Systematic and comparative morphologies of the extrinsic cardiac nervous system in lemurs (Primates: Strepsirrhini: Infraorder Lemuriformes, Gray, 1821) with evolutionary morphological implications

Abstract

The detailed systematic morphology of the extrinsic cardiac nervous system (ECNS) and its surrounding structures in lemurs, Lemuriformes, were examined using 18 sides of nine lemurs including all four families: Lemuridae, Indriidae, Lepilemuridae, and Cheirogaleidae. Although the general morphology of ECNS in lemurs is similar to that in Lorisiformes, several anatomical differences, such as the structural variation of the cervicothoracic ganglion, the positional variation of the middle cervical ganglion, and the unusual appearance of the superior cardiac nerve originating from the superior cervical ganglion, demonstrate the diversity within Lemuriformes. In other words, the comparative anatomical findings of the wide variations in ECNS in the four families of Lemuriformes compared with the lower variations in the two families of Lorisiformes possibly reflect their evolutionary history and diversity, as is shown in the recent molecular phylogeny. On the other hand, the shared common morphology of ECNS in Lorisiformes and Lemuriformes is considered to be the morphology of the common ancestor of strepsirrhines and demonstrates the gradual evolutionary changes in the primate lineage. Our present and previous results also suggest that ECNS is preserved in the primate lineage without modification and specialization because of its functional adaptation, as is seen in the somatic system.