Discovered by a shipwrecked, scurvy-ridden crew in the Bering Sea in 1741, Steller’s sea cow was a 30-foot, 8-to-10-ton sirenian covered in bark-like skin and so buoyant it could never fully submerge. This gentle, toothless giant grazed on canopy kelp, lived in tight family pods, and defended its calves with living barricades, yet it was hunted to total extinction in just 27 years.

This episode treats the sea cow’s disappearance as both an ecological puzzle and a murder mystery. We explore its bizarre anatomy, from a 35-pound heart to a 151-meter intestinal tract, the brutal mechanics of how a starving crew dragged 10-ton animals ashore, and the groundbreaking 2021 genome that revealed a “dead clade walking” already doomed by inbreeding and shrinking habitat long before the first harpoon. We also examine its role as a keystone ecosystem engineer and modern de-extinction efforts.

• The buoyancy problem and the dense bones that still left them stuck at the surface
• The keratinous mouth plates that pulverized kelp without teeth
• The 2021 genome showing severe inbreeding and a population already at 2,000
• How the sea cow thinned kelp canopies and boosted the whole ecosystem
• CRISPR de-extinction plans and the artificial-womb hurdle stalling them