title: Embryos of an early Jurassic prosauropod dinosaur and their evolutionary significance.
abstract: Articulated embryos from the Lower Jurassic Elliot Formation of South Africa are referable to the prosauropod Massospondylus carinatus and, together with other material, provide substantial insights into the ontogenetic development in this early dinosaur. The large forelimbs and head and the horizontally held neck indicate that the hatchlings were obligate quadrupeds. In contrast, adult Massospondylus were at least facultatively bipedal. This suggests that the quadrupedal gait of giant sauropods may have evolved by retardation of postnatal negative allometry of the forelimbs. Embryonic body proportions and an absence of well-developed teeth suggest that hatchlings of this dinosaur may have required parental care.
authors.affiliation: Department of Biology, University of Toronto at Mississauga, Mississauga, ON L5L 1C6, Canada. rreisz@utm.utoronto.ca
authors.forename: Robert R
authors.initials: RR
authors.lastname: Reisz
authors.forename: Diane
authors.initials: D
authors.lastname: Scott
authors.forename: Hans-Dieter
authors.initials: HD
authors.lastname: Sues
authors.forename: David C
authors.initials: DC
authors.lastname: Evans
authors.forename: Michael A
authors.initials: MA
authors.lastname: Raath
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001842:Bone and Bones / Q000196:embryology; D003817:Dentition; D025061:Dinosaurs / Q000033:anatomy & histology / Q000196:embryology*; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology*; D047108:Embryonic Development; D005269:Femur / Q000196:embryology; D005552:Forelimb / Q000033:anatomy & histology / Q000196:embryology; D005580:Fossils; D006614:Hindlimb / Q000033:anatomy & histology / Q000196:embryology; D008124:Locomotion; D009333:Neck / Q000033:anatomy & histology / Q000196:embryology; D010063:Ovum; D010161:Paleodontology; D011187:Posture; D012272:Ribs / Q000196:embryology; D012886:Skull / Q000196:embryology; D013019:South Africa; D013131:Spine / Q000196:embryology