First country outing
This path will not have been easy, after all, there are hardly any habitats more contradictory than water and solid land. And yet, a long time ago, a vertebrate ventured into a new universe - an African gill sack catfish species shows what the first step might have looked like.
Africa's animal world has so many primitive and peculiar species to offer: It starts with the "small things" with the so-called goliath beetle, which is one of the largest and heaviest insects of all, and continues with the no less impressive goliath frog - his Sign the largest amphibian on earth - and does not end with the shy okapi. Despite its size, the forest giraffe was not discovered until the beginning of the 20th century.century.
Because of the large number of different habitats, some of which are difficult or impossible to access, the continent still offers many biological surprises - even if the individual species such as the gill sack catfish Chanallabes apus have been known for some time. This fish and related species live in the muddy swampy waters of tropical Africa, to which they have evolved some remarkable adaptations that perhaps offer a glimpse into the dawn of vertebrate life.
In order to be able to survive in this inhospitable, often oxygen-poor and rapidly changing homeland, they have developed special labyrinthine gills with which they can absorb atmospheric oxygen. Even in oxygen-rich waters, they regularly swim to the surface to breathe there - if this is prevented, they die of suffocation. The device even allows them to travel short distances across land should they wish to change homes.
But Chanallabes apus uses its physical capabilities even more: it hunts - and catches - prey outside of its wet homeland. A team of scientists led by Sam Van Wassenbergh from the University of Antwerp, Belgium, has now observed exactly how he does this. Because not only the supply of oxygen, but also the supply of food works completely differently on land than in the water.
Many fish suck in the insects they attack, tadpoles, crabs or whatever else they kill with typical mouth movements. But what works well because the water is 800 times denser than air fails completely in the thin atmosphere on land: The object of desire does not move a millimeter in the direction of the throat – a dilemma that probably also the first ones faced terrestrial tetrapods of primeval times.
Of course, this also applies to the gill sac catfish, and yet, at least for Chanallabes apus, a large part of the diet consists of insects from the environment, which they actually catch on the bank. To do this, he has developed a very special technique, as video recordings by the Belgian biologists now show. After spotting a prey animal out of the water, the African catfish will screw its body partway onto the mainland, lifting its neck and head section up and finally curling them back down.
As soon as it touches a prey with its mouth or its typical catfish appendages - the barbels - it begins to snap until the prey is clamped firmly between its jaws. However, the curvature of the neck must be carried out, otherwise the scaleless fish would rather push the coveted food in front of it than grab it. At the same time, this movement allows the hyoid bone to be lowered at any time, which is part of the suction mechanism. However, a prerequisite for this process is the correspondingly flexible spine, which Chanallabes apus has developed.
By the way, the mechanism of the animal's snapping movements remains the same as under water, which leads the researchers to assume that the first prehistoric land walkers only had to make minor changes to their mouthparts, at least in this area. And the lack of robust pectoral fins to support the front body did not present too much of an obstacle for the first tasters of land air – as long as the daring fish were flexible enough not only in ecological but also in physical terms.