A fossil record of lampreys has previously been unknown. A new genus demonstrates the presence of this group in the Pennsylvanian. The body outline, parts of the head skeleton, rasping tongue mechanism, gill basket, and other internal organs are preserved. The fossils are very similar in structure to modern forms. The absence of hagfish characters in the fossil supports the view that the common ancestor of lampreys and hagfishes lived prior to the Pennsylvanian.
An entirely new group of Pennsylvanian fishes, belonging to the class Chondrichthyes, is described and their comparative anatomical and phylogenetic relations are discussed.Seven species belonging to five genera are distinguished and placed within the subclass Holocephali as a separate order, Iniopterygia. The iniopterygians are structural, but not phyletic, intermediates between the chimaeroids (as here denned) and the elasmobranchs. Present analysis permits the notion that the holocephalians and the elasmobranchs are sister groups sharing a common ancestor that never possessed a bony dermal armor but an even spread of lepidomorial denticles over the entire skin and the stomodaeum. Iniopterygians and chimaeroids, in turn, appear to be sister groups having evolved from a common ancestor that combined an autostylic jaw suspension with a generalized shark-like dentition.Iniopterygians are presently known only from carbonaceous, sheety shales of the Pennsylvanian basin complex of central North America. IX Logan Quarry PF6661, cf , LQS level J, articulated skeleton, lacking tail fin (XR: LQ237) PF6660, cf , LQS level J, isolated pectoral clasper hooks XR: LQ228)Hajji Hollow PF6587, cf, partly articulated skeleton, incomplete (XR: HH5) Characterization. -Anterior finrays of pectoral fins in males much enlarged and provided with a single file of about 13 fishhook-shaped denticles, diminishing in size distad. Description. -The largest skeletons (i.e., PF6678 or PF6645) are between 30 and 35 cm. in overall length. U.N.S.M. = University of Nebraska State Museum. "XR=X ray plate.
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