. Bulletin of the British Museum (Natural History) Geology Supplement. 92 nsppu2 ELOPIFORM FISHES ep1-3 un 7. Fig. 45. Pachythrissops laevis Woodward. Caudal skeleton in left lateral view, on 40333 (holotype) and Based Allothrissops and Thrissops, however, have retained the Leptolepis coryphaenoides type. Instead of the fifth uroneural remaining short, this and succeeding uroneurals extend basally to lie lateral to the preural and ural centra. Concomitant with this development the anterior uroneurals tend to extend forward and in the Cretaceous ichthyodectids, which also show
. Bulletin of the British Museum (Natural History) Geology Supplement. 92 nsppu2 ELOPIFORM FISHES ep1-3 un 7. Fig. 45. Pachythrissops laevis Woodward. Caudal skeleton in left lateral view, on 40333 (holotype) and Based Allothrissops and Thrissops, however, have retained the Leptolepis coryphaenoides type. Instead of the fifth uroneural remaining short, this and succeeding uroneurals extend basally to lie lateral to the preural and ural centra. Concomitant with this development the anterior uroneurals tend to extend forward and in the Cretaceous ichthyodectids, which also show at least five elongate uroneurals, the anterior members of the series extend as far forwards as the fourth preural centrum. The development of this unique uroneural arrangement is probably correlated with greater rigidity in the tail. The body form of the ichthyodectids suggests fast swimming fishes. The caudal fin is very deeply forked with the caudal fin-rays crossing the hypurals at a steep angle and those of the upper lobe lying in line with the uroneurals. In the Cretaceous ichthyodectids, and to a lesser degree in Allo- thrissops and Thrissops, various degrees of hypurostegy are shown. Hypurostegy is by no means confined to the ichthyodectids but is found in several groups of higher teleosts, Scombridae, yet the combination of this feature with the uroneural development is unique. The caudal skeleton of Pachythrissops is virtually identical with that of Leptolepis dubia in showing two distinct series of uroneurals, the anterior group consisting of four uroneurals and the posterior of three. To derive an Allothrissops- and Thrissops- like caudal skeleton from the Pachythrissops type a simplification of the uroneural. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History).
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