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

First record of the megatoothed shark Carcharocles megalodon from the Mio-Pliocene Purisima Formation of Northern California.

Megatoothed sharks (Family: Otodontidae) are among the most widely reported sharks in Cenozoic marine sediments worldwide, and certain species such as the famed Carcharocles megalodon are particularly abundant in Neogene deposits on the Atlantic margin of the United States. Cenozoic marine strata on the Pacific margin of North America have yielded one of the most densely sampled marine vertebrate records anywhere, but published occurrences of shark assemblages are uncommon. Rarer yet are published occurrences of C. megalodon from this region with unambiguous provenance and robust age control — critical data required for the study of recent marine vertebrate faunal evolution in the eastern North Pacific. A tooth of C. megalodon from near Santa Cruz, California, represents the first record of this species from the Purisima Formation and the geochronologically youngest occurrence (6.9–5.6 Ma, uppermost Miocene; late Messinian) of this species from northern California

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

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

Herpetocetine (Cetacea: Mysticeti) dentaries from the Upper Miocene Santa Margarita Sandstone of Central California

Two fossil baleen whale (Mysticeti) dentaries from the Upper Miocene (10–12 Ma) Santa Margarita Sandstone of Central California preserve several distinct features similar to the enigmatic herpetocetine whale Herpetocetus. These features include an elongate coronoid process, a mandibular condyle with a planar articular surface, and a posteriorly extended angular process. The dentary is unknown for several Herpetocetinae (and the more inclusive clade Cetotheriidae), including the coeval Nannocetus eremus. This occurrence would extend the known record of Herpetocetus by 6 Ma. Given the currently poor knowledge of Pacific Cetotheriidae during the Miocene, these specimens are identified to the subfamily Herpetocetinae, despite the similarity of these specimens to Herpetocetus. As the morphology of the supposedly distinctive lectotype dentary of Herpetocetus scaldiensis (the type species of Herpetocetus) may not be unique to Herpetocetus, this study suggests that the mandibular morphology of fossil mysticetes may be more homoplastic (or conservative) than previously assumed. Mysticete taxonomy should employ autapomorphic characters beyond the morphology of the dentary alone