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| The four new species; Top left: Imocetus piscatus , top right: Choneziphius leidyi , bottom left: Tusciziphius atlanticus , bottom right: Globicetus hiberus.
Picture: SGHN | http://www.sghn.org
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Abstract
Forty partial fossil skulls belonging to beaked whales (Cetacea, Odontoceti, Ziphiidae) were collected by trawling and long-line fishing on Neogene (probably Late Early to Middle Miocene) layers of the Atlantic floor off the coasts of Portugal and Spain (Asturias and Galicia). e systematic study of the most diagnostic Iberian specimens, those preserving the rostrum and the dorsal part of the cranium, led to the recognition of two new genera (Globicetus n. gen. and Imocetus n. gen.) and four new species (Choneziphius leidyi n. sp., G. hiberus n. gen., n. sp., I. piscatus n. gen., n. sp., and Tusciziphius atlanticus n. sp.). Based on the matrix of a previous work, the phylogenetic analysis places all the new taxa in the subfamily Ziphiinae Gray, 1850. More fragmentary specimens are tentatively referred to the genera Caviziphius Bianucci & Post, 2005 and Ziphirostrum du Bus, 1868.
Among these new ziphiids, extremely bizarre skull morphologies are observed. In G. hiberus n. gen., n. sp. the proximal portion of the rostrum bears a voluminous premaxillary spheroid. In T. atlanticus n. sp. a medial premaxillary bulge is present on the rostrum; together with asymmetric rostral maxillary eminences at the rostrum base, this bulge displays various degrees of elevation in different specimens, which may be interpreted as sexual dimorphism. Specimens of I. piscatus n. gen., n.sp. bear two sets of even crests: spur-like rostral maxillary crests and longitudinal maxillary crests laterally bordering a wide and long facial basin. A preliminary macroscopic observation of these elements indicates very dense bones, with a compactness comparable with that of cetacean ear bones. Questioning their function, the high medial rostral elements (the premaxillary spheroid of G. hiberus n. gen., n. sp. and the medial bulge of T. atlanticus n. sp.) remind the huge rostral maxillary crests of adult males of the extant Hyperoodon ampullatus (Forster, 1770). In the latter, the crests are very likely related to head-butting. However, they are made of much more spongy bone than in the fossil taxa studied here, and therefore possibly better mechanically suited for facing impacts. Other interpretations of these unusual bone specializations, related to deep-diving (ballast) and echolocation (sound reflection), fail to explain the diversity of shapes and the hypothetical sexual dimorphism observed in at least part of the taxa. e spur-like rostral maxillary crests and long maxillary crests limiting the large facial basin in I. piscatus n. gen., n. sp. and the excrescences on the maxilla at the rostrum base in Choneziphius spp. are instead interpreted as areas of origin for rostral and facial muscles, acting on the nasal passages, blowhole, and melon. From a palaeobiogeographic point of view, the newly described taxa further emphasize the differences in the North Atlantic (including Iberian Peninsula) and South African Neogene ziphiid faunal lists. Even if the stratigraphic context is poorly understood, leaving open the question of the geological age for most of the dredged specimens, these differences in the composition of cold to temperate northern and southern hemisphere fossil ziphiid faunas may be explained by a warm-water equatorial barrier.
Keywords: Cetacea, Odontoceti, Ziphiidae, Neogene, Miocene, Portugal, Spain, phylogeny, skull morphology, new genera, new species.
CONCLUSION
The systematic study of 40 partial fossil ziphiid skulls dredged from the Atlantic Ocean floor off Portugal and Spain lead to the description of two new genera, Globicetus n. gen. and Imocetus n. gen., and four new species, G. hiberus n. gen., n. sp., I. piscatus n. gen., n. sp., Choneziphius leidyi n. sp., and Tusciziphius atlanticus n.sp. In addition, members of the genera Caviziphius and Ziphirostrum are tentatively reported.
The phylogenetic analysis of the new taxa places them in the subfamily Ziphiinae here redefined, also including Choneziphius planirostris, Tusciziphius crispus, and the genera Izikoziphius and Ziphius. Bizarre elements observed on the skull of Globicetus n. gen. (large premaxillary spheroid) and T. atlanticus n.sp. (medial premaxillary bulge, likely sexually dimorphic), are commented from a functional point of view; these structures are confronted to various hypotheses proposed for the function of pachyosteosclerotic parts of the rostrum in several ziphiid lineages.
Other peculiar features of the skull of Imocetus (spur-like rostral maxillary crests and long maxillary crests limiting a large facial basin) and Choneziphius spp. (excrescences on the maxilla at the rostrum base) are interpreted as areas of origin for rostral and facial muscles.
The palaeobiogeography of Neogene ziphiids is discussed in the light of the new discoveries. Differences in the composition of cold to temperate northern and southern hemisphere ziphiid communities might be explained by a warm equatorial barrier.
Finally, by comparison with other fossil ziphiid assemblages in the world and on the basis of a few geological and stratigraphic data for the Atlantic Ocean floor off Portugal and Spain, a late early to middle Miocene age is very tentatively proposed for the studied specimens. However, this hypothesis should be considered cautiously; a younger age cannot be excluded for part or all of these specimens
Bianucci G., Miján I, Lambert O., Post K. & Mateus O. 2013. Bizarre fossil beaked whales (Odontoceti, Ziphiidae) fished from the Atlantic Ocean floor off the Iberian Peninsula. Geodiversitas. 35 (1): 105-153. http://dx.doi.org/10.5252/g2013n1a6
Fossil beaked whales fished off the Iberian Peninsula
Four new species of whale from 15 million years ago.