Thelodus | 3D Dinopedia

Thelodus

Period of life:

443 – 423 million years ago

Period:

Silurian period

Habitat:

Marine environment

Taxonomy:

Fish

Height:

0.2 m

Countries:

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Thelodus (443 – 423 million years ago)

Thelodus is a genus of extinct jawless fish that lived in the seas of the Silurian period. Fossils have been found across a wide area including Europe, Asia, and North America. Thelodus represents an important evolutionary stage in fish history, showing a transition to mid-water life and improved swimming abilities.

Generally small, these fish ranged from 5 to 15 cm in length. However, scales of Thelodus parvidens found in the UK are just 1 mm long; comparing them with other thelodonts (e.g., Loganellia) suggests a total body length of 10 – 30 cm. In contrast, Thelodus macintoshi from Canada had scales up to 3 mm long, and its overall length is estimated at up to 1 m!

The body was covered with small, non-overlapping scales adorned with spines and grooves. Unlike the heavy armour of some other ancient fish, these lightweight scales gave Thelodus greater manoeuvrability and speed — evolution clearly chose agility over defence.

A well-developed caudal (tail) fin provided propulsion, while a dorsal fin acted as a stabiliser. Rudimentary paired pectoral fins were also present. Lacking jaws, Thelodus could not bite hard food. Its body was flattened on top, typical of bottom-dwelling fish. It probably fed on plankton and tiny invertebrates near the sea floor.

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