Histomorphogenesis of embryos of Upper Jurassic Theropods from Lourinha (Portugal)

Remains of dinosaurian embryos, hatchlings and early juveniles are currentl y the subject of increasing interest, as new discoveries and techniques now allow to analyse palaeobiological subjects such as growth and life history strategies of dinosaurs. So far, available 'embryonic' material mainly inv olved Ornithopods and some Theropods of Upper Cretaceous age. We describe h ere the histology of several bones (vertebrae, limb bones) from the tiny bu t exceptionally well preserved in ovo remains of Upper Jurassic Theropod di nosaurs from the Paimogo locality near Lourinha (Portugal). This Jurassic m aterial allows to extend in time and to considerably supplement in great de tails our knowledge of early phases of growth in diameter and in length of endoskeletal bones of various shape, as well as shape modelling among carni vorous dinosaurs. Endochondral ossification in both short and long bones in volves extensive pads of calcified cartilages permeated by marrow buds. We discuss the likely occurrence of genuine cartilage canals in dinosaurs and of an avian-like 'medullary cartilaginous cone' in Theropods, :Patterns of periosteal ossification suggest high initial growth rates (20 mum . day(-1) or more), at once modulated by precise and locally specific changes in rat es of new bone deposition. The resulting very precise shape modelling appea rs to start early and to involve at once some biomechanical components. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.