The Society of Vertebrate Paleontology (SVP) Annual Conference 2018
Conference Abstract: Dr Andrew Cuff
Reconstructing the Ontogeny of the Sauropodomorph Mussaurus and Implications for Locomotion
CUFF, Andrew, Royal Veterinary College, Hatfield, United Kingdom; OTERO, Alejandro, Museo de La Plata, La Plata, Argentina; SUMNER-ROONEY, Lauren, Oxford University Museum of Natural History, Oxford, United Kingdom; POL, Diego, Museo Paleontológico Egidio Feruglio, Trelew, Argentina; HUTCHINSON, John R., Royal Veterinary College, Hatfield, United Kingdom
Mussaurus patagonicus is a sauropodomorph from the Early Jurassic of Argentina, originally described from hatchling remains. Further discoveries of juvenile and mature specimens provide a sufficiently complete series to reconstruct general patterns of ontogeny. Here, one each of a hatchling, juvenile (~1 year old), and adult (8+ years old) individual was studied. Digital models of the bones were created for each specimen, from segmented μ-CT scans for the smaller bones and photogrammetry and laser scans for the larger bones. Modeled bones were then articulated to produce complete skeletons, with missing bones being replaced by scaled versions of adults or closely related taxa. Each skeleton was wrapped in convex hulls or more anatomically realistic shapes, which were used to estimate body mass and center of mass, and to conduct sensitivity analyses of these calculations. Both methods show consistent results that Mussaurus rapidly grew from about 60 g at hatching, to ~7 kg at one year old, and reaching ~1430 kg at adulthood. During this time, the body’s center of mass moved from a position in the mid-thorax to a more caudal position nearer the pelvis, consistent with a shift from quadrupedalism to bipedalism that might have occurred early in ontogeny in Mussaurus and other early sauropodomorphs. Our findings offer important new insights into the evolution of locomotion across Sauropodomorpha, consistent with a heterochronic shift to quadrupedalism near Sauropoda.
Conference Abstract: Dr Peter Bishop
Testing associations between centre of mass, body proportions and locomotor habit in Archosauria
P.J. Bishop1, V.R. Allen1, K.T. Bates2, D.M. Henderson3 and J.R. Hutchinson1.1Structure and Motion Laboratory, Comparative Biomedical Sciences, Royal Veterinary College, Hatfield, United Kingdom.2Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, University of Liverpool, Liverpool, United Kingdom.3Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada.
Archosauria contains many species with divergent locomotor habits, ranging from quadrupedal through facultatively and habitually bipedal forms, in both the pseudosuchian and ornithodiran lineages. Locomotor ability is influenced by numerous factors, including body mass, limb size and proportions, and the location of the whole-body centre of mass (COM). In particular, COM position has frequently been estimated and used to evaluate locomotor habits in extinct terrestrial archosaurs. Here, we synthesize previously published digital volumetric estimates of mass and COM with estimates of gross body proportions (glenoacetabular distance, femur length and hindlimb vs forelimb length ratio) in 65 species of extant and extinct archosaurs. In addition, new modelling results are derived for two previously unstudied taxa, the ornithopod Muttaburrasaurus and the pseudosuchian Batrachotomus, to test their hypothesized locomotor habit. Phylogenetically-informed principal component (PC) analysis is used to test associations between anatomical parameters and the consensus locomotor habit for each taxon (‘bipedal’, ‘quadrupedal’, ‘facultative bipedal’ or ‘unknown’). We find a very strong distinction between bipedal and quadrupedal taxa in PC space, as indicated by both one-way, non-parametric, multivariate analysis of variance (F2,62 = 8.8955, P < 0.001) and minimal overlap of their respective morphospaces (<4% by volume). These findings are robust to alterations in assumed phylogenetic relationships between taxa. Facultatively bipedal taxa neatly bridge between the bipedal and quadrupedal groups, and both Muttaburrasaurus and Batrachotomus are found to likely be quadrupeds. No PC is strongly loaded by COM in isolation of the other parameters; in particular, the first PC is also markedly loaded by femur length and limb length ratio. These results highlight the utility that a holistic, multivariate approach can bring to quantitative assessments of locomotor habit in extinct archosaurs. Interestingly, despite being largely distinct from quadrupeds in PC space, bipeds still show high variance in the first two PCs, which account for >65% of total data variance. This suggests that bipedal archosaurs may have had fewer constraints on body dimensions compared to quadrupedal archosaurs, which may underlie their proliferation and radiation throughout the Mesozoic era.
The Society for Integrative and Comparative Biology (SICB), Annual Conference 2018
Conference Abstract: Dr Andrew Cuff
139-8 Sunday, Jan. 7 15:15 – 15:30 Ontogenetic changes in the body plan of the sauropodomorph Mussaurus and their implications for locomotion CUFF, AR*; OTERO, A; ALLEN, VA; MICHEL, KB; SUMNER-ROONEY, L; POL, D; HUTCHINSON, JR; Royal Veterinary College, UK; Museo de La Plata, Argentina; Royal Veterinary College, UK; Royal Veterinary College, UK; Oxford University Museum of Natural History, UK; Museo Paleontológico Egidio Feruglio, Argentina; Royal Veterinary College, UK acuff@rvc.ac.uk
Mussaurus patagonicus is a sauropodomorph from the Early Jurassic of Argentina, originally described from hatchling remains. Further discoveries of juvenile and mature specimens provide a sufficiently complete series to reconstruct general patterns of ontogeny. Here, one each of hatchling, juvenile (~1 year old), and adult (8+ years old) individuals was studied. Digital models of the bones were created for each specimen, from segmented μ-CT scans for the smaller bones and photogrammetry and laser scans for the larger bones. Modelled bones were then articulated to produce complete skeletons, with missing bones being replaced by scaled versions of adults or closely related taxa. Each skeleton was wrapped in convex hulls and more anatomically realistic shapes, which were used to estimate body mass and centre of mass, and to conduct sensitivity analyses of these calculations. Our results show that Mussaurus rapidly grew from about 50g at hatching, to ~7kg at one year old, and reaching ~1540kg at adulthood. During this time the body’s centre of mass moved from a position in the mid-thorax to a more caudal position nearer the pelvis, consistent with a shift from quadrupedalism to bipedalism that might have occurred early in ontogeny in Mussaurus and other early sauropodomorphs. Our findings offer important new insights into the evolution of locomotion across Sauropodomorpha; consistent with a heterochronic shift to quadrupedalism near Sauropoda.
Conference Abstract: Dr Krijn Michel
76-8 Saturday, Jan. 6 09:45 – 10:00 Locomotion in Nile crocodiles: Kinematic effects of speed and posture MICHEL, KB*; CUFF, AR; ALLEN, VA; HUTCHINSON, JR; Royal Veterinary College kmichel@rvc.ac.uk
The study of locomotion in extant crocodylians is important because they are unusual reptiles with a mix of ancestral and derived traits, and because these traits provide insight into the evolution of locomotion in the broader archosaur lineage. Extant crocodylians show a unique ability amongst extant archosaurs by using a spectrum from more sprawling to more erect postures as well as a wide range of symmetrical and asymmetrical gaits. Ten young Nile crocodiles (Crocodylus niloticus) ranging from 1.5-7kg were filmed using a combination of light video and fluoroscopy (XROMM) to analyse their locomotion at a range of speeds and gaits, in both straight lines and around bends. These data were supplemented with kinetic measurements from force platforms. We found that the Nile crocodiles showed a range of postures at slow speeds, using a combination of sprawling ‘low walks’ and belly slides, as well as upright ‘high walks’; as in alligators. However, no matter the posture, the duty factor decreased significantly across the range of speeds from 0.1 to 0.7m/s (P < 0.01), with no significant difference between fore- and hindlimb duty factors. Our study provides an extensive new dataset on Nile crocodile locomotor dynamics, amplifying our understanding of archosaur locomotion.
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