Mammalodon colliveri, PRITCHARD, 1939

Fitzgerald, Erich M. G., 2010, The morphology and systematics of Mammalodon colliveri (Cetacea: Mysticeti), a toothed mysticete from the Oligocene of Australia, Zoological Journal of the Linnean Society 158 (2), pp. 367-476 : 374-376

MAMMALODON COLLIVERI PRITCHARD, 1939

‘Mammalodon’ colliveri Hills, 1958: 101 . Mammalodon pritchardi Pledge & Rothausen, 1977:

286. [lapsus calami]

Holotype: NMV P199986 (formerly MUGD 1874), an incomplete skull including the right periotic, stapes and tympanic bulla, right mandible with p2–m 3 in situ, loose left upper or right first lower incisor, right thyrohyoid, manubrium of sternum, axis vertebra, and rib fragments; NMV P17535, left lower cheek tooth (associated with NMV P199986 and certainly representing the same individual). Collected by George Baxter Pritchard, Frederick Stanley Colliver, and Alan Frostick, early January 1932 ( Fig. 3 ). Note that Mahoney & Ride (1975: 160) considered only NMV P199986 the holotype specimen, whereas they referred to NMV P17535 as a syntype, an opinion subsequently followed by Mitchell (1989: 2231). I follow Pritchard’s (1939) original referral of NMV P17535 to the holotype, which has been reiterated in subsequent publications (e.g. Fordyce, 1982a, 1984; Fitzgerald, 2006). The degree of dental wear, fusion of cranial sutures, and fusion of the posterior epiphysis to the axis vertebra, indicates that the holotype specimen of Ma. colliveri represents a mature adult individual.

Referred specimens: NMV P173220, Mammalodon sp. cf. Ma. colliveri , an incomplete left periotic lacking the posterior process; NMV P199587, Mammalodon sp. cf. Ma. colliveri , a partial skeleton including the left tympanic bulla, right mandible with m 2 in situ, seven loose teeth, one cervical vertebra, seven thoracic vertebrae, two lumbar vertebrae, ribs, radius, and left metacarpal II. An associated ulna (NMV P198871) undoubtedly represents the same individual as NMV P199587.

Other specimens: NMV P48794,? Mammalodontidae gen. et sp. indet., an incomplete cranium with the left periotic in situ, and associated thoracic vertebrae and rib fragments; NMV P16417, Mysticeti gen. et sp. indet., an incomplete right mandible consisting of the symphysis and body of the mandible including the alveoli for i1-p3.

Etymology: Mammal from the English mammal and odon from the Greek odontos meaning tooth (hence ‘mammal tooth’), an allusion to the supposed similarity of the cheek teeth of the holotype to the postcanine teeth of terrestrial placental mammals (‘It is in my opinion, a very early type of Tertiary whale, showing the closest approach to descent from a mammalian type of ancestor.’; Pritchard, 1939: 158); the species name colliveri honours Mr Frederick Stanley Colliver who discovered the holotype specimens ( Pritchard, 1939).

Locality, horizon, and age: The holotype specimen of Ma. colliveri was discovered ‘... in the cliff face about 12 feet above the level of the beach... barely a hundred yards around [i.e. south-west of] the Bird Rock [a prominent rock stack] corner...’ ( Pritchard, 1939: 151), Jan Juc Beach, south-west of Torquay in central coastal Victoria, south-east Australia (near 38°20′54″S, 144°18′35″E) ( Fitzgerald, 2004) ( Fig. 4). In his original description, Pritchard (1939: 159) did not explicitly determine the unit from which the holotype specimen was obtained, instead noting that the horizon was ‘Jan Jukian’ and that the age of the rocks was ‘Eocene’. Subsequently, Singleton (1945: 284) reported that NMV P199986 and P17535 were derived from the ‘Lower beds, Bird Rock cliffs’ and ‘... about a foot above the Spring Creek ledge [a prominent hard band] at its extreme S.W. margin (F. S. Colliver, personal communication, 23.10.44) and is thus from within the Glycymeris beds’. According to Singleton (1941: 39) the Glycymeris beds are sandy marls with abundant fossils of the pelecypod Glycymeris ornithopetra . These beds lie immediately below a fine-grained quartz calcarenite hard band laterally correlative with the top of the Bird Rock stack (i.e. the Bird Rock Cap; marker bed ‘E’ of Raggatt & Crespin, 1955) ( Fig. 5 ). The Bird Rock Cap horizon occurs about 1.8 m below the top of the Jan Juc Formation, the latter being conformably overlain by the Lower Miocene Puebla Formation. The matrix associated with NMV P199986 consists of richly fossiliferous grey, sandy, glauconitic marl, consistent with the Jan Juc Formation, but inconsistent with the Puebla Formation, which is sparsely fossiliferous, grey, clayey calcareous silt with sparse glauconite ( Raggatt & Crespin, 1952, 1955; Abele, 1979; Abele et al., 1988; Webb, 1995; Holdgate & Gallagher, 2003). These data confirm that the holotype of Ma. colliveri was collected from within the upper 5 m of the Jan Juc Formation, in a section bounded above by the Bird Rock Cap hard band, and below by the Spring Creek Ledge hard band. This section, which corresponds to Abele’s (1979) unit BR-5, is 2 m below the top, and about 5 m above the base, of the Jan Juc Formation,

sandy marl glauconite representing a thickness of approximately 3.30 m ( Abele, 1979; Webb, 1995; Holdgate & Gallagher, 2003) ( Fig. 5 ).

The geological age of the onshore Jan Juc Formation has, until recently, been quite contentious with age determinations vacillating between Eocene ( Hall & Pritchard, 1896, 1902; Raggatt & Crespin, 1952, 1955), Late Oligocene ( Li, Davies & McGowran, 1999; Holdgate & Gallagher, 2003; McGowran et al., 2004), and Late Oligocene to Early Miocene ( Singleton, 1941; Siesser, 1979; Darragh, 1985; Abele et al., 1988; Boreen & James, 1995; Webb, 1995; Nicolaides & Wallace, 1997). These widely varying estimates of the formation’s age have inevitably been reflected in disparate citations of the geological age of Ma. colliveri: Eocene ( Anonymous, 1939; Pritchard, 1939; Romer, 1966); Early–Late Oligocene ( Hills, 1958; McLeod, Whitmore & Barnes, 1993; McKenna & Bell, 1997); Late Oligocene ( Fordyce, 1982a, 1984, 1985a, b; Fitzgerald, 2004, 2005, 2006); Late Oligocene to Early Miocene ( Fordyce, 1978, 1987, 1991a, 1992, 2006; Fordyce & Barnes, 1994; Barnes et al., 1995; Domning, 1996; Milinkovitch, 1997; Fordyce & Muizon, 2001); and Early Miocene ( Singleton, 1945).

Li et al. (1999) have demonstrated that the Jan Juc Formation– Puebla Formation contact is the local manifestation of the Oligocene–Miocene boundary. They base their conclusion on the first occurrence of the planktonic foraminifer Globoquadrina dehiscens immediately above the Jan Juc Formation– Puebla Formation contact, as well as other locally significant biofacies change evidence ( Li et al., 1999). Globoquadrina dehiscens first occurs in southern Australian sequences at the base of the Early Miocene, indicating planktonic foraminifer zone M1 ( Li et al., 1999; McGowran et al., 2004). This implies that sediments below the Jan Juc Formation– Puebla Formation contact are pre-Miocene in age, and more specifically, that the onshore Jan Juc Formation was deposited during planktonic foraminifer zones P21b–P22 and is thus entirely Chattian in age ( Li et al., 1999; Holdgate & Gallagher, 2003; Gradstein, Ogg & Smith, 2004) ( Fig. 1 ).

This biostratigraphical evidence is corroborated by 87 Sr/ 86 Sr isotope ratios from foraminifer tests in sediments directly above the Jan Juc Formation– Puebla Formation contact, which yielded a date of 23.9 Mya ( Kelly, Webb & Maas, 2001). Dickinson (2002) measured 87 Sr/ 86 Sr ratios from calcitic bioclasts and phosphate intraclasts and concretions from the cliff section near Bird Rock. Her study recovered dates of 23.9 Mya from 10 m up-section (just below the top of the Jan Juc Formation), 25.7 Mya from immediately below the Spring Creek Ledge horizon (about 4 m up-section), and a date of 27.3 Mya from 3 m up-section (dates also cited in Holdgate & Gallagher, 2003). These analyses show that the onshore Jan Juc Formation is entirely Chattian (Late Oligocene) in age, approximately spanning 23.0–28.4 Mya (following Gradstein et al., 2004). The 87 Sr/ 86 Sr dates and their relative heights within the section suggest that Ma. colliveri was collected from a horizon that may have a minimum age of 23.9 Mya and a maximum age of 25.7 Mya ( Fig. 5 ). In this case, Ma. colliveri has a stratigraphical distribution restricted to the late Chattian.

Emended diagnosis of Mammalodon colliveri : Mammalodon colliveri is a mammalodontid mysticete distinguished from J. hunderi by the following autapomorphic characters: rostrum has a bluntly rounded apex; viewed dorsally, the rostrum has a gently convex lateral profile; alveoli for the upper incisors are coalesced; body of the premaxilla is gracile and foreshortened; premaxilla is dorsoventrally flattened; nasal expands in width towards its anterior end; five dorsal infraorbital foramina in facial fossa; ascending process of the maxilla is transversely narrow and linguiform; posterior edge of the ascending process of maxilla lies in transverse line with the posterior edge of the nasal; orbit directed further anteriorly and anterodorsally; anteriormost point on the posterior edge of the supraorbital process of the frontal is laterally positioned; in cross-section, the parietals have a gently convex dorsal profile, with no salient sagittal crest along the midline of the braincase; nuchal crest projects anterodorsally and anterolaterally; alisphenoid forms most of the roof of the pterygoid sinus fossa, with the superior lamina of the pterygoid limited to the anteromedial corner of the sinus fossa; involucrum of the tympanic bulla bears a transverse groove on its dorsal surface, which divides it into a wider posterior part and a narrower anterior one; in dorsal or ventral view the mandible is straight; body of the mandible is relatively gracile; mental foramina relatively large; and three upper and four lower molars present (i.e. polydont lower dentition).

Figures

Figure 1. Geochronology and correlation of key stratigraphical units that have produced fossils of toothed archaic mysticetes, or cetaceans that were formerly considered archaic mysticetes. Note that the vertical range of stratigraphical units represents the current best estimates of geological age maxima and minima, not discrete time-spans of deposition. The geological time scale is after Gradstein et al. (2004). Stratigraphy and geological ages of units from Applegate (1986), Fordyce (1991b, 2003a), Alley et al. (1995), Barnes et al. (1995), Barnes (1998), Prothero et al. (2001), Sanders & Barnes (2002a), Holdgate & Gallagher (2003), Cooper (2004), Fitzgerald (2004), McGowran et al. (2004), Calvano et al. (2008), and Staley & Barnes (2008). Abbreviations: Fmn., Formation; Mbr., member; NE, north-east; NW, north-west; Plankt. Foram., planktonic Foraminifera.

Figure 3. George Baxter Pritchard and Frederick Stanley Colliver (second and third from the left, respectively) in the field at Jan Juc, date unknown, but probably between 1920 and 1940. Note the ladder used to access cliff exposures of the Jan Juc Formation. Unknown photographer. Image from the Museum Victoria archives.

Figure 5. Generalized stratigraphical section at the type locality of Mammalodon colliveri, being a composite section of Bird Rock stack and the cliffs opposite and immediately west-south-west of Bird Rock. 87Sr/86Sr dates from Dickinson (2002) and Holdgate & Gallagher (2003). This section is based on Raggatt & Crespin (1955), Abele (1979), and Holdgate & Gallagher (2003).