Water Bears, Beorn and Tolkien

Posted by John Blatchford Mar 12, 2009

The first fossil tardigrade was named after a character in one of J. R. R. Tolkien’s books.

Fossil in Amber

Beorn was a ‘skinshifter’ who could turn from human form into a bear. Kenneth W. Cooper found the first fossil tardigrade in amber from western Canada (Journal of Entomology 1964), and used Tolkien’s mythical creature’s name for the genus. The specific name (leggi) was chosen for one of Cooper’s students (William M. Legg) – although personally I wonder if he was also alluding to the eight stumpy legs!

Discovery of Tardigrades

Goeze (in 1773) was the first to describe a living Water Bear, although some people think that Anton van Leeuwenhoek was actually the first to see them. Leeuwenhoek took some dried dust and added distilled water – things came to life! (This sounds very much like tardigrades to me.)

DNA and RNA Studies

• Modern research (looking at sequences of DNA) suggests that the tardigrades are closely related to the arthropods, and also to a ‘sister phylum’ the Onychophora. This seems to fit well with the way they look – all are segmented, and the stumpy little legs look remarkably like those of the Onychophora and the ‘prolegs’ of caterpillars.

• Things get more confusing when RNA is studied – this seems to suggest that the tardigrades also share a relationship with the nematodes (roundworms), and not the annelids (segmented worms) as previously thought. It is true that the mouthparts of tardigrades are a bit ‘nematode-like’, but the fact that they are segmented makes them look like annelid allies. Further research is needed.

Family Trees

Modern animal classification tries to group animals in a way that shows evolutionary relationships, and it relies more and more on molecular research. Many zoologists are now pointing out that ‘lateral DNA and RNA transfer between species’ is known to occur on occasion (regularly in bacteria, and occasionally when a virus moves from one species to another) – and they urge caution when using molecular similarities to infer evolutionary relationships. Some have gone so far as to suggest that we should stop thinking in a ‘tree-like’ way and imagine ‘webs’ of relationships. (See ‘Mesozoan Orthonectids and Rhombozoans’ , which adds to this debate.)