Microanatomy and histology of bone pathologies of extant and extinct phocid seals

ABSTRACT

This study investigates three presumed fractured phocid seal bones: An isolated metapodial and an ulna belonging to different individuals of the extinct phocid, Homiphoca capensis, from Langebaanweg and a mandible of a juvenile elephant seal (Mirounga leonina), which was included to assess the validity of the assumption that changes to bones caused by fractures are consistent across extant and extinct members of the same groups. The bones were studied using a multi-method approach, including gross morphology, microcomputed tomography (micro-CT) and histology. Micro-CT showed that the metapodial was not fractured and information drawn from other analyses suggested that the pathology was an osteosarcoma. Histology of normal and fractured regions of the mandible and ulna permitted an estimate about the fracture healing stage, and showed the bone tissue at the fracture sites to be histologically similar. A birth line found on the lateral surface of the elephant seal mandible emphasised its young age and marked the first example of a birth line in a bone of a semi-aquatic mammal. A large scope of information was obtained using this multi-method approach, which could permit insight into the life events and lifestyles of modern and extinct individuals, such as H. capensis.

KEYWORDS:

• Palaeopathology
• pathology
• phocid
• bone histology
• Homiphoca
• elephant seal
• osteosarcoma

Acknowledgments

The authors are grateful for the specimen loans from Iziko South African Museums and BayWorld and to the South African Heritage Resources Agency (SAHRA) for allowing them to perform histological sectioning on the modern and fossil bones. Thank you to two anonymous reviewers for their insightful comments, which improved the manuscript. A huge thanks is extended to Caitlin Smith for her help during the histological sectioning process, as well as the rest of the Palaeobiology Research Group at UCT for their guidance and advice. The authors are grateful for the funding provided by NRF-DST Centre of Excellence in Palaeosciences to Megan Rose Woolley, NRF African Origins Programme (AOP) Grant awarded to Prof A Chinsamy-Turan (Grant No. 117716) NRF African Origins Programme (AOP) Grant awarded to Dr R Govender (Grant No. 98834).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the DST-NRF Centre of Excellence in Palaeosciences [COE2018-07Hon]; NRF (South Africa) African Origins Programme (AOP) [117716]; NRF (South Africa) African Origins Programme (AOP) [98834].