Applying 3D surface scanning technology to create photorealistic three-dimensional printed replicas of human anatomy.

Aim: To describe advances in 3D data capture and printing that allow photorealistic replicas of human anatomical specimens for education and research, and discuss advantages of current generation printing for replica design and manufacture. Materials & methods: We combine surface scanning and computerized tomography datasets that maximize precise color and geometric capture with ultra violet (UV) curable resin printing to replicate human anatomical specimens. Results: We describe the process for color control, print design and translation of photorealistic 3D meshes into 3D prints in durable resins. Conclusion: Current technologies allow previously unachievable ability to capture and reproduce anatomical specimens, and provide a platform for a new generation of 3D printed teaching materials to be designed and used in anatomy education environments.

The teaching of human anatomy has undergone significant change in the last 30­40 years, especially in respect to the technologies available to augment or replace traditional teaching using dissection of human bodies. This has included plastic models, software teaching packages, digital visualization tables and virtual/augmented reality. Our group initially developed a range of 3D printed replicas (Series 1) of human anatomy dissections. Our method involved computed tomography scanning a dissected specimen to capture the geometry and then digitally coloring the model with a standardized color palette to 'false color' the resulting 3D prints (e.g., yellow for nerves and red for arteries). This present report details how advances in full-color, high-resolution surface scanning can create a true colored photorealistic model of preserved human anatomical specimens. When these surface scanned models are 3D printed with the current generation of UV curable resin-based printers, it is possible to achieve photographic quality replicas comparable to the original anatomy specimens. This new generation of 3D printed replicas resembling traditional anatomy specimens (Series 1.1), while simultaneously still allowing color augmentation to further enhance their educational value. These replicas have an advantage over plastinated cadaver specimens as they can be utilized in any teaching environment such as peripheral or rural medical school locations, teaching hospitals and clinical environments.

Australian Aboriginal techniques for memorization: Translation into a medical and allied health education setting.

BACKGROUND: Writing and digital storage have largely replaced organic memory for encoding and retrieval of information in the modern era, with a corresponding decrease in emphasis on memorization in Western education. In health professional training, however, there remains a large corpus of information for which memorization is the most efficient means of ensuring: A) that the trainee has the required information readily available; and B) that a foundation of knowledge is laid, upon which the medical trainee builds multiple, complex layers of detailed information during advanced training. The carefully staged progression in early- to late- years' medical training from broad concepts (e.g. gross anatomy and pharmacology) to in-depth, specialised disciplinary knowledge (e.g. surgical interventions and follow-on care post-operatively) has clear parallels to the progression of training and knowledge exposure that Australian Aboriginal youths undergo in their progression from childhood to adulthood to Tribal Elders. METHODS: As part of the Rural Health curriculum and the undergraduate Nutrition and Dietetics program in the Monash University Faculty of Medicine, Nursing, and Health Sciences, we tested Australian Aboriginal techniques of memorization for acquisition and recall of novel word lists by first-year medical students (N = 76). We also examined undergraduate student evaluations (N = 49) of the use of the Australian Aboriginal memory technique for classroom study of foundational biomedical knowledge (the tricarboxylic acid cycle) using qualitative and quantitative analytic methods drawing from Bloom's taxonomy for orders of thinking and learning. Acquisition and recall of word lists were assessed without memory training, or after training in either the memory palace technique or the Australian Aboriginal narrative technique. RESULTS: Both types of memory training improved the number of correctly recalled items and reduced the frequency of specific error types relative to untrained performance. The Australian Aboriginal method resulted in approximately a 3-fold greater probability of improvement to accurate recall of the entire word list (odds ratio = 2.82; 95% c.i. = 1.15-6.90), vs. the memory palace technique (odds ratio = 2.03; 95% c.i. = 0.81-5.06) or no training (odds ratio = 1.5; 95% c.i. = 0.54-4.59) among students who did not correctly recall all list items at baseline. Student responses to learning the Australian Aboriginal memory technique in the context of biomedical science education were overwhelmingly favourable, and students found both the training and the technique enjoyable, interesting, and more useful than rote memorization. Our data indicate that this method has genuine utility and efficacy for study of biomedical sciences and in the foundation years of medical training.

The reproduction of human pathology specimens using three-dimensional (3D) printing technology for teaching purposes.

The teaching of medical pathology has undergone significant change in the last 30-40 years, especially in the context of employing bottled specimens or 'pots' in classroom settings. The reduction in post-mortem based teaching in medical training programs has resulted in less focus being placed on the ability of students to describe the gross anatomical pathology of specimens. Financial considerations involved in employing staff to maintain bottled specimens, space constraints and concerns with health and safety of staff and student laboratories have meant that many institutions have decommissioned their pathology collections. This report details how full-colour surface scanning coupled with CT scanning and 3 D printing allows the digital archiving of gross pathological specimens and the production of reproductions or replicas of preserved human anatomical pathology specimens that obviates many of the above issues. With modern UV curable resin printing technology, it is possible to achieve photographic quality accurate replicas comparable to the original specimens in many aspects except haptic quality. Accurate 3 D reproductions of human pathology specimens offer many advantages over traditional bottled specimens including the capacity to generate multiple copies and their use in any educational setting giving access to a broader range of potential learners and users.

A Novel 3-Dimensional Printing Fabrication Approach for the Production of Pediatric Airway Models.

BACKGROUND: Pediatric airway models currently available for use in education or simulation do not replicate anatomy or tissue responses to procedures. Emphasis on mass production with sturdy but homogeneous materials and low-fidelity casting techniques diminishes these models' abilities to realistically represent the unique characteristics of the pediatric airway, particularly in the infant and younger age ranges. Newer fabrication technologies, including 3-dimensional (3D) printing and castable tissue-like silicones, open new approaches to the simulation of pediatric airways with greater anatomical fidelity and utility for procedure training. METHODS: After ethics approval, available/archived computerized tomography data sets of patients under the age of 2 years were reviewed to identify those suitable for designing new models. A single 21-month-old subject was selected for 3D reconstruction. Manual thresholding was then performed to produce 3D models of selected regions and tissue types within the dataset, which were either directly 3D-printed or later cast in 3D-printed molds with a variety of tissue-like silicones. A series of testing mannequins derived using this multimodal approach were then further refined following direct clinician feedback to develop a series of pediatric airway model prototypes. RESULTS: The initial prototype consisted of separate skeletal (skull, mandible, vertebrae) and soft-tissue (nasal mucosa, pharynx, larynx, gingivae, tongue, functional temporomandibular joint [TMJ] "sleeve," skin) modules. The first iterations of these modules were generated using both single-material and multimaterial 3D printing techniques to achieve the haptic properties of real human tissues. After direct clinical feedback, subsequent prototypes relied on a combination of 3D printing for osseous elements and casting of soft-tissue components from 3D-printed molds, which refined the haptic properties of the nasal, oropharyngeal, laryngeal, and airway tissues, and improved the range of movement required for airway management procedures. This approach of modification based on clinical feedback resulted in superior functional performance. CONCLUSIONS: Our hybrid manufacturing approach, merging 3D-printed components and 3D-printed molds for silicone casting, allows a more accurate representation of both the anatomy and functional characteristics of the pediatric airway for model production. Further, it allows for the direct translation of anatomy derived from real patient medical imaging into a functional airway management simulator, and our modular design allows for modification of individual elements to easily vary anatomical configurations, haptic qualities of components or exchange components to replicate pathology.

Advanced 3D printed model of middle cerebral artery aneurysms for neurosurgery simulation.

BACKGROUND: Neurosurgical residents are finding it more difficult to obtain experience as the primary operator in aneurysm surgery. The present study aimed to replicate patient-derived cranial anatomy, pathology and human tissue properties relevant to cerebral aneurysm intervention through 3D printing and 3D print-driven casting techniques. The final simulator was designed to provide accurate simulation of a human head with a middle cerebral artery (MCA) aneurysm. METHODS: This study utilized living human and cadaver-derived medical imaging data including CT angiography and MRI scans. Computer-aided design (CAD) models and pre-existing computational 3D models were also incorporated in the development of the simulator. The design was based on including anatomical components vital to the surgery of MCA aneurysms while focusing on reproducibility, adaptability and functionality of the simulator. Various methods of 3D printing were utilized for the direct development of anatomical replicas and moulds for casting components that optimized the bio-mimicry and mechanical properties of human tissues. Synthetic materials including various types of silicone and ballistics gelatin were cast in these moulds. A novel technique utilizing water-soluble wax and silicone was used to establish hollow patient-derived cerebrovascular models. RESULTS: A patient-derived 3D aneurysm model was constructed for a MCA aneurysm. Multiple cerebral aneurysm models, patient-derived and CAD, were replicated as hollow high-fidelity models. The final assembled simulator integrated six anatomical components relevant to the treatment of cerebral aneurysms of the Circle of Willis in the left cerebral hemisphere. These included models of the cerebral vasculature, cranial nerves, brain, meninges, skull and skin. The cerebral circulation was modeled through the patient-derived vasculature within the brain model. Linear and volumetric measurements of specific physical modular components were repeated, averaged and compared to the original 3D meshes generated from the medical imaging data. Calculation of the concordance correlation coefficient (ρc: 90.2%-99.0%) and percentage difference (≤0.4%) confirmed the accuracy of the models. CONCLUSIONS: A multi-disciplinary approach involving 3D printing and casting techniques was used to successfully construct a multi-component cerebral aneurysm surgery simulator. Further study is planned to demonstrate the educational value of the proposed simulator for neurosurgery residents.

Challenges in creating dissectible anatomical 3D prints for surgical teaching.

Three-dimensional (3D) printing, or additive manufacturing, is now a widely used tool in pre-operative planning, surgical teaching and simulator training. However, 3D printing technology that produces models with accurate haptic feedback, biomechanics and visuals for the training surgeon is not currently available. Challenges and opportunities in creating such surgical models will be discussed in this review paper. Surgery requires proper tissue handling as well as knowledge of relevant anatomy. To prepare doctors properly, training models need to take into account the biomechanical properties of the anatomical structures that will be manipulated in any given operation. This review summarises and evaluates the current biomechanical literature as it relates to human tissues and correlates the impact of this knowledge on developing high fidelity 3D printed surgical training models. We conclude that, currently, a printer technology has not yet been developed which can replicate many of the critical qualities of human tissue. Advances in 3D printing technology will be required to allow the printing of multi-material products to achieve the mechanical properties required.

Three-Dimensional Printing of Archived Human Fetal Material for Teaching Purposes.

The practical aspect of human developmental biology education is often limited to the observation and use of animal models to illustrate developmental anatomy. This is due in part to the difficulty of accessing human embryonic and fetal specimens, and the sensitivity inherent to presenting these specimens as teaching materials. This report presents a new approach using three-dimensional (3D) printed replicas of actual human materials in practical classes, thus allowing for the inclusion of accurate examples of human developmental anatomy in the educational context. A series of 3D prints have been produced from digital data collected by computed tomography (CT) imaging of an archived series of preserved human embryonic and fetal specimens. The final versions of 3D prints have been generated in a range of single or multiple materials to illustrate the progression of human development, including the development of internal anatomy. Furthermore, multiple copies of each replica have been printed for large group teaching. In addition to the educational benefit of examining accurate 3D replicas, this approach lessens the potential for adverse student reaction (due to cultural background or personal experience) to observing actual human embryonic/fetal anatomical specimens, and reduces the potential of damage or loss of original specimens. This approach, in combination with ongoing improvements in the management and analysis of digital data and advances in scanning technology, has enormous potential to allow embryology students access to both local and international collections of human gestational material. Anat Sci Educ 00: 000-000. © 2018 American Association of Anatomists.

Technical note: The use of 3D printing in dental anthropology collections.

OBJECTIVES: Rapid prototyping (RP) technology is becoming more affordable, faster, and is now capable of building models with a high resolution and accuracy. Due to technological limitations, 3D printing in biological anthropology has been mostly limited to museum displays and forensic reconstructions. In this study, we compared the accuracy of different 3D printers to establish whether RP can be used effectively to reproduce anthropological dental collections, potentially replacing access to oftentimes fragile and irreplaceable original material. METHODS: We digitized specimens from the Yuendumu collection of Australian Aboriginal dental casts using a high-resolution white-light scanning system and reproduced them using four different 3D printing technologies: stereolithography (SLA); fused deposition modeling (FDM); binder-jetting; and material-jetting. We compared the deviations between the original 3D surface models with 3D print scans using color maps generated from a 3D metric deviation analysis. RESULTS: The 3D printed models reproduced both the detail and discrete morphology of the scanned dental casts. The results of the metric deviation analysis demonstrate that all 3D print models were accurate, with only a few small areas of high deviations. The material-jetting and SLA printers were found to perform better than the other two printing machines. CONCLUSIONS: The quality of current commercial 3D printers has reached a good level of accuracy and detail reproduction. However, the costs and printing times limit its application to produce large sample numbers for use in most anthropological studies. Nonetheless, RP offers a viable option to preserve numerically constraint fragile skeletal and dental material in paleoanthropological collections.

3D Printed Models of Cleft Palate Pathology for Surgical Education.

To explore the potential viability and limitations of 3D printed models of children with cleft palate deformity. BACKGROUND: The advantages of 3D printed replicas of normal anatomical specimens have previously been described. The creation of 3D prints displaying patient-specific anatomical pathology for surgical planning and interventions is an emerging field. Here we explored the possibility of taking rare pediatric radiographic data sets to create 3D prints for surgical education. METHODS: Magnetic resonance imaging data of 2 children (8 and 14 months) were segmented, colored, and anonymized, and stereolothographic files were prepared for 3D printing on either multicolor plastic or powder 3D printers and multimaterial 3D printers. RESULTS: Two models were deemed of sufficient quality and anatomical accuracy to print unamended. One data set was further manipulated digitally to artificially extend the length of the cleft. Thus, 3 models were printed: 1 incomplete soft-palate deformity, 1 incomplete anterior palate deformity, and 1 complete cleft palate. All had cleft lip deformity. The single-material 3D prints are of sufficient quality to accurately identify the nature and extent of the deformities. Multimaterial prints were subsequently created, which could be valuable in surgical training. CONCLUSION: Improvements in the quality and resolution of radiographic imaging combined with the advent of multicolor multiproperty printer technology will make it feasible in the near future to print 3D replicas in materials that mimic the mechanical properties and color of live human tissue making them potentially suitable for surgical training.

The Dry Season Shuffle: Gorges Provide Refugia for Animal Communities in Tropical Savannah Ecosystems.

In the wet-dry tropics, animal species face the major challenges of acquiring food, water or shelter during an extended dry season. Although large and conspicuous animals such as ungulates and waterfowl migrate to wetter areas during this time, little is known of how smaller and more cryptic animal species with less mobility meet these challenges. We fenced off the entire entrance of a gorge in the Australian tropical savanna, offering the unique opportunity to determine the composition and seasonal movement patterns of the small vertebrate community. The 1.7 km-long fence was converted to a trapline that was deployed for 18-21 days during the early dry season in each of two years, and paired traps on both sides of the fence allowed us to detect the direction of animal movements. We predicted that semi-aquatic species (e.g., frogs and turtles) would move upstream into the wetter gorge during the dry season, while more terrestrial species (e.g., lizards, snakes, mammals) would not. The trapline captured 1590 individual vertebrates comprising 60 species. There was a significant bias for captures on the outside of the fence compared to the inside for all species combined (outside/inside = 5.2, CI = 3.7-7.2), for all vertebrate classes, and for specific taxonomic groups. The opposite bias (inside/outside = 7.3, N= 25) for turtles during the early wet season suggested return migration heading into the wet season. Our study revealed that the small vertebrate community uses the gorge as a dry season refuge. The generality of this unreplicated finding could be tested by extending this type of survey to tropical savannahs worldwide. A better understanding of how small animals use the landscape is needed to reveal the size of buffer zones around wetlands required to protect both semi-aquatic and terrestrial fauna in gorges in tropical savannah woodland, and thus in ecosystems in general.

The relationship between cranial structure, biomechanical performance and ecological diversity in varanoid lizards.

Skull structure is intimately associated with feeding ability in vertebrates, both in terms of specific performance measures and general ecological characteristics. This study quantitatively assessed variation in the shape of the cranium and mandible in varanoid lizards, and its relationship to structural performance (von Mises strain) and interspecific differences in feeding ecology. Geometric morphometric and linear morphometric analyses were used to evaluate morphological differences, and finite element analysis was used to quantify variation in structural performance (strain during simulated biting, shaking and pulling). This data was then integrated with ecological classes compiled from relevant scientific literature on each species in order to establish structure-function relationships. Finite element modelling results showed that variation in cranial morphology resulted in large differences in the magnitudes and locations of strain in biting, shaking and pulling load cases. Gracile species such as Varanus salvadorii displayed high strain levels during shaking, especially in the areas between the orbits. All models exhibit less strain during pull back loading compared to shake loading, even though a larger force was applied (pull =30N, shake = 20N). Relationships were identified between the morphology, performance, and ecology. Species that did not feed on hard prey clustered in the gracile region of cranial morphospace and exhibited significantly higher levels of strain during biting (P = 0.0106). Species that fed on large prey clustered in the elongate area of mandible morphospace. This relationship differs from those that have been identified in other taxonomic groups such as crocodiles and mammals. This difference may be due to a combination of the open 'space-frame' structure of the varanoid lizard skull, and the 'pull back' behaviour that some species use for processing large prey.

Oldest pathology in a tetrapod bone illuminates the origin of terrestrial vertebrates.

The origin of terrestrial tetrapods was a key event in vertebrate evolution, yet how and when it occurred remains obscure, due to scarce fossil evidence. Here, we show that the study of palaeopathologies, such as broken and healed bones, can help elucidate poorly understood behavioural transitions such as this. Using high-resolution finite element analysis, we demonstrate that the oldest known broken tetrapod bone, a radius of the primitive stem tetrapod Ossinodus pueri from the mid-Viséan (333 million years ago) of Australia, fractured under a high-force, impact-type loading scenario. The nature of the fracture suggests that it most plausibly occurred during a fall on land. Augmenting this are new osteological observations, including a preferred directionality to the trabecular architecture of cancellous bone. Together, these results suggest that Ossinodus, one of the first large (>2m length) tetrapods, spent a significant proportion of its life on land. Our findings have important implications for understanding the temporal, biogeographical and physiological contexts under which terrestriality in vertebrates evolved. They push the date for the origin of terrestrial tetrapods further back into the Carboniferous by at least two million years. Moreover, they raise the possibility that terrestriality in vertebrates first evolved in large tetrapods in Gondwana rather than in small European forms, warranting a re-evaluation of this important evolutionary event.

3D printed reproductions of orbital dissections: a novel mode of visualising anatomy for trainees in ophthalmology or optometry.

BACKGROUND: The teaching of human head, neck and orbital anatomy forms a critical part of undergraduate and postgraduate medical and allied health professional training, including optometry. While still largely grounded in cadaveric dissection, this method of instruction is constrained in some countries and regional areas by access to real human cadavers, costs of cadaver bequest programmes, health and safety of students and staff and the shortage of adequate time in modern curricula. Many candidates choosing a postgraduate pathway in ophthalmological training, such as those accepted into the Royal Colleges of Ophthalmology in the UK, Australia and New Zealand programmes and the American Academy of Ophthalmologists in the USA, are compelled as adult learners to revise or revisit human orbital anatomy, ocular anatomy and select areas of head and neck anatomy. These candidates are often then faced with the issue of accessing facilities with dissected human cadaveric material. METHODS: In light of these difficulties, we developed a novel means of creating high-resolution reproductions of prosected human cadaver orbits suitable for education and training. RESULTS: 3D printed copies of cadaveric orbital dissections (superior, lateral and medial views) showing a range of anatomical features were created. DISCUSSION: These 3D prints offer many advantages over plastinated specimens as they are suitable for rapid reproduction and as they are not human tissue they avoid cultural and ethical issues associated with viewing cadaver specimens. In addition, they are suitable for use in the office, home, laboratory or clinical setting in any part of the world for patient and doctor education.

The production of anatomical teaching resources using three-dimensional (3D) printing technology.

The teaching of anatomy has consistently been the subject of societal controversy, especially in the context of employing cadaveric materials in professional medical and allied health professional training. The reduction in dissection-based teaching in medical and allied health professional training programs has been in part due to the financial considerations involved in maintaining bequest programs, accessing human cadavers and concerns with health and safety considerations for students and staff exposed to formalin-containing embalming fluids. This report details how additive manufacturing or three-dimensional (3D) printing allows the creation of reproductions of prosected human cadaver and other anatomical specimens that obviates many of the above issues. These 3D prints are high resolution, accurate color reproductions of prosections based on data acquired by surface scanning or CT imaging. The application of 3D printing to produce models of negative spaces, contrast CT radiographic data using segmentation software is illustrated. The accuracy of printed specimens is compared with original specimens. This alternative approach to producing anatomically accurate reproductions offers many advantages over plastination as it allows rapid production of multiple copies of any dissected specimen, at any size scale and should be suitable for any teaching facility in any country, thereby avoiding some of the cultural and ethical issues associated with cadaver specimens either in an embalmed or plastinated form.

An interactive three dimensional approach to anatomical description-the jaw musculature of the Australian laughing kookaburra (Dacelo novaeguineae).

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.

Embedding and publishing interactive, 3-dimensional, scientific figures in Portable Document Format (PDF) files.

With the latest release of the S2PLOT graphics library, embedding interactive, 3-dimensional (3-d) scientific figures in Adobe Portable Document Format (PDF) files is simple, and can be accomplished without commercial software. In this paper, we motivate the need for embedding 3-d figures in scholarly articles. We explain how 3-d figures can be created using the S2PLOT graphics library, exported to Product Representation Compact (PRC) format, and included as fully interactive, 3-d figures in PDF files using the movie15 LaTeX package. We present new examples of 3-d PDF figures, explain how they have been made, validate them, and comment on their advantages over traditional, static 2-dimensional (2-d) figures. With the judicious use of 3-d rather than 2-d figures, scientists can now publish, share and archive more useful, flexible and faithful representations of their study outcomes. The article you are reading does not have embedded 3-d figures. The full paper, with embedded 3-d figures, is recommended and is available as a supplementary download from PLoS ONE (File S2).

Why the long face? The mechanics of mandibular symphysis proportions in crocodiles.

BACKGROUND: Crocodilians exhibit a spectrum of rostral shape from long snouted (longirostrine), through to short snouted (brevirostrine) morphologies. The proportional length of the mandibular symphysis correlates consistently with rostral shape, forming as much as 50% of the mandible's length in longirostrine forms, but 10% in brevirostrine crocodilians. Here we analyse the structural consequences of an elongate mandibular symphysis in relation to feeding behaviours. METHODS/PRINCIPAL FINDINGS: Simple beam and high resolution Finite Element (FE) models of seven species of crocodile were analysed under loads simulating biting, shaking and twisting. Using beam theory, we statistically compared multiple hypotheses of which morphological variables should control the biomechanical response. Brevi- and mesorostrine morphologies were found to consistently outperform longirostrine types when subject to equivalent biting, shaking and twisting loads. The best predictors of performance for biting and twisting loads in FE models were overall length and symphyseal length respectively; for shaking loads symphyseal length and a multivariate measurement of shape (PC1- which is strongly but not exclusively correlated with symphyseal length) were equally good predictors. Linear measurements were better predictors than multivariate measurements of shape in biting and twisting loads. For both biting and shaking loads but not for twisting, simple beam models agree with best performance predictors in FE models. CONCLUSIONS/SIGNIFICANCE: Combining beam and FE modelling allows a priori hypotheses about the importance of morphological traits on biomechanics to be statistically tested. Short mandibular symphyses perform well under loads used for feeding upon large prey, but elongate symphyses incur high strains under equivalent loads, underlining the structural constraints to prey size in the longirostrine morphotype. The biomechanics of the crocodilian mandible are largely consistent with beam theory and can be predicted from simple morphological measurements, suggesting that crocodilians are a useful model for investigating the palaeobiomechanics of other aquatic tetrapods.