Abstract
The investigation of form-function relationships requires a detailed understanding of anatomical systems. Here we document the 3-dimensional morphology of the cranial musculoskeletal anatomy in the Australian Laughing Kookaburra Dacelo novaeguineae, with a focus upon the geometry and attachments of the jaw muscles in this species. The head of a deceased specimen was CT scanned, and an accurate 3D representation of the skull and jaw muscles was generated through manual segmentation of the CT scan images, and augmented by dissection of the specimen. We identified 14 major jaw muscles: 6 in the temporal group (M. adductor mandibulae and M. pseudotemporalis), 7 in the pterygoid group (M. pterygoideus dorsalis and M. pterygoideus ventralis), and the single jaw abductor M. depressor mandibulae. Previous descriptions of avian jaw musculature are hindered by limited visual representation and inconsistency in the nomenclature. To address these issues, we: (1) present the 3D model produced from the segmentation process as a digital, fully interactive model in the form of an embedded 3D image, which can be viewed from any angle, and within which major components can be set as opaque, transparent, or hidden, allowing the anatomy to be visualised as required to provide a detailed understanding of the jaw anatomy; (2) provide a summary of the nomenclature used throughout the avian jaw muscle literature. The approach presented here provides considerable advantages for the documentation and communication of detailed anatomical structures in a wide range of taxa.
Highlights
The relationship between form and function is a central concept in biology (Lauder et al, 1995; Russell, 1916; Thompson, 1917); it determines the extent to which the anatomy of an organism permits specific behaviours and ecology
The resulting DICOM images were imported into MIMICS v11 (MATERIALISE, Belgium) segmentation software, wherein the skull of the kookaburra was digitally separated from the soft tissue by combining a scalar threshold with manual selection tools; the high density of the bone compared to the surrounding soft tissue allowed for quick and simple segmentation of the skull by applying a threshold based on the grey scale pixel values representative of the bone
Temporal muscles The external adductor complex—M. adductor mandibulae externus—has three parts: 2. M. adductor mandibulae externus profundus originates along the length of the temporal fossa; the attachment extends from the sagittal midline of the cranium (Figs. 4G and 4H) to the region just dorsal to the zygomatic process and along the posterior edge of the post orbital process
Summary
The relationship between form and function is a central concept in biology (Lauder et al, 1995; Russell, 1916; Thompson, 1917); it determines the extent to which the anatomy of an organism permits specific behaviours and ecology. Investigating form-function relationships requires a detailed understanding of anatomical systems, i.e., the discipline of anatomy and morphology. For functional questions concerning feeding ecology, the relevant anatomical system is the feeding apparatus; for the majority of vertebrates, this consists of the jaws. The jaw is a functional unit, consisting of a rigid framework—the skull bones of the cranium and mandible, operated by a system of jaw muscles. The skull bones must be able to withstand the forces of catching a struggling prey item, whilst transferring the bite force generated from the jaw muscles to hold, kill and process the prey without sustaining fracture. The mechanical limits of the jaw’s ability to bite the prey item determines the type and size of prey that can be taken (Ferrara et al, 2011; Herrel, O’Reilly & Richmond, 2002; Wroe, McHenry & Thomason, 2005)
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