Fossil Bone Histology

Sexual maturity in growing dinosaurs does not fit reptilian growth models

by Sarah Werning

Recent histological studies suggest relatively rapid growth in dinosaurs. However, the timing of reproductive maturity... more Recent histological studies suggest relatively rapid growth in dinosaurs. However, the timing of reproductive maturity (RM) in dinosaurs is poorly known because unambiguous indicators of RM are rare. One exception is medullary bone (MB), which is an ephemeral bony tissue that forms before ovulation in the marrow cavities of birds as a calcium source for eggshelling. Recently, MB also was described in a single specimen of the saurischian dinosaur Tyrannosaurus rex. Here, we report two other occurrences of MB: in another saurischian dinosaur, Allosaurus, and in the ornithischian dinosaur Tenontosaurus. We show by counting lines of arrested growth and performing growth curve reconstructions that Tenontosaurus, Allosaurus, and Tyrannosaurus were reproductively mature by 8, 10, and 18 years, respectively. RM in these dinosaurs coincided with a transition from growth acceleration to deceleration. It also far precedes predictions based on the growth rates of living reptiles scaled to similar size. Despite relatively rapid growth, dinosaurs were similar to reptiles in that RM developed before reaching asymptotic size. However, this reproductive strategy also occurs in medium- to large-sized mammals and correlates with a strategy of prolonged multiyear growth. RM in actively growing individuals suggests that these dinosaurs were born relatively precocial and experienced high adult mortality. The origin of the modern avian reproductive strategy in ornithuran birds likely coincided with their extreme elevations in growth rate and truncations to growth duration.

The Ontogenetic Osteohistology of Tenontosaurus tilletti

by Sarah Werning

Tenontosaurus tilletti is an ornithopod dinosaur known from the Early Cretaceous (Aptian-Albian) Cloverly and Antlers... more Tenontosaurus tilletti is an ornithopod dinosaur known from the Early Cretaceous (Aptian-Albian) Cloverly and Antlers formations of the Western United States. It is represented by a large number of specimens spanning a number of ontogenetic stages, and these specimens have been collected across a wide geographic range (from central Montana to southern Oklahoma). Here I describe the long bone histology of T. tilletti and discuss histological variation at the individual, ontogenetic and geographic levels. The ontogenetic pattern of bone histology in T. tilletti is similar to that of other dinosaurs, reflecting extremely rapid growth early in life, and sustained rapid growth through sub-adult ontogeny. But unlike other iguanodontians, this dinosaur shows an extended multi-year period of slow growth as skeletal maturity approached. Evidence of termination of growth (e.g., an external fundamental system) is observed in only the largest individuals, although other histological signals in only slightly smaller specimens suggest a substantial slowing of growth later in life. Histological differences in the amount of remodeling and the number of lines of arrested growth varied among elements within individuals, but bone histology was conservative across sampled individuals of the species, despite known paleoenvironmental differences between the Antlers and Cloverly formations. The bone histology of T. tilletti indicates a much slower growth trajectory than observed for other iguanodontians (e.g., hadrosaurids), suggesting that those taxa reached much larger sizes than Tenontosaurus in a shorter time.

Osteoderm morphology in recent and fossil euphractine xenarthrans

by Martin Ciancio

C. M. Krmpotic, M. R. Ciancio, C. Barbeito, R. C. Mario and A. A. Carlini

Acta Zoologica

Volume 90, Issue 4, pages 339–351, October 2009

The presence of osteoderms within the integument, forming a carapace, is one of the most distinctive features of... more The presence of osteoderms within the integument, forming a carapace, is one of the most distinctive features of armadillos with the external morphology of these elements forming the basis of most systematic schemes. This is especially true for fossil taxa, where these elements are most frequent in the palaeontological record. A detailed study of osteoderms from the cephalic shield and different regions of the dorsal armour of Chaetophractus villosus (Euphractinae, Xenarthra) was made and compared to those of the extant genus Dasypus (Dasypodinae, Xenarthra), and the extinct genus †Eutatus. Three distinct histological zones were recognized: outer and inner zones are thin, formed by regular compact bone, the middle zone is thicker, with large cavities that contain mainly adipose tissue, hair follicles, and sweat and sebaceous glands. The internal structure of †Eutatus (also a member of Euphractinae) osteoderms is close to that of C. villosus, consistent with the notion that these taxa are phylogenetically closely related. In contrast, Dasypus shows marked differences. Dasypus shows hair follicles associated with both gland types (sweat and sebaceous) and connected to foramina on the external surface. Although not observed in adult C. villosus, it has been documented during embryonic development, only to atrophy later in ontogeny. Furthermore, the presence of red bone marrow is rare in C. villosus, but widespread in Dasypus novemcinctus osteoderms. These results suggest an early split of both subfamilies and support the hypothesis that the Euphractinae are more derived than the Dasypodinae.

First histological and skeletochronological data on temnospondyl growth: palaeoecological and palaeoclimatological implications

by Michel Laurin

Perspectives on vertebrate evolution: Topics and problems

by Michel Laurin

Salamander-like development in a seymouriamorph revealed by palaeohistology

by J.Sébastien Steyer

Palaeoecological and palaeoenvironmental influences revealed by long-bone palaeohistology: the example of the Permian branchiosaurid Apateon

by J.Sébastien Steyer

Developmental plasticity of limb bone microstructural organization in Apateon: histological evidence of paedomorphic conditions in branchiosaurs

by J.Sébastien Steyer

First histological and skeletochronological data on temnospondyl growth: palaeoecological and palaeoclimatological implications

by J.Sébastien Steyer

Sauropod Bone Histology and Its Implications for Sauropod Biology

by Oliver Wings

Tooth histology of the parareptile Soturnia caliodon from the Upper Triassic of Rio Grande do Sul, Brazil

by Juan Carlos Cisneros

Osteoderm microstructure indicates the presence of a crocodylian-like trunk bracing system in a group of armoured basal tetrapods

by Michael Buchwitz

by Michael Buchwitz, Florian Witzmann, Sebastian Voigt & Valeriy Golubev (in press). Acta Zoologica.

The microstructure of dorsal osteoderms referred to the chroniosuchid taxa Chroniosuchus, Chroniosaurus,... more The microstructure of dorsal osteoderms referred to the chroniosuchid taxa Chroniosuchus, Chroniosaurus, Madygenerpeton and cf. Uralerpeton is compared to existing data on the bystrowianid chroniosuchian Bystrowiella and further tetrapods. Chroniosuchid osteoderms are marked by thin internal and relatively thick external cortices that consist of lowly vascularised parallel-fibred bone. They are structured by growth marks and, in case of Madygenerpeton, by lines of arrested growth. The cancellous middle region is marked by a high degree of remodelling and a primary bone matrix of parallel-fibred bone that may include domains of interwoven structural fibres. Whereas the convergence of Bystrowiella and chroniosuchid osteoderms is not confirmed by our observations, the internal cortex of the latter displays a significant peculiarity: It contains distinct bundles of shallowly dipping Sharpey’s fibres with a cranio- or caudoventral orientation. We interpret this feature as indicative for the attachment of epaxial muscles which spanned several vertebral segments between the medioventral surface of the osteoderms and the transversal processes of the thoracic vertebrae. This finding endorses the hypothesis that the chroniosuchid osteoderm series was part of a crocodylian-like trunk bracing system that supported terrestrial locomotion. According to the measured range of osteoderm bone compactness, some chroniosuchian species may have had a more aquatic lifestyle than others.

Osteoderm microstructure indicates the presence of a crocodylian-like trunk bracing system in a group of armoured basal tetrapods

by Michael Buchwitz

by Michael Buchwitz, Florian Witzmann, Sebastian Voigt & Valeriy Golubev (in press). Acta Zoologica.

The microstructure of dorsal osteoderms referred to the chroniosuchid taxa Chroniosuchus, Chroniosaurus,... more The microstructure of dorsal osteoderms referred to the chroniosuchid taxa Chroniosuchus, Chroniosaurus, Madygenerpeton and cf. Uralerpeton is compared to existing data on the bystrowianid chroniosuchian Bystrowiella and further tetrapods. Chroniosuchid osteoderms are marked by thin internal and relatively thick external cortices that consist of lowly vascularised parallel-fibred bone. They are structured by growth marks and, in case of Madygenerpeton, by lines of arrested growth. The cancellous middle region is marked by a high degree of remodelling and a primary bone matrix of parallel-fibred bone that may include domains of interwoven structural fibres. Whereas the convergence of Bystrowiella and chroniosuchid osteoderms is not confirmed by our observations, the internal cortex of the latter displays a significant peculiarity: It contains distinct bundles of shallowly dipping Sharpey’s fibres with a cranio- or caudoventral orientation. We interpret this feature as indicative for the attachment of epaxial muscles which spanned several vertebral segments between the medioventral surface of the osteoderms and the transversal processes of the thoracic vertebrae. This finding endorses the hypothesis that the chroniosuchid osteoderm series was part of a crocodylian-like trunk bracing system that supported terrestrial locomotion. According to the measured range of osteoderm bone compactness, some chroniosuchian species may have had a more aquatic lifestyle than others.

Hydroxylapatite lattice preferred orientation in bones: A study on macaque, human, and bovine samples

by Juan Gomez Barreiro

Katachi no Gakko 14: Ecology and paleoecology from the viewpoint of bone histology

by Yasuhisa Nakajima

Endo, H., Nakajima, Y. and Hayashi, S. 2010. Honyurui Kagaku (Mammalian Science) 50(1), 87-89, 2010  (Japanese)

Secondary osteon and Haversian canal dimensions as behavioral indicators

by Lesley Harrington

Evolution of ruminant headgear: a review

by K Brakora

Open access / free download of full paper

The horns, ossicones and antlers of ruminants are familiar and diverse examples of cranial appendages. We collectively... more The horns, ossicones and antlers of ruminants are familiar and diverse examples of cranial appendages. We collectively term ruminant cranial appendages ‘headgear’; this includes four extant forms: antlers (in cervids), horns (in bovids), pronghorns (in pronghorn antelope) and ossicones (in giraffids). Headgear evolution remains an open and intriguing question because phylogenies (molecular and morphological), adult headgear structure and headgear development (where data are available) all suggest different pictures of ruminant evolution. We discuss what is known about the evolution of headgear, including the evidence motivating previous hypotheses of single versus multiple origins, and the implications of recent phylogenetic revisions for these hypotheses. Inclusion of developmental data is critical for progress on the question of headgear evolution, and we synthesize the scattered literature on this front. The areas most in need of attention are early development in general; pronghorn and ossicone development in particular; and histological study of fossil forms of headgear. An integrative study of headgear development and evolution may have ramifications beyond the fields of systematics and evolution. Researchers in organismal biology, as well as those in biomedical fields investigating skin, bone and regenerative medicine, may all benefit from insights produced by this line of research.

Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria)

by José Luis Carballido

Stein, Csiki, Curry Rogers, Weishampel, Redelstorff, Carballido,
and Sander. Published in pnas

Sauropods were the largest terrestrial tetrapods (>105 kg) in Earth’s history and grew at rates that rival those of... more Sauropods were the largest terrestrial tetrapods (>105 kg) in Earth’s history and grew at rates that rival those of extant mammals. Magyarosaurus dacus, a titanosaurian sauropod from the Upper Cretaceous (Maastrichtian) of Romania, is known exclusively from small individuals (<103 kg) and conflicts with the idea that all sauropods were massive. The diminutive M. dacus was a classical example of island dwarfism (phyletic nanism) in dinosaurs, but a recent study suggested that the small Romanian titanosaurs actually represent juveniles of a larger-bodied taxon. Here we present strong histological evidence that M. dacus was indeed a dwarf (phyletic nanoid).
Bone histological analysis of an ontogenetic series of Magyarosaurus limb bones indicates that even the smallest Magyarosaurus specimens exhibit a bone microstructure identical to fully mature or old individuals of other sauropod taxa. Comparison of histologies with large-bodied sauropods suggests that Magyarosaurus had an extremely reduced growth rate, but had retained high basal metabolic rates typical for sauropods. The uniquely decreased growth rate and diminutive body size in Magyarosaurus were adaptations to life on a Cretaceous island and show that sauropod dinosaurs were not exempt from general ecological principles limiting body size.

ONTOGENETIC HISTOLOGY OF STEGOSAURUS PLATES AND SPIKES

by Shoji Hayashi

SHOJI HAYASHI, KENNETH CARPENTER, MAHITO WATABE and
LORRIE A. MCWHINNEY. Palaentology (in press)

The dinosaur Stegosaurus is characterized by osteoderms of alternating plates and terminal paired spikes. Previous... more 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 fibers in young adult forms. In old adult forms, the bone tissues in the spikes become more compact and are extensively remodeled.This might contribute to the structural reinforcement of the spikes. The plates in old adult forms also show extensive remodeling and LAGs, 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 defense ontogenetically late.

New Genus of Chondrichthyans From the Silurian-–Devonian Boundary Deposits of Tuva (Russia)

by Živilė ŽIGAITĖ