The Head and Neck Anatomy of Sea Turtles (Cryptodira: Chelonioidea) and Skull Shape in Testudines

Abstract

BackgroundSea turtles (Chelonoidea) are a charismatic group of marine reptiles that occupy a range of important ecological roles. However, the diversity and evolution of their feeding anatomy remain incompletely known.Methodology/Principal FindingsUsing computed tomography and classical comparative anatomy we describe the cranial anatomy in two sea turtles, the loggerhead (Caretta caretta) and Kemp’s ridley (Lepidochelys kempii), for a better understanding of sea turtle functional anatomy and morphological variation. In both taxa the temporal region of the skull is enclosed by bone and the jaw joint structure and muscle arrangement indicate that palinal jaw movement is possible. The tongue is relatively small, and the hyoid apparatus is not as conspicuous as in some freshwater aquatic turtles. We find several similarities between the muscles of C. caretta and L. kempii, but comparison with other turtles suggests only one of these characters may be derived: connection of the m. adductor mandibulae internus into the Pars intramandibularis via the Zwischensehne. The large fleshy origin of the m. adductor mandibulae externus Pars superficialis from the jugal seems to be a characteristic feature of sea turtles.Conclusions/SignificanceIn C. caretta and L. kempii the ability to suction feed does not seem to be as well developed as that found in some freshwater aquatic turtles. Instead both have skulls suited to forceful biting. This is consistent with the observation that both taxa tend to feed on relatively slow moving but sometimes armoured prey. The broad fleshy origin of the m. adductor mandibulae externus Pars superficialis may be linked to thecheek region being almost fully enclosed in bone but the relationship is complex.

The Tendinous Framework in the Temporal Skull Region of Turtles and Considerations About Its Morphological Implications in Amniotes: A Review

“…As reviewed by Werneburg (2011), and contra Schumacher (1954/55), actually two parts of the temporal fascia are present in turtles. This is supported by the observations by Lakjer (1926), Jones et al (2012), and others. Poglayen-Neuwall (1953) described a ventral insertion of the temporal fascia to the rictal plate (German: "Mundplatte") in turtle species, which lack a postorbital (zygomatic) bridge.…”

“…Discussion of that, however, was beyond the focus of the present paper. Recently, Jones et al (2012) mentioned that "the ligamentum quadratomaxillare […] may represent a passive tension cord [Sverdlova and Witzel, 2010] for resisting tensile strains that might arise along the ventrolateral edge of the dome-like cranium during biting. This hypothesis may be tested using finite element modeling similar to that used in Curtis et al [2011]."…”

Jaw musculature during the dawn of turtle evolution

“…This is again because emarginations are a secondary phenomenon among extant turtles involving a high degree of derived jaw muscle characters (Table 2). Future studies using jaw muscle characters to reconstruct tetrapod phylogeny should be careful when either using turtles with emarginations or using marine turtles with their mostly complete temporal armour, including related secondary jaw muscle arrangements, which was acquired secondarily (Jones et al 2012). …”

“…The character coding corresponds to Werneburg (2010) with few modifications in characters 9, 80, 89, 96, 104, 114-117, 125, and 198 for Caretta caretta and Lepidochelys kempii following new data by Jones et al (2012). Multiple characters states for all characters A0(0,1), B0(0,2), C0(1,2), D 0(1,3), E0(2,3).…”

Comparing the Organs and Vasculature of the Head and Neck in Five Murine Species

“…In addition, it produced artifacts and distortion between the normal anatomy and that following fixation of the tissues (1,2).…”