1,721,205 research outputs found
Caviziphius altirostris, a new beaked whale from the Miocene southern North Sea basin
No full textAn odontocete cranium from Miocene deposits in northern Belgium is examined and referred to
Caviziphius altirostris, a new genus and species of beaked whale. In the general architecture of
its vertex and closed mesorostral canal, Caviziphius resembles the fossil genera Ziphirostrum and
Choneziphius, but differs from all known ziphiids by a very deep excavated prenarial basin with a
semicircular outline in lateral view. This peculiar cranial architecture of Caviziphius might indicate an
advanced and efficient mechanism of sound production in this fossil ziphiid
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Beaked whale mysteries revealed by seafloor fossils trawled off South Africa
No full textAn unexpectedly large number of well-preserved fossil ziphiid (beaked whale) skulls trawled from the seafloor off South Africa significantly increases our knowledge of this cetacean family. The eight new genera and ten new species more than double the known diversity of fossil beaked whales and represent more than one-third of this family (fossil and extant). A cladistic parsimony analysis based on 18 cranial characters suggested that some of these fossil taxa belong to the three extant ziphiid subfamilies, whereas others might represent extinct ziphiid lineages. Such high fossil ziphiid diversity might be linked to the upwelling system and the resulting high productivity of the Benguela Current, which has been in place and influenced conditions of the shallower waters along the southwest coast of South Africa and Namibia since the Middle Miocene.
Both fossil and extant South African beaked whale faunas show a wide range in body size, which is probably related to different dietary niches and to wide exploration of the water column. Moreover, most South African fossil ziphiids share two morphological traits with extant species, which indicates that some of the behaviours associated with these traits had likely already developed during the Neogene: 1) the absence of functional maxillary teeth—providing clear evidence of suction feeding; and 2) the heavy ossification of the rostrum in specimens assumed to represent adult males—a feature which likely helps prevent injury and damage on impact during male–male fighting
Tusk-bearing beaked whales from the Miocene of Peru: sexual dimorphism in fossil ziphiids
No full textNew well-preserved fossils from Peru reveal details of the dentition and morphology of the mandible and rostrum in 2 late middle to early late Miocene beaked whales (Cetacea, Odontoceti, Ziphiidae). Apical mandibular tusks are present in both Nazcacetus urbinai and Messapicetus sp. In the former the tusks are associated with a strong reduction of the postapical dentition, whereas in Messapicetus sp. a complete series of functional upper and lower teeth is retained. The larger sample of Messapicetus sp. from a single locality and age reveals intraspecific variation in size and shape of the tusks and surrounding structures. In addition, the rostrum of Messapicetus displays thickened premaxillae, dorsally closing the mesorostral groove. By comparison with modern beaked whales, most of them highly sexually dimorphic at the level of the tusks and rostrum, we propose that the tusks of Messapicetus were used in intraspecific fights between adult males. Strengthening of the rostrum through the dorsal closure of its transverse section would have reduced the risk of fractures when facing impacts
A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa
No full textEight new genera and 10 new species of fossil beaked whales (Cetacea, Odontoceti, Ziphiidae) are described on the basis of cranial material recovered by trawling from the sea floor off South Africa. Although no exact stratigraphic information is known for these fossils, most are strongly phosphoritised (some even have phosphorite concretions attached), indicating that their fossilization could be related to one or more of the phosphogenic episodes that occurred in the South African coastal waters since the latest Oligocene. Considering the main phosphogenic epochs and the evolutionary level of the majority of the ziphiids here described, a middle-late Miocene age may be suggested for most, but not all, of these fossils. The new genera named here more than double the known diversity of the fossil beaked whales and represent more than one third of the total diversity of this family (fossil and extant). A parsimony analysis within the family including the Recent taxa reveals that some of the new fossil taxa belong to three extant subfamilies redefined here, while the others are outside these subfamilies; this indicates the presence in the past of some ziphiid lineages now extinct. In detail, Microberardius africanus n. gen., n. sp. is placed in the subfamily Berardiinae together with the Recent Berardius; Izikoziphius rossi n. gen., n. sp. and I. angustus n. gen., n. sp. are related to the Recent Ziphius inside the subfamily Ziphiinae and Khoikhoicetus agulhasis n. gen., n. sp., Ihlengesi saldanhae n. gen., n. sp., and Africanacetus ceratopsis n. gen., n. sp. belong to the Hyperoodontinae together with the Recent Hyperoodon, Mesoplodon, and Indopacetus. However, Nenga meganasalis n. gen., n. sp., Pterocetus benguelae n. gen., n. sp., and Xhosacetus hendeysi n. gen., n. sp., together with the Recent Tasmacetus, do not fit in any of the three subfamilies mentioned above. Taking into account the high number of unnamed fragmentary specimens, the fossil taxa listed above, together with Mesoplodon slangkopi n. sp. and Ziphius sp., probably represent only a part of the South African fossil ziphiid fauna(s), revealing an unexpected high diversity for the previously poorly known southern hemisphere fossil beaked whales. Such a high ziphiid diversity might be locally related to the upwelling system and resulting high productivity linked to the northward running cool oceanic Benguela Current entering the shallower waters along the south-west coast of South Africa and Namibia since the middle Miocene
First record of Tusciziphius crispus (Cetacea, Ziphiidae) from the Neogene of the US east coast
No full textLivyatan vs. Zygophyseter: two large raptorial sperm whales (Cetacea, Physeteroidea) from two extraordinary Miocene marine bone beds.
No full textA new beaked whale (Odontoceti, Ziphiidae) from the middle Miocene of Peru
No full textOn the basis of a partial odontocete (toothed whale) skeleton (complete skull with associated ear bones, mandible, teeth, hyoid bones, and cervical vertebrae) from the middle Miocene (ca. 14-12 Ma) levels of the Pisco Formation at Cerro los Quesos, Pisco-Ica desert, southern coast of Peru, a new genus and species of beaked whale (Ziphiidae), Nazcacetus urbinai, is described. This small ziphiid, the best documented fossil species to date, is characterized by a strong reduction of the upper and lower dentitions except for a pair of large apical mandibular teeth, a Tasmacetus-like vertex, a short mandibular symphysis, and the abrupt elevation of the dorsal margin of the mandible towards the coronoid process. A phylogenetic analysis indicates that Nazcacetus is a crown ziphiid, in a more crownward position than Berardiinae and Tasmacetus, but branching before the Hyperoodontinae and Ziphiinae lineages. Several morphological traits observed in Nazcacetus, including the reduction of teeth, the small temporal fossa, and the large hamular process, suggest that this taxon possessed the suction feeding capacities of Recent ziphiids, a specialization possibly related to the exploitation by the early ziphiids of a new ecological niche. The presence of large apical teeth on the mandible of Nazcacetus, a character highly dimorphic in recent ziphiids, might indicate that sexual dimorphism was already present as early in ziphiid evolutionary history as the middle Miocene, a hypothesis supported by the nested position of Nazcacetus in the ziphiid phylogenetic tree
High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru
No full textEight skulls of beaked whales (Cetacea, Odontoceti, Ziphiidae), in six cases associated with elements of the mandible, were collected from a limited area (about 1.5 km2) and roughly from the same stratigraphic horizon at Cerro Colorado, 35 km south-south-west of the city of Ica (Peru), where the late Middle Miocene basal strata of the Pisco Formation crop out. They represent the highest concentration reported of fossil Ziphiidae. These finely preserved Cerro Colorado fossils are described and assigned to a new species Messapicetus gregarius, together with another specimen collected from sediments of the same age at Cerro la Bruja (33 km south-east to Cerro Colorado). Messapicetus gregarius shares with M. longirostris Bianucci, Landini and Varola, 1992 (Tortonian of Italy), an extremely elongated rostrum, but is clearly different from the Italian species in the more distinct maxillary tubercle and prominential notch, the more robust premaxillary crest, and the abrupt ventrolateral descent of the medial margin of the maxilla from the vertex. A parsimony analysis reveals that Messapicetus belongs to a basal clade, which includes other ziphiids with a dorsally closed mesorostral groove and prenarial basin. The high concentration of specimens belonging to the same species (some of them tentatively identified as adult males and females), combined with the presence of a calf, supports the hypothesis of site fidelity; these cetaceans might have lived in a limited region for a long period for both breeding and feeding. Besides the eight specimens of M. gregarius, strata at Cerro Colorado include many other cetacean remains (with several specimens of the pontoporiid Brachydelphis including a foetus), pinnipeds, turtles, fishes, and birds
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