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Proc Biol Sci. 2014 Mar 19;281(1782):20140299. doi: 10.1098/rspb.2014.0299. Print 2014 May 7.

The humerus of Eusthenopteron: a puzzling organization presaging the establishment of tetrapod limb bone marrow.

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  • 1Department of Physiology and Developmental Biology, Uppsala University, , Norbyvägen 18A, Uppsala 752 36, Sweden, European Synchrotron Radiation Facility, , BP220, 6 rue Jules Horowitz, Grenoble Cedex 38043, France.

Abstract

Because of its close relationship to tetrapods, Eusthenopteron is an important taxon for understanding the establishment of the tetrapod body plan. Notably, it is one of the earliest sarcopterygians in which the humerus of the pectoral fin skeleton is preserved. The microanatomical and histological organization of this humerus provides important data for understanding the evolutionary steps that built up the distinctive architecture of tetrapod limb bones. Previous histological studies showed that Eusthenopteron's long-bone organization was established through typical tetrapod ossification modalities. Based on a three-dimensional reconstruction of the inner microstructure of Eusthenopteron's humerus, obtained from propagation phase-contrast X-ray synchrotron microtomography, we are now able to show that, despite ossification mechanisms and growth patterns similar to those of tetrapods, it also retains plesiomorphic characters such as a large medullary cavity, partly resulting from the perichondral ossification around a large cartilaginous bud as in actinopterygians. It also exhibits a distinctive tubular organization of bone-marrow processes. The connection between these processes and epiphyseal structures highlights their close functional relationship, suggesting that either bone marrow played a crucial role in the long-bone elongation processes or that trabecular bone resulting from the erosion of hypertrophied cartilage created a microenvironment for haematopoietic stem cell niches.

KEYWORDS:

early tetrapod limb bone; evolution; growth plate; life history; synchrotron virtual bone histology

PMID:
24648231
PMCID:
PMC3973280
DOI:
10.1098/rspb.2014.0299
[PubMed - indexed for MEDLINE]
Free PMC Article
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