Acanthostega gunnari

Overview

Acanthostega gunnari is an early tetrapod that had hands and feet but lived mainly in water. It also has evidence of a fish-like tail and gills. This fossil raised the question of whether limbs or life on land came first.^[1][3]

Key facts

Its forefoot had eight digits, unlike the five familiar in many tetrapods today. This shows that the number of digits in early limbs was not fixed to one pattern from the outset.^[3][1]

Time and place

It is an animal from the Late Devonian, around 365 million years ago. Fossils came from the Britta Dal Formation of present-day eastern Greenland. The region reveals the diversity of tetrapods living in aquatic worlds at that time.^[2]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

It had paddle-like limbs and a deep tail with fin rays. Eight digits in the forefoot are compared with at least eight known in the hind foot. Evidence of fish-like internal gills is also present behind the head.^[1][3]

Habitat and reproduction

Four limbs did not necessarily serve only walking on land. The limbs, tail, and gills of Acanthostega support an interpretation of mainly aquatic life. It invites exploration of how structures used in water later connected with other environments.^[1]

Fossil discovery

During a 1987 expedition, Jenny Clack’s team found new body-skeleton material in Greenland. Some pieces connected with skulls collected during earlier expeditions. Returning to the field after a long interval reconnected the story of one animal.^[5]

References

1. Clack2006 — Acanthostega gunnari
2. Fukui Prefectural Dinosaur Museum — Fossil records of Acanthostega
3. Coates & Clack1990 — Multiple digits in early tetrapods
4. Clack2009 — The transition from fishes to tetrapods
5. Jenny Clack — The story of research on Acanthostega
6. Ahlberg et al.2008 — Ventastega and the origin of the tetrapod body
7. Clack2006 — Acanthostega gunnari
8. Approximate size comparison — Genus guide and reconstruction of Acanthostega

Research questions

In what sequence did changes from fins to hands and feet occur? The head, shoulder, limbs, and respiratory structures are compared together. The discovery of eight digits shows that the past cannot be drawn simply from present-day body patterns.^[1][3]

Observation

After looking at the forefoot digits, examine the paddle-like limbs and deep tail. Remembering that it was an aquatic animal with legs reveals an appearance different from familiar terrestrial animals.^[1]