Bone microstructure of M. intrepidus (NCSM 33392). From Zanno et al., 2019.
The aim of Paleohistology is the study of the microstructure of fossilized skeletal tissues. Despite that the organic components of mineralised tissues decay after death, the inorganic components of bone preserve the spatial orientation of organic components such as osteocyte lacunae, vascular canals, and collagen fibres.
The techniques for the microscopic study of biological tissues began in 1828, when two British scientists, Henry Witham and William Nicol, experimented by grinding sheets of petrified tree trunk into traslucents sheets so that they could viewed under the microscope. Few years later the new technique was applied to fossil vertebrates by Agassiz. In 1849, John Thomas Quekett published his most important paper on the histological structure of bone in mammals, birds, reptiles, and fish. He described vascular canals, lacunae and canaliculi, and trabecular endosteal bone.
Dorsal dermal spine of the Hylaerosaurus (From Mantell, 1850a. Plate XXVII)
The next important advance was the first clear description of dinosaur bone microstructure: Hylaerosaurus made by British paleontologist Gideon Mantell in 1850. In his work, Mantell provides a drawing of a thin section from a “dorsal dermal spine” of Hylaerosaurus. The same year, Mantell described a transverse thin section from a humerus of Pelorosaurus, and notes that the bone exhibits an “intimate structure beautifully preserved; the bone cells, and Haversian canals, are as distinct as in recent bones.” In 1871, John Phillips described the structure of pterosaur bones from the Stonesfield ‘Slate’ (Bathonian, Middle Jurassic, England) and noted that pterosaur bones contained longitudinal “Haversian canals” and figured “lacunae… with many short excurrent somewhat branched tubules”.
Detail of the humerus of Vegavis iaai (MACN-PV 19.748) in polarised light. Scale = 1 mm. (From G, Marsà et al., 2017)
A century later, the introduction of hard plastic resins, the development of tungsten carbide microtome blades, the use of very thin diamond-edged saw blades, and the examination of bone tissue with surgically implanted orthopedic devices fostered new methods for studying the histology of fully mineralized bone.
Armand de Ricqlès, in the 1960s and 1970s, observed that paleohistological features could be correlated with growth rates and thus could indirectly shed light on the thermal physiology of extinct organisms. He based his conclusions on the neontological observations of Rodolfo Amprino. Quantitative studies confirmed that avascular bone is deposited more slowly than vascular bone, and radial bone is deposited faster than laminar bone. De Ricqlès early histological examinations of dinosaur bones suggested that they did not grow in a manner similar to extant cold-blooded reptiles (which deposit poorly vascularized cortical bone, interrupted by many lines of arrested growth). On the contrary, the evidence indicated that dinosaurs had a physiology that more closely approximated that of extant, fast-growing, endothermic birds. He included pterosaurs in a discussion on reptile bone histology and emphasised the structural similarities with bird bones such as the large diaphyseal medullary cavities enclosed by a dense cortex, with spongiosa in the epiphyseal region. The studies conducted by de Ricqlès opened a new path for paleohistology and his work continues to influence the field today.
References:
2019. Dinosaur paleohistology: review, trends and new avenues of investigation. PeerJ 7:e7764 https://doi.org/10.7717/peerj.7764
Quekett J. (1849) On the intimate structure of bone, as composing the skeleton, in the four great classes of animals, viz., mammals, birds, reptiles, and fishes, with some remarks on the great value of the knowledge of such structure in determining the affinities of minute fragments of organic remains. Transactions of the Microscopical Society of London. 1849;2(1):46–58. doi: 10.1111/j.1365-2818.1849.tb05102.x.
Mantell Gideon Algernon (1850) XVII. On a dorsal dermal spine of the Hylæosaurus, recently discovered in the strata of Tilgate Forest140 Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0018
Mantell Gideon Algernon (1850b) XVI. On the pelorosaurus; an undescribed gigantic terrestrial reptile whose remains are associated with those of the iguanodon and other saurians in the strata of Tilgate Forest, in Sussex140Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0017
De Ricqlès (1969) De Ricqlès A. L’histologie osseuse envisagée comme indicateur de la physiologie thermique chez les tétrapodes fossiles. Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, Serie D: Sciences Naturelles. 1969;268:782–785
Letters from Gondwana. 