The world before the bite
About 380 million years ago, during the Devonian Period, Earth's oceans were on the cusp of radical change. Before this time, marine ecosystems consisted mostly of animals living on or near the seafloor (benthic) or those drifting with the currents (planktonic). The concept of "nekton"—actively swimming creatures that could move independently of currents—was not a dominant feature of ocean life. The seas were filled with jawless fish, trilobites, and other invertebrates.
This began to change with the evolution of two features in a group of armored fish called placoderms: jaws and effective fins. Jaws, which likely evolved from the first pair of gill arches, turned fish from passive filter-feeders or bottom-grubbers into active predators. This single development triggered what paleontologists call the Devonian Nekton Revolution. The appearance of efficient, swimming predators created intense evolutionary pressure. Prey animals had to adapt or perish, leading to new defenses like thicker shells, faster swimming abilities, and more complex behaviors. This predator-prey dynamic drove a rapid increase in the diversity and population of nektonic animals.
The Gogo Formation, a fossil-rich site in the Kimberley region of Western Australia, records this period. Once a massive tropical barrier reef, the area's geology led to exceptional fossil preservation. Fish that died and sank into the oxygen-poor basins were encased in limestone nodules, which preserved them in three dimensions with minimal distortion. This allows scientists to study their anatomy in incredible detail, even preserving soft tissues like nerves and muscles.
An evolutionary arms race
The dominant new predators of the Devonian were the placoderms, a class of fish whose head and thorax were covered in articulated bony plates. While many were small, some grew to enormous sizes. The most famous, Dunkleosteus, reached lengths of over 6 meters (20 feet) and was the apex predator of its time. Instead of teeth, it had self-sharpening bony plates on its jaws that functioned like guillotine blades. Biomechanical studies estimate its bite force reached up to 5,300 newtons, comparable to a large crocodile, and its jaws could open in just 20 milliseconds to create a powerful suction force that pulled prey into its mouth.
The Gogo Formation hosts a smaller but equally significant placoderm, Mcnamaraspis kaprios. Growing up to 50 cm long, it was an active predator with large eyes and sharp jaw plates, likely used for cracking the shells of arthropods. Proclaimed the state fossil of Western Australia in 1995, its discovery revealed new anatomical details, including cartilaginous snout rings previously only inferred.
The fossils at Gogo reveal a predator-prey struggle; they record the evolution of complex biology. The most remarkable discovery from the site is a fossil of Materpiscis attenboroughi, a 380-million-year-old placoderm found with an embryo still inside, connected by a mineralized umbilical cord. This is the oldest known evidence of live birth (viviparity) in any vertebrate, pushing back the known history of internal fertilization by 200 million years. The presence of claspers in male placoderms and smooth pelvic fin bases in females also points to widespread sexual dimorphism and advanced reproductive strategies.