African Wild Dogs (Lycaon pictus) Show Adaptations to Sociality and Hypercarnivory in Their Cranial Musculature

Abstract

African wild dogs (Lycaon pictus) are highly social canids that live in large, hierarchical packs and engage in coordinated hunts. Recent research has suggested that enlarged muscles associated with expressive movement of the eyes and eyebrows may have evolved in domestic dogs (Canis familiaris) to facilitate interspecies communication with their human owners. In L. pictus, communication is reported to occur predominantly through vocalization with reduced reliance on facial expressions; however, the mimic muscles in L. pictus have never been described and evaluated. L. pictus is also hypercarnivorous with the highest documented bite force quotient of any mammalian carnivore. It has large, mobile ears, which enhance its auditory capabilities while hunting and assist with thermoregulation. We performed detailed dissections of the muscles of facial expression, mastication, and auricular movement in an adult male L. pictus,and conducted diffusible iodine‐based contrast‐enhanced computed tomographic (diceCT) scans of the head. Musculus levator anguli oculi medialis (LAOM) and retractor anguli oculi lateralis (RAOL), muscles of hypothesized importance in domestic dog‐human non‐verbal communication, are enlarged in L. pictus, suggesting that ocular expressions represent a significant component of communication. LAOM exhibits an intricate relationship with adjacent orbital musculature including partial fusion along its borders with mm. orbicularis oculi and frontalis. Muscles that draw the angles of the mouth caudally (e.g., m. zygomaticus major) are expanded. Numerous ramifying branches of CN VII and CN V2 course across the face to provide extensive sensory and motor innervation. These findings indicate that facial expression musculature of African wild dogs is well‐equipped for non‐verbal communication and that the same adaptations argued to facilitate communication between domestic dogs and humans may also facilitate intraspecific communication in L. pictus. Muscles of mastication are especially enlarged in L. pictus, with multiple bellies of mm. masseter and temporalis separated by deep layers of thick intermuscular fascia and with expanded insertions onto the mandible. Musculus digastricus is composed of a single, large belly without intervening tendon, and it receives its innervation exclusively from CN V3. These enlargements reflect increased masticatory capabilities in L. pictus, which enable its powerful bite force and hypercarnivorous diet. Auricular muscles are also well‐developed, supporting greater leverage and fine manipulation of its large, mobile ears. Musculus frontoscutularis is well‐developed and distinctly separable from m. frontalis, suggesting greater leverage of the auricle via attachments to the scutiform cartilage. The intrinsic ear muscles differ in pattern and orientation from all other published canids, demonstrating unique muscular control over rotation and fine manipulation of the auricle. Taken together, these morphological patterns illustrate that specific adaptations in the cranial muscul...