Specializations in Tail Anatomy of the Lesser Egyptian Jerboa ( Jaculus jaculus ) Compared with the Mouse and Rat

Mammal tails have long been recognized for their diversity of morphological form and function, however, there remains a substantial gap between the motivation to understand and emulate the various performance functions of the tail and what is known about tail anatomy. In this study, we were motivated to discover the anatomical foundations of the fast, whipping motions of the tail of the lesser Egyptian jerboa ( Jaculus jaculus ), which may aid in the quick changes of direction as the animal escapes from predators using ricochetal bipedal hopping. We employed microCT scans, dissections, and museum data to describe the musculoskeletal anatomy of the jerboa in comparison with the laboratory mouse ( Mus musculus ) and rat ( Rattus norvegicus ). While many aspects of tail anatomy are conserved across these species, the jerboa does possess unique characteristics such as an extremely long tail arising from caudal vertebral elongation, development of extensive dorsal musculature differentiated into lateral and medial components to increase points of skeletal attachment, and a novel anatomical feature – the bi-lobed cranial transverse process – which serves as a supernumerary dorsal tendon attachment site and possible brace to protect the ventral tendons and intrinsic muscles for a section of caudal vertebrae which likely experiences high mechanical stress.