Ganawamaya aediculis Cooke, 1992

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 : 13-17

Ganawamaya aediculis Cooke, 1992

Figure 4

Holotype. QM F16843 , right dentary with p3, m1– m4 from White Hunter Site , Riversleigh WHA, northwestern Queensland, Australia ( Cooke, 1992).

Referred specimens. Gillespie's Gully Site: QM F30076, right dentary with i1, p3, m1–m4. LSO Site: QM F58658, right maxilla with P3, M1–M4; QM F30298, right dentary with p3, m1–m4; QM F31463, left dentary with p3. White Hunter Site: QM F58660, left dentary with p3, m1–m4; QM F58661, isolated m2–m3; QM F58662, isolated p3; QM F19584, left dentary with p3, m1, m 3 in crypt; QM F19605, right dentary with m4; QM F19876, left dentary with m2–m4; QM F19878, left dentary with dp3, unerupted p3, m1; QM F19993, right dentary with m3, broken m4; QM F19994, left dentary with m 3 in crypt; QM F20146, right isolated broken m2, m3; QM F20633, Left maxilla with m2–m4; QM F23354, left maxilla with M1–M2, broken M3; QM F31182, left dentary with p3, m1–m3, broken m4; QM F57791, left maxilla with P3, M1–M2.

Emended species diagnosis. Ganawamaya aediculis differs from all other species of Ganawamaya in having the following unique combination of features: long and sinuous i1 with dorsal and ventral flanges; additional cuspid on posterior end of p3 below the occlusal margin; linear occlusal edge on p3; inclined ridge from the anteriormost cuspid on p3; prominent hypocristid on m1 and m2; reduced paraconid on m1; no hypoconulid; no marked convexities on the lateral margins of the interloph valley of the lower molars; m1 anterior cingulid not extending from paracristid right across to buccal surface of the tooth; poorly developed anterior cingulum of M1; poorly developed anterior cingulum on M1; stylar cusp C on M1 reduced and connected to the postparacrista.

Description

Description follows Cooke (1992) but we note the following additional features.

Premaxilla. In lateral view, the maxillary-premaxillary suture extends ventrally to the posterior margin of the canine alveolus.

Maxilla and palatine. The infraorbital canal is tube-like and positioned at the anterior extremity of the suborbital shelf. The sphenopalatine foramen is oval in shape, anteriorly positioned on the palatine, posterior to the infraorbital canal.

Upper dentition. Description of the upper dentition of Gan. aediculis is based on QM F58658 and 20633. In ventral view ( Figure 4 ) the canine alveolus is larger than each of the three incisor alveoli. The I1 is preserved, lightly recurved and anteroventrally directed. The size of the incisor alveoli may indicate that I2 is the largest incisor, followed by I1 and then I3. The left and right I1 alveoli are separated by a wide diastema. In occlusal view, I1 is long, elongate and laterally compressed. I1 is slightly recurved in lateral view. No I2, I3 or C1 are preserved, however their presence is indicated by alveoli.

The P3 is flexed anterobuccally such that is not in line with the molar row. The tooth is roughly rectangular in occlusal outline but is tapered anteriorly. Five cuspules are visible with the posteriormost cusp being the largest. Each cuspule has an associated transcrista. A prominent posterior lingual cuspule is present from which a well-developed lingual cingulum extends. In lateral view, the occlusal margin of the P3 is slightly concave.

In occlusal view, the M1 is roughly rectangular in outline. The protoloph and metaloph are roughly equal in height, however, the metaloph is narrower than the protoloph. The paracone is shorter but more massive than the protocone. A short, well-developed preparacrista extends from the paracone connecting to a well-developed anterior cingulum at the anterior end of the tooth. The anterior cingulum is bordered lingually by a faint forelink, representing a remnant preprotocrista. No precingulum is present. On the face of the paracone and lingual to the preprotocrista, a shallow concavity is present. The postparacrista is prominent and extends towards the interloph valley from the paracone. The postparacrista on M1 extends posteriorly to meet a small but distinct cusp. This cusp is interpreted to represent stylar cusp C in N. gillespieae by Kear et al. (2007). A poorly developed postprotocrista extends posteriorly to the interloph valley where it forms a midlink. The metacone is slightly taller than the metaconule. A premetacrista extends anteriorly to meet the postparacrista in the interloph valley. A prominent postmetacrista extends from the metacone to meet the postmetaconule crista. Both the neometaconule and postlink are absent.

The M2 is similar in morphology to M1 except as follows: it is slightly larger; the preparacrista is more buccally positioned; the anterior cingulum is wider; a precingulum is present lingual to the very faint forelink and borders the anterolingual margin of the tooth; the postparacrista is straighter anteriorly but meets the premetacrista more lingually in the interloph valley; the premetacrista is less developed; StC is present as a distinct cusp on the postparacrista only on QM F20633 where it is, however, poorly defined.

The M3 is similar in morphology to the M2 except as follows: StC is absent; the premetacrista, postprotocrista, and midlink are reduced.

The M4 is similar in morphology to the M3 except as follows: the metaloph is markedly narrower than the protoloph; the postparacrista and premetacrista are reduced; the forelink is more lingually situated.

Lower dentition. The description in Cooke (1992) is sufficient except for as follows: The protostylid on the m1 is present on unworn adult specimens e.g., QM F31181; and there are five cuspids on p3. Remarks. Cooke 1992 described the holotype of Gan. aediculis ( QM F16843) as having six cuspids on p3 with five associated transcristids. However, upon further inspection we clarify that like in other Ganawamaya species, only five cuspids and four transcristids appear to be present on the occlusal surface ( Figure 5 ). However, an additional in Gan. aediculis , previously interpreted a sixth cuspid at the posterior of the p3 on the holotype, is present below the occlusal margin. The presence of a posterior cuspid on the p3 bellow the occlusal margin may be a distinguishing feature of Gan. aediculis ( Figure 5 ). We propose that all Ganamwaya have five cuspids along the occlusal row of the p3 while Gan. aediculis has an additional posterior cuspid below the occlusal row. On a number of specimens attributed here to Gan. aediculis , the presence of this cuspid cannot be confirmed as the posterior end of the p3 has been obscured and worn by a slightly overlapping m1, making it difficult to determine whether this additional cusp is diagnostic of all Gan. aediculis . All specimens referable to species of Ganawamaya (and some previously referred to Nambaroo ) from Faunal Zone A, also exhibit variation in apparent cuspid morphology that can be attributed to differences in inter-proximal dental wear similar to that of specimens reassigned to Gan. acris . These variations include the presence, or apparent absence, of the protostylid on m1, the shape of the paracristid on m1 and the complexity of enamel ridges on i1. However, specimens from Faunal Zone A assemblages differ from those in Faunal Zone B in having a better defined posthypocristid on m1 and m2. Specimens previously attributed to ‘N. sp. 8’ ( Cooke, 1996, 1997a) are referred here to Gan. aediculis because they lack features that would warrant separation as a distinct taxon.

Age and distribution. The holotype of Gan. aediculis is from White Hunter Site, Riversleigh WHA, northwestern Queensland. The White Hunter Site is interpreted to be part of Faunal Zone A, which is 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). Several other referred specimens are also from sites considered to belong to Faunal Zone A: Gillespie's Gully and LSO Site ( Travouillon et al., 2006, 2011).

Figures

FIGURE 4. Ganawamaya aediculis partial cranium (QM F58658) in ventral view (1) and left lateral view (2). Abbreviations: I1, first upper incisor; ioc, infraorbital canal; iof, infraorbital foramen; M1–M4, upper first to fourth molar; mx, maxilla; P3, upper third premolar; pmx, premaxilla.

FIGURE 5. Lower third premolar of Ganawamaya aediculis holotype (QM F16843) in buccal view (1) and lingual view (2). Black arrows indicate each cuspid along the occlusal surface of the p3. Grey arrows indicate the additional sixth cuspid present below the occlusal margin.