Dr. Carter et al., EPIGENETIC MECHANICAL FACTORS IN THE EVOLUTION OF LONG-BONE EPIPHYSES, Zoological journal of the Linnean Society, 123(2), 1998, pp. 163-178
In developing vertebrate long bones in which endochondral ossification
occurs, it is preceded or accompanied by perichondral ossification. T
he speed and extent of perichondral apposition relative to endochondra
l ossification varies in different taxa. Perichondral ossification dom
inates early long bone development in extinct basal tetrapods and dino
saurs, extant bony fish, amphibians, and birds. In mammals and lizards
, perichondral and endochondral ossification proceed more synchronousl
y. One of the most important epigenetic factors in skeletogenesis is m
echanical loading caused by muscle contractions which begin in utero o
r in ovo. It has been previously shown that the stress distributions c
reated perinatally in the chondroepiphysis during human skeletal devel
opment can influence the appearance of secondary ossification centres.
Using finite element computer models representing bones near birth or
hatching, we demonstrate that in vertebrates in which perichondral os
sification significantly precedes endochondral ossification, the distr
ibution of mechanical stresses in the ossifying cartilage anlagen tend
s to inhibit the appearance of secondary ossification centres in the e
nds of long bones. In models representing vertebrates in which endocho
ndral ossification keeps pace with perichondral apposition, the appear
ance of secondary centres is promoted. The appearance of secondary cen
tres leads to the formation of bony epiphyses and growth plates, which
are most common in mammals and extant lizards. We postulate that geno
typic factors influencing the relative speed and extent of perichondra
l and endochondral ossification interact with mechanical epigenetic fa
ctors early in development to account for many of the morphological di
fferences observed in vertebrate skeletons. (C) 1998 The Linnean Socie
ty of London.