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Rachel A Racicot - One of the best experts on this subject based on the ideXlab platform.

  • Dolphins, Porpoises, and Monodontids, Evolution
    Encyclopedia of Marine Mammals, 2018
    Co-Authors: Rachel A Racicot
    Abstract:

    Summary The Delphinoidea comprise some of the most diverse and disparate extinct and extant cetaceans, including oceanic dolphins (Delphinidae), true porpoises (Phocoenidae), and the narwhal and beluga (Monodontidae). The relationships within delphinoids and their relationships among other odontocetes are fairly well established by phylogenetic analyses using genotypic, phenotypic, and combined datasets. Extinct lineages that may be related to delphinoids, including the Kentriodontidae, a temporally and geographically widespread, “generalized” dolphin-like taxon, and Eurhinodelphinidae, swordfish-like toothed whales with dramatically long beaks, are also reviewed.

  • comparative anatomy of the bony labyrinth of extant and extinct porpoises cetacea Phocoenidae
    Biological Journal of The Linnean Society, 2016
    Co-Authors: William Gearty, Naoki Kohno, Rachel A Racicot, John J. Flynn
    Abstract:

    The inner ear anatomy of cetaceans, now more readily accessible by means of nondestructive high-resolution X-ray computed tomographic (CT) scanning, provides a window into their acoustic abilities and ecological preferences. Inner ear labyrinths also may be a source for additional morphological characters for phylogenetic analyses. In this study, we explore digital endocasts of the inner ear labyrinths of representative species of extinct and extant porpoises (Mammalia: Cetacea: Phocoenidae), a clade of some of the smallest odontocete cetaceans, which produce some of the highest-frequency clicks for biosonar and communication. Metrics used to infer hearing ranges based on cochlear morphology indicate that all taxa considered could hear high-frequency sounds, thus the group had already acquired high-frequency hearing capabilities by the Miocene (9–11 Mya) at the latest. Vestibular morphology indicates that extant species with pelagic preferences have similarly low semicircular canal deviations from 90°, values indicating more sensitivity to head rotations. Species with near-shore preferences have higher canal deviation values, indicating less sensitivity to head rotations. Extending these analyses to the extinct species, we demonstrate a good match between those predicted to have coastal (such as Semirostrum cerutti) preferences and high canal deviation values. We establish new body length relationships based on correlations with inner ear labyrinth volume, which can be further explored among other aquatic mammals to infer body size of specimens consisting of fragmentary material.

  • Unique Feeding Morphology in a New Prognathous Extinct Porpoise from the Pliocene of California
    Current biology : CB, 2014
    Co-Authors: Rachel A Racicot, Thomas A. Deméré, Brian L. Beatty, Robert W. Boessenecker
    Abstract:

    Summary Modern porpoises (Odontoceti: Phocoenidae) are some of the smallest cetaceans and usually feed near the seafloor on small fish and cephalopods [1–3]. Within both extinct and extant phocoenids, no evidence for specialized mandibular morphology has been documented [4–7]. Here we describe a new species of extinct porpoise, Semirostrum ceruttii , from the marine Pliocene San Diego (4.2–1.6 mega-annum, Ma) and Purisima (5–2.5 Ma) formations of California. The mandibles comprise a long, fused, and nearly edentulous prognathous symphysis, extending farther beyond the rostrum than in any known mammal. Phylogenetic analyses based on morphology reconstruct Semirostrum ceruttii as sister to extant (crown) porpoise species with moderate support. We describe the spectacularly preserved holotype specimen based on computed tomography (CT) scans, which allowed visualization of the elongate mental and accessory canals within the symphysis. The elongate canals are similar to those found in Rynchops birds [8] and were likely involved in sensory function. Oblique labial wear facets present on numerous small conical mandibular teeth posterior to the symphysis suggest regular contact with benthic substrate. The unique mandibular and dental characteristics, along with robust scapulae, sternum, and unfused cervical vertebrae, support the interpretation that this species employed a form of benthic skim feeding by using its mandible to probe for and obtain prey.

  • Endocranial anatomy of a new fossil porpoise (Odontoceti, Phocoenidae) from the Pliocene San Diego Formation of California
    Journal of Paleontology, 2014
    Co-Authors: Rachel A Racicot, Timothy B. Rowe
    Abstract:

    The Pliocene fossil porpoise SDSNH 65276 has extremely elongate mandibular morphology, unlike that of any marine amniote, and is superficially most similar to the living bird species known as skimmers (Rynchops sp.). Endocasts of the pterygoid sinuses and endocranial cavity were digitally segmented from high-resolution X-ray CT scans of the specimen to explore internal anatomy of functionally and phylogenetically important anatomical features of this specimen and odontocetes in general. The sinuses are similar in volume and shape to extant porpoise species, but the dorsal extension of the preorbital lobes are particularly elongate as in the harbor porpoise (Phocoena phocoena). The cranial endocast also shows similarities with extant porpoises, but has much deeper interhemispheric fissures, which are filled by ossified meninges, particularly a deep falx cerebri and shallower tentorium cerebelli. Ossifications of these parts of the meninges may reflect faster angular accelerations of the head, deeper diving ability, or both. Penetrations of the endocranial cavity for cranial nerves and blood vessels are like those of extant porpoises. The internal skull morphology of this unique delphinoid sheds additional light both on its phylogenetic affinities and novel odontocete adaptations.

  • Morphology and variation in porpoise (Cetacea: Phocoenidae) cranial endocasts
    The Anatomical Record, 2013
    Co-Authors: Rachel A Racicot, Matthew W. Colbert
    Abstract:

    Evolution of endocranial anatomy in cetaceans is important from the perspective of echolocation ability, intelligence, social structure, and alternate pathways for circulation to the brain. Apart from the importance of studying brain shape and asymmetries as they relate to aspects of behavior and intelligence, cranial endocasts can show a close correspondence to the hydrostatic shape of the brain in life, and canals and grooves can preserve features of the circulatory system. Multiple samples are rarely available for studies of individual variation, especially in fossils, thus a first step in quantifying variation and making comparisons with fossils is made possible with CT scans of osteological specimens. This study presents a series of high-resolution X-ray CT-derived cranial endocasts of six extant species of Phocoenidae, a clade including some of the smallest and one of the rarest cetaceans. Degree of gyrification varies interspecifically and intraspecifically, possibly resulting from variation in preservation of the ossified meninges. Computed tomographic data show that visually assessed asymmetry in the cranial endocasts is not correlated with volumetric measurements, but nonetheless may reflect torsion in the skull’s shape such that the right cerebral and cerebellar hemispheres extend rostrally and laterally more than the left. Vasculature and canals are similar to other described cetacean species, but the hypophyseal casts are unusual. Similarities between brain shape and volume measurements in the different species can be attributed to paedomorphism and concomitant variation in ecological preferences. This may explain similarities Neophocaena phocaenoides and Phocoena sinus share with the juvenile Phocoena phocoena specimen studied. Anat Rec, 296:979–992, 2013. V C 2013 Wiley Periodicals, Inc.

William F. Perrin - One of the best experts on this subject based on the ideXlab platform.

  • Phylogenetic relationships among the true porpoises (Cetacea:Phocoenidae).
    Molecular phylogenetics and evolution, 1995
    Co-Authors: Patricia E. Rosel, Margo G. Haygood, William F. Perrin
    Abstract:

    Portions of the cytochrome b gene and control region of the mitochondrial DNA molecule were sequenced to investigate systematic relationships among the six extant species of true porpoises, (Cetacea: Phocoenidae). Phylogenetic analyses of mitochondrial cytochrome b sequences support a close relationship between Burmeister's porpoise, Phocoena spinipinnis, and the vaquita, Phocoena sinus, and the association of these two species with the spectacled porpoise, Australophocaena dioptrica. The latter result is not in concordance with a recent morphological reclassification which groups A. dioptrica with Dall's porpoise, Phocoenoides dalli, in the subfamily Phocoenoidinae. The molecular analysis found no support for this grouping. A. dioptrica was originally described as a member of the genus Phocoena, and our results support returning it to that genus at this time. Finally, the data suggest that the tropical species Neophocaena phocaenoides, the finless porpoise, may represent the most basal member of the family. The control region sequences corroborated the relationships among the closely related taxa P. sinus, P. spinipinnis, and A. dioptrica, but were unable to resolve the deeper branches of the tree, probably as a result of a high level of saturation of these sequences.

L. T. Findley - One of the best experts on this subject based on the ideXlab platform.

  • Life history of the vaquita, Phocoena sinus (Phocoenidae, Cetacea)
    Journal of Zoology, 1996
    Co-Authors: Aleta A. Hohn, Omar Vidal, Andrew J. Read, S. Fernandez, L. T. Findley
    Abstract:

    The vaquita, Phocoena sinus, is the most endangered marine cetacean primarily due to incidental mortality in fishing nets. We examined a sample of 56 vaquitas to study the life history of this poorly known species. The age structure was bimodal, with 62% of the specimens from 0-2 years and 31% from 11-16 years; the sample contained no specimens from ages 3-6 years. The oldest individual was estimated to be 21 years old. All specimens less than three years old were sexually immature and all greater than six years old were mature. The asymptotic length of females (140.6cm) was significantly greater than that of males (134.9 cm), although no difference was detected in asymptotic girth or body mass. Reproduction is synchronous; births occurred from late February to early April and maximum testes activity occurred from mid-March through to at least mid-April. Our observations from this small sample suggest that the calving interval is greater than one year. The sample was too small for many quantitative analyses, although it appears that lifespan, patterns of growth, age at sexual maturation, seasonal reproduction, and large testis size are similar to the harbour porpoise, P. phocoena, in a highly exploited and wellstudied population from the Bay of Fundy. A significant difference, however, is that harbour porpoise females give birth annually, indicating that the rate of increase in the vaquita population is likely to be lower than that in the harbour porpoise. Without immediate cessation of fishing pressure, this fragile population will collapse, resulting in extinction of the vaquita.

Michael J. Stanhope - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Phylogenetic Examination of the Delphinoidea Trichotomy: Congruent Evidence from Three Nuclear Loci Indicates That Porpoises (Phocoenidae) Share a More Recent Common Ancestry with White Whales (Monodontidae) Than They Do with True Dolphins
    Molecular phylogenetics and evolution, 2000
    Co-Authors: Victor G. Waddell, Michel C. Milinkovitch, Martine Bérubé, Michael J. Stanhope
    Abstract:

    Porpoises (Phocoenidae), dolphins (Delphinidae), and the two species of Monodontidae (beluga and narwhal) together constitute the superfamily Delphinoidea. Although there is extensive evidence supporting the monophyly of this superfamily, previous studies involving morphology, as well as sequence analysis of mitochondrial genes, have failed to yield a clear picture of the relative relationships within the group. Here we present the first examination of this issue from the perspective of single-copy nuclear genes at the DNA sequence level. The data involve three such loci: von Willebrand factor (vWF), interphotoreceptor retinoid binding protein (IRBP), and lactalbumin. The vWF and IRBP data sets consist of protein-coding fragments, whereas the sequenced lactalbumin fragment is predominately intronic. All phylogenetic analyses involving at least one representative from each of the three Delphinoidea families congruently support a beluga/porpoise clade. The levels of sequence divergence for most of these data appear to roughly concur with a paleontological date for the radiation of the Delphinoidea at 11-15 MYA but, in agreement with mitochondrial DNA sequence analyses, suggest that the extant major groups of cetaceans radiated approximately 25 MYA, 10 million years later than inferred from paleontological data.

R. Natalie P. Goodall - One of the best experts on this subject based on the ideXlab platform.

  • Interspecific variation of ontogeny and skull shape among porpoises (Phocoenidae).
    Journal of Morphology, 2010
    Co-Authors: Anders Galatius, Marie Schou Frandsen, Annalisa Berta, R. Natalie P. Goodall
    Abstract:

    All extant members of Phocoenidae (por- poises) have been characterized as pedomorphic based on skeletal characters. To investigate the ontogenetic background for pedomorphosis and assess interspecific differences in ontogeny among phocoenids, samples of the six extant species were compared in terms of devel- opment of both epiphyseal and cranial suture fusion. Across all species, full maturity of the vertebral column was rare. Vertebral epiphyseal development did not pro- gress so far in most Phocoena phocoena as in Phocoe- noides dalli and Phocoena dioptrica. P. phocoena, Phocoena spinipinnis, Ph. dalli, and P. dioptrica, for which large series were available, were further compared in terms of ontogeny of cranial shape by three-dimen- sional geometric morphometrics. Ph. dalli and P. diop- trica generally showed further development of cranial sutures than the other species. Postnatal skull shape de- velopment was similar for all species studied; the major- ity of interspecific shape differences are present at partu- rition. Smaller species had a higher rate of shape develop- ment relative to growth in size than Ph. dalli and P. dioptrica, but they still showed less allometric develop- ment due to less postnatal growth. Interspecific shape dif- ferences indicate phylogenetic relationships similar to that proposed based on morphology or convergent evolu- tion of the two pelagic species, Ph. dalli and P. dioptrica, under the scenarios suggested by recent molecular stud- ies. A shape trend coinciding with habitat preference was detected; in species with pelagic preference the position and orientation of the foramen magnum aligned the skull with the vertebral column; the rostrum showed less ven- tral inclination, and the facial region was larger and more concave in lateral aspect. J. Morphol. 272:136-148, 2011. 2010 Wiley-Liss, Inc.

  • THE PHYLOGENETIC RELATIONSHIPS AND BIOGEOGRAPHY OF TRUE PORPOISES (MAMMALIA: Phocoenidae) BASED ON MORPHOLOGICAL DATA
    Marine Mammal Science, 2006
    Co-Authors: Liliana Fajardo‐mellor, Robert L. Brownell, Annalisa Berta, Claudia Clementina Boy, R. Natalie P. Goodall
    Abstract:

    Prior studies of phylogenetic relationships among phocoenids based on morphology and molecular sequence data conflict and yield unresolved relationships among species. This study evaluates a comprehensive set of cranial, postcranial, and soft anatomical characters to infer interrelationships among extant species and several well-known fossil phocoenids, using two different methods to analyze polymorphic data: polymorphic coding and frequency step matrix. Our phylogenetic results confirmed phocoenid monophyly. The division of Phocoenidae into two subfamilies previously proposed was rejected, as well as the alliance of the two extinct genera Salumiphocaena and Piscolithax with Phocoena dioptrica and Phocoenoides dalli. Extinct phocoenids are basal to all extant species. We also examined the origin and distribution of porpoises within the context of this phylogenetic framework. Phocoenid phylogeny together with available geologic evidence suggests that the early history of phocoenids was centered in the North Pacific during the middle Miocene, with