Dinosaur Growth: Egg to Adult


The integrity of the microstructure of fossilised bones generally survives millions of years of fossilisation. Analysis of the preserved bone microstructure of dinosaurs permits a direct assessment of the nature and type of bone that was present in the once living animal. By comparison with the bone microstructure of living vertebrates, deductions pertaining to various aspects of the life history and biology of the dinosaur can be made. Studies of the bone microstructure of dinosaurs suggest that the growth strategies of dinosaurs varied: some dinosaurs grew rapidly and uninterruptedly, whereas others experienced periodic pauses in growth. If growth rings are present in the fossil bones of different sized individuals of a particular taxon, skeletochronology can be applied to deduce the growth trajectory for the dinosaur. Such growth curves suggest that dinosaurs had a unique growth strategy that was faster than that of extant reptiles, but not as fast as similar sized birds and mammals.

Key Concepts:

  • Fossilisation generally preserves the integrity of the dinosaur bone microstructure.

  • Bone microstructure of dinosaurs can be directly compared to extant vertebrates.

  • Different types of bone microstructure suggest different rates of bone deposition.

  • Dinosaurs have an abundance of fibro‐lamellar bone.

  • Many dinosaurs have an interrupted (zonal) type of bone tissue.

  • Changes in bone microstructure through ontogeny can be assessed.

  • Growth lines are assumed to be annually formed.

  • Skeletochronology can be applied to many dinosaur taxa to assess age.

  • Growth curves can be deduced for dinosaurs.

  • Growth curves suggest dinosaurs grew faster than similar sized reptiles, but not as fast as similar sized birds and mammals.

Keywords: dinosaurs; growth; palaeobiology; bone; histology

Figure 1.

Fossilised skin casts of an Auca Mahuevo titanosaur embryo. Image courtesy of Luis Chiappe.

Figure 2.

Cross‐section of a juvenile hypsilophodontid femur. Fibrolamellar bone is in the process of being deposited. Some primary osteons are completely formed while osteonal bone around some blood vessels is still forming. Note the uneven peripheral and medullary margins (arrows). Bar, 63 μm. Abbreviation: M, medullary cavity.

Figure 3.

Longitudinal section of the distal articular surface of a juvenile hypsilophodontid femur. Note the large amount of calcified cartilage (foam‐like structures indicated by the arrow). Bar, 57 μm.

Figure 4.

Resorption cavities result when primary bone is sometimes resorbed. Later new bone is deposited to form secondary osteons. Arrows indicate secondary osteons.

Figure 5.

Cross‐section of a metatarsal of Archaeornithomimus. Note the lines of arrested growth (LAGs) and annuli (indicated by arrows), which alternate with zones consisting of fibrolamellar bone tissue. Bar, 150 μm.

Figure 6.

Cross‐section of an adult Dryosaurus femur. Bone formed later in ontogeny (nearer the periphery) is formed at a slower rate, whereas the younger bone (indicated by the doubled headed arrow) consists of fibrolamellar bone, which was formed at a faster rate. Bar, 83 μm.



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Further Reading

Chinsamy A (2008) Were Dinosaurs Warm. In: Benton MK (ed.) Seventy Greatest Mysteries of the Natural World. Thompson, UK. ISBN 978‐0‐500‐25143‐0.

Chinsamy‐Turan A (in press) The Forerunners of Mammals – Radiation. Histology. Biology. Indiana University Press.

Reid REH (1997) How dinosaurs grew. In: Farlow JO and Brett‐Surman MK (eds) The Complete Dinosaur. Bloomington: Indiana University Press.

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Chinsamy‐Turan, Anusuya(Apr 2011) Dinosaur Growth: Egg to Adult. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003319.pub2]