Wikipedia and the scientific community
Pachyostosis & pachyosteosclerosis
Strictly speaking, pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. The term “pachyostosis” is often used loosely, referring to all osseous specializations characterized by an increase in bone compactness and/or volume. It occurs in both terrestrial and, especially, aquatic or semi-aquatic vertebrates. In aquatic animals, such as seacows (manatees and dugongs) and plesiosaurs it provides, or provided, ballast as an adaptation for an aquatic existence. 
Of the genus Homo, Homo erectus fossils are those which consist of abnormally thick, heavy, mineral rich bones, especially in the cranium and leg bones. This can only be explained as a clear adaptation towards a shallow diving lifestyle and in no way towards a life of running across the savannah. Until now, there have been few theories put forward to suggest why Homo erectus' bones were so thick and heavy.
(Above: manatee and dugong skeletons showing thick, heavy bones for diving / ballast).
Pachyosteosclerosis in Archaic Homo: Heavy Skulls for Diving, Heavy Legs for Wading?Stephen Munro and Marc Verhaegen
Compared to the skeletons of all other primates, including Homo sapiens, the crania and postcrania of Homo erectus were typically massive, displaying extremely thick bones with compact cortices and narrow medullary canals. Even outside the primate order, examples of animals displaying such massive bones are rare. Although this feature is sometimes seen as diagnostic of H. erectus, few convincing hypotheses have been put forward to explain its functional and adaptive significance.
Here, we present data showing that unusually heavy bones were atypical, although not exclusive nor indispensable, characteristic of H. erectus populations through the early, middle and late Pleistocene in areas of Asia, Africa and Europe. A comparative review of the occurrence of massive skeletons in other mammals suggests that they have an important buoyancy control function in shallow diving aquatic and semi-aquatic species, and are part of a set of adaptations that allow for the more efficient collection of slow, sessile and immobile foods such as aquatic vegetation and hard-shelled invertebrates. We therefore consider the possibility that part-time shoreline collection of aquatic foods might have been a typical element of the lifestyle of H. erectus populations. We discuss the alternative explanations for heavy bones from the literature, as well as apparent exceptions to the rule, such as thin-boned H. erectus and thick-boned Homo sapiens fossils. A review of the palaeo-ecological data shows that most, if not all, H. erectus fossils and tools are associated with water-dependent molluscs and large bodies of permanent water. Since fresh and salt water habitats have different densities, we hypothesize that in H. erectus as well as in some Homo sapiens populations, there might have been a positive correlation between massive bones and dwelling along sea or salt lake shores.
Original fossils of Pithecanthropus erectus (now Homo erectus) found in Java in 1891.
 Stephen Munro and Marc Verhaegen, Pachyosteosclerosis in Archaic Homo, Chapter 5. Was Man More Aquatic in the Past? Fifty Years after Alister Hardy, Waterside Hypotheses of Human Evolution, Bantham science publishers, 2011. p. 82 - 105.
"Pachyostosis" in aquatic amniotes: a review.
During the course of amniote evolution, numerous taxa secondarily adapted to an aquatic life. It appears that many of these taxa primitively display "pachyostosis," an osseous specialization characterized by an increase in bone compactness and/or volume. The term "pachyostosis" is used in morphological and histological descriptions to describe what in fact corresponds to different patterns. The aim of this paper is to present the current state of knowledge relative to this adaptation among aquatic amniotes. All the taxa that have returned to an aquatic environment are listed. Moreover, their degree of adaptation to the marine environment, their life environment, and the nature of their "pachyostotic" pattern, when present, are described. This inventory enables the evaluation of the current quality of the data relative to this specialization and provides an indication of the work that remains to be done. The functional consequences of "pachyostosis," and notably its importance for buoyancy control in the context of hydrostatic regulation of the body trim, are discussed and opposed to the requirement of improved swimming abilities in the case of a hydrodynamic mode of trim regulation. Questions are posed about the signification of the polymorphism displayed by this specialization between different taxa, different specimens of the same taxon and different bones of the same specimen, and the problem of quantification of pachyostosis is discussed.
© 2009 ISZS, Blackwell Publishing and IOZ/CAS.
|Website: F. Mansfield, 2015|
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