Chieko Shimada

Two new extinct basal phocoenids (Cetacea, Odontoceti, Delphinoidea), from the upper Miocene Koetoi Formation of Japan and their phylogenetic significance

ABSTRACT Two new extinct porpoises—Archaeophocaena teshioensis, gen. et sp. nov., and Miophocaena nishinoi, gen. et sp. nov.—are described from the upper Miocene Koetoi Formation (5.5-6.4 Ma) of Hokkaido, Northern Japan. The holotype of the former is composed of a partial skull, whereas the holotype of the latter is composed of a partial skull, right periotic, right stylohyoid, and pelvis. Both species are assigned to Phocoenidae on the basis of a unique combination of phocoenid characters: presences of frontal bosses, nasal protuberances, premaxillary eminences, and fossae for the inferior vestibule. However, they do not have dorsally developed preorbital sinus fossae or high premaxillary eminences, unlike derived phocoenids. Furthermore, their premaxillae contact the nasals (or the right premaxilla alone contacts the right nasal), unlike all other known phocoenids except Pterophocaena. A comprehensive morphological cladistic analysis indicates that the two new extinct species are the second-most basal phocoenids next to Pterophocaena and that Phocoenidae is the sister group of Delphinidae. The cranial morphology of the two new extinct species is intermediate in form between that of phocoenids and delphinids, supporting the hypothesis of a sister relationship for the two groups. Thus, these new species fill not only the morphological gap between Phocoenidae and other families of Delphinoidea but also a temporal gap in the fossil record of phocoenids in the western North Pacific.

A new basal porpoise, Pterophocaena nishinoi (Cetacea, Odontoceti, Delphinoidea), from the upper Miocene of Japan and its phylogenetic relationships

ABSTRACT Pterophocaena nishinoi, gen. et sp. nov. (Phocoenidae), from the upper Miocene Wakkanai Formation (9.2–9.3 Ma) in Hokkaido, northern Japan, is described. This is the oldest fossil phocoenid in the western North Pacific, thus extending the fossil record of Phocoenidae an additional approximately 4 million years in the region compared with the previous record. The holotype, composed of a partial skull, with right periotic and tympanic bulla and a postcranial skeleton, has the following apomorphic characters: absence of the premaxillary eminence; posterior half of the hamular process of the pterygoids not separated by palatines; prominent dorsolaterally projecting premaxilla in the facial area; supraorbital process of the maxilla steeply sloping ventrolaterally; posteriorly protruding temporal crest; anteroventrally narrowed and inverted teardrop-shaped temporal fossa; and several short ridges on the tympanosquamosal recess of the squamosal. A comprehensive cladistic analysis (66 ingroup taxa and 278 morphological characters) indicates that Pterophocaena is the most basal phocoenid yet discovered, and that Phocoenidae and Delphinidae are closely related. The discovery of Pterophocaena leads to a review of previous hypotheses for the origin of Phocoenidae, and indicates that phocoenids had already diversified in the Pacific Ocean by late Miocene.

Eodelphis kabatensis, a new name for the oldest true dolphin Stenella kabatensis Horikawa, 1977 (Cetacea, Odontoceti, Delphinidae), from the upper Miocene of Japan, and the phylogeny and paleobiogeography of Delphinoidea

ABSTRACT The oldest reported fossil record of Delphinidae is from the late Miocene (11 Ma) of California. Reliable Miocene fossil delphinids, however, are few. Eodelphis kabatensis from the upper Miocene Mashike Formation (8.5–13.0 Ma), Hokkaido, northern Japan, is the oldest described Miocene delphinid including a skull. Therefore, this species is a significant clue to understanding the early evolutionary history of Delphinidae. The original taxonomic assignment of this species within the genus Stenella is questionable; thus, we propose a new combination for the species, Eodelphis kabatensis Horikawa, 1977. Eodelphis is a basal delphinid, and comprehensive morphological cladistic analysis, including molecular topological constraints, supported this taxonomic revision. Paleobiogeographic analyses based on the present morphological cladistic analysis and analysis under the molecular constraints suggest that the origin and early diversification of Delphinidae occurred in the middle Miocene Pacific Ocean or elsewhere, respectively.

Timing of Shell Size Increase and Decrease of the Planktic Foraminifer Neogloboquadrina pachyderma (Sinistral) During the Pleistocene, IODP Exp. 303 Site U1304, the North Atlantic Ocean

We made shell size measurements of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) using samples from IODP Site U1304, the North Atlantic. We found that mean and maximum shell sizes began to increase around 1.1 Ma, and that several episodic changes in test size occurred during 0.6 - 0.35 Ma. Test size reached a maximum during the late Quaternary. Based on correlation with previous investigations, we have confirmed that these changes in fo- raminiferal shell size occurred on an inter-ocean scale.

Spatial variability in valve morphology of Neodenticula seminae, an oceanic diatom in the subarctic North Pacific and the Bering Sea

ABSTRACT To gain basic insights into the marine pelagic diatom species Neodenticula seminae, and particularly the relationships between morphology, evolution and environment, we conducted a scanning electron microscopic image analysis using modern specimens collected in the subarctic North Pacific and Bering Sea during the summers of 1955 and 1996–2003. We recognized an apparent intraspecific variability between two biogeographic provinces in terms of morphology: (1) the Oyashio Region (in the northwestern margin of the Pacific Ocean) and (2) other oceanic regions. This variability may reflect spatial variation in the availability of nutrients such as silicate. Specimens from the Oyashio morphological province had thinly silicified valves, whereas those from the other oceanic provinces were extraordinarily rich in heavily silicified valves.

New fossil remains from the Pliocene Koetoi Formation of northern Japan provide insights into growth rates and the vertebral evolution of porpoises

Extant porpoises (Phocoenidae) are odontocetes characterized by their small size, short and wide rostrum, late (or absent) completion of epiphyseal ankylosis in the vertebral column (= physical maturity), and short life cycles, all of which are thought to have resulted from progenetic evolution. We describe a small fossil phocoenid from the lower Pliocene Koetoi Formation of Hokkaido (northern Japan), preserving a small, narrow rostrum, as well as anteroposteriorly elongate thoracic and lumbar vertebral centra with completely fused epiphyses. Physical maturity in this specimen occurred significantly earlier than in extant phocoenids, as shown by dental data indicating that the specimen died at only four years of age. The difference between the present material and extant porpoises may be attributable to different growth rates during ontogeny. The long centra and caudally inclined neural spines of the specimen from Hokkaido are primitive characters among phocoenids. By contrast, the great height of its neural spines is highly derived, even among extant species, and suggestive of a fast swimmer. In terms of its vertebral morphology, the new specimen falls within a morphological continuum defined by the archaic Numataphocoena yamashitai and the highly derived vertebral morphology of Phocoenoides dalli. Phocoenid vertebral evolution has been complex and frequently convergent, as opposed to stepwise and unidirectional. The different vertebral morphologies of the new specimen and the contemporaneous extinct taxa Numataphocoena and Piscolithax longirostris indicate that they were adapted to different environments.

Asymmetrical basal delphinoid skull from the upper lower Miocene Yamato Formation of Hokkaido, northern Japan: implications on evolution of cranial asymmetry and symmetry in Odontoceti

Abstract. We describe an asymmetrical basal delphinoid skull from the upper lower Miocene Yamato Formation of Hokkaido, northern Japan. The skull shows clear cranial asymmetry: the nasal process of the left premaxilla is longer than that of the right one; the mesethmoid and frontals are left skewed 2.9°; and the right nasal is larger than the left one. Evaluation of the deformation of the fossil based on the carbonate content of the matrix indicates that the concretion in which the skull was found formed in an early stage of diagenesis and that the present specimen was not affected by compaction during diagenesis. A cladistic analysis including the new specimen shows cranial asymmetry among Delphinoidea extends back to the late early Miocene in the fossil record, and supports the hypothesis that cranial asymmetry in basal delphinoids is more common than previously thought. On the other hand, trait analyses suggest that the common ancestor of Delphinoidea had a symmetrical skull. We hypothesize that some extinct odontocetes that had symmetrical crania were able to produce narrow-band high-frequency clicks to avoid predation, as in extant symmetrical cranial species.

Eodelphinus kabatensis, a replacement name for Eodelphis kabatensis (Cetacea: Delphinoidea: Delphinidae)

Stenella kabatensis Horikawa, 1977, the oldest true dolphin (Mammalia, Cetacea, Delphinoidea; holotype HMH 68037), was recently redescribed and renamed Eodelphis kabatensis Horikawa, 1977 from the late Miocene of Japan (Murakami et al., 2014). The new generic name Eodelphis was proposed in reference to the oldest true dolphin (the Ancient Greek ‘Eo,’ for dawn referring to the earliest delphinid; and delphis, the Greek name for dolphin). Unfortunately, Eodelphis is preoccupied by a Cretaceous marsupial (Eodelphis browni Matthew, 1916). The Latin suffix delphis (from the Greek delphys), which is often used in the generic names of marsupials, is derived from the extant opossum Didelphis Linnaeus, 1758 (Marsupialia, Didelphimorphia, Didelphidae). This use of delphis does not mean ‘dolphin’, but is derived from the Greek delphys meaning “uterus”. Thus, the genus name Eodelphis is unavailable and the fossil delphinid needs a nomenclatural correction, despite the different etymology of these taxa. Therefore, here we propose Eodelphinus gen. nov. for the late Miocene delphinid Eodelphis kabatensis Horikawa, 1977 to replace Eodelphis Murakami et al., 2014, which is a junior homonym of Eodelphis Matthew, 1916. A new combination for the species is Eodelphinus kabatensis. The diagnosis and content of the new genus follows Murakami et al. (2014). Eodelphinus derives its name from the Ancient Greek ‘Eo,’ for dawn referring to the earliest delphinid; and delphinus, the Latin name for dolphin. Institutional Abbreviation—HMH, Historical Museum of Hokkaido, Hokkaido, Japan. ACKNOWLEDGMENTS