RichardMM_Coelacanth_deep_underwater_Photography_7f17e465-d3de-464c-928f-822ddb246323.png

450 Mya
First Bony Fish

The first animals swimming in the open seas were not like those we would see in our present oceans. They were jawless and did not have hard skeletons.

There are very few left today, but the Lamprey and Hagfish are the nearest of the species we know today to these precursors. These feed by latching on and grinding the skin of other fish until they can suck nutrients from them.

Lampray

Jawless mouth of Lamprey

Hagfish

There were other types of fish that evolved but have since become extinct. These include the jawless armoured types known as Ostracoderms.

The next type to evolve were fish with jaws. This obviously gave them a huge advantage in feeding. Unlike the Lamprey they could bite and tear off flesh or crush shells and extract the meat. They were still armoured with hard plates but had no skeleton. These are known as Placoderms.

None of these are around today either.

At last we start to come to fish with which we are more familiar. Still without a bony skeleton, these have a very similar backbone to vertebrates, but it is not bone, it is cartilage. These are very successful creatures in our present-day oceans and they are the Sharks and Rays.

The bony fish that most of us envisage when thinking ‘Fish’ developed from these earlier ancestors.

The earliest known Bony fish dates from around 430 - 450Ma

It shows some features of both Ray-finned and Lobe-finned.

There are 2 main types of bony fish, the more familiar ‘Ray-finned’ fish, and the ‘Lobe-finned’ fish.

The vast majority are Ray-finned. Their fins being webs of skin supported by bony or horny spines ("rays"), They are called this because they have bony skeletons and jaws, and the fins are attached to the body mass and are moved by muscles on the body. The fins do not have bones in them.

There are more than 28,000 species known and they are found in pretty well all aquatic environments.

Lobe-finned fish differ from their bony relatives in several ways. Primarily the arrangement of the fins of course. Early lobe-finned fishes had fleshy, lobed, paired fins, joined to the body by a single bone. Their fins differ from those of all other fish in that each is borne on a fleshy, lobe-like, scaly stalk extending from the body. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs. They are more closely related to tetrapods than to the ray-finned fish.

Most famous is the Coelacanth. In 1938 the first specimen was caught off the E Cape coast and between them Marjorie Courtenay-Latimer and Prof. JLB Smith determined it was a Coelacanth. They had been thought to have become extinct 40 million years ago.

“Old Fourlegs” A live specimen of Latimeria chalumnae seen off the KZN coast.

These have been found subsequently off the East Coast of S Africa and also in the Comoro Islands.

The Lungfish is also part of this group and has similar arrangements of bones in its limbs.

They are even more closely related to tetrapods as they can breathe air. They are found in Africa, S America and Australia

The relationships of all these fish types are summarised in this diagram.

450 Mya First Bony Fish

450 Mya
First Bony Fish