Tetrapods Lobe-finned fishes Other fish groups
Invertebrates plants Traces
Bony fishes (Osteichthyes) are divided into two main groupings: the ray-fins (actinopterygians) and the lobe-fins (sarcopterygians). Nearly all the bony fish around today are ray-fins — lungfish and coelacanth being the only surviving lobe-fins. During the Paleozoic era there were a great many more lobe-fins, including groups that are now extinct, like the rhizodontids.
Letognathus was up to 5 meters
(16 ft.) long and could
weigh about 3-tons.
Maxilla (upper jawbone) of Letognathus,
top predator of Blue Beach
The best-known vertebrate creature from Blue Beach is Letognathus, the rhizodont, with over 2500 specimens now at the BBFM. This is the only site in Canada known to contain rhizodonts. Letognathus means “jaws of death, annihilation or ruin”, and it was a fish that could grow to about 5 meters long (16 ft.). It was a remarkable predator that had numerous sharp teeth of several different shapes and sizes, all within the same mouth.

Like many other lobe-fins, the strong skeleton and musculature of the front fins actually enabled this fish to lift itself out of the water and crawl. They also possessed rudimentary lungs and could breath air.

Letognathus was a top predator of the early Carboniferous. It was an ‘ambush predator’, preferring to wait patiently for the unwary to venture too close. Like alligators, they could spring into action, snapping up surprised fishes or tetrapods. When their prey was too large to swallow whole, rhizodonts probably thrashed their prey like the alligators of today, perhaps dragging them back to the deep water.

Scientists still know very little about these enigmatic fish because nobody has ever found a complete adult skeleton. Most of what we know about them comes from fragmentary or incomplete material. The abundance of remains from Blue Beach is destined to make Letognathus the best-known rhizodont ever. By examining each fossil bone, a little more knowledge is gained toward an understanding the whole skeleton. Common finds include teeth and scales. Less common are platy skull bones or elements of the fin or shoulder. Scarce specimens like the impressive jawbones with teeth, which gave these creatures their terrifying name, are still discovered at least once every year.

The stout humerus shows why rhizodonts
were able to support themselves on their fins.

Lungfishes – A second lobe-fin known from the fossils at Blue Beach is a fairly large lungfish tentatively identified as ?Ctenodus. Very few examples are known, suggesting the population was quite small. Lungfishes are usually fairly common finds at other early tetrapod localities, but not so at Blue Beach. This shoreline seems to have had too many rhizodonts!

Like their name implies, lungfishes had lungs and could breath air. They probably ambushed prey like the larger rhizodonts rather than swimming around looking for meals. Lungfish bones are even more easily confused with tetrapod bones than are rhizodonts, so identifications at are sometimes necessarily tentative ones.