Porro Lab: Research Projects

Development, Diversity and Evolution of the Reptilian Skull

Complex, interacting forces drive and constrain vertebrate form and function, including internal (genetics, phylogeny) and external (environment, diet) factors. Our lab combines massive anatomical datasets, cutting-edge 3D visualization, biomechanical techniques and evolutionary modelling to untangle the multiple influences on organismal shape, performance, ecology and biodiversity.

Reptiles are an ideal model system to investigate the impact of different factors on skull shape due to vast differences in body size (from tiny chameleons to gigantic dinosaurs), occupation of diverse habitats, a wide range of feeding mechanisms and diet, and a fossil record stretching back hundreds of millions of years. With previous and current funding from diverse sources, we use reptiles to identify the determinants of head anatomy, shedding new light on the forces shaping vertebrate morphology and biodiversity.

Development, diversity and evolution of the reptilian skull: Funded by a UKRI Future Leaders Fellowship, our flagship research project takes a multi-scale approach that is fundamentally changing our view of how different forces act both during the life of an individual and across evolutionary time to shape form, function and biodiversity. We began by focusing on two extant reptiles – American alligator and veiled chameleon – for which we collected abundant in vivo experimental data during feeding, including high-speed and X-ray video, bite forces, and bone strains. We use microCT scanning – including contrast-enhanced staining to visualize soft tissues – and traditional dissection to capture head shape and characterize anatomy. Shape analyses (3D geometric morphometrics) allow us to quantify changes in skull shape during growth and biomechanical modelling, such as finite element analyses, allow us to rigorously test long-standing hypotheses of skull function. Our results have demonstrated increased mechanical performance during growth in both alligator and chameleon skulls; however, we show that increased performance is driven by different factors in each taxon. Additionally, we have uncovered unexpected patterns in sexual dimorphism in the veiled chameleon, overturning earlier hypotheses.

Going forward, the project will focus on how mechanical forces influence skull shape prior to hatching and will investigate the interaction between intrinsic genetic/developmental programme and external forces. We will also compare different drivers of skull shape across a broad taxonomic sample of extant reptiles, and investigate the impact of major environmental transitions and dramatic increases/decreases in body size on skull shape, performance and diet.

Skull form and function in early dinosaurs: Dinosaurs capture the imagination due to their enormous body size, incredible diversity and dominance of Mesozoic terrestrial ecosystems for over 130 million years. But how did dinosaurs achieve such success? During a NERC-funded project (NE/R000077/1 “The role of cranial biomechanics and feeding in clade diversification and early dinosaur evolution” 2018-2021) with Paul Barrett at the Natural History Museum our team integrated 3D visualization and biomechanical modelling methods to comprehensively understand the consequences of functional changes in skull performance during the origin and early evolution of dinosaurs. Working with partners across the globe we CT-scanned and reconstructed skull shape in a range of early dinosaur and dinosauriform taxa, then used these reconstructions to predict muscle and bite forces, mechanical advantage and skull stress during feeding. Our results demonstrated how the evolution of a crucial system – feeding – can be governed by diverse solutions to a biological challenge. Among early ornithischian dinosaurs, for example, increased bite force necessary for high-fibre herbivory was achieved via multiple pathways, including increasing body size, increasing relative jaw muscle size, and changing skull geometry to increase mechanical advantage.

The project continues as part of a NERC DTP PhD studentship (2025 – 2028) which is using similar data and methods to investigate trends in the evolution of skull shape, performance and diet among saurischian dinosaurs and dinosaur ancestors to build a comprehensive picture of how feeding may have played a role in the initial radiation and success of dinosaurs.

Feeding in crocodilian evolution and conservation: Work carried out at the University of Chicago in the lab of Callum Ross from 2008-2012 collected experimental in vivo feeding data from American alligator which were used to construct, refine and validate finite element models of alligator skulls. This work led to a series of papers validating results from finite element analysis (FEA) against in vivo data to demonstrate model accuracy in terms of predicting the mechanical response of the skull under feeding loads. Our research demonstrated greater accuracy of FEA compared to other modelling methods (e.g., beam modelling) and quantified model sensitivity to varying constraints and material properties. This work has been widely cited by the community as setting the gold standard for validation and sensitivity analyses of finite element models.

Our focus on feeding mechanics in crocodilians continues as part of an ongoing UKRI FLF project (see above) and as part of a BBSRC LIDo PhD studentship (2024 – 2027) looking at changes in skull shape and performance during growth in crocodilians, and the impact of the largest crocodilians on population structure and ecosystems.

Evolutionary drivers and functional consequences of cranial kinesis: Although mammals feature rigid skulls, many vertebrates – fish, lizards, snakes and birds – exhibit cranial kinesis, in which individual skull bones can move relative to each other and often cited as a key innovation that promotes diversification. Given the skull’s importance in protecting the brain and sense organs and generating/resisting feeding forces, why introduce movement and weakness to such a crucial structure? Funded by a Leverhulme Trust Research Project Grant, this upcoming project (start 2026) will provide new insights into the importance of skull kinesis across vertebrates, using lizards as a model system. We will use experiments to characterize kinetic movements across a representative sample of lizards, microCT imaging and visualization software to produce 3D models of over 200 species of lizards. These will be used for geometric morphometrics to quantify skull shape and for finite element and musculoskeletal modelling to test the functional consequences of cranial kinesis. Finally, we will apply phylogenetic comparative methods to reconstruct the evolution of skull kinesis in lizards and assess the pressures driving its evolution. A major focus will be evaluating the true impact of this widely cited but untested key innovation.

Skull Form and Function across the Fish-Tetrapod Transition

The conquest of the land by vertebrates during the Devonian and Carboniferous Periods is one of the landmark transitions in the history of life on Earth and established the roots of terrestrial biodiversity that we see today. The transition is marked by dramatic skeleton evolution, with most research focusing on the iconic fin-to-limbs transition. However, the vertebrate skull also evolved to accommodate changes in sensory systems, breathing, locomotion and feeding. Two previous projects funded by Marie Curie (303161 “Tetrapods Rising” 2012-2014) and NERC (NE/P013090/1 “Skull evolution and the terrestrialisation and radiation of tetrapods” 2017-2021), both with Emily Rayfield at the University of Bristol and Jenny Clack at the University Cambridge, used microCT scanning to capture skull shape across a broad sample of fossil tetrapods (as well as extant bracketing taxa) spanning the transition. During this project, we pioneered new techniques to retrodeform fossil skulls, removing hundreds of millions of years of damage and deformation to produce 3D models more accurately reflecting original skull shape. These models formed the basis for finite element models that are used to predict the mechanical behaviour of fossil skulls under feeding loads.

Through both worldwide collaborations established through this project and ongoing PhD student projects based at the University of Bristol and the University of Uppsala we continue our research on this fascinating group of fossil animals.

Vertebrate Palaeontology

One of our main objectives is understanding how vertebrate form and function change through time. Thus, good fossil material forms the core of most of our research projects. We have worked with dozens of institutions and research teams around the world to capture the morphology of fossil fish, early tetrapods, and fossil amphibians, reptiles and birds. We use 3D visualization software to digitally prepare fossils, stripping away matrix and separating individual bones, and have pioneered techniques to digitally repair fossils, removing hundreds of millions of years of damage and deformation, giving us a first look at the real-life appearance of long extinct animals. These reconstructions yield new insight into the biology and ecology of fossil animals and form the basis for downstream analyses such as geometric morphometrics and biomechanical modelling. All of these data provide new evidence to piece together worlds lost in deep time.

The Evolution of Amphibian Locomotion

As part of an ERC project (PIPA, 2014-2019) headed by Chris Richards at the Royal Veterinary College, we sough to understand how musculoskeletal transformations drove the origin and radiation of frogs. We collected in vivo experimental data – including high-speed video, X-ray reconstruction of moving morphology (XROMM), EMG data, and force plate data – alongside anatomical data of pelvic and hindlimb bones and muscles to build cutting-edge inverse dynamic and musculoskeletal models. This allowed us to better understand the interactions between muscles, bones and external forces and resolve long-standing questions on the evolution of frogs and limbs. During this project, we became pioneers in the use of contrast-enhanced microCT scanning to create high-resolution, freely accessible 3D digital dissections that preserved the 3D relationships of anatomical structures, including the first ever full-body digital dissection of the model taxon Xenopus.

This work was continued by LIDo funded PhD student Alice Leavey (2019-2023) who created the world’s largest comparative dataset of digital dissections during a project to link pelvic and hindlimb anatomy, locomotor style and evolutionary history in frogs.