THE FURCACAUDIFORMES - A NEW ORDER OF JAWLESS VERTEBRATES WITH THELODONT SCALES, BASED ON ARTICULATED SILURIAN AND DEVONIAN FOSSILS FROM NORTHERN CANADA

A new order of ''fork-tailed'' agnathans (jawless vertebrates). the Fu rcacaudiformes, is described from Wenlockian (Silurian) and Lochkovian (Devonian) fossils from the Northwest Territories of Canada. Six new species are classified in five new genera and two new families. One Si lurian species is in the genus Pezopallichthys, family Pezopallichthyi dae, One Devonian species is described in each of the genera Cometicer cus, Drepanolepis, and Sphenonectris. The Devonian genus Furcacauda in cludes two species, one new and another that was previously described as Sigurdia heintzae Dineley and Loeffler. Preliminary phylogenetic an alysis suggests the following relationships within Furcacaudiformes: ( Pezopallichthys (Cometicercus (Drepanolepis (Sphenonectris (Furcacauda )))). Furcacaudiforms resemble some previously described thelodonts in structure of their scales, which are of loganellid and nikoliviid typ es, but differ in having generally smaller scales, as well as in havin g laterally compressed. hump-backed bodies, large eyes, branchial open ings in an oblique. condensed row. a prominent anal notch, and large, nearly symmetrical, forked and lobed tails. The distinctive tail may i ndicate a close relationship with Heterostraci. A large, barrel-shaped stomach-like chamber dominates the gut and is connected to the anal o pening by a short, tapered intestine. Several Devonian species possess paired, ventral 'fin-flaps' and/or a dorsal Bn: these structures are not universally present and may have been secondarily lost in some lin eages.