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Bactrosaurus growth study

From: Ben Creisler

New in online Palaeontology:

Cranial and appendicular ontogeny of Bactrosaurus johnsoni, a hadrosauroid
dinosaur from the Late Cretaceous of northern China.
Palaeontology (online advance publication)
Article first published online: 9 MAY 2011
DOI: 10.1111/j.1475-4983.2011.01053.x

The juvenile anatomy of various cranial and appendicular elements of the
hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth
changes are documented from juvenile to adult stages for each skeletal
element available. In the studied skull, ontogenetic trends consist of:
development of features on the ventral surface of the frontal; reduction in
the slope of the posteromedial process of the premaxilla; a posterior shift
of the dorsal process of the maxilla; development of concavities on the
medial surface of the prefrontal; increased robustness and development of
the ventral flange of the jugal; decreased curvature of the long axis of
the quadrate; increased ventral deflection of the dentary; and changes in
the length/width proportions and depth of the anterior surface of the
predentary. In the appendicular skeleton, the majority of ontogenetic
variation from juvenile to adult occurs in the limb bones, including
increased robustness of the deltopectoral crest of the humerus; relative
shortening of the ulna; increased development of the fourth trochanter and
mediolateral widening of the distal end of the femur; increased expansion
of the cnemial crest of the tibia; and the increased prominence of
articular protuberances and flanges of the metatarsals. A survey of the
phylogenetically informative characters present in B. johnsoni indicates
that several characters concerning the frontal, maxilla, jugal, quadrate,
predentary, dentary, scapula, humerus and ilium are affected by ontogeny.
Nevertheless, the majority of phylogenetic characters are not
ontogenetically variable, suggesting that a substantial amount of the
information provided by juvenile and subadult specimens for phylogenetic
inference is reliable in basal hadrosauroids.

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