The myology of the Amazonian Manatee, Trichechus inunguis (Natterer) (Mammalia: Sirenia)

ABSTRACTThe muscles of the Amazonian manatee are described and compared with those of other manatees and the dugong. Maps of muscle attachments and data on weights of muscles are included. The manatee species differ in the forms of the mm. rectus capitis lateralis and biceps brachii. The mechanisms of protrusion of upper-lip bristles and opening of the nostrils are described. The jaw apparatus is uniquely specialized, with a very large temporalis muscle constituting more than half the adductor muscle mass, and development of a joint between the pterygoid process and the mandible which probably braces the mandible during transverse chewing. The center of mandibular rotation in transverse chewing probably lies posteromedial to the pterygoid process on the active sidethe contralateral temporalis is dominant in transverse chewing. Trichechus inunguis is more specialized for surface-feeding and for swimming than T. manotus.: Os músculos do peixe-boi da Amazônia são descritos e comparados àqueles dos outros peixes-bois e do dugong. Mapas das ligações dos músculos aos ossos, e dados sobre pesos dos músculos, são incluídos. Notam-se diferenças entre as espécies de peixes-bois com respeito aos músculos rectus capitis lateralis e biceps brachii. Descrevem-se o mecanismo de protrusão das cerdas do lábio superior, e o mecanismo de abertura das narinas. O aparelho masticatório é unicamente especializado, com um temporalis muito grande, constituindo mais que metade do peso dos músculos adutores, e com uma articulação entre o processo pterigoídeo e a mandíbula. Esta provavelmente apoia a mandíbula na mastigação transversal. O centro de rotação da mandíbula na mastigação transversal parece ficar posteromedial ao processo pterigoídeo no lado ativo; o temporalis do outro lado fornece a maioria da força para esta rotação. O Trichechus inunguis é mais especializado do que o T. manatus para se alimentar perto da superfície da água, e para nadar

Morphological and systematic re-assessment of the late Oligocene “Halitherium” bellunense reveals a new crown group genus of Sirenia

“Halitherium” bellunense is exclusively known from a single individual from upper Oligocene glauconitic sandstone near Belluno, northern Italy. According to a review of its morphological basis, which consists of associated cranial elements, some vertebrae and ribs, this specimen is identified as a juvenile, because the first upper incisor (I1) and supposedly second upper molar (M2) are not fully erupted. However, its juvenile status allowed only cautious conclusions on its taxonomy and systematic affinity. The presence of a nasal process of the premaxilla with a broadened and bulbous posterior end, and a lens-shaped I1, corroborate an evolutionarily-derived status of this species that places it well within the sirenian crown group Dugonginae. Considering these new data and in order to avoid continued misuse of the inappropriate generic name of Halitherium, a new generic name, Italosiren gen. nov., and emended species diagnosis are supplied for this taxon

Taxa de substituição horizontal de dentes no peixe-boi

Teeth shed from the horizontally-advancing tooth rows of captive Amazonian manatees (Trichechus inunguis) indicate a rate of tooth row movement of about 1 mm/month. The movement appears to be initiated by weaning and continues throughout life, with variations in rate correlated with overall growth rate but independent of rate of tooth wear

SIRENIA FOSSILS FROM QOM FORMATION (BURDIGALIAN) OF THE KABUDAR AHANG AREA, NORTHWEST IRAN

Fossil remains of sirenians (Mammalia; Dugongidae) are reported from the late early Miocene (Burdigalian) Qom Formation near the town of Shirin Su, northwest Kabudar Ahang region, west of Tehran, Iran. The fossils consist of partial postcranial skeletons preserved mostly as natural molds in limestone. In the absence of skulls or other diagnostic elements, it is not evident which dugongid subfamily these specimens represent: Halitheriinae or Dugonginae. Both subfamilies were present in contemporaneous Western Tethys (Mediterranean) deposits, but so far only dugongines have been found in Neogene rocks of Eastern Tethys. Since the Iranian deposits are located between these two parts of the former Tethys Seaway, it will be interesting to see which group(s) the Iranian sirenians prove to represent, once their taxonomic identity has been determined through future discoveries

Potências cerebrais através do estímulo acústico (AEP) mostram a audição no peixe-boi (Sirenia: Trichechus inunguis)

A young Amazonian manatee (Trichechus inunguis) showed peak auditory sensitivity at about 3 kHz and averaged evoked potentials (AEP) from 200 Hz to 35 kHz but not at 40 kHz as measured by transcranial evoked potentials. The maximum sensitivity was recorded about 20 mm rostral to the auditory meatus, possibly implicating the broad posterior part of the zygomatic process of the squamosal bone in the acoustic system of the manatee. The techniques used in this study are recommended for studies of acoustic sensitivity of animals to simple and complex natural sounds that have relatively abrupt onsets.Um jovem peixe-boi da Amazônia (Trichechus inunguis) mostrou boas respostas auditivas evocadas, com a máxima sensibilidade em cerca de 3 kHz e alcançando de 200 Hz a 35 kHz. mas não a 40 kHz. A sensibilidade máxima foi encontrada a cerca de 20 mm rostralmente ao canal auditivo externo, possivelmente implicando a larga parte posterior do processo zigomático do osso squamosal, no sistema acústico desta espécie. As técnicas utilizadas nesta pesquisa são recomendadas para estudos futuros de sensibilidade acústica de animais para sons simples ou sons complexos que tem começos relativamente bruscos

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

The Magnitude of Global Marine Species Diversity

Background: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. Results: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000–72,000 species are collected but not yet described, and that 482,000–741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7–1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. Conclusions: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century

Manati And Trichechus exunguis Mammalia Sirenia Proposal To Place These Names On The Official Indexes Of Rejected And Invalid Names In Zoology

Volume: 38Start Page: 130End Page: 13

Halianassa studeri Von Meyer 1838 Mammalia Sirenia Proposed Designation Of A Neotype And Proposed Conservation Of Halitherium Kaup 1838 By Designation Of A Type Species

Volume: 44Start Page: 122End Page: 13

Bibliography and index of the Sirenia and Desmostylia

Includes index