Functional Morphology of the Feeding Apparatus of the Snaggletooth Shark, Hemipristis elongata (Carcharhiniformes: Hemigaleidae).

The anatomy of the feeding apparatus of the snaggletooth shark, Hemipristis elongata (Klunzinger, 1871) is illustrated in detail from the dissection of three heads. Two new muscles are described: the Adductor mandibularis internus and the Levator mandibularis. A subdivision of the Levator palatoquadrati is described and named the Pronator subdivision of the Levator palatoquadrati. Also, eight new anatomical features associated with the mandibular arch and with the chondrocranium (CR) are described. Three are cartilages: the suprapalatine cartilages, the craniopalatoquadrate cartilage and the calcified Meckelian dental fold. The remaining five features are processes: the Pronator process of the palatoquadrate (PQ), the Levator palatoquadrati alpha process, the proquadrate process, the ectorbital process (ECP) and the Meckelian Intermandibularis ridge. Some of them are not restricted to H.elongata. The function of these new muscles and anatomical features is discussed and a hypothesis about the functional morphology of the feeding apparatus of the snaggletooth shark is proposed. The extent and the assumptive importance of the pronation of the mandibular arch in the snaggletooth shark feeding behaviour is described and discussed. An alternative for the main function of the Levator palatoquadrati as hypothesized by Motta et al. (1997) and Wilga et al. (2001) is proposed for the families Hemigaleidae, Carcharhinidae and Sphyrnidae. We anticipate this muscle is more involved in the pronation rather than in the protrusion of the mandibular arch.

Slingshot feeding of the goblin shark Mitsukurina owstoni (Pisces: Lamniformes: Mitsukurinidae).

Five striking and prey capture events of two goblin sharks were videotaped at sea for the first time, showing their extraordinary biting process. The goblin sharks swung their lower jaw downward and backward to attain a huge gape and then rapidly protruded the jaws forward a considerable distance. The jaws were projected at a maximum velocity of 3.1 m/s to 8.6-9.4% of the total length of the shark, which is by far the fastest and greatest jaw protrusion among sharks. While the jaws were being retracted, the mouth opened and closed again, which was considered a novel feeding event for sharks. Phylogenetic evidence suggested that their feeding behavior has evolved as an adaptation to food-poor deep-sea environments, possibly as a trade-off for the loss of strong swimming ability.