Halecostomi

Abstract: The Recent bowfin, Amia calva, is a primitive neopterygian fish distinguished by a very long dorsal fin, a posteriorly rounded, hemicercal caudal fin with epaxial fin-rays, “amiid” scales, uniquely ossified centra that are diplospondylous in the caudal region, a double articulation (quadrate and symplectic) with the lower jaw, loss of suborbitals, and other characters. Of the cited characters, the hemicercal caudal fin is primitive for neopterygians; the double articulation of the lower jaw is a derived feature for all Halecomorphi; diplospondylous vertebrae are derived within the Amiidae; and expaxial caudal fin-rays, the loss of suborbitals, and the loss of the endoskeletal basipterygoid process are acquired in parallel by amiids and teleosts. Many additional characters unite amiids with teleosts and certain other neopterygians in the Halecostomi (see Chapter 16, Fig. 2).

Abstract: An overview is presented of the actinopterygian fishes from the Late Jurassic (Late Kimmeridgian and Early Tithonian) ‘Plattenkalke’ near Solnhofen (Solnhofen lithographic limestone), Bavaria, Germany. The fish fauna is very diverse, with the palaeonisciform Coccolepis, halecostomes such as Lepidotes, Heterostrophus, three genera of macrosemiids and six genera of pycnodontiforms, halecomorphs including two genera of caturids, two genera of amiids, Ophiopsis, ‘Furo’, Ionoscopus, Brachyichthys, Callopterus, Liodesmus, ?Lophiurus, five genera of pachycormids, three genera of pholidophorids, Pleuropholis, two genera of aspidorhynchids and eleven genera of basal teleosts. Although several groups have been subject of revision, most of the fauna remains poorly known. Study of this rich fauna will provide a lot of information on the phylogeny and interrelationships of halecostome fishes.

Abstract: One of the main pending, unsolved problems concerning the study of the pycnodont fishes is their phylogenetic relationships with other major actinopterygian groups. The Pycnodontiformes have often been proposed as the sister group of the Telostei or the Teleosteomorpha. The first extensive cladistic analysis on pycnodont relationships is hereby attempted by coding Pycnodontiformes into a previously existing data matrix with major neopterygian groups: Lepisosteiformes, Semionotiformes, Macrosemiiformes, Halecomorphi, and Teleostei. This analysis has resulted on the Pycnodontiformes having an unexpected position as the most basal Neopterygii among the groups included. Therefore, pycnodonts are not the sister-group of teleosteans, and they are not holosteans either. The phylogenetic relationships and the definition of the Holostei and the Gynglimodi are not affected by the inclusion of the Pycnodontiformes, but the basal position of the latter among Neopterygii may affect the definition of this traditional major actinopterygian group. A collateral consequence of these results is that the Halecostomi can be re-defined as the clade formed by [Holostei + Teleostei]. The phylogenetic relationships of pycnodonts should, consequently, be solved among basal neopterygian groups, mostly from the Triassic, as well as relevant non-neopterygian actinopterygians in order to confirm the neopterygian affinities of the Pycnodontiformes and to verify the definition and diagnosis of the Neopterygii and the Halecostomi.