Naoki Kohno

Cope's rule and the evolution of body size in Pinnipedimorpha (Mammalia: Carnivora)

Copes rule describes the evolutionary trend for animal lineages to increase in body size over time. In this study, we tested the validity of Copes rule for a marine mammal clade, the Pinnipedimorpha, which includes the extinct Desmatophocidae, and extant Phocidae (earless seals), Otariidae (fur seals and sea lions), and Odobenidae (walruses). We tested for the presence of Copes rule by compiling a large dataset of body size data for extant and fossil pinnipeds and then examined how body size evolved through time. We found that there was a positive relationship between geologic age and body size. However, this trend is the result of differences between early assemblages of small‐bodied pinnipeds (Oligocene to early Miocene) and later assemblages (middle Miocene to Pliocene) for which species exhibited greater size diversity. No significant differences were found between the number of increases or decreases in body size within Pinnipedimorpha or within specific pinniped clades. This suggests that the pinniped body size increase was driven by passive diversification into vacant niche space, with the common ancestor of Pinnipedimorpha occurring near the minimum adult body size possible for a marine mammal. Based upon the above results, the evolutionary history of pinnipeds does not follow Copes rule.

Predictive equations for the estimation of body size in seals and sea lions (Carnivora: Pinnipedia).

Body size plays an important role in pinniped ecology and life history. However, body size data is often absent for historical, archaeological, and fossil specimens. To estimate the body size of pinnipeds (seals, sea lions, and walruses) for today and the past, we used 14 commonly preserved cranial measurements to develop sets of single variable and multivariate predictive equations for pinniped body mass and total length. Principal components analysis (PCA) was used to test whether separate family specific regressions were more appropriate than single predictive equations for Pinnipedia. The influence of phylogeny was tested with phylogenetic independent contrasts (PIC). The accuracy of these regressions was then assessed using a combination of coefficient of determination, percent prediction error, and standard error of estimation. Three different methods of multivariate analysis were examined: bidirectional stepwise model selection using Akaike information criteria; all‐subsets model selection using Bayesian information criteria (BIC); and partial least squares regression. The PCA showed clear discrimination between Otariidae (fur seals and sea lions) and Phocidae (earless seals) for the 14 measurements, indicating the need for family‐specific regression equations. The PIC analysis found that phylogeny had a minor influence on relationship between morphological variables and body size. The regressions for total length were more accurate than those for body mass, and equations specific to Otariidae were more accurate than those for Phocidae. Of the three multivariate methods, the all‐subsets approach required the fewest number of variables to estimate body size accurately. We then used the single variable predictive equations and the all‐subsets approach to estimate the body size of two recently extinct pinniped taxa, the Caribbean monk seal (Monachus tropicalis) and the Japanese sea lion (Zalophus japonicus). Body size estimates using single variable regressions generally under or over‐estimated body size; however, the all‐subset regression produced body size estimates that were close to historically recorded body length for these two species. This indicates that the all‐subset regression equations developed in this study can estimate body size accurately.

A new Miocene baleen whale from the Peruvian desert.

The Pisco-Ica and Sacaco basins of southern Peru are renowned for their abundance of exceptionally preserved fossil cetaceans, several of which retain traces of soft tissue and occasionally even stomach contents. Previous work has mostly focused on odontocetes, with baleen whales currently being restricted to just three described taxa. Here, we report a new Late Miocene rorqual (family Balaenopteridae), Incakujira anillodefuego gen. et sp. nov., based on two exceptionally preserved specimens from the Pisco Formation exposed at Aguada de Lomas, Sacaco Basin, southern Peru. Incakujira overall closely resembles modern balaenopterids, but stands out for its unusually gracile ascending process of the maxilla, as well as a markedly twisted postglenoid process of the squamosal. The latter likely impeded lateral (omega) rotation of the mandible, in stark contrast with the highly flexible craniomandibular joint of extant lunge-feeding rorquals. Overall, Incakujira expands the still meagre Miocene record of balaenopterids and reveals a previously underappreciated degree of complexity in the evolution of their iconic lunge-feeding strategy.

Correction: A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids

The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8–2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0–9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids.

Phylogeographic and Demographic Analysis of the Asian Black Bear (Ursus thibetanus) Based on Mitochondrial DNA.

The Asian black bear Ursus thibetanus is widely distributed in Asia and is adapted to broad-leaved deciduous forests, playing an important ecological role in the natural environment. Several subspecies of U. thibetanus have been recognized, one of which, the Japanese black bear, is distributed in the Japanese archipelago. Recent molecular phylogeographic studies clarified that this subspecies is genetically distantly related to continental subspecies, suggesting an earlier origin. However, the evolutionary relationship between the Japanese and continental subspecies remained unclear. To understand the evolution of the Asian black bear in relation to geological events such as climatic and transgression-regression cycles, a reliable time estimation is also essential. To address these issues, we determined and analyzed the mt-genome of the Japanese subspecies. This indicates that the Japanese subspecies initially diverged from other Asian black bears in around 1.46Ma. The Northern continental population (northeast China, Russia, Korean peninsula) subsequently evolved, relatively recently, from the Southern continental population (southern China and Southeast Asia). While the Japanese black bear has an early origin, the tMRCAs and the dynamics of population sizes suggest that it dispersed relatively recently in the main Japanese islands: during the late Middle and Late Pleistocene, probably during or soon after the extinction of the brown bear in Honshu in the same period. Our estimation that the population size of the Japanese subspecies increased rapidly during the Late Pleistocene is the first evidential signal of a niche exchange between brown bears and black bears in the Japanese main islands. This interpretation seems plausible but was not corroborated by paleontological evidence that fossil record of the Japanese subspecies limited after the Late Pleistocene. We also report here a new fossil record of the oldest Japanese black bear from the Middle Pleistocene, and it supports our new evolutionary hypothesis of the Japanese black bear.

Northern pygmy right whales highlight Quaternary marine mammal interchange

The pygmy right whale, Caperea marginata, is the most enigmatic living whale. Little is known about its ecology and behaviour, but unusual specialisations of visual pigments [1], mitochondrial tRNAs [2], and postcranial anatomy [3] suggest a lifestyle different from that of other extant whales. Geographically, Caperea represents the only major baleen whale lineage entirely restricted to the Southern Ocean. Caperea-like fossils, the oldest of which date to the Late Miocene, are exceedingly rare and likewise limited to the Southern Hemisphere [4], despite a more substantial history of fossil sampling north of the equator. Two new Pleistocene fossils now provide unexpected evidence of a brief and relatively recent period in geological history when Caperea occurred in the Northern Hemisphere (Figure 1A,B).

Evaluating the Phylogenetic Status of the Extinct Japanese Otter on the Basis of Mitochondrial Genome Analysis

The Japanese otter lived throughout four main Japanese islands, but it has not been observed in the wild since 1979 and was declared extinct in 2012. Although recent taxonomic and molecular phylogenetic studies suggest that it should be treated as an independent species, International Union for Conservation of Nature Red List considers it as subspecies of Lutra lutra. Therefore, the taxonomic status of this species needs to be resolved. Here we determined the complete mitochondrial genome of two Japanese otters caught in Kanagawa and Kochi prefectures and five Eurasian otters (L. lutra). We reconstructed a molecular phylogenetic tree to estimate the phylogenetic position of the Japanese otter in Lutrinae using the Japanese otters and the other 11 Lutrinae species on the basis of ND5 (692 bp) and cytochrome b (1,140 bp) sequences. We observed that the two Japanese otters had close relationships with Eurasian otters, forming a monophyletic group (100% bootstrap probability). To elucidate detailed phylogenetic relationships among the Japanese and Eurasian otters, we reconstructed a maximum likelihood tree according to mitochondrial genome sequences (14,740 bp). The Japanese otter (JO1) collected in Kanagawa was deeply nested in the Eurasian otter clade, whereas the Japanese otter (JO2) collected in Kochi formed a distinct independent lineage in the Lutra clade. The estimated molecular divergences time for the ancestral lineages of the Japanese otters was 0.10 Ma (95%: 0.06–0.16 Ma) and 1.27 Ma (95%: 0.98–1.59 Ma) for JO1 and JO2 lineages, respectively. Thus, JO1 was identified as a member of L. lutra; JO2 represented the old Japanese otter lineage, which may be a distinct new species or subspecies of Lutra. We suggest that the ancestral population of the JO2 lineage migrated to Japan via the land bridge that existed between western Japanese islands and Asian continent at 1.27 Ma.

A new Miocene pinniped Allodesmus (Mammalia: Carnivora) from Hokkaido, northern Japan

A nearly complete pinniped skeleton from the middle Miocene Okoppezawa Formation (ca 16.3–13.9 Ma), Hokkaido, northern Japan, is described as the holotype of Allodesmus uraiporensis sp. nov. The new species is distinguishable from other species of the genus by having the palatine fissure (incisive foramen) that is located anterior to the canine, an anteriorly located supraorbital process of the frontal, and by having the calcaneum with a developed peroneal tubercle. Our phylogenetic analysis suggests that the subfamily Allodesminae are represented by two genera, Atopotarus and Allodesmus, and the latter genus is represented by at least six species; Al. kernensis, Al. sinanoensis, Al. naorai, Al. packardi, Al. demerei and Al. uraiporensis sp. nov. Allodesmus uraiporensis sp. nov. is one of the oldest and the northernmost record of the genus in the western North Pacific, and it suggests that the diversification of the genus in the western North Pacific was synchronous to the time of their diversification in the eastern North Pacific.

A new desmostylian mammal from Unalaska (USA) and the robust Sanjussen jaw from Hokkaido (Japan), with comments on feeding in derived desmostylids

Derived members of the enigmatic mammalian order Desmostylia have molars comprising appressed columns whose morphology does not render their function in feeding simple to discern. Here we describe a new genus and species, Ounalashkastylus tomidai, more derived than Cornwallius but less derived than Desmostylus and Vanderhoofius, which develop a hypertrophied medial eminence on the dentary ontogenetically. Tooth morphology, vaulted palate and the medial eminence, which can rise to the level of the occlusal surface of M2, suggest that derived desmostylids clenched their teeth strongly while employing suction during feeding, most likely on marine and coastal plants.

Three-dimensional tooth surface texture analysis on stall-fed and wild boars (Sus scrofa)

Categorizing the archaeological remains of Sus scrofa as domesticated “pigs” or wild “boars” is often difficult because of their morphological and genetic similarities. For this purpose, we tested whether feeding ecological change of S. scrofa that accompanied their domestication can be detected based on the three-dimensional texture created on the tooth enamel surface by mastication. We scanned the lower tooth surface of one wild and one stall-fed populations of modern S. s. leucomystax and one wild population of S. s. riukiuanus by using a confocal laser microscope. The average body weight of S. s. leucomystax is twice as heavier as that of S. s. riukiuanus. The textures were quantified using the industrial “roughness” standard, ISO 25178, to prevent inter-observer errors and to distinguish small differences that were difficult to detect by two dimensional image observation. The values of parameters related to height and volume were significantly larger in the stall-fed population. Twenty parameters differed significantly between the stall-fed and wild population of S. s. leucomystax, which indicated that the feeding ecological difference affected the ISO parameters of the two boar populations. Six parameters also differed between the wild populations of S. s. leucomystax and S. s. riukiuanus. Surprisingly, no parameter differed between the populations of stall-fed S. s. leucomystax and wild S. s. riukiuanus. Consumption of hard nuts and/or agricultural fruits and crops by the wild population of S. s. riukiuanus may have produced a tooth surface texture similar to that of the stall-fed population of S. s. leucomystax. Further analysis of S. s. riukiuanus with a known diet is necessary to conclude whether ISO parameters reflect the dietary transition accompanying the domestication of Sus (e.g., wild, semi-domestic, and domestic). Until then, caution is needed in discriminating domesticated populations from wild populations that mainly feed on hard objects.