![]() Skeletons of this species were collected from the middle and lower part of the Kayenta Formation in the Navajo Nation in northern Arizona. Despite its charismatic presence in pop culture and dinosaurian phylogenetic analyses, major aspects of the skeletal anatomy, taxonomy, ontogeny, and evolutionary relationships of this dinosaur remain unknown. ![]() All rights reserved.ĭilophosaurus wetherilli was the largest animal known to have lived on land in North America during the Early Jurassic. ![]() Documentation of the presence and distribution of ICBs is a first step towards improving our understanding of the impact of these structures on the viscoelastic properties, and ultimately their effect on the risk of age‐related tendinopathy in energy‐storing tendons. Ageing and repetitive strain frequently cause tendon micro‐damage prior to the development of clinical tendinopathy. Histological characterisation identified distinctive cells associated with increased glycosaminoglycan and type II collagen extracellular matrix content. There were significantly more ICBs in the tendon periphery when compared to the tendon core region (P = 0.010). There was a significant difference (P = 0.008) in the ICB count between young and old horses with ICBs present in varying number (13 ‐ 467 median = 47, mean = 132.6), size and distribution in the SDFT of aged horses only. The number, size and position of ICBs was determined and compared between age groups. Morphological evaluation of the ICBs included histology, immunohistochemistry and transmission electron microscopy. Ultra‐high field magnetic resonance imaging (9.4 T) series of SDFT samples of young (1‐9 years) and aged (17‐25 years) horses were obtained, and 3D reconstruction of ICBs was performed. The purpose of this study was the detailed characterisation of intra‐fascicular chondroid‐like bodies (ICBs) in the equine SDFT, and the assessment of the effect of ageing on the presence and distribution of these structures. Circular chondroid depositions scattered amongst the fascicles of the equine SDFT are rarely reported. The superficial digital flexor tendon (SDFT) is considered functionally equivalent to the human Achilles tendon. ![]() ![]() Yet, we also discover unexpected ancestral specializations in larger Jurassic theropods, lost later in the bird-line, complicating the paradigm of gradual transformation. Our results reveal how, from the Triassic Period, bipedal theropod dinosaurs gradually modified their hindlimb form and function, shifting more from hip-based to knee-based locomotion and hip-abductor to hip-rotator balancing mechanisms inherited by birds. Our results support two hypotheses: From early theropod dinosaurs to birds, knee flexors’ moment arms decreased relative to knee extensors’, and medial long-axis rotator moment arms for the hip increased (trading off with decreased hip abductor moment arms). Using 13 three-dimensional musculoskeletal models of the hindlimbs of bird-line archosaurs, we quantify how the moment arms (i.e., leverages) of 35 locomotor muscles evolved. However, the roles of individual muscles in these changes and their evolutionary timings remain obscure. Bipedal locomotion evolved along the archosaurian lineage to birds, shifting from “hip-based” to “knee-based” mechanisms. ![]()
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