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 An up-to-date complete list of species based on the literature and unpublished data is also provided.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

Iterative Evolution of Sympatric Seacow (Dugongidae, Sirenia) Assemblages during the Past ∼26 Million Years

Extant sirenians show allopatric distributions throughout most of their range. However, their fossil record shows evidence of multispecies communities throughout most of the past ∼26 million years, in different oceanic basins. Morphological differences among co-occurring sirenian taxa suggest that resource partitioning played a role in structuring these communities. We examined body size and ecomorphological differences (e.g., rostral deflection and tusk morphology) among sirenian assemblages from the late Oligocene of Florida, early Miocene of India and early Pliocene of Mexico; each with three species of the family Dugongidae. Although overlapping in several ecomorphological traits, each assemblage showed at least one dominant trait in which coexisting species differed. Fossil sirenian occurrences occasionally are monotypic, but the assemblages analyzed herein show iterative evolution of multispecies communities, a phenomenon unparalleled in extant sirenian ecology. As primary consumers of seagrasses, these communities likely had a strong impact on past seagrass ecology and diversity, although the sparse fossil record of seagrasses limits direct comparisons. Nonetheless, our results provide robust support for previous suggestions that some sirenians in these extinct assemblages served as keystone species, controlling the dominance of climax seagrass species, permitting more taxonomically diverse seagrass beds (and sirenian communities) than many of those observed today

New heterodont odontocetes from the Oligocene Pysht Formation in Washington State, U.S.A., and a reevaluation of Simocetidae (Cetacea, Odontoceti)

Odontocetes first appeared in the fossil record by the early Oligocene, and their early evolutionary history can provide clues as to how some of their unique adaptations, such as echolocation, evolved. Here, three new specimens from the early to late Oligocene Pysht Formation are described further increasing our understanding of the richness and diversity of early odontocetes, particularly for the North Pacific. Phylogenetic analysis shows that the new specimens are part of a more inclusive, redefined Simocetidae, which now includes Simocetus rayi, Olympicetus sp. 1, Olympicetus avitus, O. thalassodon sp. nov., and a large unnamed taxon (Simocetidae gen. et sp. A), all part of a North Pacific clade that represents one of the earliest diverging groups of odontocetes. Amongst these, Olympicetus thalassodon sp. nov. represents one of the best known simocetids, offering new information on the cranial and dental morphology of early odontocetes. Furthermore, the inclusion of CCNHM 1000, here considered to represent a neonate of Olympicetus sp., as part of the Simocetidae, suggests that members of this group may not have had the capability of ultrasonic hearing, at least during their early ontogenetic stages. Based on the new specimens, the dentition of simocetids is interpreted as being plesiomorphic, with a tooth count more akin to that of basilosaurids and early toothed mysticetes, while other features of the skull and hyoid suggest various forms of prey acquisition, including raptorial or combined feeding in Olympicetus spp., and suction feeding in Simocetus. Finally, body size estimates show that small to moderately large taxa are present in Simocetidae, with the largest taxon represented by Simocetidae gen. et sp. A with an estimated body length of 3 m, which places it as the largest known simocetid, and amongst the largest Oligocene odontocetes. The new specimens described here add to a growing list of Oligocene marine tetrapods from the North Pacific, further promoting faunistic comparisons across other contemporaneous and younger assemblages, that will allow for an improved understanding of the evolution of marine faunas in the region

Sirenian taxa and ecomorphological features used in this study.

<p>A) Fossil dugongids from the late Oligocene Parachucla Formation of Florida showing categories of upper incisor 1 alveolar size and depth (outlined in gray), compared to premaxillary symphysis length (dashed line denotes mid-length). <i>Metaxytherium</i> sp. based on UF 49051, <i>Crenatosiren olseni</i> and <i>Dioplotherium manigaulti</i> modified from Domning <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Reinhart1" target="_blank">[9]</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Morgan1" target="_blank">[8]</a>, respectively. B) Comparison of body sizes among dugongids used in this study. C) Fossil dugongids from the early Miocene Khari Nadi Formation of India showing differences in rostral deflection. Illustrations modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Edwards1" target="_blank">[10]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Thewissen1" target="_blank">[12]</a>. D) Cross-sectional outline of incisors of fossil dugongids from the early Pliocene Carrillo Puerto Formation of Mexico. Skull of <i>Corystosiren varguezi</i> (modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Bajpai1" target="_blank">[11]</a>) shown to demonstrate tusk cross-section.</p

Time-calibrated phylogeny of Sirenia.

<p>Consensus tree (length = 127; ri = 0.758; ci = 0.527). Taxa included in this study are highlighted in color, as follows: green, early Pliocene of Mexico; red, early Miocene of India; blue, late Oligocene of Florida. Open circles identify node-based clades; arcs indicate stem-based taxa. The poorly integrated group “Halitheriinae” is paraphyletic in this study.</p

List of sirenian taxa and categorization of corresponding ecomorphological features used in this study.

a<p><b>Small</b>, length less than half the length of the premaxillary symphysis; <b>medium</b>, length about half the length of the premaxillary symphysis; <b>large</b>, length greater than half the length of the premaxillary symphysis.</p>b<p>Estimate based on condylobasal length of skull of 41.5 cm.</p>c<p>Based on <i>Nanosiren garciae</i> with which it shares similar dimensions of the mandible.</p

3D model related to the publication: Sperm whales (Physeteroidea) from the Pisco Formation, Peru, and their trophic role as fat-sources for Late Miocene sharks

The present 3D Dataset contains the 3D models analyzed in Benites-Palomino A., Velez-Juarbe J., Altamirano-Sierra A., Collareta A., Carrillo-Briceño J., and Urbina M. 2022. Sperm whales (Physeteroidea) from the Pisco Formation, Peru, and their Trophic role as fat-sources for Late Miocene sharks