Juvenile morphology: A clue to the origins of the most mysterious of mysticetes?

The origin of the pygmy right whale (Caperea marginata) has long been one of the most vexing conundrums of marine mammal evolution. The extremely disparate skeletal structure ofCapereaand a patchy fossil record have left morphology and molecules at odds: whereas most morphological analyses allyCapereawith right whales (Balaenidae), most molecular studies instead suggest a close relationship with rorquals (Balaenopteridae) and grey whales (Eschrichtiidae). The morphological evidence supporting aCaperea-balaenid clade consists of several shared features of the skull and mandible, as traditionally observed in adult individuals. Here, we show that at least two of these features, the ascending process of the maxilla and the coronoid process, arise from substantially different precursors early during ontogeny and therefore likely do not represent genuine synapomorphies. Both of these juvenile morphologies have adult counterparts in the fossil record, thus indicating that the ontogenetic variation in the living species may be a genuine reflection of differing ancestral states. This new evidence contradicts previous morphological hypotheses on the origins ofCapereaand may help to reconcile morphological and molecular evidence.Fil: Marx, Felix. University of Otago; Nueva ZelandaFil: Buono, Mónica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagonico; ArgentinaFil: Fordyce, R. Ewan. University of Otago; Nueva ZelandaFil: Boessenecker, Robert W.. University of Otago; Nueva Zeland

A Late Miocene potential neobalaenine mandible from Argentina sheds light on the origins of the living pygmy right whale

The origins and evolutionary relationships of the pygmy right whale (Caperea marginata),the only living member of the Neobalaeninae, have been the subject of a long-standing debate. This phylogenetic uncertainty is compounded by a limited neobalaenine fossil record. Here, we report a Late Miocene mysticete mandible from Patagonia, Argentina and provisionally refer it to Neobalaeninae, gen. et sp. indet. The new material represents only the third report of a fossil neobalaenine, and the first fossil occurrence of this lineage in the southwestern Atlantic. It is also the oldest specimen so far reported, thus corroborating the idea of an early divergence time for neobalaenines.Fil: Buono, Mónica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Dozo, Maria Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Marx, Felix G.. University Of Otago; Nueva Zelanda. National Museum of Nature and Science; JapónFil: Fordyce, R. Ewan. University Of Otago; Nueva Zeland

Gigantic mysticete predators roamed the Eocene Southern Ocean

Modern baleen whales (Mysticeti), the largest animals on Earth, arose from small ancestors around 36.4 million years ago (Ma). True gigantism is thought to have arisen late in mysticete history, with species exceeding 10 m unknown prior to 8 Ma. This view is challenged by new fossils from Seymour Island (Isla Marambio), Antarctica, which suggest that enormous whales once roamed the Southern Ocean during the Late Eocene (c. 34 Ma). The new material hints at an unknown species of the archaic mysticete Llanocetus with a total body length of up to 12 m. The latter is comparable to that of extant Omura´s whales (Balaenoptera omurai Wada et al. 2003), and suggests that gigantism has been a re-occurring feature of mysticetes since their very origin. Functional analysis including sharpness and dental wear implies an at least partly raptorial feeding strategy, starkly contrasting with the filtering habit of living whales. The new material markedly expands the size range of archaic mysticetes, and demonstrates that whales achieved considerable disparity shortly after their origin.Fil: Marx, Felix G.. Royal Belgian Institute of Natural Sciences. Directorate Earth and History of Life; Bélgica. Monash University; Australia. Museums Victoria. Geosciences; AustraliaFil: Buono, Mónica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; ArgentinaFil: Evans, Alistair R.. Monash University; Australia. Museums Victoria. Geosciences; AustraliaFil: Fordyce, Robert Ewan. University of Otago; Nueva Zelanda. National Museum of Natural History; Estados UnidosFil: Reguero, Marcelo Alfredo. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Hocking, David P.. Monash University; Australia. Museums Victoria. Geosciences; Australi

Aquatic mammal fossils in Latin America – a review of records, advances and challenges in research in the last 30 years

Records of aquatic mammal fossils (e.g. cetaceans, pinnipeds, sirenians, mustelids, and desmostylians) from Latin America (Mexico to Tierra del Fuego, including Antartica) span since the mid-1800s. Aquatic mammal fossils received little attention from the scientific community, with most of the first studies conducted by Northern Hemisphere researchers. Over the last 30 years, paleontological research in Latin America has increased considerably, with descriptions of several new species and revisions of published original records. The Latin American fossil record of marine mammals spans from the Eocene to the Pleistocene, with formations and specimens of global significance. All three main groups of cetaceans are represented in the continent (Archaeoceti, Mysticeti, and Odontoceti). Pinnipedia are represented by the families Otariidae and Phocidae, with records starting in the Middle Miocene. Both living families of Sirenia (Trichechidae and Dugongidae) are recorded. While less common, but still relevant, records of desmostylians and mustelids are known from Oligocene and Miocene deposits. This review provides a summary of the aquatic mammals known to date, with a special focus on the advances and developments of the last 30 years, since Cozzuol’s (1996) review of the South American fossil record. An up-to-date complete list of species based on the literature and unpublished data is also provided. The study also provides future directions for paleontological research in Latin America, and discusses the challenges and opportunities in the field, including the emergence of a strong new generation of Latin American researchers, many of whom are women. Keywords: Cetacea, Pinnipedia, Sirenia, Southern Hemispher

Análisis osteológico de ejemplares delfín de Fraser (Lagenodelphis hosei Fraser, 1956) provenientes de la costa de la provincia de Buenos Aires, Argentina

The presence of Lagenodelphis hosei in temperate waters of the Argentinian Sea is a rare event because of its preference for pelagic and tropical waters. With the aim to increment the available information on the Fraser´s dolphin in Soutwestern Atlantic waters, we made a morphological and morphometric analysis of skull and postcranial skeleton of five specimens stranded at the end of the 2000 year, in the La Plata River, between Punta Lara and Magdalena localities, at Buenos Aires Province, Argentina. The results were compared with data source from non-South American areas. We observed that specimens of the Southwestern Atlantic described in this study tend to have larger braincase size and the size relation of external nares between males and females is inverse to that seen in specimens of geographically distant areas.La presencia de Lagenodelphis hosei en las aguas templadas del Mar Argentino es un hecho raro, debido a su preferencia por la aguas tropicales y pelágicas. Con motivo de aumentar la información disponible sobre el delfín de Fraser en aguas del Atlántico sudoccidental se realizó un análisis morfológico y morfométrico del cráneo y el esqueleto postcraneal sobre cinco ejemplares varados a fines del año 2000 en el Río de La Plata, entre las localidades de Punta Lara y Magdalena, provincia de Buenos Aires, Argentina. Los resultados obtenidos fueron comparados con datos provenientes de ejemplares de otras regiones geográficas. De esta comparación se observó que los ejemplares del Atlántico Sudoccidental descritos en el presente estudio presentan una caja craneana de mayor tamaño, y la relación en el ancho de las narinas, entre machos y hembras, es inversa a la observada en otros especímenes de áreas extra sudamericanas

The early Miocene balaenid Morenocetus parvus from Patagonia (Argentina) and the evolution of right whales

Balaenidae (right and bowhead whales) are a key group in understanding baleen whale evolution, because they are the oldest surviving lineage of crown Mysticeti, with a fossil record that dates back ∼20 million years. However, this record is mostly Pliocene and younger, with most of the Miocene history of the clade remaining practically unknown. The earliest recognized balaenid is the early Miocene Morenocetus parvus Cabrera, 1926 from Argentina. M. parvus was originally briefly described from two incomplete crania, a mandible and some cervical vertebrae collected from the lower Miocene Gaiman Formation of Patagonia. Since then it has not been revised, thus remaining a frequently cited yet enigmatic fossil cetacean with great potential for shedding light on the early history of crown Mysticeti. Here we provide a detailed morphological description of this taxon and revisit its phylogenetic position. The phylogenetic analysis recovered the middle Miocene Peripolocetus as the earliest diverging balaenid, and Morenocetus as the sister taxon of all other balaenids. The analysis of cranial and periotic morphology of Morenocetus suggest that some of the specialized morphological traits of modern balaenids were acquired by the early Miocene and have remained essentially unchanged up to the present. Throughout balaenid evolution, morphological changes in skull arching and ventral displacement of the orbits appear to be coupled and functionally linked to mitigating a reduction of the field of vision. The body length of Morenocetus and other extinct balaenids was estimated and the evolution of body size in Balaenidae was reconstructed. Optimization of body length on our phylogeny of Balaenidae suggests that the primitive condition was a relatively small body length represented by Morenocetus, and that gigantism has been acquired independently at least twice (in Balaena mysticetus and Eubalaena spp.), with the earliest occurrence of this trait in the late Miocene–early Pliocene as represented by Eubalaena shinshuensis