Paleontologia De Vertebrados

Osteohistology of Indian fossil vertebrates

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Growth patterns of fossil vertebrates as deduced from bone microstructure: case studies from India
S RAY1,*, D MUKHERJEE1 and S BANDYOPADHYAY2
1

Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, India 2 Geological Studies Unit, Indian Statistical Institute, 203 B T Road, Kolkata 700 108, India*Corresponding author (Email, sray@gg.iitkgp.ernet.in)

Bone microstructure is affected by ontogeny, phylogeny, biomechanics and environments. These aspects of life history of an extinct animal, especially its growth patterns, may be assessed as fossil bone generally maintains its histological integrity. Recent studies on the bone histology of fossil vertebrates from India encompass different types oftemnospondyls and dicynodonts from different Permian and Triassic horizons. The examined taxa show that they had distinct bone histology and varied growth patterns. The Early Triassic trematosaurids had an overall fast growth, which contrasts with that of the Middle and Late Triassic temnospondyl taxa examined. The dicynodonts on the other hand, were characterized by an overall fast growth withperiodic interruptions, variable growth rates dependent on ontogeny and indeterminate growth strategy. A comparative study encompassing several neotherapsid genera including the dicynodonts shows significant evolutionary trends towards determinate growth strategy and reduced developmental plasticity.
[Ray S, Mukherjee D and S Bandyopadhyay S 2009 Growth patterns of fossil vertebrates as deducedfrom bone microstructure: case studies from India; J. Biosci. 34 661–672] DOI 10.1007/s12038-009-0055-x

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Introduction

Bone is a mineralized connective tissue, produced by the deposition of hydroxyapatite [Ca10(PO4)6(OH)2] microcrystals on a framework of collagen fibres (Chinsamy and Dodson 1995). Within this structure the bone cells (osteocytes), blood and lymph vessels, and numerous smallcanals are present. These components are almost constant in all vertebrates, starting from the earliest fishes to the present day reptiles, birds and mammals. When an animal dies the organic components including the cells and blood vessels decompose, whereas the inorganic component becomes fossilized and retains the overall bone microstructure. Bone microstructure provides substantial informationabout the palaeobiology of the fossil animal. Bone tissue reflects ontogeny (juvenile to adult stages), age, life style adaptations and biomechanical function as well as various other events that punctuate the life history of an individual

(Chinsamy 1997). In general, the rate of growth changes during ontogeny and the principal difference between organisms lies in whether growth eventuallyceases. Mammals and birds have a determinate growth where a mature stage is reached in which structural growth stops though the organism continues to live (Chinsamy and Dodson 1995; Foote and Miller 2007). However, in many forms the growth is indeterminate where the organism continues to grow throughout life. There are numerous works dealing with the bone histology and growth patterns of fossilvertebrates, especially the archosaurs such as the avian and non-avian dinosaurs (Chinsamy 1990, 1995; Chinsamy et al. 1998; Curry 1999; Horner et al. 1999, 2000, 2001; Erickson and Tumanova 2000; Sander 2000; Chinsamy-Turan 2005). For example, Chinsamy and Elzanowski (2001) deduced the evolutionary path of the growth patterns in avian dinosaurs and suggested that these have evolved through a stage ofslowed postnatal growth and precocious flight. Another

Keywords.

Bone microstructure; dicynodonts; India; osteohistology; temnospondyls J. Biosci. 34(5), November 2009, 661–672, © Indian Academy ofNovember 2009 J. Biosci. 34(5), Sciences 661

http://www.ias.ac.in/jbiosci

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S Ray, D Mukherjee and S Bandyopadhyay some of the recent works on the osteohistology of the Indian vertebrates...