Archeognathus

Archeognathus; Temporal range: Mid Ordovician PreꞒ Ꞓ O S D C P T J K Pg N
	Articulated Archeognathus primus fossils from the Winneshiek Shale of Iowa
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Conodonta
Family:	†Archeognathidae
Genus:	†Archeognathus; Cullison, 1938
Species
	A. primus Cullison, 1938 (type) ; A. carinatus Cullison, 1938 ;
Synonyms
	Coleodus

Archeognathus is a fossilized jaw apparatus of a large predatory conodont^[2] from the Ordovician period (Darriwilian to Sandbian stages). Its large size has made classification difficult, and it has historically been compared to conodonts and gnathostomes (jawed fish) since its remains were first discovered in Missouri.^[3] Complete articulated jaw apparatus of Archeognathus primus are common in the Winneshiek Shale lagerstätte of Iowa, allowing its identity as a conodont to be secured.^[2]

The jaw apparatus of Archeognathus primus is much more simple than that of most conodonts, with only six elements in its jaw. These include a pair of long, small-toothed, sawblade-like "coleodiform" S elements at the front of the jaw, followed by two pairs of smaller "archeognathiform" P elements with large teeth. The S elements are indistinguishable from those of many species of Coleodus, a wastebasket taxon of Ordovician conodonts. This strongly suggests that most specimens referred to Coleodus actually belong to Archeognathus.^[4]^[2]

References

^ Cullison, J. S. (1938). "Dutchtown Fauna of Southeastern Missouri". Journal of Paleontology. 12 (3): 219–228. JSTOR 1298590.
^ ^a ^b ^c Liu, Huaibao P.; Bergström, Stig M.; Witzke, Brian J.; Briggs, Derek E. G.; McKay, Robert M.; Ferretti, Annalisa (2017-05-01). "Exceptionally preserved conodont apparatuses with giant elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA". Journal of Paleontology. 91 (3): 493–511. doi:10.1017/jpa.2016.155. ISSN 0022-3360.
^ Klapper, G.; Bergström, S. M. (1984). "The Enigmatic Middle Ordovician Fossil Archeognathus and Its Relations to Conodonts and Vertebrates". Journal of Paleontology. 58 (4): 949–976. JSTOR 1304860.
^ Liu, H. P.; McKay, R. M.; Young, J. N.; Witzke, B. J.; McVey, K. J.; Liu, X. (2006). "A new Lagerstätte from the Middle Ordovician St. Peter Formation in northeast Iowa, USA". Geology. 34 (11): 969. Bibcode:2006Geo....34..969L. doi:10.1130/G22911A.1.

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[1] Cullison, J. S. (1938). "Dutchtown Fauna of Southeastern Missouri". Journal of Paleontology. 12 (3): 219–228. JSTOR 1298590.

[conodonts-2] Liu, Huaibao P.; Bergström, Stig M.; Witzke, Brian J.; Briggs, Derek E. G.; McKay, Robert M.; Ferretti, Annalisa (2017-05-01). "Exceptionally preserved conodont apparatuses with giant elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA". Journal of Paleontology. 91 (3): 493–511. doi:10.1017/jpa.2016.155. ISSN 0022-3360.

[3] Klapper, G.; Bergström, S. M. (1984). "The Enigmatic Middle Ordovician Fossil Archeognathus and Its Relations to Conodonts and Vertebrates". Journal of Paleontology. 58 (4): 949–976. JSTOR 1304860.

[4] Liu, H. P.; McKay, R. M.; Young, J. N.; Witzke, B. J.; McVey, K. J.; Liu, X. (2006). "A new Lagerstätte from the Middle Ordovician St. Peter Formation in northeast Iowa, USA". Geology. 34 (11): 969. Bibcode:2006Geo....34..969L. doi:10.1130/G22911A.1.

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