Walrus of the Norwich Crag: Alachtherium cretsii

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Alister Cruickshanks (UK)

The Norwich Crag at Easton Bavents, Southwold in Suffolk is one of the only locations where mammalian remains from the Pleistocene Epoch can be found, in situ, at an accessible location in the UK. The Norwich Crag splits the Antian and the Baventian. At Easton Bavents South Cliff, the Norwich Crag Shell Bed is missing. Instead, there is a fine gravel layer with laminated clay and sand, which yields occasional remains. This bed is equivalent to the Lower Shell Bed of the North cliff at Easton Bavents, One of the latest theories suggests that this was once a pre-historic fast flowing river, which flowed into a larger estuary that was present at the North Cliff during the Pliocene Era.

The North Cliff itself has a stone layer above the Norwich Crag Shell Bed. This bed comprises three main bands: the upper, middle and lower beds, but varies considerably along this stretch of cliff. The Norwich Crag Stone bed is directly below the Baventian Clay, both of which are from the Baventian stage which is 1.55 to 1.6 million years old, from the Pliocene Era. The Norwich Crag Shell Bed is Antian in age, which is 1.6 to 1.7 million years old.

Fig. 1. Fine gravel layer with laminated clay and sand.

A complete lower mandible of a walrus was discovered in situ after high tides during 1993, by my father and me. At this time, the specimen could not be fully identified and spent ten years at Norwich Castle Museum, while experts sought professional knowledge from abroad. The mandible was found in the Gravel Bed, which is Baventian in age.

Fig. 2. The walrus jaw.

During this period of identification, one of the most confusing aspects of the find was that the canines differed from other walrus specimens found at this latitude. Odobenus rosmarus, the same walrus that is around today, can be found in the North Sea and has previously been used to formally identify other walrus specimens found at Easton Bavents and other Norwich Crag.

Fig. 3. Walrus vertebra.

It was Dr Kohno of Japan who first highlighted the importance of this find and the unusual differences with other Odobenus rosmarus mandible specimens. Klaas Post from The Natural Museum of Rotterdam (Netherlands) then formally identified it and said that the canine teeth are very typical of Alachtherium cretsii.

Fig. 4. Walrus tibia.

Other canine teeth held at the Ipswich Museum (also from Easton Bavents) and other walrus specimens in other UK museums have been incorrectly identified as Odobenus rosmarus and can now be re-identified as Alachtherium cretsii. Before being formally identified in 2003, Alachtherium cretsii was previously only believed to come as far north and as far east as Spain. This discovery therefore proves that the distribution of this species was much further to the north and east than previously suggested. The lower jaw is also the most complete specimen to have been found from this species.

Fig. 5. Map of walrus (Alachtherium cresii) distribution.

During the identification process, Klaas came over to examine the rest of the Cruickshanks’ collection and identified many other bones from Alachtherium cretsii, along with some other extremely interesting specimens, such as the most complete antler of Eucladocerous falconeri and a possible new species of orca (killer whale).

The discoveries of further remains of Alachtherium cretsii shows that this animal was quite active during the early Pliocene around this area. This unique find will enable further research into the life of this walrus. Therefore, because of the unique importance of our find, we donated the walrus jaw specimen to Norwich Castle Museum and it is currently on display there.

Fig. 6. A very young-looking Alister, Technical Controller of Deposits, and his father, Ian Cruickshanks at Easton Bavents.

Further reading

Vlees op de Botten Van Alachtherium cretsii, de Pliocene walrus van de Noordzee. by Klaas Post, Natuurmuseum Rotterdam

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