Abstract
Abstract. Histology and microanatomy of vertebrae, ribs, haemal
arch, and humeri and femora of 10 individuals of Stereosternum and two dorsal ribs of
1 individual of Brazilosaurus were studied. All individuals had achieved a body length
of 50 cm (equal to 65 % of the maximum known body length) or larger. All sampled
bones are highly osteosclerotic due to the reduction of medullary cavities
and the filling of medullary regions by endosteal bone. Calcified cartilage
occurs – if at all – only locally in small clusters in the medullary
regions of midshaft and in higher amounts only in non-midshaft sections of
long bones and towards the medio-distal rib shaft, respectively. The primary
bone tissue consists of highly organized parallel-fibred tissue and/or
lamellar tissue, which is in most samples relatively lightly vascularized or
even avascular. If present, vascular canals are mainly longitudinally
oriented; some show a radial orientation. Simple vascular canals as well as
primary osteons occur. Some of the latter are secondarily altered, i.e. widened. Remodelling of the periosteal cortex is only documented by few
scattered erosion cavities and secondary osteons. The tissue is regularly
stratified by lines of arrested growth (LAGs), which usually appear as double or multiple rest lines,
indicating strong dependence on exogenous and endogenous factors. Because of
the inhibition of periosteal remodelling the growth record is complete and
no inner cycles are lost. Individuals of Stereosternum show a poor correlation of body
size and number of growth marks, which might be the result of developmental
plasticity. Brazilosaurus shows a highly organized, avascular lamellar tissue and a high
number of regularly deposited rest lines throughout the cortex of the ribs.
The medullary region in the ribs of Brazilosaurus is distinctly larger when compared to ribs
of Stereosternum. However, strong osteosclerosis is obvious in both taxa, pointing to a
high degree of aquatic adaption. Ribs of Stereosternum, Brazilosaurus, and Mesosaurus are clearly distinguishable
from each other by the distribution of the periosteal and endosteal
territory. Furthermore, Brazilosaurus differs in its growth pattern (i.e. spacing of rest
lines) when compared to Stereosternum and Mesosaurus.
Cited by
6 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献