A group of researchers looking at the evolution of chewing have shown fish are more like mammals than lepidosaurs (snakes and lizards) when it comes to eating.
By looking at a range of fish – including bowfish, a number of salmonids and pike – lepidosaurs and mammals, the researchers hoped to find similarities or differences in how each group processed its food.
Chris Gintof and colleagues used a method that may be slightly unsettling to the average aquarist: electrodes were implanted into the test fish and then the output monitored when the fish caught a prey item – an unsuspecting goldfish that was added to the test fish's tank.
The main findings of the group were all nine species chewed their food, as opposed to bolting it straight down, which more closely resembles the behaviour of mammals than lepidosaurs. The group also discovered that fish also took considerably longer than mammals to chew their food, and the variation in chewing time is greater in fish than in mammals.
The researchers results point to that fact that chewing behaviour is very old – a common ancestor related to both fish and mammals must have been able to chew, and that as the two groups separately evolved, so did their chewing behaviour.
Factors that may have been important in the evolution of fish chewing are thought to include their lack of a fleshy tongue, and the importance of maintaining waterflow through the jaws during chewing.
Differences in the environments, i.e. living on land or in water probably also played a role as it is likely harder to chew when there is also water – as well as supper – in the animal's mouth.