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For the first time, a dipnoan tooth plate is described from the Lower Cretaceous (Kiowa Formation) of Kansas. The pterygoid tooth plate is referred to Ceratodus frazieri Ostrom, 1970. The histology shows anomalies in the formation of the tooth plate, osteodentine occurring within petrodentine. Ceratodus is an additional indication of freshwater influence in the marine Kiowa Formation deposits. Fossil vertebrates have been collected in Cretaceous rocks of western Kansas by members of the University of Kansas and parties of many other universities and museums during more than 100 years. The marine Niobrara Chalk, Upper Cretaceous, is the formation preferred by many for collecting. Fossil vertebrates are scarce and not as well preserved in the more terrestrially influenced Lower Cretaceous. The upper unit of the Lower Cretaceous in this area, the Dakota Formation, is known for its plant content, and has yielded very few vertebrate remains. The armoured dinosaur Silvisaurus (Eaton, 1960) indicates terrestrial environment, the crocodile Dakotasuchus and tracks referred questionably to crocodiles (Vaughn, 1956) indicates coastal environment, and one known plesiosaur (Sternberg Memorial Museum, Hays, Kansas) signifies a marine environment for the Dakota Formation. The present interpretation of the depositional environment of the Dakota Formation is that of a coastal plain with low relief in central Kansas and a shallow, epicontinental sea in western and southern Kansas (Scott, 1970). The Kiowa Formation underlies the Dakota Formation, but both formations may interdigitate at their boundary. The fossil remains, invertebrates and most vertebrates (all partial: plesiosaurs, selachians, and actinopterygians, Scott, 1970: Table I), indicate a marine environment for the Kiowa Formation. M. Williams, a former student at the University of Kansas, found one lungfish tooth plate (KUVP 16262 mentioned by Chorn, 1977) in the Kiowa Formation in Clark County, Kansas, 1969. Lungfish tooth plates in late Mesozoic and Cenozoic deposits are normally interpreted as an indicator of This content downloaded from 157.55.39.217 on Mon, 18 Apr 2016 07:45:17 UTC All use subject to http://about.jstor.org/terms 188 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCES freshwater. They are found together with dinosaur remains, goniopholid crocodiles and turtles in the Lower Cretaceous, Aptian-Albian, Cloverly Formation of Wyoming (Ostrom, 1970), Paluxy Formation of the Trinity Division of Texas (Thurmond, 1974), and in the Lower Cretaceous, AptianAlbian, of Northern Africa (Tabaste, 1963; Taquet, 1970; Broin, Grenot and Vernet, 1971). These indicators of terrestrial conditions (very few dinosaur remains, goniopholid crocodiles, and carapace remains of presumably baenoid turtles) are also known from the Kiowa Formation (Scott, 1970: Table 1). These remains, together with the lungfish tooth plate, must be interpreted as allochthonous within the marine community; they have drifted in from a not too distant shore. Since Agassiz (1833-44), isolated ceratodontid tooth plates of Mesozoic and Tertiary age have been referred to the genus Ceratodus, although it is known that the tooth plates do not reflect generic differences (Peyer, 1918). Skull roofs of Mesozoic lungfishes with ceratodontid tooth plates are so distinct from each other that they have been referred to new genera (Paraceratodus Lehman, Chateau, Laurain and Nauche, 1959; Asiatoceratodus Vorobyeva, 1967; Tellerodus Lehman, 1976; Arganodus Martin, 1979). All these genera have ceratodontid tooth plates with sharp-crested ridges, while no skull roof with flat tooth plates as in the type species Ceratodus latissimus Agassiz 1838 has yet been described. Even Ceratodus is a form genus for Mesozoic and Tertiary tooth plates; it is at present the best way to determine ceratodontid tooth plates which are not associated with skull roof material. In the Lower Cretaceous, flat ceratodontid tooth plates and ceratodontid tooth plates with sharp-crested ridges occur together in the Lower Cretaceous of Northern Africa (Tabaste, 1963; Martin, 1979). In the Lower Cretaceous of North America, only two flat ceratodontid tooth plates are known, one from the Cloverly Formation, Wyoming (C. frazieri Ostrom, 1970) and a partial one from the Morrison Formation, Wyoming (C. robustus Knight, 1898). All other North American ceratodontid tooth plates (C. guentheri, C. americanus) of Lower Cretaceous age have sharp-crested ridges and are therefore not comparable to the Kiowa tooth plate. Recently, many papers on the histology of lungfish tooth plates have been published (Denison, 1974; Smith, 1979; Kemp, 1979; and others). The authors differ in their terminology of the hard tissue, and the terminology of Smith (1979) is used here. Tabaste (1963) described and figured a special tissue as "tissue osteoide" which forms small grooves on the surface of the tooth plates. There exists no agreement on the nature of this tissue, therefore lungfish tooth plates from the Lower Cretaceous of Africa are investigated here for clarification and as comparison with similar structure on the Kiowa tooth plate. This content downloaded from 157.55.39.217 on Mon, 18 Apr 2016 07:45:17 UTC All use subject to http://about.jstor.org/terms VOLUME 84, NUMBER 4 189 Ceratodus frazieri Ostrom, 1970 Holotype. Left prearticular tooth plate YPM 5276 (Peabody Museum, Yale University). Horizon/Locality. Cloverly Formation, Albian, Lower Cretaceous/approximately 75 m southeast of Princeton University locality 49-1; NW 14 Sec. 34, T58N, R75W, Big Horn County, Wyoming. Diagnosis. (Ostrom, 1970, p. 54) "Dental plate very large, broad and thin with four broad and apparently non-tuberculated radial ridges. The ridges are not sharp crested distally as in C. guentheri, nor do they extend to the medial margin of the plate. Externally, these ridges end in broad projections separated by shallow notches. Anterior ridge, the largest, ends in the longest distal projection. Posterior ridge very faint, terminates distally in a very slight lateral projection. These radial ridges so subdued, apparently by excessive wear, that the typical ceratodontid radiation pattern is not clear, except near the external margin. Internal margin broadly rounded and not angled as in most other ceratodontids." Material from Kansas. One right pterygoid tooth plate with part of the pterygoid (KUVP 16262, Museum of Natural History, Lawrence, Kansas) from 6 miles north of Sitka (near the center of Sec. 18, T32S, R21W, Clark County, Kansas)/Kiowa Formation, Lower Cretaceous. Description. The large tooth plate (maximal width 32 mm, maximal length approximately 60 mm or more; greatest thickness 6.5 mm) is attached to the partially preserved pterygoid bone. The surface of the tooth plate shows irregularly arranged circular fields (Fig. la) reflecting a change in tooth histology (see below). The tissue forming the boundary of the circular fields is softer than the surrounding tissue so that narrow furrows are formed. Small pits on the ventral surface (Fig. ib: right side) correspond to the circular fields on the occlusal surface. There are two possible explanations for these pits: the hard tissue was not mineralized or it was so soft that it has been eroded away. The tooth plate is flat. Four low ridges occur near the buccal margin only, and a fifth ridge is weakly developed. The valleys between the ridges are very shallow, nearly undifferentiated from the main occlusal surface. The first ridge-as far as can be judged from the preserved portion-extends nearly parallel to the medial margin and forms an angle of 450 to the second ridge. The crests of the following 3 ridges are parallel to each other, and the fifth very shallow ridge is oblique to the fourth. The medial margin forms an obtuse angle with the lingual margin, and the lingual margin with the posterior one. The medial and posterior margins include an angle of about 900. The inner surface of the tooth plate is nearly planar so that the thickness of the plate varies, being thicker below the ridges. This content downloaded from 157.55.39.217 on Mon, 18 Apr 2016 07:45:17 UTC All use subject to http://about.jstor.org/terms 190 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCES |
