Cetacean Evolution

Monografía realizada para la materia "EVOLUCIÓN" de la Licenciatura en Ciencias Biológicas (2007) de la Universidad Nacional de Mar del Plata.
Es una breve compilación de los autores mas destacados en evolución de mamíferos marinos, incluye gráficos y conflictos taxonómicos históricos en la temática recorriendo los diferentes taxones de cetáceos que se reconocen a fecha de 2016.

The demand for live bottlenose dolphins for commercial use is growing in Mexico, making the need for stock assessment and management ever more essential given their protected status. Tursiops truncatus is known to exhibit high levels of phenotypic polymorphisms. In the Gulf of California (GC), coastal and offshore ecotypes have been identified based on morphological, behavioral and ecological evidence, including different prey and habitat preferences. However, the extent to which this ecological and phenotypic variation is genetically correlated is unknown. Here we assess this correlation in GC bottlenose dolphins classified as coastal or offshore based on habitat, morphological and trophic evidence. Significant (p < 0.0001) haplotype heterogeneity (exact test) and genetic differentiation (FST = 0.069) were found in the mitochondrial control region, indicating some reproductive isolation between ecotypes. As elsewhere, coastal dolphins were less diverse than offshore. Phylogenetic analyses revealed paraphyletic coastal and offshore lineages and no evidence of lineage sorting, possibly due to recent isolation or gene flow. This is the first time that genetic, morphological and stable isotope evidence has been used to recognize ecotypes as different stocks for management purposes in bottlenose dolphins. Our results indicate that diversifying forces are shaping their phenotypic and genetic variation in the GC. Management and conservation efforts in this strategic region should aim to preserve these forces.

Esperante, R., Muñiz Guinea, F., Nick, K.E., 2009, Taphonomy of a mysticeti whale in the Lower Pliocene Huelva Sands Formation (Southern Spain): Geologica Acta 7(4), 489-504.

Abstract: This paper reports the occurrence of an incomplete fossil baleen whale skeleton in the Lower Pliocene Huelva Sands Formation (Guadalquivir basin) near the town of Bonares, southwestern Spain. The skeleton was found in the highly bioturbated glauconitic sandstone unit in association with Neopycnodonte cochlear shells. Several morphological features of the mandibles, scapula and vertebrae suggest that the specimen belongs in the suborder
Mysticeti, family Balaenopteridae. Most bones show abrasion due to a long exposure on the seafloor, and some bones show shark tooth marks and both micro- and macro-bioerosion by scavengers. The position of the bones suggests that the carcass landed on the seafloor on its left side and then turned right side up. Sedimentological and paleontological features indicate that the whale was buried in shallow platform waters under low
sedimentation rates.

"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."

A fossil kentriodontid has been recovered from the lower Miocene Arakida Formation, Tomikusa Group (Burdigalian: ca., 18.1-17.2 Ma), Nagano Prefecture, Japan. The specimen consists of isolated left periotic, tympanic bulla, malleus, incus, and stapes. The anterior process of the periotic represents a rectangular outline in lateral view and this suggests that the specimen belongs to the Delphinoidea. The specimen lacks the
synapomorphies for the families in each Delphinoidea except Kentriodontidae (e.g., well developed parabullary ridge for Delphinidae). In comparison with previously described kentriodontid genera, the specimen represents a unique combination of the morphological characters: e.g., the anterior process of the periotic is well rounded and lacks anterior keel, the apex of the anterior process is not pointed, and the lateral process of the periotic is moderately projected laterally. The specimen described here is an early member of the kentriodontids and may expand our knowledge of the early evolution of the Kentriodontidae.

During the Eocene epoch, archaic cetaceans made the land-to-sea transition, giving rise to modern whales, dolphins, and porpoises. During this transition, the feeding apparatus of fossil remingtonocetines displayed morphologies that are distinct from other cetaceans, confounding straightforward interpretations of their feeding behaviors. This study utilized a novel combined ordination of morphology and feeding strategy, while accounting for phylogeny, in a sample of 2 remingtonocetines and 18 extant cetartiodactylans, to assess the morphological signal of feeding behaviors. Results showed that differences between prey acquisition in extant taxa were driven by a suite of mandibular characters and width of the palatal arch, providing a behaviorally constrained morphospace. Remingtonocetinae clustered closest to the snap-feeding river dolphins, suggesting that they too were snap feeders. The methods presented here represent a novel application for constrained ordination that links morphology with performance, and may be widely applied in the fossil record.

The extinct edentulous mysticete family Cetotheriidae historically has been viewed as a notoriously paraphyletic group, and only recently have rigorous studies been executed to rectify this issue. These problems do not necessarily just stem from lack of phylogenetic analyses, but are in part because of a general lack of complete specimens, poor descriptions of taxa, and long-lived taxonomic instability issues. The fossil mysticete genus Herpetocetus is a poster child of these problems as it is primarily only known from a few relatively incomplete and poorly described specimens. A new species of Herpetocetus from the upper Pliocene of California, Herpetocetus morrowi sp. nov., provides an archetypal model for the genus based on a multitude of well-preserved specimens. These specimens reveal a diminutive mysticete characterized by an elongate rostrum and roughly quadrate cranium. A mosaic of primitive and derived features preserved in this new species underscores its potential value in helping to resolve a number of taxonomic and phylogenetic problems. The occurrence of specimens assignable to juvenile through to mature adult individuals provides a basis for investigating ontogenetic changes. Functional analysis of the unusual craniomandibular anatomy of H. morrowi suggests a limited degree of mandibular gape and an enhanced capacity for longitudinal rotation of the dentary, features that support a hypothesis of suction feeding convergent with that of living grey whales. A phylogenetic analysis provides support for recognition of a redefined and monophyletic Cetotheriidae and Herpetocetinae, and also serves as a basis for evaluating the recent proposal that the pygmy right whale (Caperea marginata) is a living cetothere. Morphological features of Herpetocetus morrowi, including features of the cranium and petrosal, suggest that a number of the purported synapomorphies supporting a Caperea−cetothere grouping are either symplesiomorphies, nonhomologous features, or are highly variable. © 2014 The Linnean Society of London