“No matter how exquisite it may seem, as if it were some sort of magic, evolution is at most a good trick… and there is a way to make it work. In case of turtle evolution, a major part of the trick was found to be embryonic folding.”

Dr Shigeru Kuratani
Riken Center for Developmental Biology

Ever wondered how the turtle got its shell? So has a Japanese team of scientist and they decided to investigate the subject by comparing turtle embryos with those of chicks and mice.

In turtles, it is the ribs that grow outward and fuse together to form the shell, formally known as the carapace. Having your ribs folded around your body is such a great leap from being a soft bodied animal that scientists have long puzzled over how this change happened in the course of evolution. Just like mammals and birds, turtles hail from a soft-bodied ancestor without any external carapace.

Through their embryological studies, the Japanese team of researchers from the Riken Center for Developmental Biology in Kobe, Japan, was able to identify the key event in the development of a turtle embryo that changes its fundamental “body plan”; the moment when the upper part of its body wall folds in on itself, forcing the ribs outward. This folding process results in a thickening of the deep layer of the turtle’s skin that maps out the position of the shell. As the turtle embryo grows bigger, the folding prevents the ribs from growing inwards.

“In the early embryo, the muscles and skeleton are in similar positions to those of the chicken and mouse”, Dr Kuratani explains.

Last year, a 220-million-year-old fossil was found in China, consisting of a fossilized turtle with an incomplete shell covering the underside of it body.

“The developmental stage of the modern turtle, when the ribs have not encapsulated the shoulder blade yet, resembles the (body) of this fossil species,” says Dr Kuratani.

The team has not yet been able to determine what causes the folding to happen in the first place

“That belongs to a future project,” says Dr Kuratani.

Since the early days of the 20^th century, marine biologists have pondered one of the world’s most puzzling questions – if a tree falls in the ocean, can the cephalopods hear it?

Fish use their swim bladder to hear, but cephalopods – a group of marine invertebrates that includes octopus, squid, cuttlefish and nautiluses – do not have any gas-filled chamber to use for this purpose and this has lead some scientists to suggest that these creatures are incapable of detecting the pressure wave component of sound.

A team led by sensory physiologist Hong Young Yan of the Taiwan National Academy of Science in Taipei has now, for the first time in history, been able to show that cephalopods can hear sounds underwater using their statocysts.

A statocyst is sac-like structure containing sensitive hairs and a mineralised mass. Fish can use their statocysts to detect sounds, so Yan suspected that other underwater creatures might do the same. After successfully showing that prawns use their statocysts to detect sounds underwater, Yan extended his experimentation from to prawns to cephalopods.

A quandary when researching cephalopods is their delicate bodies. When researchers wish to determine if an organism is capable of hearing or not, they normally attach electrodes to exposed nerves and measure how the nervous system electrically responds to sound. This type of invasive procedure can however easily injure a cephalopods and Yan was therefore forced to come up with a better method. Instead of attaching electrodes to exposed nerves, Yan placed the electrodes on the cephalopods’ body and measured the electrical activity in the brain. Thanks to this method, Yan could show that cephalopods do have a sense of hearing.

The lack of any gas-filled chamber means that cephalopods can’t amplify sounds the way a fish can, but their hearing is probably as good at that of prawns and similar invertebrates.

Yan now wish that his discovery will be used to further the understanding of cephalopod behaviour.

“The key question which I would like to investigate is what kind of sounds are they listening to?” says Yan. “Perhaps they listen to sound to evade predators and can eavesdrop to sounds made by their prey. […]Squid are heavily preyed upon by toothed whales including

dolphins. So perhaps their hearing would aid them to avoid the pinging sounds made by

dolphins. […] Or, perhaps they even could make sounds to communicate among themselves. “