Node Calibrated. Divergence between Morelia and Liasis.

Fossil Taxon. Morelia riversleighensis Smith and Plane, 1985 vide Scanlon, 2001.

Specimen. QM F12926, right maxilla (holotype). “AR” is not listed as a formal collection abbreviation, but likely represents field numbers associated with specimens housed in the Queensland Museum.

Additional Materials. AR 13392, partial right mandible; AR 5658, premaxilla; AR 16880, left palatine. Other specimens are listed in Scanlon (2001).

Phylogenetic Justification. The hypodigm of M. riversleighensis is assigned to the genus on the basis of: 1) two teeth per side of the premaxilla; 2) anterior palatine teeth longer, thicker, and more vertical than posterior teeth; 3) deeply concave posterior margin of palatine choanal process; 4) concave anterior margin of premaxilla; 5) ventral openings of premaxilla channels posterior to tooth positions; and 6 maxillary lateral budges present (Scanlon, 2001, p. 6).

Minimum Age. 12.5 Ma.

Soft Maximum Age. Indeterminate.

Age Justification. Morelia riversleighensis was recovered from the Henk’s Hollow Site in System C of the Riversleigh fossil sites (Scanlon, 2001). The minimum age estimate is based on faunal correlation between System C and the Bullock Creek Local Fauna (Travouillon et al., 2006; Travouillon et al., 2009, figure 1).

Discussion. Morelia riversleighensis was originally described as Montypythonoides riversleighensis (Smith and Plane, 1985), but was subsequently synonymized with Morelia by Kluge (1993). Scanlon (2001) provided a detailed description of Miocene pythonine fossils and synonymized Morelia antiqua from the middle Miocene Camfield Beds (Smith and Plane, 1985) with M. riversleighensis.

Other pythonine fossil records have been documented from the Neogene and Quaternary of Africa, Asia, Europe, and Australia (e.g., Portis, 1901; Hoffstetter, 1964; Rage, 1976; Thomas et al., 1982; Smith and Plane, 1985; Rage and Ginsburg, 1997; Ivanov, 2000; Scanlon, 2001; Scanlon and Mackness, 2002; Rage, 2003; Szyndlar and Rage, 2003; Head, 2005; Rage and Bailon, 2005; Head and Bell, 2008; Ivanov and Böhme, 2011). Most records have been assigned to extant genera based on overall similarity of vertebral morphology. Python europaeus was erected using a precloacal vertebra as holotype (Szyndlar and Rage, 2003) on the justification of shared provenance with a partial palatine that had previously been assigned to the genus on the basis of an enclosed maxillary nerve foramen (Ivanov, 2000). An enclosed maxillary nerve foramen is plesiomorphic for pythonines, however (Kluge, 1993), and the character cannot differentiate between Python and other taxa. As a result, there is no other published record that can be unambiguously assigned to a crown genus or species on the basis of discrete apomorphy, despite very likely belonging to extant taxa.

Molecular phylogenetic analyses have resulted in paraphyly of multiple pythonine taxa, including Python and Morelia (Rawlings et al., 2008; Reynolds et al., 2014). As a result, the morphological topology incorporating M. riversleighensis (Scanlon, 2001) cannot be directly compared to molecular hypotheses. The Riversleigh and Camfield records do provide a minimum occurrence for divergence of Liasis relative to the grade of taxa currently and previously included in Morelia (Kluge, 1993; Reynolds et al., 2014). The Liasis - Morelia divergence calibrated here additionally constrains minimum divergence timings of Antaresia, Simalia, Aspidites, and Bothrochilus (Reynolds et al., 2014).