Biomechanics of the rostrum in crocodilians: A comparative analysis using finite‐element modeling

Abstract

This article reports the use of simple beam and finite-element models to investigate the relationship between rostral shape and biomechanical performance in living crocodilians under a range of loading conditions. Load cases corresponded to simple biting, lateral head shaking, and twist feeding behaviors. The six specimens were chosen to reflect, as far as possible, the full range of rostral shape in living crocodilians: a juvenile Caiman crocodilus, subadult Alligator mississippiensis and Crocodylus johnstoni, and adult Caiman crocodilus, Melanosuchus niger, and Paleosuchus palpebrosus. The simple beam models were generated using morphometric landmarks from each specimen. Three of the finite-element models, the A. mississippiensis, juvenile Caiman crocodilus, and the Crocodylus johnstoni, were based on CT scan data from respective specimens, but these data were not available for the other models and so these-the adult Caiman crocodilus, M. niger, and P. palpebrosus-were generated by morphing the juvenile Caiman crocodilus mesh with reference to three-dimensional linear distance measured from specimens. Comparison of the mechanical performance of the six finite-element models essentially matched results of the simple beam models: relatively tall skulls performed best under vertical loading and tall and wide skulls performed best under torsional loading. The widely held assumption that the platyrostral (dorsoventrally flattened) crocodilian skull is optimized for torsional loading was not supported by either simple beam theory models or finite-element modeling. Rather than being purely optimized against loads encountered while subduing and processing food, the shape of the crocodilian rostrum may be significantly affected by the hydrodynamic constraints of catching agile aquatic prey. This observation has important implications for our understanding of biomechanics in crocodilians and other aquatic reptiles. Anat Rec Part A, 288A:827-849, 2006. © 2006 Key words: crocodiles; skull biomechanics; finite-element analysis; feeding; hydrodynamics; aquatic/marine tetrapods; comparative modelingCrocodilians have long been used as a model for interpreting the paleobiology of fossil species. The range of overall head shape and dentition in living taxa is reasonably broad (Mook, 1921), and observed correlations between these anatomical features and feeding ecology in crocodilians (Iordansky, 1973;Langston, 1973;Aoki, 1977;Van Drongelen and Dullemeijer, 1982;Busbey, 1989) have formed the bases for hypotheses of feeding paleoecology in a large array of

Feeding in billfishes: inferring the role of the rostrum from a biomechanical standpoint

“…Distal stiffening of rostral material could also counteract structural tapering relating to hydrodynamic demands. Previous work has shown that the drag experienced during lateral swiping of the elongate rostrum in alligators is proportional to the height of the jaws (McHenry et al, 2006). Minimizing element height (via distal tapering) may reduce drag in billfish rostra; however, it also comes at the cost of potentially reducing cross-sectional area and resistance to bending (McHenry et al, 2006); distal stiffening of the rostrum may ultimately be a strategy for maintaining adequate flexural stiffness in areas where I is selected to be comparatively low for hydrodynamic reasons.…”

Ontogeny of bite force in a validated biomechanical model of the American alligator

“…FEA provides tools to computationally investigate stress and strain (Daniel and McHenry, 2001; and reaction forces (Porro et al, 2011(Porro et al, , 2013) under a wide range of loading conditions. Researchers have applied this technique to investigate how feeding behavior loads the rostrum in comparative samples of extant crocodylians (McHenry et al, 2006;Pierce et al, 2008), comparing among archosaurs (Rayfield et al, 2007;Rayfield and Milner, 2008), and extinct crocodylomorphs such as thalattosuchians (Pierce et al, 2009). Using multi-body dynamics, Bates and Falkingham (2012) compared estimates of bite force of Tyrannosaurus with estimates from various tetrapods including a large individual of Alligator mississippiensis.…”

Fossil Vertebrate Tracks as Paleopenetrometers: Confounding Effects of Foot Morphology

“…FEA was first applied in many fields of engineering and physics. Its modern application has gone beyond these fields and, nowadays, FEA is used in comparative biomechanics (McHenry et al 2006;Oldfield et al 2012;Walmsley et al 2013), biology (Madzvamuse et al 2003), medicine (Kraft 2012), anthropology (Panagiotopoulou 2009) and geology (Bellian et al 2005). In the field of paleontology, it is used both for bone remains and ichnology (Moreno et al 2007;Arbour et al 2009;Manning et al 2009;Xing et al 2009;Falkingham 2010).…”

“…The biggest drawback with FEA is the lack of experimental data (laboratory tests) to define the parameters involved in the model. For this reason, assumptions and simplifications have to be adopted in many cases (McHenry et al 2006). …”