Osteohistological study on both fossil and living Caimaninae (Crocodyliformes, Crocodylia) from South America and preliminary comments on growth physiology and ecology

ABSTRACT

Caimaninae is a South American lineage of crocodylians widely distributed in Brazil and composed of six species within three genera. Currently, there is insufficient information regarding growth strategies, growth rates, and ecology extracted from the bone microstructure. Here we present the first osteohistological study of both Caiman yacare and an unidentified fossil Caiman. Long bones of one specimen of C. yacare and of one fossil Caiman found at Solimões Formation (Acre Basin), were used to prepare the histological slides. The microstructure of C. yacare shows fibrolamellar complex present in the femur and tibia, while the humerus and radius of both C. yacare and the fossil Caiman revealed a slow-growing bone matrix with gradual decrease and effective stops. According to the results found here, Caimaninae seem to have the capability to adjust their growth rates in response to seasonal changes. The extant Caiman is classified as juvenile, but for the fossilized specimen no ontogenetic stage can be determined. Caiman yacare shows the presence of intraskeletal variability regarding the record of bone growth. We conclude that Caimaninae likely have been experiencing cyclical changes in growth rates in direct correlation to changes in seasons and environmental conditions since the Miocene.

KEYWORDS:

• Bone tissue
• Caiman yacare
• osteohistology
• Miocene
• Caimaninae

Acknowledgments

The authors thank Rodolfo dos Santos, graduated biologist at Universidade Federal de Uberlândia (UFU), for helping with specimens processing, slides preparations and hospitality in the initial stages of this work. We thank the Centro de Pesquisa de Biomecânica, Biomaterials e Biologia Celular at Faculdade de Odontotologia da Universidade Federal de Uberlândia (FOUFU) for helping with the slides preparation. We also thank Dr. Sarah Werning and the Department of Anatomy at Des Moines University (DMU) for helping with imaging and processing the specimens. We also thank Chad Bittle for assitance with translations and image processing.This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) under Grant 88881.132283/2016-01; Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco FACEPE under Grant BIC-1327-2.04/17; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) under Grant 147466/2014-8.

Additional information

Funding

This work was supported by [Conselho Nacional de Desenvolvimento Científico e Tecnológico] [under the grant 147466/2014-8] to RCLPA; [Coordenação de Aperfeiçoamento de Pessoal de Nível Superior] [under the grant 88881.132283/2016-01] to RCLPA; [Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco] [under the grant BIC-1327-2.04/17] to MVAS;[Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico] [under the grant BMD-0124-00302.01.01/19] to RAMB.