Final answer:
The distinctive double-pulley-like morphology in the leg of an ox, an artiodactyl, is found in the astragalus bone. (option 4)
Step-by-step explanation:
The distinctive double-pulley-like morphology of the astragalus bone serves as a synapomorphy, or shared derived trait, for the artiodactyl lineage. Artiodactyls, which include animals like oxen and ancient members of the whale lineage, exhibit this specialized feature in the ankle joint. The astragalus bone forms a unique articulation with the tibia and fibula, contributing to the characteristic weight-bearing and locomotor adaptations seen in artiodactyls. This synapomorphy is a crucial anatomical characteristic that sets the artiodactyl lineage apart from other mammalian groups.
The specialized structure of the astragalus bone reflects the evolutionary history and adaptations of artiodactyls to their diverse habitats and ecological niches. This synapomorphy is a key aspect of their skeletal anatomy, highlighting the evolutionary relationships within this group of mammals.
The double-pulley-like morphology of the astragalus bone is a defining synapomorphy for the artiodactyl lineage, providing insights into the evolutionary adaptations that have shaped the anatomy and locomotion of these animals over time.