Fossil Record 21(1): 11-32, doi: 10.5194/fr-21-11-2018
Description of the skeleton of the fossil beaked whale Messapicetus gregarius: searching potential proxies for deep-diving abilities
expand article infoBenjamin Ramassamy, Olivier Lambert§, Alberto Collareta|, Mario Urbina, Giovanni Bianucci|
‡ Department of Natural History and Palaeontology, the Museum of Southern Jutland, Gram, 6100, Denmark§ D.O. Terre et Histoire de la Vie, Institut royal des Sciences naturelles de Belgique, Brussels, 1000, Belgium| Dipartimento di Scienze della Terra, Università di Pisa, Pisa, 56126, Italy¶ Departamento de Paleontologia de Vertebrados, Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, avenida Arenales 1256, Lima 14, Peru
Open Access

Ziphiidae (beaked whales) are a successful family of medium- to large-sizedtoothed whales. Their extant members perform regular deep dives beyond thephotic zone to forage for cephalopods and fish. Conversely, extinctlong-snouted stem ziphiids are interpreted as epipelagic predators. However,some aspects of this hypothesis remain unclear due to the lack of clearmorphological proxies for recognizing regular deep divers.

We compared the forelimb, neck, and pterygoid sinus system of the fossilziphiid Messapicetus gregarius with those of other odontocetes to evaluate the potential of thesebody regions as proxies to assess deep-diving specialization. Thereconstructed musculature of the neck and forelimb of M. gregarius was also comparedwith that of other odontocetes. We also quantified variation in theproportions of the forelimb and the hamular fossa of the pterygoid sinus(HF) using 16 linear measurements. The degree of association between divingbehaviour in extant odontocetes and these measurements was evaluated with andwithout phylogenetic correction.

Reconstruction of the neck musculature suggests that M. gregariuspossessed a neck more flexible than most extant ziphiids due to the lowerdegree of fusion of the cervical vertebrae and the large insertions for theM. longus colli and Mm. intertransversarii ventrales cervicis. While neckrigidity might be related to deep diving, differences in neck flexibilityamong extant ziphiids indicate a more complex functional interpretation. Therelationship between forelimb morphology and diving behaviour was notsignificant, both with and without phylogenetic correction, suggesting that it cannot be used to assess deep-divingabilitieswith the parameters considered here. Measurements of the HF revealed successful to evaluate deep-divingabilities in odontocetes, with an enlargement of this structure in deepdivers. Considering other evidence that suggests an epipelagic behaviour, wepropose different scenarios to explain the observation of an enlarged HF inM. gregarius: (1) this species may have fed at different depths; (2)it performed deep dives to avoid potential predators; or (3) the enlarged HFand deep-diving habitat correspond to an ancestral condition, with M. gregarius returning to a more epipelagic habitat.