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Long bone histology and growth patterns in ankylosaurs: implications for life history and evolution.

Stein M, Hayashi S, Sander PM - PLoS ONE (2013)

Bottom Line: In contrast to other taxa, ankylosaurs substitute large amounts of their primary tissue early in ontogeny.Metabolically driven remodeling processes must have liberated calcium to ossify the protective osteodermal structures in juveniles to subadult stages, which led to further remodeling due to increased mechanical loading.Abundant structural fibers observed in the primary bone and even in remodeled bone may have improved the mechanical properties of the Haversian bone.

View Article: PubMed Central - PubMed

Affiliation: Steinmann Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Bonn, Germany.

ABSTRACT
The ankylosaurs are one of the major dinosaur groups and are characterized by unique body armor. Previous studies on other dinosaur taxa have revealed growth patterns, life history and evolutionary mechanisms based on their long bone histology. However, to date nothing is known about long bone histology in the Ankylosauria. This study is the first description of ankylosaurian long bone histology based on several limb elements, which were sampled from different individuals from the Ankylosauridae and Nodosauridae. The histology is compared to that of other dinosaur groups, including other Thyreophora and Sauropodomorpha. Ankylosaur long bone histology is characterized by a fibrolamellar bone architecture. The bone matrix type in ankylosaurs is closest to that of Stegosaurus. A distinctive mixture of woven and parallel-fibered bone together with overall poor vascularization indicates slow growth rates compared to other dinosaurian taxa. Another peculiar characteristic of ankylosaur bone histology is the extensive remodeling in derived North American taxa. In contrast to other taxa, ankylosaurs substitute large amounts of their primary tissue early in ontogeny. This anomaly may be linked to the late ossification of the ankylosaurian body armor. Metabolically driven remodeling processes must have liberated calcium to ossify the protective osteodermal structures in juveniles to subadult stages, which led to further remodeling due to increased mechanical loading. Abundant structural fibers observed in the primary bone and even in remodeled bone may have improved the mechanical properties of the Haversian bone.

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Long bone histology of the nodosaurid Edmontonia rugosidens.A, Inner cortex of the humerus of TMP 1998.98.1 showing secondary osteons which are strongly imprinted by unmineralized structural fibers which fray out towards the osteon margins (see a white arrow). B, Same view in cross-polarized light. C, Outer cortex of the radius of TMP 1998.98.1 showing strong remodeling and active resorption cavities. D, Same view in cross-polarized light. E, Outer cortex of the ulna of TMP 1998.98.1 with small amounts of parallel-fibered primary bone; F, Same view in cross-polarized light. G, Outer cortex of the fibula of TMP 1998.98.1 with large resorption cavities and parallel-fibered primary bone tissue. H, Same view in cross-polarized light.
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pone-0068590-g005: Long bone histology of the nodosaurid Edmontonia rugosidens.A, Inner cortex of the humerus of TMP 1998.98.1 showing secondary osteons which are strongly imprinted by unmineralized structural fibers which fray out towards the osteon margins (see a white arrow). B, Same view in cross-polarized light. C, Outer cortex of the radius of TMP 1998.98.1 showing strong remodeling and active resorption cavities. D, Same view in cross-polarized light. E, Outer cortex of the ulna of TMP 1998.98.1 with small amounts of parallel-fibered primary bone; F, Same view in cross-polarized light. G, Outer cortex of the fibula of TMP 1998.98.1 with large resorption cavities and parallel-fibered primary bone tissue. H, Same view in cross-polarized light.

Mentions: In the humerus, the core sampled the posterior and anterior cortex as well as the medullary region. The medullary region of the humerus is characterized by a dense network of thick trabeculae. The lamellar tissue of the trabeculae, as well as the Haversian bone of the inner cortex, is overprinted by structural fibers resulting in frayed margins of secondary osteons, which are a common feature throughout the whole cortex. Osteocyte lacunae are flattened and elongated in regions with a high accumulation of fibers, but generally they are larger and round within the secondary osteons. There is an accumulation of unmineralized structural fibers in the inner cortex (Figure 5A–B), appearing as a darker zone under plane-polarized light. Towards the outer cortex the amount of primary bone tissue gradually increases, revealing poorly vascularized tissue intermediate between parallel-fibered and fibrolamellar bone.


Long bone histology and growth patterns in ankylosaurs: implications for life history and evolution.

Stein M, Hayashi S, Sander PM - PLoS ONE (2013)

Long bone histology of the nodosaurid Edmontonia rugosidens.A, Inner cortex of the humerus of TMP 1998.98.1 showing secondary osteons which are strongly imprinted by unmineralized structural fibers which fray out towards the osteon margins (see a white arrow). B, Same view in cross-polarized light. C, Outer cortex of the radius of TMP 1998.98.1 showing strong remodeling and active resorption cavities. D, Same view in cross-polarized light. E, Outer cortex of the ulna of TMP 1998.98.1 with small amounts of parallel-fibered primary bone; F, Same view in cross-polarized light. G, Outer cortex of the fibula of TMP 1998.98.1 with large resorption cavities and parallel-fibered primary bone tissue. H, Same view in cross-polarized light.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3722194&req=5

pone-0068590-g005: Long bone histology of the nodosaurid Edmontonia rugosidens.A, Inner cortex of the humerus of TMP 1998.98.1 showing secondary osteons which are strongly imprinted by unmineralized structural fibers which fray out towards the osteon margins (see a white arrow). B, Same view in cross-polarized light. C, Outer cortex of the radius of TMP 1998.98.1 showing strong remodeling and active resorption cavities. D, Same view in cross-polarized light. E, Outer cortex of the ulna of TMP 1998.98.1 with small amounts of parallel-fibered primary bone; F, Same view in cross-polarized light. G, Outer cortex of the fibula of TMP 1998.98.1 with large resorption cavities and parallel-fibered primary bone tissue. H, Same view in cross-polarized light.
Mentions: In the humerus, the core sampled the posterior and anterior cortex as well as the medullary region. The medullary region of the humerus is characterized by a dense network of thick trabeculae. The lamellar tissue of the trabeculae, as well as the Haversian bone of the inner cortex, is overprinted by structural fibers resulting in frayed margins of secondary osteons, which are a common feature throughout the whole cortex. Osteocyte lacunae are flattened and elongated in regions with a high accumulation of fibers, but generally they are larger and round within the secondary osteons. There is an accumulation of unmineralized structural fibers in the inner cortex (Figure 5A–B), appearing as a darker zone under plane-polarized light. Towards the outer cortex the amount of primary bone tissue gradually increases, revealing poorly vascularized tissue intermediate between parallel-fibered and fibrolamellar bone.

Bottom Line: In contrast to other taxa, ankylosaurs substitute large amounts of their primary tissue early in ontogeny.Metabolically driven remodeling processes must have liberated calcium to ossify the protective osteodermal structures in juveniles to subadult stages, which led to further remodeling due to increased mechanical loading.Abundant structural fibers observed in the primary bone and even in remodeled bone may have improved the mechanical properties of the Haversian bone.

View Article: PubMed Central - PubMed

Affiliation: Steinmann Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Bonn, Germany.

ABSTRACT
The ankylosaurs are one of the major dinosaur groups and are characterized by unique body armor. Previous studies on other dinosaur taxa have revealed growth patterns, life history and evolutionary mechanisms based on their long bone histology. However, to date nothing is known about long bone histology in the Ankylosauria. This study is the first description of ankylosaurian long bone histology based on several limb elements, which were sampled from different individuals from the Ankylosauridae and Nodosauridae. The histology is compared to that of other dinosaur groups, including other Thyreophora and Sauropodomorpha. Ankylosaur long bone histology is characterized by a fibrolamellar bone architecture. The bone matrix type in ankylosaurs is closest to that of Stegosaurus. A distinctive mixture of woven and parallel-fibered bone together with overall poor vascularization indicates slow growth rates compared to other dinosaurian taxa. Another peculiar characteristic of ankylosaur bone histology is the extensive remodeling in derived North American taxa. In contrast to other taxa, ankylosaurs substitute large amounts of their primary tissue early in ontogeny. This anomaly may be linked to the late ossification of the ankylosaurian body armor. Metabolically driven remodeling processes must have liberated calcium to ossify the protective osteodermal structures in juveniles to subadult stages, which led to further remodeling due to increased mechanical loading. Abundant structural fibers observed in the primary bone and even in remodeled bone may have improved the mechanical properties of the Haversian bone.

Show MeSH
Related in: MedlinePlus