A SPECIALISED THYLACINID, THYLACINUS MACKNESSI; (MARSUPIALIA: THYLACINIDAE) FROM MIOCENE DEPOSITS OF RIVERSLEIGH, NORTHWESTERN QUEENSLAND JEANElTE MUIRHEAD M uirhead, J ., 1992. A specialised thylacinid, Thylacinus macknessi, (Marsupialia: Thylacinidae) from Miocene deposits of Riversleigh, northwestern Queensland. Australian Mammalogy 15: 67-76. Thylacinus macknessi is described from Miocene sediments of Riversleigh, northwestern Queensland. Comparisons with other thylacinids and dasyurids reveal it to be a new species of Thy/acinus. In most features it is as specialised as T. cynocepha/us and it is not considered to be ancestral to any other taxon. The presence of such a specialised thylacine in the Riversleigh deposits argues for a pre-Late Oligocene divergence of this group from the Dasyuridae. Key words: Thylacine, 1h)'lacinus macknessi, Thylacinidae, Riversleigh, Tertiary, Queensland, Marsupialia. I. Muirhead. Schoo/ of Bi%gica/ Sciences, University of New South Wa/es, PO Box I Kensington New South Wales 2033. Manuscript received /4 September 1991. THE Thylacinidae is a small family consisting of a abbreviations used are: QMF, Queensland Museum recently extinct form Thy/acinus cynocepha/us Harris, palaeontological collection; AR, temporary catalogue and two Tertiary taxa. Although thylacinid premolars number in School of Biological Science, U niversity of have been recovered from the Miocene Wipajiri New South Wales. Measurements of tooth dimensions Formation of South Australia and the late Pliocene of 7: macknessi are presented in Table I. The regions Otibanda Formation of New Guinea (Campbell 1976, measured are presented in Fig. 1. Plane 1976,Archer 1982),only two distinct thylacinids have been described from the fossil record: the late Miocene Thy/acinus potens from the Alcoota Local SYSTEMATICS Fauna (Woodbume 1967) and the late Oligocene to middle Miocene Nimbacinus dicksoni from the Henk's Thylacinidae Bonaparte, 1838 Hollow Local Fauna, the Riversleigh Local Fauna Thylacinus Temminck, 1827 and the Bullock Creek Local Fauna (Muirhead and Thylacinus macknessi n. sp. Archer 1990). Thy/acinus potens is larger than T. HOLOTYPE cynocepha/us and slightly less specialised. It was considered by Archer ( 1982) to represent a sister QMFI6848a (formerly ARI6491), right dentary taxon to the modem form. Nimbacinus dicksoni is a portion with broken M3, complete M4 and M5. smail and very plesiomorphic thylacinid, evidently not far removed from the group's dasyuroid origins REFERREDSPECIMENS and a possible ancestor to Thy/acinus. Material QMFI6848b(formerlypartof ARI6491), right canine described here as Thy/acinus macknessi is of com- closely associated but not attached to holotype, parable age to the plesiomorphic Nimbacinus dicksoni but, in contrast, represents a specialised thylacine QMFI6849formerly (ARI1046) isolated left M4, and QMFI6850 formerly (AR4794), isolated right M2. whose closest relative appears to be the modem Thy/acinus cynocepha/us. TYPE LOCALITY, LocAL FAUNA AND AGE Dental and taxonomic nomenclature follows that QMFI6848 Neville's Garden Local Fauna, Neville's of Muirhead and Archer (1990). Dental terminology Garden Site, Riversleigh Station, northwestern is also presented in Fig. I. Catalogue number Queensland; early t{) middle Miocene. QMFI6849, 68 AUSTRALIAN MAMMALOGY Fig. J. Diagram showing terminology of morphology on an upper and lower molar of 7: macknessi. Regions used for measurements in Table I are also presented using the measurement for two teeth as examples taken from Table I. A = QMFI6850. B = QMFI6849. Arrow indicates anterior of molar. Star indicates region of lost metaconid. Abbreviations: a.c., anterior cingulum; co, cristid obliqua; end, entoconid; hyd, hypoconid; hyld, hypoconulid; mc, metaconid; mcl, metaconule; med, metac paracone; pacd, paracristid; pad, paraconid; p.c., posterior cingulum; phd, posthypocristid; pmc, postmetacrista; ppc, preparacrista; prd, protoconid. MUIRHEAD: THYLACINUS MACKNESSI FROM MIOCENE DEPOSITS IN QUEENSLAND 69 LOWER MOLARS MJ M4 M5 QMF number 16848 16848 16849 16848 Tooth length 9.10 9.00 8.75 Tooth width 4.38 4.92 4.30 4.66 Proto-hypo 5.08 5.49 6.02 Hypo-hypoconulid 2.09 2.27 2.25 1.01 Hypoconulid-ento 1.10 0.85 0.95 Proto-para 3.72 3.75 4.17 Proto-para (horizontally) 4.87 5.25 5.04 UPPER MOLARS M2 QMF number 16850 Anterior 5.50 Tooth length 6.55 Posterolingual dimension 6.65 Para-meta 2.70 Meta-proto 4.35 Proto-para 2.50 Table I. Tooth measurements of Thylacinus macknessi in mm. All measurements are actual distance between cusps except 'Proto-para (horizontally)' in which measurements are taken from a horizontal plane above these cusps. Mike's Menagery Local Fauna, Mike's Menagerie DESCRIPTION Site, Godthelp Hill, Riversleigh Station, northwestern The dentary is preserved posteriorly from the region Queensland. QMFl6850 Dwornamor Local Fauna, of the M3. The coronoid process departs from the Gag Site, Gag Plateau, Riversleigh Station, north- ramus at approximately 120°. The anterior margin of western Queensland. Neville's Garden Site and Mike's the coronoid process is very straight. The articular Menagerie Site are part of System B of the Riversleigh condyle and angular process are absent. The articular Sequence and are estimated to be approximately condylar appears to have departed from the remaining Early to Middle Miocene in age (Archer, Godthelp, bone at a level no higher than the ramus. The inferior Hand and Megirian, 1989).Gag Site is part of System dental foramen is low lying and directly below the C estimated at Middle to early? Late Miocene (Archer highest dorsal point of the coronoid process. et al 1989). Precise locality details have been lodged with the Queensland Museum. Lower canine represented by Q MF 16848b(Fig. 2). Crown broken at tip. Root laterally compressed and SPECIFICNAME striated. Crown thick at base. Thegosed facet on Named in honour of Brian Mackness in recognition anterior surface (sensu Every 1975). M3 represented of his support for, and long term involvement in by QMFI6848a (Fig. 2). Crown broken anteriorly at Australian vertebrate palaeontology . protoconid. Hypoconid tallest cusp on talonid follow- ed in decreasingheight byentoconid and hypoconulid. Well developed posterior cingulum extends from DIAGNOSIS hypoconulid to posterobuccal comer of crown. Cristid Differs from all other species of Thy/acinus in the obliqua orientated almost perpendicular to antero- following combination of features: I, distinct entoco- posterior dimension of tooth. Both entoconid and nid; 2, vestigial metaconid; 3, long cristid obliqua hypoconulid high and distinct. M4 is represented by orientated centrally on the crown and parallel to the QMF 16849a (Figs 3A, 3B) and QMFI6848 (Figs long axis of the dentary; 4, no stylar shelf; 5, well- I B, 2). Protoconid largest cusp followed in decreasing developed and unnotched anterior cingulum that is height by paraconid, hypoconid, entoconid and continuous with the preparacrista; 6, centrocfista hypoconulid. Vestigial metaconid represented by .(postparacrista plus premetacrista) straight; 7, small slight thickening of enamel in position usually metaconule but no paraconule; 8, relatively unreduced occupied by metaconid on dasyurids and in the paracone; and 9, M5 antero-posteriorly shorter in plesiomorphic Nimbacinus. Anterior cingulum length than preceding molar. continues to anterobuccal base of protoconid. In 70 AUSTRALIAN MAMMALOGY Fig. 2. ThylacinusmacknessiholotypeQMFI6848a. Bar= I cm. A, occlusal view stereo pair, anterior at top. B, lingual view, anterior to left. occlusal view the protocristid is the longest crest. It is retained St E). Although postmetacrista broken, 'V'-shaped and almost vertical in the valley between posteriorly it appears to have been the longest crest on the paraconid and protoconid. Cristid obliqua slightly crown, followed (in decreasing order) by prepara- shorter, terminating on flank of protoconid. Remain- crista, postprotocrista, preprotocrista, premetacrista, ing crests (in decreasing length): metacristid, post- postparacrista. Preprotocrista connects with anterior hypocristid, pre-entocristid. Metacristid terminates at cingulum and extends continually up anterior face of vestigial metaconid. M5 represented by QMFI6848a crown. Angle formed at junction of crestsat protocone (Fig. 2). Morphology follows that of M4 except as approximately 90°. Postparacrista and premetacrista follows. Talonid reduced in size by lingual shift in connect in straight line as centrocrista and forms hypoconid and reduction of height, loss of entoconid sharp valley between cusps. Postmetacrista departs and reduction in posterior cingulum. from metacone almost parallel to premetacrista and then bends. Preparacrista forms sharper angle with M2 represented by QMFI6850 (Figs IA, 3C, 3D). postparacrista. Anterior width of crown lessthan buccal length which is less than posterior width. Major cusps present (in COMPARISON decreasing height): metacone, paracone, protocone. Minuscule metaconule present. No cusps or crests Thy/acinus macknessi is a very specialised thylacinid present on stylar shelf which is represented by steep sharing many derived features with Tocynocephalus. regular slope to buccal flank of crown. Posterobuccal It is in some respects more plesiomorphic than To region of crown missing (mayor may not have cynocepha/us and, in most features, far more special- 70 AUSTRALIAN MAMMALOGY Fig. 2. 1hylacinusmacknessiholotypeQMFI6848a. Bar= 1 cm. A, occlusal view stereo pair, anterior at top. B,