Furcacaudidae, the "'fork-tailed'

agnathan Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both living ( cyclostomes such as hagfishes and lampreys) and ext ...

s," is an extinct family of

thelodont Thelodonti (from Greek: "nipple teeth")Maisey, John G., Craig Chesek, and David Miller. Discovering fossil fishes. New York: Holt, 1996. is a class of extinct Palaeozoic jawless fishes with distinctive scales instead of large plates of armor. T ...

id agnathans from the

Lochkovian The Lochkovian is one of three faunal stages in the Early Devonian Epoch. It lasted from 419.2 ± 3.2 million years ago to 410.8 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian Stage. It is ...

stage of the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

epoch and

Wenlockian The Wenlock Epoch (sometimes referred to as the Wenlockian) is the second epoch of the Silurian. It is preceded by the Llandovery Epoch and followed by the Ludlow Epoch. Radiometric dates constrain the Wenlockian between and million years ago. ...

epoch of the

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

, known from fossils found in Northern Canada. It is the type family of the order

Furcacaudiformes Furcacaudiformes is an extinct order of jawless fish in the class Thelodonti. Because the paucity of intact fossils, especially since some families are known entirely from scale fossils, taxonomy of thelodonts is based primarily on scale morphol ...

, and itself currently includes 6 known species. It was officially described in 1998 by Mark V. H. Wilson and Michael W. Caldwell. A study in 2009 published by Wilson and Tiiu Märss moved members of Furcacaudiformes (and by extension Furcacaudidae) into a more basal position based on a more up-to-date data matrix, suggesting the divergence of Furcacaudidae from other thelodonts occurred earlier than previously theorized.

Phylogeny

According to Wilson and Märss' 2009 study, Furcacaudidae are more basal members of Furcacaudiformes, having diverged earlier than other members of the order. The following is a portion of the 2009 revised cladogram, demonstrating Furcacaudidae's position in relation to the order Furcacaudiformes.

Genera

''
Furcacauda ''Furcacauda'' is a genus of thelodontid agnathan from the Lower Devonian of Canada, and is the type genus of the order Furcacaudiformes Furcacaudiformes is an extinct order of jawless fish in the class Thelodonti. Because the paucity of int ...
''

''Furcacauda'', the type genus of the order

, includes two species, ''F. heintzae'' and ''F. fredholmae''. Fossils of the genus have been dated to the Lower Devonian. Its discovery and analysis gave rise to Wilson's and Caldwell's theory that stomachs evolved before jaws, based on sediment infillings found in fossils of ''F. heintzae''.

'' Canonia''

''Canonia'' was a part of the family Furcacaudidae, and the order Furcacaudiformes. It is the earliest discovered member of Furcacaudiformes, described in 1980 by palaeontologist Jutta Vieth. There are two species, ''C. costulata'' and ''C. grossi'', with the latter being the type species of the genus.Vieth, J., 1980: Thelodontier-, Acanthodier-, und Elasmobranchier- Schuppen aus dem Unter-Devon der kanadischen Arktis (Agnatha, Pisces). Göttinger Arbeiten zur Geologie und Paläontologie, 23: 1-69.

'' Cometicercus''

''Cometicercus'' was a member of the family Furcacaudidae that lived during the Early Devonian. It is only known from fragmentary fossilized remains of its caudal fin and parts of its dorsal surface, including its dorsal fin.

'' Sphenonectris''

''Sphenonectris'', like ''Cometicercus'', lived during the Early Devonian. Its body was hunched and pomacanthid-esque, almost resembling modern marine angelfish in its qualities. Like other Furcacaudids, its only visible fin was the caudal fin.

References

External links

* {{Taxonbar, from=Q21291104 Devonian jawless fish Thelodonti Prehistoric jawless fish families Early Devonian first appearances Early Devonian extinctions