Friday, October 7, 2016

[PaleoMammalogy • 2016] Dagonodum mojnum • A New Long-snouted Beaked Whale (Cetacea: Odontoceti) from the Late Miocene of Denmark: Evolution of Suction Feeding and Sexual Dimorphism in the Ziphiidae


Dagonodum mojnum 
Ramassamy, 2016 


Abstract

A new genus and species of Ziphiidae, Dagonodum mojnum gen. nov., sp. nov., from the upper Miocene Gram Formation (c. 9.9–7.2 Ma) represents the first occurrence of the family in Denmark. This long-snouted ziphiid is characterized by two pairs of mandibular tusks, the Eustachian outlet that approximately levels with the dorsalmost margin of the posterior portion of the involucrum, and the left trapezoid nasal with a posteromedial projection into the frontal. A phylogenetic analysis including 25 species and 69 characters was conducted. Dagonodum mojnum is placed in a basal ziphiid clade as the sister taxon of Messapicetus. The specimen is probably a male, because it has enlarged tusks. Alternatively, females could also be involved in fights and develop erupted tusks as in the extant Berardius. Although less well supported, this interpretation proposes that aggressive interactions were not restricted to males in stem-ziphiids. With a thickened thyrohyal and the presence of a precoronoid crest, D. mojnum was able to use suction feeding, but was less specialized to it compared to extant ziphiids. The elongated neck of D. mojnum less optimized to perform deep dives, and the shallow depth at which the Gram Formation was deposited corroborates the hypothesis that at least part of the stem-ziphiids were not regular deep divers.

 KEYWORDS: evolution – phylogeny – postcranial – systematics.

SYSTEMATIC PALAEONTOLOGY

ORDER CETACEA BRISSON, 1762
SUBORDER ODONTOCETI FLOWER, 1867

FAMILY ZIPHIIDAE GRAY, 1850

DAGONODUM GEN. NOV.
Type species. Dagonodum mojnum sp. nov.
Etymology of genus name. Dagon refers to the Canaanite divinity of crop fertility pictured as a fish-god and a fictive divinity related to the deep sea created by the American author H. P. Lovecraft.


DAGONODUM MOJNUM SP. NOV.

Holotype. MSM1001x, a partial skeleton including a fragmentary cranium, the left periotic and tympanic, both mandibles, 75 isolated teeth, five cervical vertebrae including the atlas and the axis, two thoracic vertebrae, several fragmentary ribs, the basihyal and left thyrohyal.

Diagnosis. Dagonodum mojnum is a medium-sized ziphiid with an elongated rostrum (approximately 70% of the total condylobasal length). It differs from all odontocetes except ziphiids in having the vertex bearing a strong premaxillary crest; the enlargement of the apical mandibular tooth, and the reduction of the dorsal keel on the posterior process of the periotic.
It shares with Anoplonossa forcipata and Berardius the presence of a pair of apical and subapical tusks; with the genera Messapicetus and Ziphirostrum the medial fusion of the premaxillae dorsal
to the mesorostral groove on the rostrum anterior to the premaxillary sac fossae; and with Aporotus, Beneziphius, Messapicetus and Ziphirostrum the presence of a prenarial basin laterally margined by the maxilla.  ......

 Etymology of species name. From the word ‘mojn’ meaning ‘morning’ in South Jutlandic. Originally of German origin, this is still used as a greeting for ‘hello’ and ‘goodbye’ in Southern Jutland.


CONCLUSION
The holotype of Dagonodum mojnum is a unique discovery in Europe due to the association of the cranium with the mandible, the numerous isolated teeth including the tusks, the earbones and some postcranial remains. It is dated to the mid- to late Tortonian (c. 9.9–7.2 Mya) and is one of the few welldated occurrences of the family Ziphiidae. Dagonodum mojnum is nested within the Messapicetus clade and, as such, expands our knowledge of the earliest diversification of the Ziphiidae.

Based on the presence of erupted tusks and surrounding structures on the mandible, MSM1001x is interpreted as a male, indicating that fights between males may occur in this species. An alternative hypothesis is also proposed in which aggressive intraspecific interactions would be more generalized, not only restricted to males as in the genus Berardius. Although less well supported, this hypothesis cannot be totally discarded in the case of D. mojnum.

The morphology of D. mojnum suggests that it was a predator that was less specialized to suction feeding than extant ziphiids. Its numerous interlocked teeth and its long rostrum with a less restricted lateral gape compared to extant ziphiids are more indicative of a ram-feeder. However, D. mojnum was probably also able to use suction feeding, as seen by its thickened thyrohyal and the laterally enclosed posterior part of the oral cavity due to the presence of a precoronoid crest. Lingual tooth wear of the most apical tusk may be the result of battle tooth raking along the opponent’s body during intraspecific fights and/or contact of the tooth with the seafloor.

Based on the present specimen alone, it is not possible to precisely assess if D. mojnum was able to perform deep dives, although like other long-snouted stem-ziphiids, D. mojnum was probably feeding in epipelagic foraging grounds

The Ziphiidae remain a poorly understood group. The use of independent proxies to assess their diving abilities or their diet might be a key to understand more precisely their evolution and the establishment of their specialization to deep diving.


Benjamin Ramassamy. 2016. Description of A New Long-snouted Beaked Whale from the Late Miocene of Denmark: Evolution of Suction Feeding and Sexual Dimorphism in the Ziphiidae (Cetacea: Odontoceti). Zoological Journal of the Linnean Society. 178(2); 381–409. DOI: 10.1111/zoj.12414

Mød Mojn-hvalen fra Gram
For ti millioner år siden svømmede den tandrige næbhval rundt i havet over Gram. Nu har en fransk Ph.d. studerende artsbestemt og navngivet den: Dagonodum mojnum - eller kort og godt: Mojn.
Ten million years ago swam the tooth rich beaked whale in the sea of Gram.  Now a French Ph.D. students being generic and named it: Dagonodum mojnum - or in short: Moin.

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