Diversity of cortical bone morphology in anuran amphibians

• Published in: Development, growth & differentiation Vol. 65; no. 1; pp. 16 - 22
• Main Authors: Kondo, Yoshiaki, Iwamoto, Rina, Takahashi, Takumi, Suganuma, Kaito, Kato, Hideaki, Nakamura, Hiroaki, Yukita, Akira
• Format: Journal Article
• Language: English
• Published: Japan Wiley Subscription Services, Inc 01.01.2023
• Subjects: amphibian; Amphibians; Animals; Anura - anatomy & histology; Biological Evolution; bone formation; Bone growth; Bones; Ceratophrys cranwelli; Computed tomography; Cortical Bone; Frogs; Lamellar bone; Mammals; Metamorphosis; Osteogenesis; Reptiles & amphibians; X-Ray Microtomography; amphibian; bone formation; cortical bone
• ISSN: 0012-1592; 1440-169X
• DOI: 10.1111/dgd.12831

The cortical bones of mammals, birds, and reptiles are composed of a complex of woven bone and lamellar bone (fibrolamellar bone) organized into a variety of different patterns; however, it remains unclear whether amphibians possess similar structures. Importantly, to understand the evolutionary process of limb bones in tetrapods, it is necessary to compare the bone structure of amphibians (aquatic to terrestrial) with that of amniotes (mostly terrestrial). Therefore, this study compared the cortical bones in the long bones of several frog species before and after metamorphosis. Using micro‐computed tomography (CT), we found that the cortical bones in the fibrolamellar bone of Xenopus tropicalis (Pipoidea superfamily) and Lithobates catesbeianus (Ranoidea superfamily) froglets are dense, whereas those of Ceratophrys cranwelli (Hyloidea superfamily) are porous. To clarify whether these features are common to their superfamily or sister group, four other frog species were examined. Histochemical analyses revealed porous cortical bones in C. ornata and Lepidobatrachus laevis (belonging to the same family, Ceratophryidae, as C. cranwelli). However, the cortical bones of Dryophytes japonicus (Hylidae, a sister group of Ceratophryidae in the Hyloidea superfamily), Microhyla okinavensis (Microhylidae, independent of the Hyloidea superfamily), and Pleurodeles waltl, a newt as an outgroup of anurans, are dense with no observed cavities. Our findings demonstrate that at least three members of the Ceratophryidae family have porous cortical bones similar to those of reptiles, birds, and mammals, suggesting that the process of fibrolamellar bone formation arose evolutionarily in amphibians and is conserved in the common ancestor of amniotes. In this paper, we show that during amphibian metamorphosis, porous cortical bones are formed in the long bones of the limbs (a‐c). Similar to previously observed porous cortical bones in other tetrapods, a blood vessel was observed in the center of the cavity (white arrows in a, b). In mature individuals, the cortical bone of the long bone was mainly composed of dense bone rather than porous bone (d). Although porous woven bone was observed only in the Ceratophryidae family in this study, this study demonstrates that porous cortical bone is formed in amphibians as well as in other tetrapods.