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| Title | Outstanding features of a new Late Jurassic pachycormiform fish from the Kimmeridgian of Brunn, Germany and comments on current understanding of pachycormiforms |
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| Abstract | A new pachycormiform, †Orthocormus roeperi n. sp., is described from the upper Kimmeridgian of Brunn, Bavaria, Germany. The well-preserved specimen provides new information on features of the head, vertebral column and fins. The rostrodermethmoid bears a pair of straight, large paramedial teeth; the premaxilla is sutured with the rostrodermethmoid; there are small conical teeth on the upper jaw, a large tooth on the posterior part of the premaxilla, and both large and small teeth on the maxilla; the lower jaw carries large teeth anteriorly and smaller ones posteriorly; a dermosphenotic with a short anterior process forms only a portion of the complete dorsal margin of the orbit. The vertebral column is formed by a persistent notochord without chordacentra, but with well-developed, protruding arcocentra in the caudal region. The scythe-like pectoral fins possess rays with long bases, scarcely segmented, and finely branched distally; the characteristic Y-like branching pattern described for other pachycormiforms is apparently missing. The dorsal and anal fins present characteristic lateral expansions at their bases, possibly to facilitate water flow. The unpaired fins have numerous long and slender basal fulcra preceding the principal rays. There are more than 100 caudal rays, including 32 epaxial and 24 hypaxial principal rays. Large lateral processes are present on the lateral wall of the well-developed arch of the parhypural and on the hypural plate, suggesting the presence of a powerful hypochordal longitudinalis muscle. A protruding structure, named here the scaly caudal apparatus, covers laterally part of the hypural plate and the bases of the principal rays. This peculiar structure has not been previously reported in any pachycormiform. The scaly caudal apparatus, formed by large modified scales with a precise arrangement, is interpreted as an adaptation to fast swimming comparable to that of modern tunas and may occur in other pachycormiforms such as †Sauropsis as well. The results of a survey of other pachycormiforms as well as of the literature suggest that incomplete knowl- edge of pachycormiform morphology can be explained by incomplete and poor preservation of many specimens. There has been a tendency to generalize the presence of structures based on few taxa. The fish described here is the best-preserved pachycormiform from Bavaria, Germany, as well as from the Upper Jurassic worldwide. It presents previously unknown characters and also characters that contradict some previous assumptions. In- complete knowledge of most characters confounds the placement of Pachycormiformes within Neopterygii. |
| Author(s) | Gloria Arratia Hans-Peter Schultze |
| Pages | 87--120 |
| ISBN | 9783899371598 |
| http://www.pfeil-verlag.de/07pala/pdf/4_59d04.pdf | |
| SHA1 | d8e29d22dab5ef86d3c7bd4399b7223099fbd4d8 |
| Year | 2013 |
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