Tursiops sp. Gervais, 1855

Fitzgerald, Erich M. G., 2005, Pliocene marine mammals from the Whalers Bluff Formation of Portland, Victoria, Australia, Memoirs of Museum Victoria 62 (1), pp. 67-89 : 75-78

cf. Tursiops sp. Gervais, 1855 sp.

Referred specimen. NMV P218266, virtually complete right periotic ( Fig. 6 ).

Description. P218266 is typically delphinid in possessing: (1) posterior process of the periotic projects laterally and posterolaterally; (2) longitudinal grooves on the articular facet of the posterior process of the tympanic (this feature also occurs in Monodontidae ); (3) relatively low crista transversa; (4) internal facial foramen opens at the same level as the tractus spiralis foraminosus in the internal acoustic meatus; (5) a short, blunt, rectangular anterior process of the periotic which in anterior, dorsal and ventral views appears laterally compressed; (6) a large fovea epitubaria for the accessory ossicle eliminates the anterior bullar facet on the anterior process; (7) prominent parabullary ridge; (8) inflated pars cochlearis; and (9) relatively shallow internal acoustic meatus ( Kasuya, 1973; Fordyce et al., 2002). The first character is usually only seen in Delphinidae but several taxa in the extinct delphinoid grade-taxon Kentriodontidae possess a posterolaterally projecting posterior process of the periotic (eg., Barnes and Mitchell, 1984; Dawson, 1996) as does Albireo whistleri ( Albireonidae ) (Barnes, 1984). P218266 and the other odontocete periotics described below possess all of the characters listed above, justifying their assignment to Delphinidae . Table 3 presents comparative measurements of selected dimensions for all delphinid periotics described herein.

Discussion. Within Delphinidae , P218266 is most similar to Tursiops and Lissodelphis . P218266 is similar to the periotics of Tursiops in: (1) its overall size; (2) having the aperture of the internal acoustic meatus opening at the same level as the endocranial surface of the body of the periotic; (3) having a deep internal facial foramen; and (4) having an aquaeductus vestibuli located at the same level as the foramen for the vestibular branch of the vestibulocochlear nerve. P218266 differs from Tursiops in: (1) the possession of a more acute angle between the anterior process and pars cochlearis; (2) having an aquaeductus cochleae positioned further from the fenestra cochleae, and further dorsally on the endocranial side of the pars cochlearis; (3) having a lower crista transversa; (4) having a poorly developed septum between the tractus spiralis foraminosus and the foramen for the vestibular branch of the vestibulocochlear nerve; and (5) having a less rounded pars cochlearis.

P218266 shares with the periotic of Lissodelphis : (1) endocranial surface of the periotic bordering the posterior margin of the internal acoustic meatus, aperture of aquaeductus vestibuli, and aquaeductus cochleae, is uniformly flat; and (2) aperture of the aquaeductus cochleae opens on the same plane as the aperture of the internal acoustic meatus (note that this condition is also seen in Steno ). P218266 differs from the periotic of Lissodelphis by: (1) being markedly larger in overall size; and (2) having a mediolaterally broader aperture of the internal acoustic meatus.

The balance of features noted above indicates that P218266 is a delphinid with close affinities to Tursiops . This periotic is not identified as undoubtedly as such due to the subtle differences between P218266 and the periotic of extant Tursiops spp. Barnes (1990) provided a thorough review of the fossil record of Tursiops . He recognised four fossil species of Tursiops : T. cortesii Sacco, 1891 ( Italy; Late Pliocene, c. 1.75–3.5 Ma, and possibly Early Pliocene, c. 5 Ma); T. astensis Sacco, 1891 ( Italy; early Late Pliocene, c. 3-3.5 Ma); T. capellinii del Prato, 1898 ( Italy; middle Pliocene, c. 3.5 Ma); T. ossenae Simonelli, 1911 ( Italy; middle Pleistocene or late Pleistocene, c. 0.5–0.8 Ma). Other unnamed pre-Pleistocene records of Tursiops include: aff. Tursiops from the Purisima Formation, California (Late Pliocene, 1.8–3 Ma) ( Barnes, 1977); and Tursiops sp. from the Yorktown Formation, North Carolina (Early Pliocene, 3.5–4.5 Ma) ( Whitmore, 1994).

The record from the Pliocene of Victoria is the first probable pre-Pleistocene fossil record of Tursiops from the Southwest Pacific. Furthermore, this fossil occurrence provides corroboration for Barnes’ (1990: 18) hypothesis that Tursiops has been as geographically widespread during the last six million years as it is at the present time.

Figures

Figure 6. cf. Tursiops sp. (Pliocene Whalers Bluff Formation, Portland, Victoria, Australia), right periotic, NMV P218266 (AC). A, ventral view. B, cranial view. C, medial view. D, lateral view. Scale bar equals 10 mm.