Birkenia elegans, a Silurian fish

Birkenia elegans Traquair 1898

    Upper Silurian

    Llandovery

    Birk Knowes

    Lesmahagow

    Scotland

    The Anaspida are classically regarded as the ancestors of lampreys. They were small marine agnathans (Greek, "no jaws") that lacked paired fins and often scales. They first appeared in the early Silurian and flourished until the late Devonian. Birkenia was a derived form of anapsid that grew to a maximum length of about 10cm. The Anaspids were simple dorso-laterally compressed fish that probably led a bottom-dwelling existence. It was adepted for aktive swimming and had a sucking mouth that was terminal rather than ventral. Birkenia has a characteristic row of anterior and posterior pointing dorsal scales. The gills opened as a row of holes along the side of the animal, typically numbering from 6-15. The tail is hypocercal which means that the lower lob is the longest. Traquair reconstructed Birkenia upside down because he never met this condition in a fish before.

    Many important collections of Silurian arthropods and vertebrates have been made near Lesmahagow since the mid to late 1800's. The Lesmahagow Inlier is a block of Silurian sediments surrounded by sediments of Carboniferous age. The inlier consists of shales and sandstones with occasional pebble conglomerates of a lagoon or lake. The sediments are thought to be of Llandovery (Silurian) age. This fish is from Birk Knowes SSSI (Site of Special Scientific Interest), now off-limits to all collecting due to overzealous collecting.

    Henry C. Stetson, A Restoration of the Anaspid Birkenia elegans Traquair.

    The Journal of Geology, Vol. 36, No. 5 (Jul. - Aug., 1928), pp. 458-470