What ancestral feature confirms H. nasicus's developmental inclusion in Phylum Chordata?
Answer
Possession of a notochord at some developmental stage
Inclusion in the Phylum Chordata is determined by the presence of four key anatomical features at some point during the organism's life cycle. These features include a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail. Although the adult Western Hognose Snake has undergone metamorphosis where structures like the notochord are replaced by the more complex vertebral column that forms the backbone, the retention of these ancestral traits during development confirms its membership in Chordata. This placement is essential for understanding its fundamental evolutionary relationship with vertebrates.
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