Final answer:
The first whale ancestor exhibiting the aforementioned traits was Pakicetus. Pakicetus and Rodhocetus are thought to be whale ancestors, with Rodhocetus being more aquatic. These transitionary species illustrate the evolution of whales from terrestrial to fully aquatic lifestyles.
Step-by-step explanation:
The first whale ancestor to exhibit a thick bony wall around the middle ear and a semi-aquatic habitat was Pakicetus. Scientific research and the fossil record have provided evidence that modern whales evolved from terrestrial ancestors. Pakicetus and Rodhocetus are considered to be among these ancestors. Pakicetus is believed to have been semi-aquatic, with some characteristics suited for life in the water, including modifications of the middle ear for hearing underwater. However, the extent of its aquatic lifestyle is debated among scientists. Rodhocetus, on the other hand, is regarded as having been more adapted to an aquatic environment, and its fossil remains include a type of ankle bone found in land animals. This suggests a transition from a terrestrial to an aquatic lifestyle.
It is important to note that aquatic tetrapods, like Ichthyostega and Acanthostega, existed in the Devonian period and were ancestral to modern tetrapods. They lived in freshwater environments and had both gills and lungs, showing early stages of adaptation to land. As we look at phylogenetic trees, we can identify that Cetaceans descended from even-toed ungulates and have evolutionary links with hippopotami, cattle, and other ungulates, but not with the horse, whose most closely related extant animal among the given options is the armadillo. As these transitions occurred, significant changes took place in the physiology of these animals, leading to the evolution of whales from land-dwelling ancestors to fully aquatic mammals.