Cranial muscles of the anuransleiopelma hochstetteriandascaphus trueiand the homologies of the mandibular adductors in lissamphibia and other gnathostomes

Abstract

The frogs Ascaphus truei and Leiopelma hochstetteri are members of the most basal lineages of extant anurans. Their cranial muscles have not been previously described in full and are investigated here by dissection. Comparison of these taxa is used to review a controversy regarding the homologies of the jaw adductor muscles in Lissamphibia, to place these homologies in a wider gnathostome context, and to define features that may be useful for cladistic analysis of Anura. A new muscle is defined in Ascaphus and is designated m. levator anguli oris. The differences noted between Ascaphus and Leiopelma are in the penetration of the jaw adductor muscles by the mandibular nerve (V3). In the traditional view of this anatomy, the paths of the trigeminal nerve branches define homologous muscles. This scheme results in major differences among frogs, salamanders, and caecilians. The alternative view is that the topology of origins, insertions, and fiber directions are defining features, and the nerves penetrate the muscle mass in a variable way. The results given here support the latter view. A new model is proposed for Lissamphibia, whereby the adductor posterior (levator articularis) is a separate entity, and the rest of the adductor mass is configured around it as a folded sheet. This hypothesis is examined in other gnathostomes, including coelacanth and lungfish, and a possible sequence for the evolution of the jaw muscles is demonstrated. In this system, the main jaw adductor in teleost fish is not considered homologous with that of tetrapods. This hypothesis is consistent with available data on the domain of expression of the homeobox gene engrailed 2, which has previously not been considered indicative of homology. Terminology is discussed, and "adductor mandibulae" is preferred to "levator mandibulae" to align with usage in other gnathostomes.

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

“…Moreover, no jaw muscle descriptions of Lepidochelys kempii or Natator depressus are known to the authors, and only a few aspects of this anatomy in L . olivacea have been reported ([144]: 12). For a recent review of previous work, terminology, and muscle synonymies, see Werneburg [143].…”

The Digital Fish Library: Using MRI to Digitize, Database, and Document the Morphological Diversity of Fish

“…How the data and methods are subsequently used is entirely up to the “user”. To date, our methods and data have been successfully applied to a broad range of research and educational projects [8]–[15], [104]. We do recognize that there is a lot more work to be done in optimizing web-based tools for both research and educational purposes.…”

“…However, while we have focused on a particular imaging modality and a specific collection of specimens, the methods and integrated infrastructure, which we report here, are applicable to a wide range of applications. This is demonstrated with examples of research projects that have developed from, and the use of the techniques developed for, the DFL [8]–[15]. Moreover, the DFL infrastructure serves as one successful model for digital library creation and maintenance.…”

Homology of the Jaw Muscles in Lizards and Snakes—A Solution from a Comparative Gnathostome Approach

“…). Modified from Johnston (). Terminology is given as typically used in amphibians (in italics, underlined) (Haas, ; Johnston, ) (m. levator or adductor mandibulae internus‐longus‐externus‐lateralis) and in amniotes (plain font), see Table .…”