From the magnificent spiral-shelled ammonites to the squid and octopus,
The thrilling evolutionary story of the 500 million-year-old cephalopod family

“This fascinating book tells what paleontologists did to dinosaurs in the 1960s.
It seems to be given to primitive cephalopods.
The public appreciates the true value of these wonderful animals.
“It’s something that opens the door to finding out again.”
—Jennifer Ouellette, author of Me, My Self, and My Reason

Ammonites from the Paleozoic and Mesozoic Eras, belemnites from the Mesozoic Era, and squids from the Cenozoic Era…
For 500 million years, cephalopods have been a keystone species in the ecosystem!

Squids have 10 legs, octopuses have 8 (hence their English name, octopus), and the nautilus, a branch of the cephalopod family known as the living "animals with legs on their heads," has 60 to 90.
There were originally 10, and you can tell by looking at the embryonic stages of these three.
However, in the case of squid, the fourth pair of legs elongated into tentacles, in the case of octopus, the second pair transformed and eventually disappeared, and in the case of nautilus, the top two tentacles fused together to form a head cover.
Remember the documentary "My Octopus Teacher" and the fortune-telling octopuses, including "Paul" from the 2010 South Africa World Cup? What do fried squid and boiled octopus taste like?

“Those poor things were born delicious.” Squid, which live for about a year, lay hundreds to hundreds of thousands of eggs before dying.
Most of the eggs and chicks are eaten.
The hatchlings are smaller than a fingernail and are food for other baby fish and aquatic insects.
But squid grow quickly, and the surviving young ones turn the tables in a matter of days or weeks, preying on animals that were once their enemies.
The fattened squid now attracts the attention of larger predators.
Currently, the South Georgia Island elephant seal population consumes 2.3 million tons of squid and octopus each year.
A single sperm whale can eat 700 to 800 squid 'every day'.
Because of this unique fate, squid are considered an 'ecological keystone' and form the center of the food web.

Squids did so in the Cenozoic, and their ancestors, ammonites and belemnites, did so in the Paleozoic and Mesozoic.
Was the Devonian Period of the Paleozoic Era truly the "Age of Fish" and the Mesozoic Era the "Age of Dinosaurs"? A look at the top predators suggests otherwise.
However, the 'Age of Fish' was also the 'Age of Ammonites', the center of the food web, and many paleontologists studying the Mesozoic Era even consider that "the proportion of ammonites was more than 1,000 times greater than that of dinosaurs" as representative fossil animals.
Moreover, the 500 million-year history of the cephalopod family, through its shells, which can be called "heirlooms," provides fascinating clues to the questions, "How does evolution occur? How do new creatures come into being?"
Because all the evidence of the individual's development from the egg remains intact in that shell.

This book, which takes a fresh look at squid and octopus, is a grand epic of the cephalopod family, which first appeared 500 million years ago with an "animal-like" body, invented "swimming" to rise from the seabed, and became the king of the sea. Since then, they have overcome numerous extinction events and co-evolved with "terrifying predators" such as fish and whales.
(Unfortunately, octopuses and cuttlefish do not appear in this book.
(It seems to be a collateral line, not a direct line.)

It was a process of tremendous innovation, first building a shell, layering it, coiling it into a spiral… and later embedding that shell (unlike its spiny relatives) inside a soft body (squid) or eliminating it altogether (octopus), and in return acquiring camouflage that rivals chameleons, vision comparable to the human eye, swimming techniques that use fins for jet propulsion, and an intelligence we have not yet properly measured.
Let's take a peek at the genealogy that will "change our view of squid, octopus and their relatives" (New Scientist).

The word 'coleoid' comes from the Greek word meaning 'sheath'.
The scabbard encloses the sword, and the body of the super-shape encloses its own shell (or the vestiges of a degenerated shell).
The cephalopods include all living cephalopods that are not nautiluses—octopuses, squid, cuttlefish, etc.—as well as numerous fossil species.
Octopuses are so soft that there is hardly any trace of their shell left, but both squid and cuttlefish retain a faint trace of it.
The squid has a thin rod called the 'gladius' (pen, squid bone) inside its body that supports its body stiffly and serves as the center of muscle movement.
Cuttlefish look similar to squid at first glance, but they have a more complex calcareous structure called 'cuttlebone' inside their body.
Many people have probably seen cuttlebone hanging in a cage, and the calcium contained in it is a nutritious supplement for companion birds.

--- p.29

Scientists believe that the process of creating multiple chambers in the shell occurred in three simple steps:
First, some monotremes began to secrete a liquid with a lower salt concentration than seawater into their shells.
Just as the air inside a hot air balloon becomes lighter than the surrounding air when heated, the water inside the shell also becomes lighter than the surrounding water when its salt concentration is reduced.
This would have made it easier for the animal to continue crawling on the seabed carrying its heavy shell.
Second, some of the descendants of these first light-shelled animals began to alternate between secreting liquid and adding lime (a shell component).
If the limestone had been secreted periodically like that, the chambers within the shell would have been sealed, preventing the fluid from escaping.
Third, the descendants of these descendants used thin, fleshy tubes that extended through all the chambers of the shell to drain liquid and replace it with gas.
As buoyancy increased, the animal's shell and soft parts floated together into the middle layer.

--- p.54~55

The shells of primitive cephalopods were straight and elongated, and were generally between 30 centimeters and 2 meters long.
However, one species, aptly named Endoceras giganteum, grew to about 3.5 meters (11 feet).
It was taller than the rim of a basketball hoop and much larger than any other Anomalocaris.
In fact, it was larger than any creature that had appeared up to that time.
The shell was so buoyant that Endoceras had to backfill some of the chambers on the pointed end with heavy minerals.
When injecting minerals, a sac-shaped tubule was probably used.
This offset the weight of the soft tissue on the other end, allowing Endoceras to swim horizontally like its smaller relatives rather than bobbing around in an awkward exclamation point fashion.

--- p.65

During the Ordovician period, when cephalopods, large and small, were distributed throughout the oceans, hunting, filter-feeding, or grazing (or perhaps all three), the first proper fish emerged from the docile "vertebrate" lineage, which had little to do with the cephalopods.
They had fins, tails, gills, and even skulls, but no jaws.
So, any food that did not require biting or chewing would have been inhaled, so it would probably not have been a threat to the cephalopods.
But then, in the Silurian period that followed, something truly dangerous developed in the bodies of these strange, bony animals.

--- p.69

Similar changes occurred in cephalopods.
By the end of the Devonian, cephalopods with straight or loosely rolled shells were declining in diversity and numbers, while those with tightly rolled shells were thriving.
The spiral shell not only gave the same advantages as the truncated shell in terms of speed and maneuverability, but also protected the soft tissues from predation by predators.
The spiral shell is difficult to grasp, difficult to hold, and difficult to break.
Cephalopods needed just such a defense mechanism.

--- p.75

If volcanic eruptions at the end of the Permian caused the dramatic changes in ocean pH that we see today, that may be why the largest mass deaths during the mass extinction occurred underwater.
At that time, 96 percent of all species in the oceans disappeared.
Invertebrates were hit harder than vertebrates, but sharks and rays also lost significant numbers of lives.
Ammonites were also, of course, scorched.
But the parrotfish was not scorched.
(...) Paleontologists usually note that the two had different reproductive strategies.
Clearly, some factor related to environmental change would have favored the long-lived, large-egged nautiluses, while disfavoring the short-lived, small-egged ammonites.

--- p.94

Many of the features we consider unique to choriomorphs, such as suckers, leg hooks, and ink, begin to appear in the fossil record from the Triassic.
Such evolutionary innovations seem to be related to the loss of the shell.
As the amphibians became faster swimmers, they were able to chase faster prey.
Suction cups or hooks would have made it much easier to catch and hold such prey.
But without a shell, they become more vulnerable to attack, so a new means of defense was developed.
It's ink.
Ink, which has never been seen in nautiluses or ammonites, is often preserved in fossils of coelenterates, thanks to the stability of a pigment called melanin.
Fossilized belemnite ink was first discovered in 1826 by British paleontologist Mary Anning.
Her friend and fellow fossil collector Elizabeth Philpott reconstructed the ink and drew an ichthyosaurus, starting a trend of fossil ink drawings that continues to this day.

--- p.129~30

If you look at the picture of Belemnites, you will notice a pair of fins, making Belemnites the first finned cephalopod we see in our journey through cephalopod history.
Why fins? Jet propulsion is inherently less efficient than the sloshing or wave-like strokes employed by most swimming creatures, including fish, marine reptiles, and marine mammals.
So, cephalopods have evolved convergently into various similar swimming techniques to alleviate such inefficiencies.
Parrots developed an alternative method of locomotion by wiggling their fins, and echinoderms developed fins.
Some modern herbivores, such as cuttlefish, now move almost entirely by fins, resorting to jet propulsion only in dire situations.

--- p.135~36

Examining the various aspects of the Cenozoic Era will help us complete the picture.
The first is the aspect of climate change.
This also includes the return of cephalopods to coastal waters as glaciation began.
Second, the evolution of whales and the radiation of modern fishes acted as powerful selective pressures inducing habitat change and eventual shell reduction in herbivores.
In modern squid, the spindle has completely disappeared, and a method of regulating buoyancy using ammonia has developed, which has had the unusual side effect of erasing squid from the fossil record.
Meanwhile, the parrot has somehow managed to keep its outer shell.

--- p.178