New records of the archaic dolphin Agorophius (Mammalia: Cetacea) from the upper Oligocene Chandler Bridge Formation of South Carolina, USA

The stem odontocete Agorophius pygmaeus (Ashley Formation, lower Oligocene, South Carolina; 29.0–26.57 Ma) has been a critical point of comparison for studies of early neocete evolution owing to its early discovery as well as its transitional anatomy relative to archaeocete whales and modern odontocetes. Some time during the late nineteenth century the holotype skull went missing and has never been relocated; supplementary reference specimens have since been recently referred to the species from the Ashley Formation and the overlying Chandler Bridge Formation (upper Oligocene; 24.7–23.5). New crania referable to Agorophius sp. are identifiable to the genus based on several features of the intertemporal region. Furthermore, all published specimens from the Chandler Bridge Formation consistently share larger absolute size and a proportionally shorter exposure of the parietal in the skull roof than specimens from the Ashley Formation (including the holotype). Furthermore, these specimens include well-preserved ethmoid labyrinths and cribriform plates, indicating that Agorophius primitively retained a strong olfactory sense. These new crania suggest that at least two species of Agorophius are present in the Oligocene of South Carolina, revealing a somewhat more complicated taxonomic perspective

Juvenile morphology: A clue to the origins of the most mysterious of mysticetes?

The origin of the pygmy right whale (Caperea marginata) has long been one of the most vexing conundrums of marine mammal evolution. The extremely disparate skeletal structure ofCapereaand a patchy fossil record have left morphology and molecules at odds: whereas most morphological analyses allyCapereawith right whales (Balaenidae), most molecular studies instead suggest a close relationship with rorquals (Balaenopteridae) and grey whales (Eschrichtiidae). The morphological evidence supporting aCaperea-balaenid clade consists of several shared features of the skull and mandible, as traditionally observed in adult individuals. Here, we show that at least two of these features, the ascending process of the maxilla and the coronoid process, arise from substantially different precursors early during ontogeny and therefore likely do not represent genuine synapomorphies. Both of these juvenile morphologies have adult counterparts in the fossil record, thus indicating that the ontogenetic variation in the living species may be a genuine reflection of differing ancestral states. This new evidence contradicts previous morphological hypotheses on the origins ofCapereaand may help to reconcile morphological and molecular evidence.Fil: Marx, Felix. University of Otago; Nueva ZelandaFil: Buono, Mónica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagonico; ArgentinaFil: Fordyce, R. Ewan. University of Otago; Nueva ZelandaFil: Boessenecker, Robert W.. University of Otago; Nueva Zeland

The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific

The extinct giant shark Otodus megalodon is the last member of the predatory megatoothed lineage and is reported from Neogene sediments from nearly all continents. The timing of the extinction of Otodus megalodon is thought to be Pliocene, although reports of Pleistocene teeth fuel speculation that Otodus megalodon may still be extant. The longevity of the Otodus lineage (Paleocene to Pliocene) and its conspicuous absence in the modern fauna begs the question: when and why did this giant shark become extinct? Addressing this question requires a densely sampled marine vertebrate fossil record in concert with a robust geochronologic framework. Many historically important basins with stacked Otodus-bearing Neogene marine vertebrate fossil assemblages lack well-sampled and well-dated lower and upper Pliocene strata (e.g., Atlantic Coastal Plain). The fossil record of California, USA, and Baja California, Mexico, provides such an ideal sequence of assemblages preserved within well-dated lithostratigraphic sequences. This study reviews all records of Otodus megalodon from post-Messinian marine strata from western North America and evaluates their reliability. All post-Zanclean Otodus megalodon occurrences from the eastern North Pacific exhibit clear evidence of reworking or lack reliable provenance; the youngest reliable records of Otodus megalodon are early Pliocene, suggesting an extinction at the early-late Pliocene boundary (∼3.6 Ma), corresponding with youngest occurrences of Otodus megalodon in Japan, the North Atlantic, and Mediterranean. This study also reevaluates a published dataset, thoroughly vetting each occurrence and justifying the geochronologic age of each, as well as excluding several dubious records. Reanalysis of the dataset using optimal linear estimation resulted in a median extinction date of 3.51 Ma, somewhat older than a previously proposed Pliocene-Pleistocene extinction date (2.6 Ma). Post-middle Miocene oceanographic changes and cooling sea surface temperature may have resulted in range fragmentation, while alongside competition with the newly evolved great white shark (Carcharodon carcharias) during the Pliocene may have led to the demise of the megatoothed shark. Alternatively, these findings may also suggest a globally asynchronous extinction of Otodus megalodon

Odontoceti Flower 1867

Odontoceti gen. et sp. indet. REFERRED MATERIAL. — UCMP 219175, one partial left humerus collected by R.W. Boessenecker from UCMP locality V99854. STRATIGRAPHIC OCCURRENCE. — Lowermost part of the San Gregorio section of the Purisima Formation, latest Miocene (6.4-5.6 Ma; Messinian equivalent; Fig. 2). DESCRIPTION Ŋe partial humerus (UCMP 219175) is missing the distal end, and is slightly transversely crushed (Fig.31). UCMP 219175 is tentatively identified as a left humerus, and is relatively large for an odontocete.Ŋe humeral head is large and oval in articular aspect, and was possibly circular prior to diagenetic compaction. Ŋe lesser tubercle is anteroposteriorly broad and oval-shaped in proximal aspect.An anteromedially oriented crest occurs on the proximal end, connecting the humeral head and the lesser tubercle. Ŋe humeral head is narrower than the lesser tuber- cle, and is oriented dorsomedially (Fig. 31). UCMP 219175 appears to lack a greater tubercle. REMARKS AND COMPARISONS Ŋis specimen (UCMP 219175) differs from all fossil and modern phocoenids and many non-globicephaline delphinids(except Tursiops Gervais, 1855) in its larger size;although a humerus is not yet known for Parapontoporia Barnes,1984, this specimen is almost certainly too large to belong to it. UCMP 219175 is similar in size and morphology to Albireo whistleri Barnes, 1984. Ŋis specimen differs from kogiid humeri in lacking a prominent deltopectoral crest, and by having a lesser tubercle that is wider than the humeral head (Kazár &Bohaska 2008).UCMP 219175differs from pontoporiids in its much larger size and exhibiting a transversely wider lesser tubercle (Kazár & Bohaska 2008).Ŋis specimen differs from larger physeteroids in lacking a proximally small lesser tubercle and having a relatively thinner shaft (Kazár & Bohaska 2008); it is not a ziphiid because of its possession of a larger and more prominent lesser tubercle. Ŋis specimen further differs from non-globicephaline delphinids in having a more elongate shaft (Kazár & Bohaska 2008). Because this specimen is similar to both the monodontid Delphinapterus Lacépède, 1804, Albireo Barnes, 1984, and globicephaline delphinids, it is not identified to a more exclusive clade.Published as part of Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, pp. 815-940 in Geodiversitas 35 (4) on pages 871-872, DOI: 10.5252/g2013n4a5, http://zenodo.org/record/453820

A new Early Pliocene record of the toothless walrus Valenictus (Carnivora, Odobenidae) from the Purisima Formation of Northern California

The walrus (Odobenus rosmarus) is a large tusked molluskivore that inhabits the Arctic and is the sole living member of the family Odobenidae. In contrast to the modern walrus, extinct walruses lived in temperate and even subtropical climates as far south as Baja California and Japan in the Pacific, and Florida and Morocco in the Atlantic. Multispecies walrus assemblages are now documented from several localities in the North Pacific, the center of origin for the family. The genus Valenictus is a toothless dense-boned walrus reported from several localities in southern California and Baja California. An isolated astragalus from lower Pliocene (5.33–4.89 Ma, Zanclean correlative) sediments of the Purisima Formation of northern California (Santa Cruz County, California) matches the highly derived morphology of Valenictus chulavistensis, and is identifiable as Valenictus sp. This specimen is the first record of Valenictus from the Purisima Formation and the first from northern California

Eubalaena Gray 1864

cf. Eubalaena sp. 1 REFERRED MATERIAL. — UCMP 219100, a small partial right tympanic bulla; and UCMP 219481, a small partial right tympanic bulla. Collected by R.W. Boessenecker from UCMP locality V99851. STRATIGRAPHIC OCCURRENCE. — Lowermost part of the San Gregorio section of the Purisima Formation, latest Miocene (6.4-5.6 Ma, Messinian equivalent; Fig. 2). DESCRIPTION Except where noted, this description is based primarily on UCMP 219100. Ŋis tympanic bulla has a large involucrum with a greatly expanded medial surface which is anteriorly truncated (Fig. 10 A-C). Several elongate, deep, and anterolaterally directed transverse creases occur on the involucrum. Posteriorly, the involucrum is much deeper dorsoventrally. A deep sulcus runs adjacent to the involucral ridge; the involucral ridge is slightly retracted from the ventral margin, and diverges posteriorly from the main ridge. Ŋe ventral surface is relatively smooth and convex and lacks a keel-like main ridge. Laterally adjacent to the main ridge there is an indistinct involucrum longitudinal furrow. Ŋe posteromedial portion of the bulla is rather robust and inflated in medial aspect. A fragment of the anterior portion of the outer lip is present, and it is broadly convex in anterior view. Ŋis results in a eustachian opening that is narrow; anteriorly this margin is slit-like and has an angle of c. 45° (between the involucrum and outer lip). UCMP 219481 also exhibits a narrow eustachian opening, although it has an anteroventral corner of the eustachian opening that is more acutely defined and not broadly curved as in UCMP 219100 (Fig. 10F). REMARKS AND COMPARISONS Ŋese tympanic bullae share many features with extant Eubalaena Gray, 1864, including an elevated anterior lobe and a narrow eustachian opening (Ekdale et al. 2011). Nevertheless, the involucral and main ridges are posteriorly divergent, whereas in extant Eubalaena they are parallel. Ŋey differ from balaenopterids in having a convex dorsal margin of the involucrum in medial and lateral aspect; balaenopterid bullae generally differ from those of extant balaenids in having a relatively straight medial margin of the involucrum that is not broadly arched in dorsal view (Oishi & Hasegawa 1995b; Ekdale et al. 2011). Ŋese bullae differ from Balaena Linnaeus, 1758 in being relatively transversely broader; bullae of extant Balaena are transversely flattened relative to those of Eubalaena (Ekdale et al. 2011). Ŋe tympanic bulla of Caperea Gray, 1864 is similar in size, but transversely narrower than UCMP 219100; it exhibits a posteroventrally expanded involucrum and a rectangular eustachian opening, unlike UCMP 219100 and 219481 (Ekdale et al. 2011). UCMP 219100 differs from Balaenella Bisconti, 2005 in having a rounded anteroventral margin that is not shaped into a corner (Bisconti 2005), although this is seen in UCMP 219481 and Eubalaena. UCMP 219100 and 219481 differ from the tympanic bulla of B. balaenopsis Van Beneden, 1872 in exhibiting a narrow, triangular eustachian opening; UCMP 219100 further differs in exhibiting a more transversely inflated bulla, and UCMP 219481 differs in exhibiting a corner-like anteroventral margin. Ŋe tympanic bulla of Bal- aenula astensis Trevisan, 1942 is more transversely compressed than UCMP 219100, and exhibits a eustachian opening that is less acutely triangular and slit-like than UCMP 219100 and 219481, although it is somewhat narrower than the broadly rounded eustachian opening in B. balaenopsis. A balaenid tympanic bulla (UCMP 29852; identified as Balaenula sp. by Barnes 1977) from the Purisima Formation at Point Reyes (Early Pliocene) is similar in size, but appears to be transversely thinner and exhibits a flatter medial surface of the involucrum relative to UCMP 219100 and 219481. Although they are relatively small (Table 5), these specimens share enough features with Eubalaena to be tentatively identified to this genus.Published as part of Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, pp. 815-940 in Geodiversitas 35 (4) on pages 834-836, DOI: 10.5252/g2013n4a5, http://zenodo.org/record/453820

Balaenopteridae Gray 1864

Balaenopteridae gen. et sp. indet. aff. Plesiocetus – Boessenecker 2006: 43 A. REFERRED MATERIAL. — UCMP 219137, a right posterior process of a petrotympanic UCMP 219098, 219097, 219107, 219478, one left and three right tympanic bullae, and UCMP 219141, a fragment of the posterior end of a left mandible, collected by R.W.Boessenecker from UCMP localities V99834, V99835, V99836, V99840, and V99851. STRATIGRAPHIC OCCURRENCE. — Lower and middle parts of the San Gregorio section of the Purisima Formation, latest Miocene to Early Pliocene (6.4-3.35 Ma; Messinian-Piacenzian equivalent; Fig. 2). DESCRIPTION Two balaenopterid morphotypes are represented by fossil tympanic bullae (Table 5). Morphotype 1 includes UCMP 219097 and 219478; except where noted, the description of this morphotype is based primarily on UCMP 219478 (Morphotype 2 described below). In medial and lateral aspect, the tympanic bulla is roughly oval (Fig. 21A), with subequally sized anterior and posterior lobes. A vertical shelf or flange along the anteromedial margin is absent. Ŋe involucrum is smooth, gently convex, and tapers anteriorly. Ŋe involucrum bears some faint transverse striations (Fig. 21A, D) and a well-developed dorsal posterior prominence (sensu Oishi & Hasegawa 1995b; Fig. 21C, F). In medial view, the tympanic cavity is anteriorly oval -shaped, and narrows posteriorly where it is pinched between the involucrum and sigmoid process. Ŋe conical process is blunt, low, and ventrally concave. Ŋe lateral furrow is broad and situated at the midpoint of the bulla. Ŋe sigmoid fissure (= posterior border of sigmoid process) is transversely oriented, deep, and ventrally shallows (Fig. 21B). Ŋe involucral and main ridges are posteriorly divergent and faintly developed. Ŋe involucral ridge is separated from the main ridge along the ventral margin (Fig. 21A, D). The tympanic bullae (UCMP 219098 and 219107) of Morphotype 2 are generally similar to those of Morphotype 1, but differ in a few characteristics, including their smaller size (Fig. 22; Table 5). No dorsal posterior prominence is developed. Slight transverse striations occur on the involucrum of UCMP 219098 (Fig. 22A), while more deeply incised transverse creases occur in UCMP 219107 (Fig. 22B). Ŋe involucral ridge is straight and retracted from the ventral margin (in dorsal aspect), and is roughly parallel with the main ridge. A vertical shelf or flange along the anteromedial margin is absent. Ŋe lateral surface of the outer lip is greatly inflated (Fig. 22C), and tympanic bullae of Morphotype 2 are relatively transversely wider than in Morphotype 1. Ŋe conical process is acutely triangular in medial aspect (Fig. 22A). Ŋe isolated posterior process of the petrotympanic (UCMP 219137) is large (Table 9), anteroposteriorly flattened, and slightly curved posterolaterally (Fig.23). It tapers laterally to be- come bladelike, and exhibits a sharp ventral crest. Along the anterior side of this crest, a shallow facial sulcus is present. Medially, the posterior process turns anteromedially toward the neck. Ŋe mandible fragment (UCMP 219141) preserves part of the condyle, the angular process, and the ventral margin of the mandibular foramen, but lacks everything anterior to the mandibular foramen (Fig. 24). Ŋe mandibular condyle is large, hemispherical, and prominent laterally. Ŋe angular process is much smaller, and in medial and lateral views is shaped as a tabular process running ventral to the condyle along the ventral margin of the mandible. A transversely oriented groove separates the mandibular condyle from the angular process; the angular process is broadly visible in lateral view (Fig. 24B). Ŋe mandibular foramen is posterodorsally oriented, large, and transversely broad. Ŋe posteriormost section of the mandible is straight and parasagittally oriented, while anteriorly, the mandible bends strongly laterally, indicating a large degree of bowing of the horizontal ramus (Fig. 24A) as in Balaenoptera spp. and Megaptera novaeangliae. REMARKS AND COMPARISONS Ŋese tympanic bullae (morphotypes 1 and 2) are referred to the Balaenopteridae based on their oval outline in medial aspect, simple sub-cylindrical involucra, lack of a dorsoventrally expanded and medially flattened involucrum as in Balaenidae, and being dorsoventrally shallower and transversely wider than extant Eschrichtius robustus; furthermore, their much larger size and lack of a median furrow precludes their assignment to Cetotheriidae (Oishi & Hasegawa 1995b; Ekdale et al. 2011). Morphotype 1 tympanic bullae share in common with extant Megaptera a large and robust dorsal posterior prominence, a feature which is lacking in most extant species of Balaenoptera as well as Plesiobalaenoptera, although some species of Balaenoptera exhibit a weakly developed dorsal posterior prominence. A slight dorsal posterior prominence occurs in Diunatans luctoretmurgo, although its bulla is substantially larger than UCMP 219478 and 219097 and differs in having a much more robust involucrum than the Purisima Formation specimens. Ŋese specimens differ in several regards from most extant Balaenoptera spp., including their smaller size (except Balaenoptera acutorostrata and Balaenoptera bonaerensis, which have smaller tympanic bullae). Most extant species of Balaenoptera exhibit an involucral ridge that is separated from the posterior margin (except Balaenoptera musculus), similar to Megaptera novaeangliae and these Purisima specimens. In dorsal view, the anterior portion of the involucra of these specimens and M. novaeangliae are much more constricted and have a large rounded eustachian opening; the latter feature is relatively smaller in Balaenoptera. Ŋese specimens are somewhat smaller than tympanic bullae of extant M. novaeangliae, and are transversely narrower with a less convex lateral surface. Due to the variability of bullar morphology in fossil and modern balaenopterids, Morphotype 1 bullae are only identified to the family level, despite similarities with Megaptera. It is unclear whether these specimens are referable to Balaenoptera bertae n. sp. Morphotype 2 tympanic bullae differ from those of Morphotype 1 (see above) and extant Megaptera in lacking a robust dorsal posterior prominence (Fig.24). Ŋe present specimens differ from Balaenoptera, Diunatans, and Plesiobalaenoptera in lacking a transversely flattened anteromedial shelf, in having a substantially more inflated lateral surface of the outer lip, a sigmoid process that is positioned further posteriorly, and their much smaller size. UCMP 219098 further differs from Plesiobalaenoptera in lacking a distinctly convex anterior lobe in dorsal view and having a relatively larger eustachian opening; it further differs from Balaenoptera and Plesiobalaenoptera in having a smooth main ridge not developed into a slight ventral keel (Bisconti 2010a). Ŋese specimens lack the derived features of most previously described balaenopterids, and are relatively archaic in comparison to these taxa. However, they differ from all known balaenopterid and stem-balaenopteroid (= cetotheres sensu lato) taxa in exhibiting an extremely inflated lateral surface and a posteriorly positioned sigmoid process. Additional tympanic bullae from California similar to Morphotype 2 bullae include UCMP uncataloged (Field number FP 302, UCMP locality V90042) from an Upper Miocene (c. 5.33 Ma) locality in the Purisima Formation near Santa Cruz, and UCMP 88665 from the Upper Miocene San Luis Rey River Local Fauna of the San Mateo Formation (6-8 Ma) near Oceanside, California.Tympanic bullae agreeing in morphology to Morphotype 2 have occasionally been identified as “ Plesiocetus ” Van Beneden, 1859 (Barnes 1977; Oishi & Hasegawa 1995a). However, as detailed by Deméré et al. (2005), the generic taxon “ Plesiocetus ” has been applied incorrectly to a large number of different taxa, to the point where the application of this taxon has been inconsistent and confusing. Because of confusion surrounding the taxon “ Plesiocetus ” (Deméré et al. 2005; Bosselaers & Post 2010), future identifications should be avoided and Morphotype 2 bullae are only identified to the family level herein.It is unclear whether these specimens are referable to B. bertae n. sp. Ŋe posterior process of a petrotympanic (UCMP 219137) shares with Balaenopteridae an elongate and strap-like posterior process with parallel dorsal and ventral margins (Fig. 23). It differs from herpetocetine mysticetes in being more elongate and larger in size and lacking a plug-like morphology with a flattened distal apex (Whitmore & Barnes 2008). It differs from Eschrichtius in being longer and lacking a ventrally expanded crest, and is precluded from assignment to the Balaenidae in being anteroposteriorly flattened, distally tapering in ventral view, and lacking a broad and well defined sulcus for the facial nerve. UCMP 219137 differs from B. bertae n. sp. its much larger size, and in lacking a slightly inflated distal apex that is not tapered and bladelike. Ŋe mandible fragment (UCMP 219141) is also not identifiable beyond the family level because of its incompleteness. It exhibits two balaenopterid features. Ŋe first feature, a concave lateral margin of the posterior part of the mandible, results from the sigmoid curvature of the mandible; and the posterior ⅓ of the mandible in balaenopterids is medially bowed (while the anterior ½ is laterally bowed). Ŋe second feature is a robust angular process that is visible laterally, but does not extend posteriorly to the mandibular condyle; the angular process is not developed in balaenids, and in Eschrichtius, it is indistinct and not separated from the condyle by a crease as in UCMP 219141 and all balaenopterids. Based on its size, it can be eliminated from B. bertae n. sp., which is perhaps one-half the size of UCMP 219141. It is possible that it may belong to cf. Balaenoptera, “ B. ” cortesi “var.” portisi, but is too incomplete to be identified beyond the family level.Published as part of Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, pp. 815-940 in Geodiversitas 35 (4) on pages 857-860, DOI: 10.5252/g2013n4a5, http://zenodo.org/record/453820