taxonID	type	description	language	source
C60787CC4E64FFDF75D386CB3F6BF950.taxon	description	Fossil Taxon. Australophis anilioides Gómez et al., 2008. Specimen. MML-PV 181, precloacal vertebra. Phylogenetic Justification. Assignment to Aniliidae Stejneger, 1907 sensu MacDiarmid et al. (1999) is based on the following apomorphic character combination: low neural arch does not rise much above zygapophyseal plane, neural spine reduced, elongate prezygapophyses that are elongate and high-angled, concave posterior margin of neural arch (Goméz et al., 2008). Minimum Age. 72.1 Ma (Campanian-Maastrichtian boundary). Soft Maximum Age. Indeterminate. Age Justification. The Allen Formation is dated as late Campanian-Early Maastrichtian based on its stratigraphic position overlying the Anacleto Formation and underlying the Jagüel Formation (Gómez et al., 2008). The Anacleto Formation is dated to late Campanian based on magnetostratigraphic correlation to Chron C 33 R (83.5 - 79.5 Ma) (Dingus et al., 2000), whereas the Jagüel Formation is dated as mid-Maastrichtian to early Danian based on foraminiferal biostratigraphy (Leanza et al., 2004; Goméz et al., 2008). The horizon within the Allen Formation that produced Australophis specimens is measured at 48 meters below the K- Pg boundary and is considered no younger than early Maastrichtian (Goméz et al., 2008). The exact minimum age provided is for the Campanian- Maastrichtian boundary, which is likely to be slightly older than the actual age of the type specimen of Australophis.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E64FFDF75D386CB3F6BF950.taxon	discussion	Discussion. Molecular phylogenetic analyses consistently recover monophyly of Anilius with Tropidophiinae as the sister taxon to all other alethinophidians (e. g., Wilcox et al., 2002; Gower et al., 2005; Pyron et al., 2013), despite morphological support for tropidophiines being deeply nested macrostomatans and Anilius being nested within a monophyletic Anilioidea as sister taxon to South Asian Cylindrophis, Anomochilus, and Uropeltinae (e. g., Lee and Scanlon, 2002; Wilson et al., 2010; Gauthier et al., 2012). If future molecular studies corroborate morphological phylogenetic hypotheses then Australophis represents the oldest occurrence of crown group Anilioidea. The fossil record of aniliids includes specimens from the Late Cretaceous through Cenozoic of South America and the Paleogene of North America (e. g., Hecht, 1959; Hoffstetter and Rage, 1977; Hecht and LaDuke, 1997; Rage, 1998; Head et al., 2006; Hsiou et al., 2010). Among named taxa, Australophis was considered morphologically most similar to extant Anilius and Paleogene Hoffstetterella from Brazil (Goméz et al., 2008), however, the taxon shares a thickened zygosphene with Colombophis from the Miocene of Colombia and Venezuela (Hoffstetter and Rage, 1977; Head et al., 2006; Hsiou et al., 2010). No explicit phylogenetic topology yet exists for Australophis relative to other aniliids. Constraining the first occurrence of Tropidophiidae is especially problematic because the composition of the clade is controversial in addition to the aforementioned discrepancies between molecular and morphological phylogenetic hypotheses of the taxon within Alethinophidia. Fossil taxa have been assigned to Tropidophiidae based on size and general shape (e. g., Dunnophis Hecht, 1959; Falseryx Szyndlar and Rage, 2003). Attempts to devise morphological diagnoses for recognizing fossils have been based on an explicit use of a monophyletic Tropidophiidae consisting of extant (( Tropidophis + Trachyboa) + Ungaliophiinae), following McDowell (1987). Both Molecular and morphological phylogenies have proposed paraphyly of this clade (e. g., Wilcox et al., 2002; Scanlon, 2006), however, and only a single distinct vertebral apomorphy, the presence of anteroposteriorly elongate, squared off ventral hypapophyses in precloacal vertebrae, occurs in Tropidophiidae = (Tropidophis + Trachyboa). The oldest record of the clade based on this character is Szyndlaria aureomontensis from the middle Eocene of Lissieu, France (Augé and Rage, 2010). Lissieu is considered to correspond to the late Lutetian stage (Augé and Rage, 2010), which is no younger than 41.2 Ma (Vandenberghe et al., 2012). The late Lutetian is here used as the minimum first occurrence of crown Tropidophiidae (Figure 1).	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E67FFDD705086C43829FF70.taxon	description	Fossil Taxon. Corallus priscus Rage, 2001. Specimen. DGM 1332 - R precloacal vertebra (holotype). Additional Materials. 74 precloacal vertebrae. Phylogenetic Justification. Corallus priscus was assigned to the genus Corallus by Rage (2001) on the basis of: horizontal zygapophyseal articular facets, vaulted neural arch, and a tall neural spine. Additionally, C. priscus shares small, irregularly occurring paracotylar foramina with extant species of the genus. The combination of neural spine height and anteroposterior width, bi-angled interzygapophyseal ridges, and zygosphene shape make specimens of C. priscus indistinguishable from extant Corallus. Minimum Age. 50.2 Ma. Soft Maximum Age. ~ 64 Ma (Woodburne et al., 2014). Age Justification. Corallus priscus was recovered from fissure fills in travertine deposits at the locality of São José de Itaboraí in Rio de Janeiro, Brazil. The travertine layers are unconformably overlain by a basalt flow dated at 52.6 ± 2.4 Ma (Riccomini and Rodrigues-Francisco, 1992; Gomes Sant’Anna and Riccomini, 2001; Woodburne et al., 2014), which provides a hard minimum age for the taxon. The soft maximum age is the same as for Titanoboa.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E67FFDD705086C43829FF70.taxon	discussion	Discussion. The fossil record of Corallus from Itaboraí represents the oldest record of an extant boid genus, and constrains the divergence of Neotropical Boinae to no younger than approximately 50 Ma. Molecular phylogenetic analyses place Boa constrictor as the sister taxon to Corallus + Chilabothrus + (Eunectes + Epicrates) (Burbrink, 2005; Pyron et al., 2013; Reynolds et al., 2013, 2014). The first occurrence of Boa (Figure 1) and molecular topologies thus implies an approximately 19 Ma unrecovered history of the genus between the maximum age of the Barrancan SALMA and the hard minimum age for Corallus (Head et al., 2012), assuming Titanoboa is a stem boine.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E66FFD2705A86AA3B4EFECD.taxon	description	Fossil Taxon. Calamagras weigeli. Specimen. PTRM 19607, caudal vertebra. Additional Materials. 19609, 19681, caudal vertebrae. Phylogenetic Justification. Caudal vertebrae lacking paired haemapophyses, haemal keels present. This morphology is only present in Ungaliophis and Exiliboa among extant taxa (Smith, 2013). Minimum Age. 35.2 Ma. Soft Maximum Age. Indeterminate. Age Justification. Minimum age is based on faunal correlation of Medicine Pole Hills fossil localities (Bowman County, North Dakota) with Flagstaff Rim localities (Natrona County, Wyoming), which are overlain by an ash layer (Ash B) that is 40 Ar / 39 Ar dated at 35.41 ± 0.14 Ma (Obradovich et al., 1995). Smith (2011) recalculated the minimum estimate for the Medicine Pole Hills local fauna at 35.2 Ma.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E66FFD2705A86AA3B4EFECD.taxon	discussion	Discussion. Numerous fossil taxa have been described as ungaliophiines, either explicitly as related to (Ungaliophis + Exiliboa) (e. g., Rage, 2008), or as part of a “ Tropidophiidae ” (Szyndlar et al., 2008) that is not supported by either morphological (Zaher, 1994) or molecular data (e. g., Wilcox et al., 2002). As noted by Smith (2013), the only fossil record that is united with (Ungaliophis + Exiliboa) on the basis of discrete apomorphies consists of isolated cloacal vertebrae assigned to Calamagras. Generic assignment of isolated vertebrae to Calamagras is problematic in that the generic and specific diagnoses for the taxon are do not include unique apomorphies or character combinations relative to other coeval, fossils, and are redundant with each other as described (Holman, 2000). Referral to Calamagras is tentatively followed here, but until the taxonomy and systematics of the genus can be unambiguously resolved, the record described in Smith (2013) must be used as the minimum divergence timing for the total clade, and stratigraphically older records of the genus (e. g., Hecht, 1959; Rage, 1977; Danilov and Averianov, 1999) should not be cited. Usage of Charinidae follows Pyron et al. (2014).	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E66FFDD75D9860A3E9AFE10.taxon	description	Fossil Taxon. Eunectes stirtoni Hoffstetter and Rage, 1977. Specimen. MNHN, VIV 7, right prootic. Phylogenetic Justification. Eunectes stirtoni was erected and united with Eunectes within Boinae on the basis of diagnostic morphology including a shortened posterior margin behind the posterior trigeminal nerve foramen; an incomplete anterior trigeminal nerve foramen, a prominent, long “ prootic process ” (Tchernov et al., 2000) that forms the lateral edge of a narrow, well defined canal for the Vidian nerve (Hoffstetter and Rage, 1977). Minimum Age. 12.375 Ma. Soft Maximum Age. Indeterminate. Age Justification. The type specimen of E. stirtoni was recovered from the Fish Bed of the Baraya member of the lower Villavieja Formation in the upper Magdalena River valley in central Colombia (Hoffstetter and Rage, 1977). 40 Ar / 39 Ar dating of pumices from the underlying Monkey Beds and overlying San Francisco St. Beds of the Cerro Colorado Member of the Villavieja Formation constrains the ages of the Fish Bed to between 12.649 ± 0.258 and 12.111 ± 0.259 Ma (Flynn et al., 1997). The Fish Bed directly overlies the Monkey Beds, and the minimum age estimate for the Monkey Beds, 12.486 ± 0.111 Ma (Flynn et al., 1997), is used here as the minimum estimate for the Eunectes - Epicrates divergence.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E66FFDD75D9860A3E9AFE10.taxon	discussion	Discussion. Morphology of the prootic and an associated basisphenoid referred to Eunectes stirtoni are very similar in general shape and discrete characters to extant E. murinus (Hoffstetter and Rage, 1977). Other fossils referred to Eunectes have been recovered from the middlelate Miocene of periequatoral South America, including La Venta in Colombia (Hoffstetter and Rage, 1977; Hecht and LaDuke, 1997), Venezuela (Head et al., 2006; Hsiou and Albino, 2010), and Brazil (Hsiou and Albino, 2009, 2010). These records consist of isolated or associated precloacal vertebrae, and referral to genus is based on overall similarity instead of discrete apomorphies. The Villavieja Formation record of Eunectes provides a minimum divergence timing for both (Eunectes + Epicrates) and (Chilabothrus + (Epicrates + Eunectes )) (Reynolds et al., 2013). If E. stirtoni is most closely related to E. murinus, then the record described here minimally constrains divergence timings within the genus. Neogene fossil vertebrae have been compared with Epicrates (Hsiou and Albino, 2010), but this record cannot differentiate between that taxon and the newly recognized Chilabothrus, (Reynolds et al., 2013) and is not considered for calibration.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E69FFD3706B86E43B14FEB0.taxon	description	Fossil Taxon. “ Ogmophis ” compactus. Specimen. PTRM 19378, left quadrate. Phylogenetic Justification. PTRM 19378 is united with Loxocemidae on the basis of: 1) dorsal head expanded into broad plate; 2) dorsal head lies wholly in saggital plane; 3) well-defined lip present on lateral side of dorsal margin (Smith, 2013). Minimum Age. 35.2 Ma. Soft Maximum Age. Indeterminate. Age Justification. Justification follows the rationale for Charinidae above.	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E69FFD3706B86E43B14FEB0.taxon	discussion	Discussion. Morphological phylogenetic analyses of snakes have traditionally recovered either monophyly of (Loxocemus + Xenopeltis) as the sister-taxon to all other macrostomatans (e. g., Lee and Scanlon, 2002; Scanlon, 2006), or as a paraphyletic grade at the base of Macrostomata (Tchernov et al., 2000). Molecular phylogenetic analyses recover Loxocemus as the sister taxon of Pythonidae (e. g., Slowinski and Lawson, 2002; Pyron et al., 2013). Based on molecular topologies, PTRM 19378 constrains (Loxocemidae + Pythonidae) to no younger than late Paleogene. Smith (2013) associated isolated cranial elements including PTRM 19378 with vertebrae assigned to the vertebral form genus Ogmophis based primarily on relative abundances of elements collected by dry-screening and surface collection from a single locality, PTRM V 89002 (Smith, 2013). As with Calamagras (see above), the diagnosis (Holman, 2000) used to assign specimens to Ogmophis compactus by Smith (2013) is problematic because it does not include any individual apomorphies or a unique character combination for either the genus or species, following descriptions of other taxa in Holman (2000). Thus, while the generic assignment of Smith (2013) is tentatively accepted for the purposes of identifying PTRM 19378 in snake phylogeny (Figure 1), the taxonomic and systematic ambiguity of “ Ogmophis ”, requires restricting the first occurrence of Loxocemidae to cranial remains described in Smith (2013), and not to stratigraphically older published records of the genus (Holman, 2000).	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E68FFD375D5864A3FFAFBD0.taxon	description	Fossil Taxon. Morelia riversleighensis Smith and Plane, 1985 vide Scanlon, 2001. Specimen. QM F 12926, 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).	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
C60787CC4E68FFD375D5864A3FFAFBD0.taxon	discussion	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).	en	Head, JJ (2015): Fossil calibration dates for molecular phylogenetic analysis of snakes 1: Serpentes, Alethinophidia, Boidae, Pythonidae. Palaeontologia Electronica 18: 1-17, DOI: 10.26879/487, URL: http://dx.doi.org/10.26879/487
