Stephen M. Gatesy

• PhD
• Professor at Brown University

The X-ray Reconstruction of Moving Morphology (XROMM) workflow enables precise and accurate measurement of the 3D skeletal kinematics underlying animal behaviors. The dynamic endocast method built upon that workflow to measure the rate of volume change within a bounded region of interest. We measured the precision and accuracy of the dynamic endoca...

For much of the Pliocene and Pleistocene, multiple hominin species coexisted in the same regions of eastern and southern Africa. Due to the limitations of the skeletal fossil record, questions regarding their interspecific interactions remain unanswered. We report the discovery of footprints (~1.5 million years old) from Koobi Fora, Kenya, that pro...

Our knowledge of vertebrate functional evolution depends on inferences about joint function in extinct taxa. Without rigorous criteria for evaluating joint articulation, however, such analyses risk misleading reconstructions of vertebrate animal motion. Here we propose an approach for synthesizing raycast-based measurements of 3-D articular overlap...

Fossil footprints (i.e., tracks) were believed to document arch anatomical evolution, although our recent work has shown that track arches record foot kinematics instead. Analyses of track arches can thereby inform the evolution of human locomotion, although quantifying this 3‐D aspect of track morphology is difficult. Here, we present a volumetric...

The longitudinal arch of the human foot is viewed as a pivotal adaptation for bipedal walking and running. Fossil footprints from Laetoli, Tanzania, and Ileret, Kenya, are believed to provide direct evidence of longitudinally arched feet in hominins from the Pliocene and Pleistocene, respectively. We studied the dynamics of track formation using bi...

Major transformations in the locomotor system of archosaurs (a major clade of reptiles including birds, crocodiles, dinosaurs, and pterosaurs) were accompanied by significant modifications to ankle anatomy. How the evolution of such a complex multi-joint structure is related to shifts in ankle function and locomotor diversity across this clade rema...

Living birds (Aves) have bodies substantially modified from the ancestral reptilian condition. The avian pelvis in particular experienced major changes during the transition from early archosaurs to living birds1,2. This stepwise transformation is well documented by an excellent fossil record2–4; however, the ontogenetic alterations that underly it...

The stance phase of walking is when forces are applied to the environment to support, propel, and maneuver the body. Unlike solid surfaces, deformable substrates yield under load, allowing the foot to sink to varying degrees. For bipedal birds and their dinosaurian ancestors, a shared response to walking on these substrates has been identified in t...

Paleobiological reconstructions of joint mobility are an essential component of functional analyses of extinct animals. Over the past half-decade, the methods underlying mobility studies have advanced rapidly in three main areas: increasing complexity of virtual joint manipulation, formalizing pose viability criteria, and constructing more rigorous...

The last common ancestor of birds and crocodylians plus all of its descendants (clade Archosauria) dominated terrestrial Mesozoic ecosystems, giving rise to disparate body plans, sizes, and modes of locomotion. As in the fields of vertebrate morphology and paleontology more generally, studies of archosaur skeletal structure have come to depend on t...

Virtual and augmented reality (VR/AR) are new technologies with the power to revolutionize the study of morphology. Modern imaging approaches such as computed tomography, laser scanning, and photogrammetry have opened up a new digital world, enabling researchers to share and analyze morphological data electronically and in great detail. Because thi...

The emergence of bipedalism had profound effects on human evolutionary history, but the evolution of locomotor patterns within the hominin clade remains poorly understood. Fossil tracks record in vivo behaviours of extinct hominins, and they offer great potential to reveal locomotor patterns at various times and places across the human fossil recor...

Paleobiologists typically exclude impossible joint poses from reconstructions of extinct animals by estimating the rotational range of motion (ROM) of fossil joints. However, this ubiquitous practice carries the assumption that osteological estimates of ROM consistently overestimate true joint mobility. Because studies founded on ROM‐based exclusio...

Feet must mediate substrate interactions across an animal's entire range of limb poses used in life. Metatarsals, the ‘bones of the sole,’ are the dominant pedal skeletal elements for most tetrapods. In plantigrade species that walk on the entirety of their sole, such as living crocodylians, intermetatarsal mobility offers the potential for a conti...

Reconstructions of movement in extinct animals are critical to our understanding of major transformations in vertebrate locomotor evolution. Estimates of joint range of motion (ROM) have long been used to exclude anatomically impossible joint poses from hypothesized gait cycles. Here we demonstrate how comparative ROM data can be harnessed in a dif...

Starting with his first report on fossil footprints from the Connecticut Valley over 180 years ago, Edward Hitchcock described what he interpreted as a burgeoning ancient fauna founded on ever-increasing nominal track diversity. For three decades, Hitchcock made countless contributions to ichnology, but his inference of thin-toed animals (Leptodact...

Whilst bones present a static view of extinct animals , fossil footprints are a direct record of the activity and motion of the track maker. Deep footprints are a particularly good record of foot motion. Such footprints rarely look like the feet that made them; the sediment being heavily disturbed by the foot motion. Because of this, such tracks ar...

ABSTRACT Three-dimensional studies of range of motion currently plot joint poses in an "Euler space" whose axes are angles measured in the joint's three rotational degrees of freedom. Researchers then compute the volume of a pose cloud to measure rotational mobility. However, pairs of poses that are equally different from one another in orientation...

The feet of ground-dwelling birds retain many features of their dinosaurian ancestry. Experiments with living species offer insights into the complex interplay among anatomy, kinematics and substrate during the formation of Mesozoic footprints. However, a key aspect of the track-making process, sub-surface foot movement, is hindered by substrate op...

Extant archosaurs exhibit highly divergent articular soft tissue anatomies between avian and crocodilian lineages. However, the general lack of understanding of the dynamic interactions among archosaur joint soft tissues has hampered further inferences about the function and evolution of these joints. Here we use contrast-enhanced computed tomograp...

We present the results of a two-year design study to developing virtual reality (VR) flow visualization tools for the analysis of dinosaur track creation in a malleable substrate. Using Scientific Sketching methodology, we combined input from illustration artists, visualization experts, and domain scientists to create novel visualization methods. B...

We present a two-year design study of developing virtual reality (VR) flow visualization tools for the analysis of dinosaur track creation using the Scientific Sketching design methodology. We involved 25 art and computer science students from a VR design course in a rapid visualization sketching cycle, guided by paleontologist collaborators throug...

Drone footage of a large American crocodile bottom walking in shallow coastal water off Costa Rica was used to estimate oblique pace and stride lengths and pace angulations from autopodial touchdowns. The crocodile's pes stride lengths were longer but more variable than expected for an individual of comparable size high-walking on land, due in part...

Recent discoveries have made hominin tracks an increasingly prevalent component of the human fossil record, and these data have the capacity to inform long-standing debates regarding the biomechanics of hominin locomotion. However, there is currently no consensus on how to decipher biomechanical variables from hominin tracks. These debates can be l...

The collection and dissemination of vertebrate ichnological data is struggling to keep up with techniques that are becoming commonplace in the wider palaeontological field. A standard protocol is required to ensure that data is recorded, presented and archived in a manner that will be useful both to contemporary researchers, and to future generatio...

Figure S2. Estimated rotation centres for the patellofemoral joint, shown in the plane‐of‐best‐fit for patella motion.

Table S2. Moment arms calculated for M. iliotibialis cranialis (IC), M. iliotibialis lateralis preacetabularis (ILPR) and M. femorotibialis intermedius (FT) about patellofemoral rotation centres estimated by second‐order curve fitting (Curve Centres), circular arc fitting (Circle Centre) or median planar movement poles (Median Pole), with numbered...

Figure S1. Mean knee joint flexion/extension angles for specimens of Numida running at various speeds (see Kambic et al., 2015) averaged from time‐normalized data from all recorded strides, plotted against percentage stance and swing phases.

Figure S4. Mean values of r ET/r PT, taken to be a proxy for mechanical advantage (see Materials and methods).

Table S1. Flexion‐extension angles in degrees for the hip and knee joints, with numbered limb phases. See Skeletal Kinematics section of Materials and methods for details.

Figure S3. Mean values of r ET/r PT, taken to be a proxy for mechanical advantage (see Materials and methods).

Measuring range of motion (ROM) is a valuable technique that can link bone morphology to joint function in both extant and extinct taxa. ROM results are commonly presented as tables or graphs of maxima and minima for each rotational degree of freedom. We investigate the interactions among three degrees of freedom using X-ray reconstruction of movin...

Human patellae (kneecaps) are thought to act as gears, altering the mechanical advantage of knee extensor muscles during running. Similar sesamoids have evolved in the knee extensor tendon independently in birds, but it is unknown if these also affect the mechanical advantage of knee extensors. Here, we examine the mechanics of the patellofemoral j...

As purely sedimentary structures, fossil footprints are all about shape. Correctly interpreting the significance of their surface topography requires understanding the sources of morphological variation. Differences among specimens are most frequently attributed to either taxonomy (trackmaker) or to preservation quality. ‘Well-preserved’ tracks are...

Marker-based XROMM requires software tools for: (1) correcting fluoroscope distortion; (2) calibrating X-ray cameras; (3) tracking radio-opaque markers; and (4) calculating rigid body motion. In this paper we describe and validate XMALab, a new open-source software package for marker-based XROMM (C++ source and compiled versions on Bitbucket). Most...

Horse racing is a multi-billion-dollar industry that has raised welfare concerns due to injured and euthanized animals. Whilst the cause of musculoskeletal injuries that lead to horse morbidity and mortality is multifactorial, pre-existing pathologies, increased speeds and substrate of the racecourse are likely contributors to foot disease. Horse h...

Maximum principal stress (MPa) distribution results for the shod and the unshod horse foot, in dorsal view Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower maximum principal stresses respectively.

Animation of the unshod horse during walking

Ground reaction force (GRF) data in Newtons for the unshod (n = 4) and shod (n = 4) conditions

Minimum principal stress (MPa) distribution results for the shod and the unshod horse foot, in dorsal view Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower minimum principal stresses respectively.

Sensitivity analysis on the P1 constraints BC1 constraints are applied on the entire distal joint surface of the P1 and fixed in all axes. BC2 constraints involve fix constraining 3 nodes at the distal joint surface on the centroid axis of the load. The remainder nodes are fixed on the long axis of the bone only. Transparent and non-transparent ima...

Sensitivity analysis on the location of the P3 constraints and the respective von Mises stresses patterns on the palmar and dorsal views Warm (red) and cold (blue) colours show higher and lower von Mises stresses respectively.

Animation of the shod horse during walking

Raw speed data for the unshod (n = 4) and shod (n = 4) conditions Column A shows the conditions. Column B lists the name and date of the steps. Column C lists the horse’s hip height in meters. Column D lists the frame rate of the Sony camera used for the speed calculations. Columns E and F list the start and end frame of each trial and each conditi...

The position of the custom-designed calibration cube used during the fluoroscopy experiments to calibrate the 3D space in the XROMM analysis

Loading (in red) and boundary (in orange) locations for the P1, P2 and P3 bones (see Methods: Loads and constraints)

Maximum principal stress (MPa) distribution results for the shod and the unshod horse foot, in palmar view Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower maximum principal stresses respectively.

Minimum principal stress (MPa) distribution results for the shod and the unshod horse foot, in palmar view Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower minimum principal stresses respectively.

Degrees of motion for proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints for the shod (n = 4) and unshod (n = 4) conditions about the flexion-extension axis

Horse racing is a multi-billion-dollar industry that has raised welfare concerns due to disabled and euthanized animals. Whilst the cause of musculoskeletal injuries that lead to horse morbidity and mortality is multifactorial, pre-existing pathologies, increased speeds and substrate of the racecourse are likely contributors to foot disease. The ho...

Horse racing is a multi-billion-dollar industry that has raised welfare concerns due to disabled and euthanized animals. Whilst the cause of musculoskeletal injuries that lead to horse morbidity and mortality is multifactorial, pre-existing pathologies, increased speeds and substrate of the racecourse are likely contributors to foot disease. The ho...

In avian bipeds performing steady locomotion, right and left limbs are typically assumed to act out of phase, but with little kinematic disparity. However, outwardly appearing steadiness may harbor previously unrecognized asymmetries. Here, we present markerbased XROMM data showing that guineafowl on a treadmill routinely yaw away from their direct...

Significance The origins and earliest evolution of mammals can be deciphered by studying Late Triassic fossil relatives of modern mammals. The computed tomography study of Haramiyavia from the Late Triassic has revealed new information about the skull evolution and dental function in the forerunners of mammals. Haramiyavia had a unique way of chewi...

Foot anatomy and mechanics vary among herbivorous quadrupeds. Horses have one toe ending in a rigid hoof, which is effective for fast-running but generates large impact vibrations. The feet of the elephants and rhinoceroses have five and three toes, respectively, bound within a digital cushion, which absorbs locomotor forces, yet is heavy and thus...

Foot anatomy and mechanics vary among herbivorous quadrupeds. Horses have one toe ending in a rigid hoof, which is effective for fast‐running but generates large impact vibrations. The feet of the elephants and rhinoceroses have five and three toes, respectively, bound within a digital cushion, which absorbs locomotor forces, yet is heavy and thus...

Significance We reconstructed the 3D foot movements of guineafowl traversing a granular substrate from biplanar X-rays, and then incorporated those kinematics into a discrete element simulation. Digital track models permitted visualization of in vivo track formation at the surface and at virtual bedding planes for the first time. Application of the...

Ground-dwelling birds are typically characterized as erect bipeds having hind limbs that operate parasagittally. Consequently, most previous research has emphasized flexion/extension angles and moments as calculated from a lateral perspective. Three-dimensional motion analyses have documented non-planar limb movements, but the skeletal kinematics u...

Crocodylians occupy a key phylogenetic position for investigations of archosaur locomotor evolution. Compared to the well-studied hindlimb, relatively little is known about the skeletal movements and mechanics of the forelimb. In this study, we employed manual markerless XROMM (X-ray Reconstruction Of Moving Morphology) to measure detailed 3-D kine...

Theropod dinosaurs show striking morphological and functional tail variation; e.g., a long, robust, basal theropod tail used for counterbalance, or a short, modern avian tail used as an aerodynamic surface. We used a quantitative morphological and functional analysis to reconstruct intervertebral joint stiffness in the tail along the theropod linea...

Past studies have shown that birds use their wings not only for flight, but also when ascending steep inclines. Uphill flap-running or wing-assisted incline running (WAIR) is used by both flight-incapable fledglings and flight-capable adults to retreat to an elevated refuge. Despite the broadly varying direction of travel during WAIR, level, and de...

Average WAIR (blue) verses AF (red) in a sternal reference frame. (WMV)

Furcular spread WAIR. (WMV)

WAIR (blue) verses AF in a global reference frame. (WMV)

Single trial of each behavior comparing WAIR (blue) verses AF in a sternal reference frame. (WMV)

Furcular spread AF. (WMV)

Rotoscoping method. (WMV)

Eight trials (4 of each behavior) comparing WAIR (blue) verses AF in a sternal reference frame. (WMV)

Supporting Information Movie showing a sequence of hypothetical pictorial renderings of proximal, middle and distal caudal vertebrae reconstructed between the nodes, Amniota and Phasianidae (nodes 1 to 21). See Materials and Methods for more information. (MOV)

Supporting Information Tables S1–12 including a list of the taxa studied as well as the complete dataset. Table S1. List of 31 coelurosaurian theropods (including birds) studied (and 7 outgroup taxa) and their associated femoral lengths in millimetres. Table S2. Abbreviations for the institutions visited as part of data collection and whose specime...

Supporting Information Figure showing the correlations between size-normalised tail and centrum length nodal values reconstructed for amniotes. Figure S1. Correlations between size-normalised amniote tail and centrum length nodal values: A, tail length shows a strong linear correlation with proximal centrum length (EBL data: y = 59.164x−3.5387, R2...

Birds, like humans, are obligate bipeds. Although most can fly, many birds are able walkers and runners. Avian terrestrial locomotion has implications for understanding structure and function in organisms, reconstructing how extinct dinosaurs lived, and pathological models. However, until recently, studying avian locomotion has been hampered by our...

Tracks arise through a complex interplay between animal and substrate. Studying this dynamic process is challenging because most foot-sediment and sediment-sediment interactions are rapid and hidden from view. Herein, we describe a new method for visualizing and quantifying three-dimensional movements of both a morphologically accurate indenter and...

Three-dimensional skeletal movement is often impossible to accurately quantify from external markers. X-ray imaging more directly visualizes moving bones, but extracting 3-D kinematic data is notoriously difficult from a single perspective. Stereophotogrammetry is extremely powerful if bi-planar fluoroscopy is available, yet implantation of three r...

X-Ray Reconstruction of Moving Morphology (XROMM) comprises a set of 3D X-ray motion analysis techniques that merge motion data from in vivo X-ray videos with skeletal morphology data from bone scans into precise and accurate animations of 3D bones moving in 3D space. XROMM methods include: (1) manual alignment (registration) of bone models to vide...

The tail is an important structure in the dinosaurian origin of birds because this transition is correlated with a reduction of tail length and caudal number, as well as tail function. To improve our understanding of the form, function, and evolution of maniraptoran tails, we examined factors associated with dorsoventral and mediolateral vertebral...

Plausible poses were identified for the hind limb of Tyrannosaurus rex and three other non-avian thero-pod dinosaurs at mid-stance of locomotion using constraint-based exclusion. This new method, validated by analysis of two species of birds, involves applying demonstrably realistic geometric and kinetic (force-based) constraints from extant animal...