-> will be noted. The ally to abut against the posterior side of the anterior entocristid becomes less-prominent trigonid at a point directly below posteriorly and behind until on Ma it has all but disap- the protoconid. The hypoconid and entoconid peared. The postcingulum is wider and extends are further apart from one another than the further towards the lingual and buccal margins protoconid and metaconid. The hypolophid, of the tooth than on M L.. Cuspules are de- connecting the hypoconid and entoconid, is veloped posterior and slightly buccal to the convex posteriorly. A short anterior ento- entoconid on the postcingulum. Only on M 3 cristid extends anterobuccally from the however, is there a homologue of the ridge con- entoconid. Although present in other dipro- necting the postcingulum with the crest of the todontids such as Kolopsk torus, this an- hypolophid such as occurs on Ms, and even terior entocristid is best developed in Racmco- here it is not as well-developed it is as on M2 . therlum yatkolaL Along the posterior mar- In order of decreasing height, the four gin of the tooth is a well-developed, slightly principal cusps are the protoconid, metaconid, crenulated postcingulum. Near the centre of hypoconid, and entoconid. the cingulum is a small cuspule. An extremely weak vertical ridge or prominent crenulation TABLE 3 extends up the posterior slope of the hypolo- 3 Measurements (mm) of I s of phid from this cuspule, and merges with the Raemeotherium yatkolai hypolophid wear facette. A definite wear facet extends the length of this ridge. The small cus- Length Width pule is likewise truncated by a wear facet. None NMV P48538 4-6 4-6 AMNH 102183 of the nearby crenulations display any signific- 5 4-4 ant degree of wear. Of the four principal cusps, Upper dentition, P: In occlusal view, this tooth the protoconid is the tallest and the other three has the outline of an isosceles right triangle, the (metaconid, hypoconid, and entoconid) are corners of which are rounded, and the hypo- subequal in height. In occlusal view, the tri- tenuse of which forms the posterolingual side. gonid and transverse valley are subequal in On the buccal side of the tooth is a broad, dor- MIOCENE DIPROTODONTID RAEMEOTHERIUM 89

soventral groove and on the anterior side, a ferent lineages. Evidence for the presence of well-developed appression fossette resulting this cusp as the primitive condition in groups from contact 2 with I . This tooth is quite similar descendant from the selenodont diprotodonts is in morphology to the homologous ones in to be found not only in R. yatkolai in the Ngapakaldia tedjordi, Neohelos tirarensis, and case of the diprotodontids, but in an undes- Plaisodon centralis. cribed Miocene macropod as well. Compared with measurements of Ngapakal- Primitive diprotodontid features found in dia tedjordi (Stirton 1967), Kolopsis torus Raemeotherium yatkolai that are shared with (Woodburne 1967), and Plaisiodon centralis some other members of the Diprotodontidae (Woodburne 1967), the Fs described here are include the posteriorly inclined ascending ra- about the proper size to correspond with the mus, the low position of the condyle on the molars of Raemeotherium yatkolaL Because dentary, all molars nearly the same size rather no other diprotodontids of this size are known than markedly increasing in length and width from the Namba Formation and two referred posteriorly, and the well-developed anterior molars of R. yatkolai were found in the same - entocristid on M2 n . Inclination of the ascend- site and level as one of the two incisors (NMV ing ramus is a quite variable feature within a P48538 at South Prospect B), we are confident given diprotodontid species. However, the re- that reference here to R t yatkolai is justified. cumbent angle {a in fig. 2) of R. yatkolai, 62°, is so much less than in any other diprotodontid Discussion that the differences can be confidently regarded as significant. Raemeotherium yatkolai is unique within Kolopsis torus with a minimum the Diprotodontidae and the most primitive recumbent angle of 70° is the most similar member in that the paracristid and protocristid diprotodontid, others fall in the range 80°- are 100°. well-developed on M 2 . The well-developed paracristid on M 2 is a feature of tribosphenic The ratio of M2 to M4 length typifies the marsupials as well as some diprotodonts such difference between Raemeotherium yatkolai as the selenodont possums. Archer (1976) sug- and other diprotodontids in molar lengths. In gested the possibility that lophodont marsupials R. yatkolai, this ratio is 096, practically unity. (hence diprotodontids) may have been des- The closest other diprotodontids are Ngapakal- cended from selenodont or subselenodont pos- dia tedjordi where the ratio ranges from 78 sums. The well-developed paracristid on M to 0-89 in three specimens measured by Stirton 2 , and the well-developed cristid obliqua on M 2 .5 (1967), 0-84 to 86 in three specimens of in Raemeotherium yatkolai at least suggest that Palorchestes painei measured by Woodburne diprotodontids did not descend from bunodont (1967), and 85 in one specimen (AM possums, but do not prohibit derivation from F44471) of Kolopsis rotundus. All other pre-selenodont tribosphenic ancestors, such as known diprotodontids in which this feature perameloids. can be measured, have a ratio of less than 85. On the Mo of selenodont diprotodonts buccal In the same manner, the degree of primitiveness to the protoconid there is a variably-developed of R. yatkolai in each of the remaining features cusp that represents a protostylid; e.g. Phasco- listed in the preceding paragraph cannot be larctos cinerus (NMV C2660, see pi. 16, exceeded in another diprotodontid. fig. 9), and Pseudocheirus peregrinus (NMV Some slight doubt remains as to whether

C13937, see p. 16, fig. 6). On the M 2 of Rae- Raemeotherium yatkolai is properly assigned meotherium yatkolai, the protocristid appears to the Diprotodontidae because, as far as now to have terminated in a protostylid (see pi. 16, known, the species has no derived or advanced fig. 7). Apparently the protostylid appeared as character states which preclude its inclusion a neomorph on the M 2 of selenodont diproto- as a primitive member of the Macropodoidea. donts and their descendants secondarily re- Although the presence of a masseteric canal, duced and then lost it independently in dif- a derived condition within the Diprotodonta, is 90 THOMAS H. RICH, MICHAEL ARCHER, and RICHARD H. TEDFORD a feature unique to macropodoids, the oldest Literature Cited member of the superfamily may well have ARCHER, M., 1976. Phascolarctid origins and the po- lacked one. On the basis of parsimony, the tential of the selenodont molar in the evolution Mas. 17 last common ancestor of the macropodoids of cliprotodont marsupials. Mem. Qd (3): 367-371. and their immediate sister-group, whatever that (in press). The nature of the molar-pre- may have been, presumably lacked a mas- molar boundary in marsupials and a reinterpre- seteric canal, this lack being the primitive con- tation of the homology of marsupial cheekteeth. dition. This means that at the time of their Mem. Qd Mus. 18. separation, unless the masseteric canal ap- Cauhn, R. A. and R. H. Tedford, 1976. New late peared as a part of that particular speciation Cainozoic rock units and depositional environ- event, there would have been an ancestral ments. Lake Frome area, South Australia. Trans. R.Soc.S.Aust. 100(3): 125-168. macropodoid which lacked that structure. R. Stirton, R. A., 1967. The Diprotodontidae from the yatkolai could conceivably have been a des- Ngapakaldi fauna, South Australia. Pp. 1-44 in cendant of such a primitive macropodoid or Stirton, R. A., M. O. Woodburne, and M. D. near-macropodoid. Hence allocation to the Plane, Tertiary Diprotodontidae from Australia Diprotodontidae must be regarded as tentative and New Guinea. Butt. Bur. Miner. Resour. Geo!. Geopliys, At/si. 87. although highly probable, pending discovery Tedford, R. H., M. R. Banks, N. R. Kemp, I. Mc- of better preserved specimens of R. yatkolai. Doucall, F. L. Sutherland, 1975. Recognition Assignment of Raemeotherium yatkolai to of the oldest known fossil marsupials from Aus- tralia. Nature 141-142. the Zygomaturinae within the Diprotodontidae 255 (5504): Tedford, R. H., M. Archer, A. Bartholomai, M. must also be tentative because it is based on a Plane, N. S. Pledge. T. Rich, P. Rich and R. T. primitive character state. all credible By the Wells, 1977. The discovery of Miocene verte- phylogenetic hypotheses that have been pro- brates, Lake Frome area. South Australia. Bur.

posed for the Marsupialia, the presence of a Miner. Resour. Jour. Aust. Geol. Geophvs. 2 : 53-57. strong paracristid on the Mo is primitive within Woodburne, M. O., 1967. Three new diprotodontids the diprotodontids. Hence, it is to be expected from the Tertiary of the Northern Territory. Pp. in the common ancestor of the family and could 53-103 in Stirton, R. A., M. O. Woodburne, and therefore be the condition in primitive, as yet M. D. Plane, Tertiary Diprotodontidae from unknown members of the other subfamilies. Australia and New Guinea. BulL Bur. Miner. Discovery of a single P3 of R. yatkolai would Resour. Geol. Geophys. Aust. 87. probably settle the matter because all the un- Woodburne, M. O. and R. H. Tedford, 1975. The first Tertiary monotreme Australia. doubted Zygomaturinae share a unique de- from Am. Mus. Novit. 2588: 1-11. rived morphology of that tooth.

Only one diprotodontid specimen is sig- Acknowledgements nificantly older than Raemeotherium yatkolai. This is a form tentatively regarded as a palor- National Geographic Society grant no. 1562 chestine by Tedford et al. (1975) who reported to Rich made possible the 1976 expedition its presence in the late Oligocene or older during which the type and two of the referred Geilston Bay local fauna collected near Ho- specimens were discovered. Essential ground- bart, Tasmania. Unfortunately, this specimen work for this expedition was laid in 1974 by (BMNH 40157) is not directly comparable Rich in collaboration with a contingent of the with any known material of R. yatkolai, being Third Royal Australian Electrical and Mech-

2 ;^ r a maxilla with part of M and M '. However, anical Engineers Group of the Army under the lengths of the respective tooth rows indicate the command of Capt. Norman Moxey. Rich's that these two diprotodontids are about the interest in the general area east of Lake Frome same size and the smallest members of the stemmed from having been to the region as a family. They likewise show molars of similar member of Tedford's 1971 party supported by length without conspicuous backward increase National Science Foundation Grant GB in size typical of later diprotodontids. 18273X. Tedford was further supported by the MIOCENE DIPROTODONTID RAEMEOTHERWM 91 same agency and grant in 1973 when he re- view, xl; fig. 5, medial view, xl; fig. 7, occlusal view of x2; fig. 11, occlusal view xl. NMV visited the area and discovered the first referred M _ 5 , Prospect B, P48537, isolated right M, or M , South specimens. n Lake Namba, South Australia, fig. 1, occlusal view, Messrs. Roy Linke and Buddy Napier, isolated left or , South x2. AMNH 102186, M 4 M 5 managers of Frome Downes Station, and their Prospect B, Lake Namba, South Australia, fig. 2, families were most hospitable and provided occlusal view, x2. NMV P48538, isolated right I\ South Prospect B, Lake Namba, South Australia, fig. facilities necessary for the success of our field 3, occlusal view; fig. 8, lateral view, all x2. programmes. Pseudocheirine, NMV P48616, right mandible, found Mr. Frank Coffa took the photographs and one or two centimetres from type specimen of Rae- Mr. Alex Jelowyi did the lettering for the meotherium yatkolai, Lake Pinpa, South Australia, fig. 10, occlusal view, x4. plate, Miss Jeanette Cook drew fig. 1 and Mr Pseudocheirus peregrinus, NMV C13937, left man- Harley Veitch, fig. 2. dible, juvenile, fig. occlusal view of M-,__ , x4. 6, ;! Phascolarctos cinereus, NMV C2660, left mandible, Explanation of Plate 16 fig. occlusal of x2. juvenile, 9, view P8-tW8 , Raemeotherium yatkolai. SAM PI 9764, type, right Abbreviations: med, metaconid; prd, protoconid; mandible, Lake Pinpa, South Australia, fig. 4, lateral psd, protostylid. MKM. NAT, MUS. VICT. 19 PLATE 16 2b ^