The Oxford University Museum of Natural History is a wonderful place to visit.  There are some remarkable fossils on display.  Amongst the dinosaurs, giant birds and mammals there are some smaller tetrapods to marvel.  For example, during a visit to Oxford, a team member took a photograph of a beautiful Acanthostega gunnari replica on display at the museum.  The model shows a four-legged animal with a wide tail to help propel it through water. The mouth is large and lined with small, sharp teeth.  The eyes are located on top of the head.  Described as a stem tetrapod, Acanthostega evolved from lobe-finned fishes (Sarcopterygii).  It lived in freshwater swamps during the Late Devonian (365 million years ago).

A beautiful model of the Late Devonian stem tetrapod Acanthostega gunnari. This life-size model is on display at the Oxford University Museum of Natural History. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Acanthostega gunnari

The fossilised remains of this sixty-centimetre-long animal indicate that it spent most of its life in water. Although it had limbs, the front limbs were relatively immobile and therefore not capable of being positioned under the body to support the weight of the animal on land. Palaeontologists believe A. gunnari held its limbs out to the side and paddled along. The limbs would also have helped this aquatic animal push its way through dense water weeds.

It was formally named and described in 1952 by the Swedish palaeontologist and prehistoric fish expert Erik Jarvik.  The first fossilised remains of this creature were discovered in the 1930s.  However, it was the 1987 specimen found in East Greenland by a field team headed by Jenny Clack that led to the significance of this taxon being realised.

Researchers were able to identify key anatomical developments that would permit the descendants of these stem tetrapods to become fully adapted to a terrestrial existence. For example, Acanthostega had primitive lungs for breathing air as well as internal gills. In addition, it is the earliest stem-tetrapod to show the shift in locomotory dominance away from the upper part of the body (pectoral girdle) to the pelvic girdle.

Studying the Limbs

It is now known that most stem tetrapods such as Acanthostega and Ichthyostega and more than five digits associated with the manus and pes.  For example, Acanthostega had eight digits on each hand (manus).   The number of digits on each foot is uncertain, but more than five has been suggested.  It had been thought that pentadactyly (five digits associated with the end of each limb), was an ancestral trait of the Tetrapoda. The feet and hands of Acanthostega were webbed.

A close view of the pes of Acanthostega gunnari. Scientists know that this stem tetrapod had eight digits on the manus (hand). However, the number of digits on the pes (foot) remains unknown. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Mike from Everything Dinosaur commented:

“The beautiful Acanthostega replica is displayed next to Devonian fish fossils and early tetrapod specimens.  It helps visitors to visualise how the first land animals evolved from fish.”

It certainly is a fantastic, life-size replica.  We congratulate the design team and the artist who made this model.

The Everything Dinosaur website: Prehistoric Animal Models.