Dermal bone

A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including much of the skull, jaws, gill covers, shoulder girdle and fin spines rays (lepidotrichia), and the shell (of tortoises and turtles). In contrast to endochondral bone, dermal bone does not form from cartilage that then calcifies, and it is often ornamented.^[1] Dermal bone is formed within the dermis and grows by accretion only – the outer portion of the bone is deposited by osteoblasts.

The function of some dermal bone is conserved throughout vertebrates, although there is variation in shape and in the number of bones in the skull roof and postcranial structures. In bony fish, dermal bone is found in the fin rays and scales. A special example of dermal bone is the clavicle. Some of the dermal bone functions regard biomechanical aspects such as protection against predators.^[2][3][4] The dermal bones are also argued to be involved in ecophysiological implications such as the heat transfers between the body and the surrounding environment when basking (seen in crocodilians) ^[5] as well as in bone respiratory acidosis buffering during prolonged apnea (seen in both crocodilians and turtles).^[6][7] These ecophysiological functions rely on the set-up of a blood vessel network within and straight above the dermal bones. ^[8]

References

1. de Buffrénil, V.; Clarac, F.; Fau, M.; Martin, S.; Martin, B.; Pellé, E.; Laurin, M. (2015). "Differentiation and growth of bone ornamentation in vertebrates: a comparative histological study among the Crocodylomorpha". Journal of Morphology. 276 (4): 425–445. doi:10.1002/jmor.20351. PMID 25488816. S2CID 10809084.
2. Chen, I.H.; Kiang, J.H.; Correa, V.; Lopeza, M.I.; Chen, P.Y.; McKittrick, J.; Meyers, M.A. (2011). "Armadillo armor: mechanical testing and micro-structural evaluation". Journal of Animal Ecology. 4 (5): 713–722. doi:10.1016/j.jmbbm.2010.12.013. PMID 21565719.
3. Broeckhoven, Chris; Diedericks, G.; Mouton, P. le Fras N. (2015). "What doesn't kill you might make you stronger: functional basis for variation in body armour". Journal of Animal Ecology. 84 (5): 1213–1221. doi:10.1111/1365-2656.12414. PMID 26104546.
4. Clarac, F.; Goussard, F.; de Buffrénil, V.; Sansalone, V. (2019). "The function(s) of bone ornamentation in the crocodylomorph osteoderms: a biomechanical model based on a finite element analysis". Paleobiology. 45 (1): 182–200. doi:10.1017/pab.2018.48. S2CID 92499041.
5. Clarac, F.; Quilhac, A. (2019). "reptile The crocodylia skull and osteoderms: A functional exaptation to ectothermy?". Zoology. 132: 31–40. doi:10.1016/j.zool.2018.12.001. PMID 30736927. S2CID 73427451.
6. Jackson, D.C.; Goldberger, Z.; Visuri, J.; Armstrong, R.N. (1999). "Ionic exchanges of turtle shell in vitro and their relevance to shell function in the anoxic turtle". Journal of Experimental Biology. 202 (5): 503–520. doi:10.1242/jeb.202.5.513. PMID 9929454.
7. Jackson, DC.; Andrade, D.; Abe, AS. (2003). "Lactate sequestration by osteoderms of the broad-nose caiman, Caiman latirostris, following capture and forced submergence". Journal of Experimental Biology. 206 (20): 3601–3606. doi:10.1242/jeb.00611. PMID 12966051.
8. Clarac, F.; de Buffrénil, V.; Cubo, J.; Quilhac, A. (2018). "Vascularization in ornamentedosteoderms: physiological implications in ectothermy and amphibious lifestyle in the crocodylomorphs?". Anatomical Record. 301 (1): 175–183. doi:10.1002/ar.23695. PMID 29024422.