In the wake of the Battle of Little Big Horn, U.S. soldiers confiscated a number of strange rocks from their captives’ medicine pouches. Etched with lines that resembled outlines of buffalos, the rocks were sacred to the Blackfoot and other plains Indians, who used them to draw buffalo herds over cliffs. But, it turned out, they were not actually stones at all. They were the fossilized shells of ammonoids, a great race of cephalopods (distantly related to the nautilus) that once roamed the seas. For all the cultural significance humans gave the fossils, we know very little about the ammonoids themselves: how they acted, felt, communicated. We know they did not call to buffalo, but we’re at a loss as to whom they did call.

SQUID EMPIRE: THE RISE AND FALL OF THE CEPHALOPODS by Danna Staaf ForeEdge, 256 pp., $27.95

Danna Staaf’s Squid Empire: The Rise and Fall of the Cephalopods, tells the story of the world of ancient cephalopods—at least, as best anyone can—including these ammonoids. Cephalopods, which include octopi, cuttlefish, and squid, belong to the Mollusca phylum, are chiefly identified by their tentacles. Today’s species can outswim the fastest Olympians, change color at will, escape through the tiniest of holes. And they are fabulous communicators. A cuttlefish, for example, can carry on multiple visual conversations at once: A male courting a female will display a sexy, striped pattern on the side of his body facing the female, while the other side of his body will mimic a female’s mottled pattern, tricking a nearby rival into thinking he was another female and thus not a threat. Cuttlefish, apparently, won’t do this if multiple males are nearby—it’s too difficult to deceive multiple rivals, and they do not want to get caught lying, a fact that further suggests their extreme intelligence.

Cephalopods are also essential to understanding the broader web of life on Earth. Humboldt squid are a so-called “keystone species” in the Pacific: An entire ecosystem depends on them (a single sperm whale can eat 700 to 800 squid every single day). “They start so small, grow so fast, and get so big,” Staaf writes, “that they provide abundant food for marine predators of every size—a ‘one-prey-fits-all’ solution. Thus, many species of squid act as biological conveyor belts, moving energy from tiny plankton up to apex predators, including humans.”

Cephalopods have long been innovators, starting several hundred million years ago, when they reinvented the shell. Other mollusks had developed shells—think snails and clams, for example. But the cephalopod sealed off its shells (either through chambers, or a thin layer of tissue that worked to replace water with gas), creating buoyancy and allowing for faster movement. “A buoyant shell was the key innovation of cephalopods,” Staaf explains, putting it even above their dazzling light displays and physical feats. “It constituted a total transformation of the mollusk body plan, turning crawlers and oozers into floaters and swimmers.” And while this feature persists in the nautilus and a few other remaining species, subsequent cephalopods eventually shed their shells. Many predators rely on echolocation to find prey, and those echoes bounce off of shells clear as a bell, making the creature easier to find. By contrast, squishier, fleshier animals, like octopi and squid, tend to absorb those echoes, or at least mute them, making them harder to track for whales and dolphins.

During the Paleozoic and Mesozoic eras, cephalopods dominated the seas. Voracious and omnivorous predators, wildly adaptable survivors, cephalopods were far more numerous, and their reign lasted longer, than the dinosaurs. They survived an even greater extinction event: the Permian Extinction, when volcanoes in Siberia erupted for a solid 100,000 years, blotting out nearly 96 percent of all marine life. And yet we know far less about them. Why?