Morphology and Biomechanics of the Pinniped Jaw: Mandibular Evolution Without Mastication

Abstract

Pinnipeds (seals, sea lions, and walruses) underwent a shift in jaw function away from typical carnivoran mastication to more novel marine behaviors during the terrestrial-aquatic transition. Here we test the effect of aquatic prey capture and male-male combat on the morphological evolution of a mammal jaw that does not masticate. Nine three-dimensional landmarks were taken along the mandible for 25 species (N 5 83), and corpus and symphysis external and cortical breadths for a subset of five species (N 5 33). Principal components analysis was performed on size-corrected landmark data to assess variation in overall jaw morphology across pinnipeds. Corpus breadths were input to a beam model to calculate strength properties and estimated bite force of specific species with contrasting behaviors (filter feeding, suction feeding, grip-and-tear feeding, and malemale combat). Results indicate that, although phylogenetic signal in jaw shape is strong, function is also important in determining morphology. Filter feeders display an elongate symphysis and a long toothrow that may play a role in filtering krill. Grip-and-tear feeders have a long jaw and large estimated bite force relative to non-biting species. However, the largest estimated bite forces were observed in males of male-male combative species, likely due to the high selection pressure associated with male success in highly polygynous species. The suction feeding jaw is weak in biting but has a different morphology in the two suction feeding taxa. In conclusion, familial patterns of pinniped jaw shape due to phylogenetic relatedness have been modified by adaptations to specialized behavior of individual taxa.

Re-Evaluation of Morphological Characters Questions Current Views of Pinniped Origins

“…Similar to the morphological studies by Jones and Goswami (2010) and Jones et al (2013), there is higher morphological diversity in Phocidae than in Otariidae .…”

Dental anomalies in pinnipeds (Carnivora: Otariidae and Phocidae): occurrence and evolutionary implications

“…Due to the lack of refined occlusion and reduced mastication and food processing, their dentition is quite simple in comparison with other members of Carnivora (Berta 2002;Salazar-Ciudad and Jernvall 2010;Jones et al 2013). Due to the simplification and morphological similarity, premolars and molars are grouped as postcanine teeth (Eastman and Coalson 1974).…”

The evolution of jaw protrusion mechanics has been tightly coupled to bentho-pelagic divergence in damselfishes (Pomacentridae)

“…One of the most common patterns of evolution among aquatic animals is transitioning between feeding niches that lie at different points along this bentho-pelagic niche axis, and such diversification has arisen repeatedly in molluscs, crustaceans, annelids, pinnipeds, elasmobranchs and bony fishes (Bracken et al, 2009;Cooper et al, 2010;Jones et al, 2013;Lindgren et al, 2012;Regier et al, 2010;Struck et al, 2015;Wilga et al, 2007).…”