Bioacoustics of Balaenoptera

– Protororqualus cuvieri (Fischer, 1829) , in having a squamosal crease, shorter and more anteriorly oriented zygomatic process that lack a supramastoid crest that extends to the zygomatic apex, a supraoccipital apex that is anteriorly squared-off at the vertex and transversely wider, measuring 10% of bizygomatic width (compared to 5% in P. cuvieri ), little to no parietal exposure at the vertex, laterally prominent antorbital process, and a posteriorly elongate postglenoid process of the squamosal. DESCRIPTION Ŋe holotype is a partial skull including a nearly complete braincase, complete left squamosal and frontal, and vomer; the maxillae, premaxillae, and nasals are missing as well as both right and left tympanic bullae and petrosals (with the exception of the posterior processes; Figs 11-15 ). Measurements of the holotype are presented in Table 6 . UCMP 219078 was found upside-down, and many bones of the ventral portion of the skull (as well as the left supraorbital process of the frontal) are fractured and displaced ( Fig. 16 ). Ŋe vomer is broken posteriorly, and is rotated anterodorsally ( Fig. 13 ). Ŋe left supraorbital process exhibits a long, anterolaterally oriented fracture, and the portion of the bone lateral to this fracture has rotated so that the supraorbital process is oriented dorsolaterally, and the postorbital process is no longer in contact with the zygomatic process. A reconstruction of the skull of B. bertae n. sp. is depicted in Figure 17 . Occipital shield In dorsal view the occipital shield is broad and triangular with a transversely narrow apex that is rectilinear and transversely oriented in dorsal view ( Figs 11A , 15A ). Ŋe anteriormost portion of the shield is longitudinally concave, and posterior to this, it is dorsally strongly convex along the sagittal plane. A pair of faint tubercles occur in the mid- dle of the supraoccipital, anterior to each occipital condyle. Ŋe nuchal crests are formed dorsally by the supraoccipital, are oriented anterolaterally, and overhang the temporal fossa so that the medial wall of the temporal fossa is not visible in dorsal aspect. Exoccipital Ŋe posterior margin of the exoccipital is posterolaterally oriented ( Figs 11A , 12A ). In dorsal view, the lateral margin of the occipital shield is slightly sinuous. Ŋe occipital condyles are relatively large. Ŋere are no clear dorsal condyloid fossae. Ventral to the foramen magnum, a shallow furrow extends between the occipital condyles. Squamosal Ŋe squamosal has a posteriorly elongate postglenoid process that is paddle-shaped (in dorsal and ventral view), dorsoventrally compressed, and posteroventrally directed ( Figs 11B , 13A , 15C ). Ŋe posterior margin of the postglenoid process is semi-circular in dorsal aspect. In lateral aspect, the ventral border of the mandibular fossa is strongly concave ( Fig. 13 ), and both the zygomatic and postglenoid processes are somewhat ventrally directed, and in dorsal and ventral aspect, the zygomatic process is nearly anteriorly directed ( Figs 11 , 12 ). Ŋe zygomatic process is relatively short, blunt, and triangular in crosssection. Ŋe supramastoid crest runs along the dorsal margin of the squamosal from the lateral margin of the occipital shield, but does not extend far onto the zygomatic process. A distinct dorsoventrally oriented and anteriorly facing squamosal crease occurs on the anterior surface of the squamosal, at the base of the zygomatic process. Along the posteromedial wall of the temporal fossa near the parietal-squamosal suture, a faint squamosal cleft occurs and runs parallel to the parietal-squamosal suture. In dorsal aspect, postglenoid process terminates well anterior to the exoccipital. A vertical crease occurs at the squamosal-exoccipital suture at the posterolateral edge of the cranium ( Fig. 11A ). Ŋe posterolateral surface of the squamosal is relatively planar. Ventrally, the mandibular fossa is transversely broad, and anteroposteriorly concave. Basicranium Portions of the basicranium are badly shattered ( Figs 11B , 12B ). Ŋe posterior sheet and wings of the vomer and palatines are broken. Ŋe basioccipital is broad and shallowly concave between the relatively small and knoblike basioccipital crests. Ŋe basioccipital crest is elongate and transversely convex. Ŋe petrosal fossa is large, subrectangular, anteriorly bordered by the pterygoid, medially by the medial lamina of the pterygoid, laterally by the squamosal, and posteriorly by the exoccipital ( Figs 11B , 12B , 15C ). Ventrally, the exoccipital forms a transversely oriented ridge that is posterolaterally directed. Posterolaterally, the exoccipital contacts the posterior surface of the posterior process of the petrotympanic. Ŋe posterior process of the petrotympanic curves anteromedially, is distally swollen, and bears a sharp ventral crest ( Fig. 15B, C ). Ŋe posterior meatal crest anteriorly overlaps the posterior process of the petrotympanic, and anterior to this thin plate, the squamosal exhibits a posterolaterally directed, trough-like external acoustic meatus positioned posterodorsally to the postglenoid process. Ŋe anterior meatal crest continues medially on the squamosal from the postglenoid process and forms the anterior margin of the external acoustic meatus. Ŋe vomer is nearly complete, and anteriorly protrudes beyond the anterior margin of the frontals ( Figs 11-13 ). Dorsally, the transversely concave mesorostral canal is filled with matrix. Anteriorly,the vomer becomes transversely narrower. Ŋe vomer is V-shaped in cross-section and bears a sharp ventral crest. Posteriorly, the ventral ridge of the vomer becomes lower to merge with the flat wings of the vomer.Ŋe latter becomes relatively wider posteriorly, ventrally flooring the basicranium, contacting the medial lamina of the pterygoid, and underlapping the anterior portion of the basioccipital. Posteriorly, the vomer is broad and flat. Ŋe basisphenoid is not exposed. Ŋe now-fractured palatine appears to have been slightly convex transversely, medially contacting the vomer, and posteriorly contacting the pterygoid. Ŋe palatal surface of the pterygoid is triangular in shape and positioned along the anterior margin of the petrosal fossa, with a blunt, tongue-shaped hamulus. Ŋe pterygoid hamulus does not appear to be broken or to possess fingerlike posteromedial projection as in species of extant Balaenoptera , and this may tentatively considered to be natural. Medially, the blunt pterygoid hamulus overhangs the medial lamina of the pterygoid. Ŋe medial lamina is anteroposteriorly elongate, ventrally flat, and laterally forms the ventrally directed pharyngeal crest that is confluent with the basioccipital crest and forms the medial margin of the petrosal fossa. Vertex Ŋe vertex of UCMP 219078 is transversely narrow, reflecting the narrow apex of the supraoccipital ( Figs 11A ; 12A ; 14 ). A thin band of the parietal is exposed between the sutures for the rostral elements and the supraoccipital ( Fig. 14 ). As the rostral elements are missing, it is not possible to ascertain the length of the nasals and morphology of the ascending processes of the maxillae and premaxillae. Ŋe articular surface on the frontals for the rostral elements is corrugated and exhibits a series of anteroposteriorly oriented grooves and ridges; seven ridges are present on the left side; the right side is not as well-preserved. Ŋe region of the vertex as preserved on the frontal appears asymmetrical with the left side having extending further anterolaterally and with a larger angle to the midline; this is due to the slight counterclockwise rotation of the left supraorbital process of the frontal. Frontal Ŋe well-preserved left frontal ( Figs 11-13 ) has a sharp, triangular prong anteriorly. Lateral to this prong, the anterior margin of the supraorbital process is straight and transversely oriented in dorsal view ( Fig. 17 ). Ŋe base of the supraorbital process is broken and displaced dorsally along the medial crack; the postorbital process is broken off, and when the original orientation of the supraorbital process is taken into account, it would have probably dorsally overlapped or contacted the zygomatic process ( Fig.17 ). Ŋe orbital margin of the supraorbital process is concave in dorsal view, and the dorsal surface of the supraorbital process is slightly anteroposteriorly arched. Ŋe posterior margin of the supraorbital process of the frontal is oriented transversely. Medially, the frontal drops sub-vertically from the vertex to the near-horizontal supraorbital process, which is horizontally oriented. Ŋe frontal drops near vertically from the vertex, so that it faces dorsolaterally, and the overlapping sheet of the parietal can be seen in dorsal aspect. Ŋe optic canal opens anterolaterally and is positioned posteriorly on the ventral surface of the supraorbital process of the frontal ( Fig. 12 ), defined by two ridges – the posteriorly placed infratemporal crest, and an anterolaterally directed ridge anterior to the canal. Ŋis anterior ridge is laterally confluent with the preorbital process, which projects slightly laterally. Parietal Ŋe parietal forms most of the medial wall of the temporal fossa, is exposed along the anterior portion of the vertex, and forms the ventral contribution to the nuchal crests on either side of the occipital shield ( Fig. 13B ). Ŋe lateral surface of the parietal in the temporal fossa is concave. Slightly anteromedial to the junction of the nuchal crest and the supramastoid crest of the squamosal, the parietal-squamosal suture descends ventrally along a bulge in the wall of the temporal fossa; it is oriented ventromedially, and does not turn posteriorly to form a long lateral finger of the parietal as in B. acutorostrata . ONTOGENY Several features of the skull suggest that the holotype cranium of B. bertae n. sp. represents an immature individual. Ŋese include relatively large occipital condyles, large petrosal fossae, and a relatively short compound posterior process of the petrotympanic. Additionally, several cranial sutures remain unfused, including the squamosal-parietal suture and the frontal-parietal suture; young ontogenetic age may explain the ease at which basicranial elements were lost or fractured (see Taphonomy). Ŋese features suggest that UCMP 219078 was not finished growing, and highlights the possibility that the morphology may not be representative of the adult form. In concert with the size of UCMP 219078 and development of these features in comparison with juveniles of extant Balaenoptera , the holotype of B. bertae n. sp. is interpreted as an old juvenile or subadult. Ŋe primary features used for diagnosing B. bertae n. sp. include the narrow transverse width of the vertex and the dorsolaterally facing surface lateral to the vertex, permitting the anterior wing of the parietal (and proximal portion of frontal) to be visible in dorsal aspect. Examination of juvenile and neonatal specimens of B. acutorostrata and B. physalus (CAS, USNM collections) indicates these features do not change during postnatal development. For example, small juveniles of B. acutorostrata (e.g., CAS 22180) exhibit a relatively wide apex of the occipital shield, and a vertical slope adjacent to the vertex.Ŋese diagnostic features can thus reasonably be interpreted as present in fully grown adults of B. bertae n. sp. Although the compound posterior process of the petrotympanic is relatively short, it is inflated with a blunt distal apex; in extant adult Balaenoptera spp., the distal apex is tapered. Examination of juvenile Balaenoptera indicates the distal apex is also tapered, unlike the condition in Balaenoptera bertae n. sp., suggesting an additional derived feature that does not appear to be affected by ontogenetic patterns observed in extant relatives. Furthermore, the posterior process extends laterally to the level of the lateral extremity of the paroccipital process, unlike immature specimens of extant Balaenoptera ; during ontogeny, the posterior process increases in length and lags behind the exoccipital during early development ( Bisconti 2001 ). Examination of the petrosal fossae of juvenile B. acutorostrata indicates that even in neonates, the fossae are smaller relative to skull size than in UCMP 219078, suggesting that the large size is autapomorphic for B. bertae n. sp. , and possibly a paedomorphic trait. In summary, although several features suggest immaturity, other features suggest that growth was nearly completed; additionally, most of the diagnostic features for B. bertae n. sp. do not appear to be affected by ontogenetic changes in extant Balaenoptera . TAPHONOMY Ŋe skull of B. bertae n. sp. exhibits several noteworthy preservational features ( Fig. 16 ). UCMP 219078 was preserved in a monotonous succession of massively bedded, pervasively bioturbated finegrained sandstone. Ŋis facies, typically lacking any primary sedimentary structures due to thorough homogenization of the sediment by bioturbators, was interpreted by Norris (1986) as reflecting a middle shelf (or transition zone) depositional setting. Other evidence for a lag deposit such as abundant, large terrigenous or phosphatic clasts or abundant mollusks is absent from this stratum. Ŋe rostral bones (premaxillae, maxillae, and nasals), tympanic bullae, middle ear ossicles, and bodies of the pet- rosals are missing, and no postcrania were found during excavation. Ŋe vomer and other basicranial elements are shattered, and the left supraorbital process of the frontal and vomer are broken and rotated dorsally. UCMP 219078 was found ventralup in massively bedded, bioturbated sandstone with dispersed mollusks and pebbles. Ŋe cranium was likely too large to be overturned by currents and probably represents the original orientation of the skull upon arrival at the sea floor. Ŋe lack of postcrania suggests that the skull arrived on the sea floor as an isolated element. Ŋe lack of evidence for a lag deposit or erosional surface at this horizon suggests that postcrania were not dissociated by transport and submarine erosion. Many cetacean carcasses float ventral up ( Schäfer 1972 ) and it is possible that the orientation of the skull reflects this; it also may reflect the hydrodynamically stable orientation of the skull as it sank. Ŋe rostral elements could have been lost during the bloat and float stage ( Fig. 16 A-C). Due to exaggerated movement of craniovertebral joint in modern floating cetacean carcasses, the skull is lost not long after the mandibles (e.g., Fig. 16E ; Schäfer 1972 ), which is reflected in some cetacean assemblages ( Bianucci et al. 2010 ). How the basicranial elements shattered is less clear, but some features of the fossil help to constrain the timing of deformation. Parts of the skull inside the concretion are shattered, indicating that this happened prior to formation of the concretion. Rotation and displacement of the vomer and supraorbital process of the frontal would not have been possible once entombed in sediment, and must have occurred prior to burial. Ŋe sequence of events for the holotype individual of B. bertae n. sp. is inferred as follows: bloating and floating of the whale after death (whether immediate or after refloating; Fig. 16A ); initial decomposition and loss of the jaws and rostral elements ( Fig. 16B, C ); advanced decay and skeletonization of the head results in the loss of the earbones ( Fig. 16D ), and eventual loss of the skull ( Fig. 16E ). At that time, the skull sinks to the sea floor ventral-up ( Fig. 16F ), and at some point between its arrival on the seafloor and burial, the vomer and supraorbital process rotate and come into contact with the seafloor ( Fig. 16G ). Eventually the skull is buried ( Fig. 16H ). Long after burial, diagenetic compaction fractures the basicranial elements ( Fig. 16I ), and a concretion forms around the braincase ( Fig. 16J ). PHYLOGENETIC ANALYSIS Balaenoptera bertae n. sp. was coded for the 150 characters of Marx (2011) as follows: ??????????????1???????????00012?210?1? ??11???01????????1012011130210210011?0 101?111?????????21??????????????????? ????????????????????????????????????? Incorporation of B. bertae n. sp. into the matrix of Marx (2011) and cladistic analysis supported inclusion (with low branch support) of this new taxon within Balaenoptera ( Fig. 18 ). In the strict consensus tree, B. bertae n. sp. appears within a basal polytomy with Balaenoptera physalus , B. edeni , B. acutorostrata , and B. bonaerensis . Within Balaenoptera , the Peruvian fossil B. siberi is sister to a B. omurai + B. musculus clade, forming the only resolved clade within Balaenoptera ; however, this relationship is weakly supported ( Fig. 18 ). Topology among other mysticete taxa did not change relative to the phylogenetic results of Marx (2011 : fig. 3), although branch and bremer support values slightly decreased across Balaenopteroidea, and support for Eschrichtiidae slightly increased ( Fig. 18 ). Most notably, the moderately supported B. borealis - B. bonaerensis - B. acutorostrata clade ( Marx 2011 : fig. 3) collapsed in this analysis, perhaps owing to the inclusion of the somewhat incomplete B. bertae n. sp. Increased resolution of balaenopterid phylogeny would be possible with the inclusion of additional balaenopterid taxa into this matrix (such as D. luctoretmurgo , C. capellinii , P. quarantellii , and “ B. ” cortesi “var.” portisi ) and additional balaenopterid-specific characters, including petrotympanic characters recently discussed by Ekdale et al. (2011) , and other skull features such as a squamosal crease, which in the current study was only identified in modern and fossil species of Balaenoptera . BALAENOPTERA BERTAE N. SP. AS A BALAENOPTERID Balaenoptera bertae n. sp. exhibits several balaenopterid characteristics, including an abruptly depressed supraorbital process of the frontal, an anteriorly thrusted occipital shield that laterally overhangs the temporal fossa, and telescoping of the rostral elements and supraoccipital such that the parietal is only exposed as a narrow transverse band at the vertex ( Figs 11-15 , 17 ; Zeigler et al. 1997 ; Deméré et al. 2005; Bisconti 2007a , b, 2010a; Bosselaers & Post 2010 ). Balaenoptera bertae n. sp. shares with all extant Balaenoptera spp. and M. novaeangliae a broadly triangular occipital shield that laterally overhangs much of the temporal fossa so that it obscures most of the parietal and medial wall of the temporal fossa in dorsal view ( Figs 11 , 17 ; Deméré et al. 2005).In many fossil balaenopterids, the crania are less extremely telescoped and the supraoccipital is not thrust as far anteriorly and overhangs less of the temporal fossa (e.g., Archaebalaenoptera Bisconti, 2007 , “ B. ” cortesi “var.” portisi , C. capellinii , Protororqualus Bisconti, 2007 ) or only overhangs the anterior portion of the temporal fossa so that the posterior half of the medial wall is visible in dorsal aspect ( P. baulinensis , “ M. ” hubachi , “ M. ” miocaena ). Most species of Balaenoptera , including B. bertae n. sp. , exhibit a slight convex bulge along the medial wall of the temporal fossa at the position of the squamosal-parietal suture; Megaptera Gray, 1846 lacks this bulge, and is thus the only balaenopterid where the inner wall of the temporal fossa is completely obscured in dorsal view. In B. musculus , the occipital shield is transversely narrow, and the medial wall is so bulged that nearly the entire medial wall is visible in dorsal aspect (interpreted here to be a reversal). Ŋe morphology of the squamosal varies widely within balaenopterids. Most fossil balaenopterids (e.g., A. castriarquati , “ B. ” cortesi “var.” portisi , P. baulinensis , and P. cuvieri ) appear to exhibit an elongate, laterally divergent zygomatic process with well-defined supramastoid crest that run along most of the length of the zygomatic process, while lacking a squamosal crease ( Zeigler et al. 1997 ; Deméré et al. 2005; Bisconti 2007a , b). An elongate and laterally flaring zygomatic process is regarded as the primitive condition amongst balaenopteroids (Deméré et al. 2005), and among fossil and extant balaenopterids, characterize all taxa (including Megaptera ) except for D. luctoretmurgo and Balaenoptera spp., which have relatively short and anteriorly directed zygomatic process. B. musculus is exceptional amongst extant Balaenoptera in its elongate and laterally flaring zygomatic process.Ŋe most extreme condition within balaenopterids characterizes B. acutorostrata , B. bertae n. sp. , and D. luctoretmurgo , all of which have short and nearly anteriorly oriented zygomatic process. Postglenoid process morphology also varies within the Balaenopteridae , and it is short and indistinct in basal balaenopterids (e.g., Archaebalaenoptera , Parabalaenoptera , Protororqualus ) and posteriorly elongate in Balaenoptera , Diunatans Bosselaers & Post, 2010 , and Megaptera . Ŋese latter taxa (including B. bertae n. sp. ) also exhibit a posterolaterally directed postglenoid process. Ŋe early diverging balaenopterid “ B. ” cortesi “var.” portisi also exhibits posteriorly elongate postglenoid process, but it is posteriorly and not posterolaterally oriented. A squamosal crease is present in taxa with anteriorly oriented zygomatic processes. While a squamosal crease is absent in D. luctoretmurgo ( Bosselaers & Post 2010 ) and B. siberi , it is present in all extant species of Balaenoptera and B. bertae n. sp. , and absent in M. novaeangliae ( Kellogg 1922 ; Deméré et al. 2005). Ŋis feature may be a possible synapomorphy of Balaenoptera . Balaenoptera bertae n. sp. may be distinguished from all extant balaenopterids by the lack of a fingerlike posterior projection of the pterygoid hamulus ( Fig. 11B ). Ŋe condition of this character is unknown in many fossil taxa, either because the ventral side of the skull has not been prepared (e.g., Archaebalaenoptera , B. siberi ), is completely missing ( Cetotheriophanes Brandt, 1873 , Plesiobalaenoptera Bisconti, 2010 ), or is too damaged to tell (e.g., “ B. ” cortesi “var.” portisi , “ M. ” miocaena , Parabalaenoptera ). “ Megaptera ” hubachi also appears to lack a posteriorly directed finger of the pterygoid hamulus. Fingerlike pterygoid hamuli are widely distributed among modern and fossil mysticetes such as cetotheriids sensu stricto , cetotheres sensu lato ( sensu Bouetel & Muizon 2006 ), and extant Eschrichtius robustus (Lilljeborg, 1861) . BALAENOPTERA BERTAE N. SP. AS A MEMBER OF BALAENOPTERA In general, B. bertae n. sp. exhibits characteristics that are relatively derived in comparison to most fossil balaenopterids. In comparison to extant species of Balaenoptera , B. bertae n. sp. is characterized by a mosaic of primarily derived and a few plesiomorphic characters. Aside from the derived features outlined above (also see Differential diagnosis), plesiomorphic characteristics of B. bertae n. sp. include a transversely narrow vertex and supraoccipital apex, and a supraor - Caperea marginata Gray, 1846 † Eschrichtioides gastaldii Strobel, 1881 Eschrichtius robustus (Lilljeborg, 1861) 4/56

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.