An illustration of an extinct reef fish related to modern boxfish. It has a boxy body covered in heavily armored scales, a blunt face with high-set eyes, three long spines on its back and another horn-like spine on the front of its head.

Eospinus daniltshenkoi, a tetraodontiform fish from the early Eocene of Turkmenistan (~56-48 mya). Only about 5cm long (2″), it was a close relative of modern boxfish and triggerfish, as well as a completely extinct group called spinacanthids.

It was heavily armored, with large plate-like scales creating a boxfish-like carapace, but its most distinctive feature was its multiple long spines – three dorsal spines on its back, a fourth on its head resembling a “horn”, a pair of smaller spines on the sides of its body, and one on its underside formed from partially fused vestigial pelvic fins.

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