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How do chordates occupy such a wide variety of habitats?

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A translucent X-ray fish (Pristella maxillaris) swims in an aquarium, showing its visible backbone and internal structures through its body. — Chordate X-ray fish (*Pristella maxillaris*), is an example of a chordate with a visible backbone.

Chordates occupy a wide variety of habitats due to the diverse evolutionary adaptations found within the phylum, particularly among the vertebrates.1

While tunicates and cephalochordates are generally restricted to aquatic environments—often as filter feeders that either attach to surfaces or burrow into sand—vertebrates have evolved significantly more complex behaviors and ecological strategies. This complexity is supported by several key anatomical and physiological developments:1

Active Feeding and Locomotion: The evolution of the notochord, dorsal nerve tube, and pharyngeal slits improved swimming capabilities and the ability to capture prey. Vertebrates further specialized their mouths and pharyngeal structures to actively hunt larger prey, allowing them to exploit diverse food sources.2
Sensory Sophistication: Vertebrates possess highly developed brains and complex sensory organs, such as eyes and nasal chemical receptors, which allow them to navigate and interact with varied environments.34
Adaptive Flexibility: The ability to focus the eye (accommodation) and the development of specialized body forms and fins have enabled vertebrates to adapt to different aquatic and terrestrial niches.23

These advancements allow vertebrates to maintain a more active lifestyle, facilitating their success across nearly all major global habitats.1