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Stegosaurus plates and spikes histology with growth and age

From: Ben Creisler
A new online advance paper:
Ontogenetic histology of Stegosaurus plates and spikes.
Palaeontology (advance online publication)
DOI: 10.1111/j.1475-4983.2011.01122.x

The dinosaur Stegosaurus is characterized by osteoderms of alternating plates 
and terminal paired spikes. Previous studies have described the histological 
features and possible functions of these osteoderms. However, ontogenetic 
changes are poorly documented. In this study, the ontogenetic changes of the 
osteoderms are examined using eight different ontogenetic skeletons (a 
juvenile, a subadult, a young adult, and five old adults based on the cortical 
histology of their body skeletons). The juvenile plate and subadult spike show 
thin cortex and thick cancellous bone. The young adult plates have an extensive 
vascular network, which is also seen in old adults. Old adult spikes are 
different from old adult plates in having a thick cortex and a large axial 
channel. The cortical histology, in both plates and spikes, show 
well-vascularized bone tissue consisting of dense mineralized fibres in young 
adult forms. In old adult forms, the bone tissues in the
 spikes become more compact and are extensively remodelled. This might 
contribute to the structural reinforcement of the spikes. The plates in old 
adult forms also show extensive remodelling and lines of arrested growth, but 
only limited signs of compaction. The timing for acquisition of features seen 
in old adults is different between plates (an extensive vascular network in the 
young adult) and spikes (a thick cortex with a large axial channel in old 
adults). The result suggests that the timing for plate and spike functions is 
different. The extensive vascular networks seen in large plates suggest their 
function is for display and/or thermoregulation. The thick cortical bone of 
spikes of old adults suggests that spikes acquire a weapon function for defence 
ontogenetically late.