Ganawamaya couperi, Butler & Travouillon & Price & Archer & Hand, 2018

Butler, Kaylene, Travouillon, Kenny J., Price, Gilbert J., Archer, Michael & Hand, Suzanne J., 2018, Revision of Oligo-Miocene kangaroos, Ganawamaya and Nambaroo (Marsupialia: Macropodiformes, Balbaridae), Palaeontologia Electronica (8 A) 21 (1), pp. 1-58 : 18-20

Ganawamaya couperi comb. nov.

Figure 6

v* 1997 Nambaroo couperi ; Cooke, p. 270, figs. 1, 2.

Holotype. QM F30401 , right dentary with p3 and m1–m4 from White Hunter Site , Riversleigh WHA, northwestern Queensland, Australia ( Cooke, 1997b).

Referred specimens. The following specimens are referred based on casts of the original specimens. Ngapakaldi Local Fauna, South Australia: UCMP 57340, left maxilla with P3, M1–M4; UCMP 57337 right M1–M2 and right p3, m1–m3; UCMP 57334, right dentary with p3, m1–m3.

Emended species diagnosis. Ganawamaya couperi comb. nov. differs from all other species of Ganawamaya in having the following combination of features: i1 long and narrow with no ventral flange; a hypoconulid present posterior to the entoconid on the buccal side of the m1; prominent posthypocristid on the m1–m4; marked convexities on the lateral margins of m1–m4; anterior cingulum on M1 is well developed; stylar cusp C is a prominent blade-like convexity buccal to the postparacrista; generally smaller molar size; no additional cuspid on the posterior end of the p3 below the occlusal margin; a poorly developed posterolingual cusp on the P3.

Description

Upper dentition. Description of the upper dentition of Gan. couperi comb. nov. is based on casts of UCMP 57340 ( Figure 6 ) and 57337. In occlusal view, I1 is large, elongate, and laterally compressed. In lateral view, I1 is slightly recurved, with a low but distinct posterobuccal cusp present. The crown of I1 sits much higher than that of I2 and I3. In occlusal view, I2 is oval in shape but much longer than it is wide. The crown is completely flat from wear. I3 is shorter but wider than I2. I3 is distinctly bilobed buccally, with the anterior lobe being larger than the posterior lob. Lingually, the crown has been flattened by wear.

The canines sit directly posterior to the incisors with no intervening diastemata. They are tall and reach a height equal to that of the crowns of I2-3. They are recurved and are slightly laterally inclined. A large diastema separates C1 from P3.

In occlusal view, the occlusal margin of P3 is anterobuccally flexed and is out of alignment with M1. The P3 is blade-like, elliptical in shape, and tapered anteriorly. Six cuspules, each with associated lingual and buccal transcristae, are present along the occlusal margin. The posteriormost lingual and buccal transcristae are well developed as lateral blades, with a poorly developed posterolingual cusp.

The M1 is bilophodont, low crowned and roughly rectangular in outline. The metaloph is narrower than the protoloph. However, both are subequal in height. The paracone is shorter but more massive than the protocone. A short, well-developed preparacrista extends from the paracone to the anterior end of the tooth where it meets a reduced anterior cingulum. The anterior cingulum is bordered lingually by the forelink (remnant of the preprotocrista). No precingulum is present. A shallow concavity is present on the anterior face of the paracone lingual to the preparacrista. The postparacrista extends from the paracone posteriorly towards the interloph valley on UCMP 57340. The postparacrista is less developed on UCMP 57337. A prominent blade-like convexity is evident buccal to the postparacrista which is interpreted as stylar cusp C. The postprotocrista is weakly developed but extends posteriorly to the interloph valley where it forms a midlink. The metacone is taller than the metaconule. A prominent premetacrista extends into the interloph valley where it meets the postparacrista. A well-developed postmetacrista extends posteriorly from the metacone to meet the postmetaconule crista. The neometaconule and postlink are absent.

The M2 is similar in morphology to the M1 except as follows: it is larger; its protocone is taller; a long precingulum borders the anterior flank of the tooth from the forelink to the lingual side of the tooth; the premetacrista is less well developed; the postprotocrista and midlink are reduced on UCMP 57337.

The M3 is similar in morphology to the M2 except as follows: the preparacrista is more buccally situated; the postparacrista, premetacrista, postprotocrista, and midlink are reduced.

The M4 is similar in morphology to M3 except as follows: the metaloph is markedly shorter than the protoloph; the postparacrista is reduced; StC is absent; the postprotocrista and midlink are reduced; the forelink is more lingually situated, equalling the size of the anterior cingulum and precingulum.

Lower dentition. The description of Ganawamaya couperi comb. nov. is as stated by Cooke (1997b) except as follows: the i1, which is preserved in UCMP 57334, is long and narrow and rises to the level of the molar row. A dorsal enamel flange is present but there is no ventral flange.

The protostylid of the m1is tall in UCMP 10600 , a juvenile specimen, and is also present although more worn on the holotype and UCMP 57337 . The portion of the missing protostylid is represented by a flat wear facet on UCMP 57334 , which represents an even older individual.

Remarks. Flannery and Rich (1986) diagnosed species of the genus Nambaroo as exhibiting the following features: well-developed lophs and lophids, m1 with a markedly compressed trigonid, a protostylid, posthypocristid on m1, and absence of a well-developed posterior cingulid on the lower molars. Our study demonstrates, in particular, that the protostylid is present in species of Ganawamaya as well as Nambaroo . Ganawamaya couperi comb. nov. differs from species of Nambaroo in having a rectilinear rather than a third premolar with a plagiaulacoid form, a less developed preprotocrista and a postprotocrista that extends into the interloph valley on M1. These features are present in the specimen previously attributed by Cooke (1997b) to N. couperi ( QMF 30401) and for this reason we contend that Gan. couperi comb.nov. is a species of Ganawamaya rather than Nambaroo . It is currently unclear whether the protostylid is lost due to wear in other species of Nambaroo . Large upper canines are also preserved in UCMP 57340. Although canine alveoli have been described for Nambaroo ( Kear et al. 2007) and Ganawamaya in our study, this specimen is the first to be described in which the canines are preserved.

Age and distribution. The holotype is from White Hunter Site, Riversleigh WHA, northwestern Queensland, Australia. This site is part of Riversleigh’s Depositional Phase 1 and contains species interpreted to represent Faunal Zone A assemblages which have been interpreted to be late Oligocene in age ( Archer et al., 1989, 1997; Myers and Archer 1997; Travouillon et al., 2006, 2011; Arena et al., 2015). The referred specimens are from the Ngapakaldi Quarry of the Etadunna Formation is interpreted to be late Oligocene (24.6 Ma) in age ( Woodburne et al., 1993) .

Figures

FIGURE 6. Cast of lower dentition of Ganawamaya couperi comb. nov. (UCMP 57334) (1-3) and cast of upper dentition of Gan. couperi comb. nov. (UCMP 57340) (4-6) from the Ngapakaldi Local Fauna, South Australia. Right lateral view (1 and 4), left lateral view (2 and 5), and occlusal view (3 and 6). Abbreviations: C, canine, I1, first upper incisor; i1, first lower incisor, M1–M4, upper first to fourth molar; m1–m3, lower first to third molar, P3, upper third premolar; p3, lower third premolar.