Balaenoptera

Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, Geodiversitas 35 (4), pp. 815-940 : 853-854

“ Balaenoptera ” cortesi “var.” portisi Sacco, 1890

REFERRED MATERIAL. — UCMP 219135, a right petrosal collected by R.W. Boessenecker from UCMP locality V99840 .

STRATIGRAPHIC OCCURRENCE. — Middle part of the San Gregorio section of the Purisima Formation, Early Pliocene (c. 5-3.35 Ma; Zanclean-Piacenzian equivalent; Fig. 2 ).

DESCRIPTION

Ŋe pars cochlearis of this large petrosal ( Table 7 ) is dorsally elongate ( Fig. 19A ), with an elongate, posteroventrally directed posterior cochlear crest; adjacent to this crest is the small, circular fenestra cochleae. Ŋe groove for the tensor tympani muscle is situated anteroventral to the pars cochlearis, on the medial surface of the anterior process. Ŋe anterior process is triangular and bladelike, curves medially at its apex, and rugose along its medial margin ( Fig. 19A, C ). In medial aspect, the ventral margin of the anterior process is straight and directed anterodorsally. Ŋe lateral tuberosity is oriented posteroventrally and positioned at the base of the anterior process. Ŋe anterior pedicle for the tympanic bulla is positioned just dorsal to the lateral tuberosity; dorsal to the pedicle is a shallow mallear fossa. Ŋe facial sulcus is oval and dorsal to the mallear fossa; an elongate trough is not developed as in some modern Balaenoptera . Ŋe oval-shaped fenestra vestibuli is medially adjacent to the facial sulcus and at the base of pars cochlearis. Ŋe neck for the posterior process is robust and quadrate in cross-section, and the small posterior pedicle is present anteromedially on the neck. Ŋe anteroposteriorly elongate, rectangular, and shallow stylomastoid fossa is positioned on the posterior surface of the pars cochlearis and base of the posterior process. Further anterior along the dorsal surface of the petrosal are the perilymphatic and endolymphatic foramina, which are situated in a common groove an separated from the stylomastoid fossa by a thin crest. Ŋe internal acoustic meatus is deep and cavernous (resulting from the extreme dorsal elongation of the pars cochlearis) with a circular canal for the vestibulocochlear nerve (= spiral cribriform tract of Mead & Fordyce 2009) and an oval-shaped facial canal ( Fig. 19D ). Ŋe crista transversa is deeply recessed (34mm) within the internal acoustic meatus. Ŋe vestibulocochlear nerve canal is 43 mm deep, and the facial canal is 48 mm deep. An additional unidentified foramen is present anterodorsally to the facial canal on the dorsal edge of the pars cochlearis; it is unclear whether or not this foramen is the hiatus fallopii. Ŋe lateral surface of the petrosal is rugose and gently convex.

REMARKS AND COMPARISONS

Ŋis petrosal compares best with the holotype petrosal of “ Balaenoptera ” cortesi “var.” portisi from the Pliocene of Italy (Sacco 1890), as well as SDNHM 68698, a petrosal preserved with a partial skull from the Upper Pliocene San Diego Formation of southern California referred to “ B. ” cortesi “var.” portisi by Deméré et al. (2005). Deméré (1986) and Deméré et al. (2005) further indicated that the holotype mandible of “ Balaenoptera ” floridana Kellogg, 1944 , as well as the Italian Pliocene balaenopterid Cetotheriophanes capellinii may also be congeneric or conspecific with this taxon. “ B. ” cortesi “var.” portisi does not belong in Balaenoptera and requires a new genus name and reevaluation (Deméré et al. 2005). In particular, UCMP 219135 shares many distinctive features with of “ B. ” cortesi “var.” portisi such as a dorsally elongate pars cochlearis, a straight anterior margin of the anterior process, an anterior process that is pointed anterodorsally rather than anteriorly,and a flattened,bladelike anterior process. Crania of “ B. ” cortesi “var.” portisi preserving this petrosal morphology differ from Balaenoptera bertae n. sp. in exhibiting more elongate and widely flaring zygomatic processes, lacking a squamosal crease, an anteroposteriorly more elongate supraorbital process of the frontal, and an occipital shield that is more anteriorly elongate and attenuate; it is thus unlikely that UCMP 219135 is referable to B. bertae n. sp.

Some features of this specimen are shared with Megaptera novaeangliae , including the extreme elongation of the pars cochlearis, and having the perilymphatic and endolymphatic foramina situated in a common groove. However, UCMP 219135 differs from Megaptera in having deep canals for the facial and vestibulocochlear nerves, in having the internal acoustic meatus positioned in the middle of the pars cochlearis (instead of the posterior aspect as in extant Megaptera ), and in having a smaller and less acutely pointed lateral tuberosity.UCMP 219135 differs from extant Balaenoptera spp. in the extreme elongation of the pars cochlearis, and an anterior process that is directed anterodorsally (relative to the long axis of the pars cochlearis), rather than anteriorly in extant Balaenoptera and Megaptera ( Ekdale et al. 2011) .

Two additional specimens from the Purisima Formation undoubtedly represent this taxon.A large cranial fragment ( UCMP uncataloged, field no. FP 192 ) from the Santa Cruz section of the Purisima Formation exhibits a well-preserved and identical petrosal ; furthermore, a partial cranium ( SCMNH 21292 ) exhibits squamosal morphology that is identical to the holotype of “ B. ” cortesi “var.” portisi and referred skulls from the San Diego Formation ( SDNHM 65769 and 68698) .

Ŋis fossil represents an additional occurrence of “ B. ” cortesi “var.” portisi from the eastern North Pacific along with that from the San Diego Formation reported by Deméré et al. (2005). Along with other records of this taxon from the Pliocene of Florida and Italy ( Portis1885; Kellogg 1944; Deméré et al. 2005), this indicates that this taxon (whether several species within a genus, or a single species) was cosmopolitan and formerly inhabited the eastern North Pacific,the western North Atlantic, and the Mediterranean Sea during the Pliocene.

Figures

FIG. 2. — Stratigraphy of the Purisima Formation: A, Stratigraphic column of the San Gregorio section of the Purisima Formation (in meters), showing stratigraphic position of UCMP vertebrate localities, dated ash beds, diatom floras, and species of Carcharodon; thickness measurements start over above missing section in uppermost part due lack of overlapping strata; epoch and stage boundaries marked as "?" are estimated; modified from Boessenecker (2011a); Pliocene-Pleistocene boundary after Hilgen et al. (2012); B, photograph of 3-4 m thick ash within Purisima Formation at mouth of San Gregorio Creek correlated with 2.5 Ma Ishi Tuff (Powell et al.2007); C, trace fossils in pervasively bioturbated sandstone,Purisima Formation,mouth of San Gregorio Creek; D, swaley cross-stratified sandstone, mouth of San Gregorio Creek. Abbreviations: Qt, Pleistocene terrace deposits; Tp, Purisima Formation; C, claystone; St, siltstone; Ss, sandstone. Scale bars: A, 2 m; B, C, 10 cm.

FIG. 19. — Right petrosal of “Balaenoptera” cortesi “var.” portisi (UCMP 219135); A, medial view; B, lateral view; C, ventral view; D, dorsal view. Scale bar: 3 cm.