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Vertebral morphology has profound biomechanical implications and plays an important role in adaptation to different habitats and foraging strategies for cetaceans. Extant porpoise species (Phocoenidae) display analogous evolutionary patterns in both hemispheres associated with convergent evolution to coastal versus oceanic environments. We employed 3D geometric morphometrics to study vertebral morphology in five porpoise species with contrasting habitats: the coastal Indo-Pacific finless porpoise (Neophocaena phocaenoides); the mostly coastal harbor porpoise (Phocoena phocoena) and Burmeister's porpoise (Phocoena spinipinnis); and the oceanic spectacled porpoise (Phocoena dioptrica) and Dall's porpoise (Phocoenoides dalli). We evaluated the radiation of vertebral morphology, both in size and shape, using multivariate statistics. We supplemented data with samples of an early-radiating delphinoid species, the narwhal (Monodon monoceros); and an early-radiating delphinid species, the white-beaked dolphin (Lagenorhynchus albirostris). Principal component analyses were used to map shape variation onto phylogenies, and phylogenetic constraints were investigated through permutation tests. We established links between vertebral morphology and movement patterns through biomechanical inferences from morphological presentations. We evidenced divergence in size between species with contrasting habitats, with coastal species tending to decrease in size from their estimated ancestral state, and oceanic species tending to increase in size. Regarding vertebral shape, coastal species had longer centra and shorter neural processes, but longer transverse processes, while oceanic species tended to have disk-shaped vertebrae with longer neural processes. Within Phocoenidae, the absence of phylogenetic constraints in vertebral morphology suggests a high level of evolutionary lability. Overall, our results are in accordance with the hypothesis of speciation within the family from a coastal ancestor, through adaptation to particular habitats. Variation in vertebral morphology in this group of small odontocetes highlights the importance of environmental complexity and particular selective pressures for the speciation process through the development of adaptations that minimize energetic costs during locomotion and prey capture.

Commerson’s dolphin (Cephalorhynchus commersonii), Peale’s dolphin (Lagenorhynchus australis), dusky dolphin (Lagenorhynchus obscurus), and hourglass dolphin (Lagenorhynchus cruciger) are closely related species occurring in the Southern Hemisphere. Even though they are partially sympatric, they have evolved towards diverse foraging strategies, prey, and habitat preferences. Size variation occurs both among and within species. Our goal was to study the allometric patterns and ontogenetic trajectories in the vertebral column of these dolphins related to their ecology. We choose nine functionally homologous vertebrae in each column and digitized five different tridimensional configurations, containing 28 to 41 landmarks depending on the functional region under analysis. We explored different levels of allometry (static, ontogenetic, and evolutionary) using multivariate regressions of shape vs. log-transformed centroid size. We compared ontogenetic allometry regression vectors to evidence differences in growth patterns. Finally, we calculated Procrustes distances of shape configurations to determine the timing of shape shifts. Of the studied species, When compared to the Lagenorhynchus species, Commerson’s dolphin showed the highest degrees of allometry, both static and ontogenetic. The macroevolutive trends indicate a high degree of evolutionary morphological change, which could be associated with the rapid evolutionary radiation proposed for the group. This is the first time that allometric changes are studied in small cetaceans by means of 3D geometric morphometrics. Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Mora, Matias Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Dans, Silvana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: González-José, Rolamdo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

In cetaceans, increased body flexibility is associated with increased maneuverability, this affects the animal’s swimming speed and foraging behavior. A more stable body form is associated with fast swimming and wide turns. One factor that affects the flexibility of a cetacean’s body is the structure and interaction of its vertebrae. Differences in vertebral morphology confer different muscular insertion sites and affect mechanical properties of swimming muscles. We studied vertebral morphology in four closely related and partially sympatric dolphin species from the Southern Hemisphere: Commerson’s dolphin (Cephalorhynchus commersonii), Peale’s dolphin (Lagenorhynchus australis), the dusky dolphin (Lagenorhynchus obscurus) and the hourglass dolphin (Lagenorhynchus cruciger). The former two species are usually considered coastal, associated with complex habitats where foraging strategies require greater maneuverability; they also show plasticity in their prey preferences. The latter two species are considered fastswimming cooperative feeders, with long distance movements reflecting prey availability in pelagic habitats. We employed three-dimensional (3D) geometric morphometric techniques and multivariate analyses to evaluate differences in vertebral morphology. Our analyses tested whether particular morphologies that limit or enhance flexibility were associated with preferred habitats and feeding strategies. We established links between morphology and behavioral patterns based on the biomechanical significance of specific vertebral morphological features. Principal component analyses (PCA) showed great differentiation between species in all the studied regions along the vertebral column. This was especially evident in the middle area, except in the case of dusky and hourglass dolphins which showed no discernible morphological difference in their mid-column vertebrae. PCA results were supported by statistically significant Mahalanobis distances (MD) between species. Species associated with complex habitats and behaviors possessed morphological features associated with greater flexibility of the column (i.e., spool-shaped vertebrae with short erect processes), whereas cooperative-feeder species possessed features associated with greater stability (i.e., disk-shaped vertebrae with long strongly bent processes). In these closely related and partially sympatric dolphins, vertebral morphology is distinctive and varies with the differential foraging strategies and habitat of each species. These findings reveal morphological plasticity among these dolphin species, highlighting the importance of behavioral complexity and of habitat use in the evolutionary development of morphological adaptations. Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Mora, Matias Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Dans, Silvana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Coscarella, Mariano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Gonzalez-Jose, Rolando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Ciencias Sociales y Humanas; Argentina

Subdivisión funcional de la columna vertebral en cuatro delfines sudamericanos. La descripción e interpretación funcional de la variación morfológica en la columna de delfines pueden facilitarse mediante el reconocimiento de unidades estructurales a lo largo de toda la estructura de la columna. Esta información ofrece pistas importantes sobre la proporción de la columna involucrada en la oscilación y el desplazamiento de la aleta caudal, y cómo el estilo de natación puede variar entre las especies. Por lo tanto, la caracterización morfológica y la subdivisión funcional de la columna vertebral son de fundamental importancia para obtener información sobre el comportamiento locomotor de las especies de cetáceos que habitan ambientes diferentes. Se empleó morfometría tradicional para establecer la subdivisión funcional de la columna vertebral del delfín de la tonina overa (Cephalorhynchus commersonii), una especie costera, y el delfín oscuro (Lagenorhynchus obscurus), una especie de plataforma, realizando una primera caracterización morfológica de sus columnas vertebrales. Estas especies están estrechamente relacionadas y, en algunos casos, son parcialmente simpátricas. También comparamos los resultados obtenidos con información previamente reportada por Marchesi et al. (2017) para el delfín austral (Lagenorhynchus australis), una especie costera, y el delfín cruzado (Lagenorhynchus cruciger), una especie oceánica. Estos resultados apoyan nuestra hipótesis de que las especies costeras tienen rasgos morfológicos asociados con mayor flexibilidad, mientras que las especies oceánicas y de plataforma tienen características asociadas con una mayor estabilidad en una mayor proporción de su columna. Description and functional interpretation of morphological variation in the dolphin column can be facilitated by recognizing structural units. This information offers important clues to the proportion of the column involved in the oscillation and displacement of the flukes, and how swimming style can vary among species. Thus, the morphological characterization and functional subdivision of the vertebral column is of key importance to gain insights into the locomotor performance of cetacean species occurring in different environments. We employed traditional morphometrics to establish the functional subdivision of the vertebral column of Commerson’s dolphin (Cephalorhynchus commersonii), a coastal species, and the dusky dolphin (Lagenorhynchus obscurus), a shelf species. These species are closely related, and some of them are partially sympatric. We also compared the obtained results against information previously reported by Marchesi et al (2017) on Peale’s dolphin (Lagenorhynchus australis), a coastal species, and the hourglass dolphin (Lagenorhynchus cruciger), an oceanic species. These results bring further support to our hypothesis that coastal species have morphological traits associated with higher flexibility, whilst platform and oceanic species have features associated with higher stability in a greater proportion of their column. Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Mora, Matías Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Boy, Claudia C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: González-José, Rolando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Ciencias Sociales y Humanas; Argentina Fil: Prosser Goodall, Rae Natalie. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina

Long-finned pilot whales (Globicephala melas) are among the few odontocetes that show an anti-tropical distribution. The North Atlantic subspecies (G. m. melas, Traill 1809) has been widely studied in the east and west coast, but there is little previous information on the Southern subspecies (G. m. edwardii, A. Smith 1834). Here we investigated the skull morphometry of both populations, subspecies status nowadays, with the aim of characterizing and comparing them. We examined a total of 93 adult skulls. In all skulls, 21 measurements were analyzed. Our results clearly differentiated skull morphology between long-finned pilot whale subspecies, being the following characters the most important in the discrimination: width of rostrum at base, and at ¼, ½ and ¾ length, length of rostrum to internal and external nares, and length and height of temporal fossa. Overall, G. m. edwardii specimens showed a longer skull, larger rostrum, wider nares, larger temporal fossa and longer orbits than G. m. melas. We suggest that these strong dissimilarities might have functional implications for feeding habits, diving behaviour and sound production capabilities. This is the first study that proves that skull morphometry in long-finned pilot whale subspecies presents significant differences. Fil: Marina, Tomas Ignacio. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina. Universidad Nacional de General Sarmiento; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Prosser Goodall, Rae Natalie. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina

Fast swimming pelagic cetacean species have osteological characteristics that promote a more stable spine in comparison to that of coastal species. The Peale?s dolphin (Lagenorhynchus australis) and the hourglass dolphin (Lagenorhynchus cruciger) have a close phylogenetic relationship and are found in coastal and pelagic waters in the Southern Hemisphere, respectively. The aim of this work was to study the relationship between the vertebral column?s morphology and its flexibility, across these species of contrasting habitats. Vertebral counts and multiple measurements of each vertebra were used to infer intervertebral flexibility. Bivariate plots and discriminant multivariate analyses were employed to compare each functional region along the vertebral column. Both species displayed a regionalization of the column into three stable regions and two flexible areas, which statistically differ in the proportion of the skeleton occupied in each species. While the Peale?s dolphin has rounder vertebrae, associated with higher flexibility, the hourglass dolphin has disk-shaped vertebrae and strongly inclined processes related to high stability. Although the species are closely related phylogenetically, vertebral morphology is influenced by a diverse set of ecological and behavioral factors, reflecting a high degree of vertebral plasticity within the genus. Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina Fil: Mora, Matias Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Pimper, Lida Elena. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina. Administración de Parques Nacionales. Delegación Regional Patagonia; Argentina Fil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia; Argentina Fil: Prosser Goodall, Rae Natalie. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Museo Acatushún de Aves y Mamíferos Marinos Australes; Argentina

In dolphins, centrum shape is one of the features that allows determination of stable and flexible regions in the vertebral column. The Commerson's (Cephalorhynchus commersonii; n = 37), Peale's (Lagenorhynchus australis; n = 24), dusky (Lagenorhynchus obscurus; n = 29), and hourglass dolphins (Lagenorhynchus cruciger; n = 10) are closely related species inhabiting the Southern Hemisphere that have diverse prey and habitat preferences. We applied 3D geometric morphometrics to describe differences in centrum shape along the vertebral columns of these species, and hypothesize how these differences may affect swimming. On each column, we chose a maximum of eight vertebrae and digitized 18 landmarks on each centrum with a Microscribe G2X. We explored shape differences amongst regions employing principal components analyses and computing Mahalanobis distances. We describe differences in centrum shape in relation to functional regions and among species; and analyze shape changes in relation to particular biomechanical requirements. The species studied here may be partially sympatric in the Southern Hemisphere, but they have important differences in foraging ecology and habitat preferences that could be related to differences in centrum shape along the vertebral column. Fil: Marchesi, María Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Boy, Claudia Clementina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Dans, Silvana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Mora, Matias Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Gonzalez-Jose, Rolando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina