Kogiidae Gill, 1871

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 : 74

Family Kogiidae Gill, 1871

Genus and species indeterminate

Referred specimen. NMV P218407, incomplete left tympanic bulla ( Fig. 4 A-B).

Description. The most striking aspect of the morphology of P218407 is its small size. The tympanic is polished with rolled edges being rounded off. The preserved portion includes only the medial half of the bulla with very little of the outer lip present. The base of the posterior process of the tympanic has been worn off. In dorsal and ventral view, there is a distinct furrow in the medial edge of the involucrum between the inner posterior prominence and the inner anterior prominence. In ventral view, the furrow between the prominences of the involucrum forms an obtuse angle. There is no preserved ventral keel and the median furrow is very shallow such that it is poorly differentiated from the surrounding ventral surface of the tympanic. The interprominential notch is relatively broad. The anterior edge of the involucrum and outer lip is squared-off. In dorsal view, the involucrum has a consistent width along its length, but is expanded at the level of the inner posterior prominence.

Discussion. P218407 is referred to the Kogiidae on the basis of the following features shared with extant and fossil kogiids: (1) small overall size [as Kasuya (1973: 25) noted among extant Odontoceti only Pontoporia blainvillei Gervais and d’Orbigny, 1844 has a smaller tympanic, and P218407 does not resemble the tympanic of that taxon]; (2) distinct embayment in the medial edge of the involucrum between the inner anterior and posterior prominences; and (3) squared-off anterior edge of the involucrum and outer lip. It should be noted that the second feature is also seen in the tympanic bullae of Physeter macrocephalus Linnaeus, 1758 , Orycterocetus crocodilinus Cope, 1868 ( USNM 22953) ( Kellogg, 1965) ( Fig. 5C–D ), and an Early Pliocene physeterid ( USNM 183007) ( Fig. 5A, B ). Despite this similarity between P218407 and the tympanics of Physeteridae , the relatively large size of physeterid tympanics precludes P218407 from being considered as a physeterid. Furthermore, the inner posterior prominence in physeterid tympanics is generally more pointed in outline than the rounded outer posterior prominences in kogiid tympanics.

Among fossil Kogiidae , the tympanics of Praekogia cedrosensis ( Barnes, 1973b) have not been described. A skull of Scaphokogia cochlearis Muizon, 1988 ( USNM 452993) includes an associated incomplete left tympanic ( Fig. 4E, F ). The tympanic of S. cochlearis is similar to the tympanics of extant Kogia in its relatively small size and possession of a distinct embayment in the medial side of the involucrum between the inner anterior and posterior prominences. The most notable difference between the tympanic of S. cochlearis and the Portland kogiid tympanic lies in the more marked inflation of the inner posterior prominence of P218407. S. cochlearis possesses a less expanded inner posterior prominence, such that the embayment in the medial face of the involucrum is not as deep as in P218407. In this respect, Scaphokogia cochlearis is similar to two undescribed Early Pliocene kogiids from the Lee Creek Mine, North Carolina ( USNM 183008, Fig. 4G–H ; USNM 251118, Fig. 4C, D ) and the extant Kogia breviceps Blainville, 1838 ( Fig. 4I, J ).

The features which Kasuya (1973) used to differentiate between Recent Kogia breviceps and K. sima Owen, 1866 are not preserved in P218407. However, comparison between figures of the tympanic of K. sima ( Kasuya, 1973: plate VIII), and actual specimens of K. breviceps (C24972, C24976), indicate that P218407 differs from both extant Kogia species in: (1) embayment in medial edge of involucrum between the inner prominences is markedly deeper; and (2) the involucrum is less dorsoventrally and mediolaterally inflated. Despite these differences, P218407 is almost identical in size to the tympanics of Kogia breviceps . Given that the currently available evidence is meagre, P218407 is not identified below family level. Table 2 compares some dimensions of the tympanics of kogiids and physeterids discussed above.

P218407 is the first fossil record of Kogiidae from Australia. Fossil kogiids have previously been reported in the SW Pacific region, from the?Late Miocene of the Chatham Rise, east of New Zealand ( Fordyce, 1984a) but that record has a poorly constrained age ( Fordyce, 1989, 1991b).

Figures

Figure 4. Miocene to Recent Kogiidae tympanics. A-B, Kogiidae gen. et sp. indet. (Pliocene Whalers Bluff Formation, Portland, Victoria, Australia), incomplete left tympanic, NMV P218407 (AC). C-D, Kogiidae gen. et sp. undet. (Lower Pliocene Yorktown Formation, Lee Creek Mine, North Carolina, U.S.A.), incomplete left tympanic, USNM 251118. E-F, Scaphokogia cochlearis (Upper Miocene Pisco Formation,Aguada de Lomas level, Arequipa Department, Peru), incomplete left tympanic, USNM 452993. G-H, Kogiidae gen. et sp. undet. (Lower Pliocene Yorktown Formation, Lee Creek Mine, North Carolina, U.S.A.), incomplete right tympanic, USNM 183008. I-J, Kogia breviceps (Recent, Shelley Beach, Victoria, Australia), incomplete left tympanic, NMV C24976. A, C, E, G, I, all in dorsal view. B, D, F, H, J, all in ventral view. Scale bars equal 10 mm.

Figure 5. Miocene to Pliocene Physeteridae tympanics. A-B, Physeteridae gen. et sp. undet. (Lower Pliocene Yorktown Formation, Lee Creek Mine, North Carolina, U.S.A.), right tympanic, USNM 183007. C-D, Orycterocetus crocodilinus (Middle Miocene Calvert Formation, Zone 14, south of Randle Cliff Beach, Calvert County, Maryland, U.S.A.), right tympanic, USNM 22953. A and C in dorsal view. B and D in ventral view. Scale bars equal 10 mm.