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Soft tissue anatomy of the archosaur hip joint

Ben Creisler

A new paper that may be of interest:

Henry P. Tsai and Casey M. Holliday (2014)
Articular soft tissue anatomy of the archosaur hip joint: Structural
homology and functional implications.
Journal of Morphology (advance online publication)
DOI: 10.1002/jmor.20360

Archosaurs evolved a wide diversity of locomotor postures, body sizes,
and hip joint morphologies. The two extant archosaurs clades (birds
and crocodylians) possess highly divergent hip joint morphologies, and
the homologies and functions of their articular soft tissues, such as
ligaments, cartilage, and tendons, are poorly understood.
Reconstructing joint anatomy and function of extinct vertebrates is
critical to understanding their posture, locomotor behavior, ecology,
and evolution. However, the lack of soft tissues in fossil taxa makes
accurate inferences of joint function difficult. Here, we describe the
soft tissue anatomies and their osteological correlates in the hip
joint of archosaurs and their sauropsid outgroups, and infer
structural homology across the extant taxa. A comparative sample of 35
species of birds, crocodylians, lepidosaurs, and turtles ranging from
hatchling to skeletally mature adult were studied using dissection,
imaging, and histology. Birds and crocodylians possess topologically
and histologically consistent articular soft tissues in their hip
joints. Epiphyseal cartilages, fibrocartilages, and ligaments leave
consistent osteological correlates. The archosaur acetabulum possesses
distinct labrum and antitrochanter structures on the supraacetabulum.
The ligamentum capitis femoris consists of distinct pubic- and ischial
attachments, and is homologous with the ventral capsular ligament of
lepidosaurs. The proximal femur has a hyaline cartilage core attached
to the metaphysis via a fibrocartilaginous sleeve. This study provides
new insight into soft tissue structures and their osteological
correlates (e.g., the antitrochanter, the fovea capitis, and the
metaphyseal collar) in the archosaur hip joint. The topological
arrangement of fibro- and hyaline cartilage may provide mechanical
support for the chondroepiphysis. The osteological correlates
identified here will inform systematic and functional analyses of
archosaur hindlimb evolution and provide the anatomical foundation for
biomechanical investigations of joint tissues.

Also, a number of articles about the limbs of ratites that appeared in
preprint form in PeerJ are now out in final form:

Lamas LP, Main RP, Hutchinson JR. (2014)
Ontogenetic scaling patterns and functional anatomy of the pelvic limb
musculature in emus (Dromaius novaehollandiae).
PeerJ 2:e716
doi:  http://dx.doi.org/10.7717/peerj.716

Regnault S, Pitsillides AA, Hutchinson JR. (2014)
Structure, ontogeny and evolution of the patellar tendon in emus
(Dromaius novaehollandiae) and other palaeognath birds.
doi: http://dx.doi.org/10.7717/peerj.711


Chadwick KP, Regnault S, Allen V, Hutchinson JR. (2014)
Three-dimensional anatomy of the ostrich (Struthio camelus) knee joint.
PeerJ 2:e706
doi:  http://dx.doi.org/10.7717/peerj.706