Peter L. Forey

Conodont affinity and chordate phylogeny.

Current information on the conodonts Clydagnathus windsorensis (Globensky) and Promissum pulchrum Kovács‐ Endrödy, together with the latest interpretations of conodont hard tissues, are reviewed and it is concluded that sufficient evidence exists to justify interpretation of the conodonts on a chordate model. A new phylogenetic analysis is undertaken, consisting of 17 chordate taxa and 103 morphological, physiological and biochemical characters; conodonts are included as a primary taxon. Various experiments with character coding, taxon deletion and the use of constraint trees are carried out. We conclude that conodonts are cladistically more derived than either hagfishes or lampreys because they possess a mineralised dermal skeleton and that they are the most plesiomorphic member of the total group Gnathostomata. We discuss the evolution of the nervous and sensory systems and the skeleton in the context of our optimal phylogenetic tree. There appears to be no simple evolution of free to canal‐enclosed neuromasts; organised neuromasts within canals appear to have arisen at least three times from free neuromasts or neuromasts arranged within grooves. The mineralised vertebrate skeleton first appeared as odontodes of dentine or dentine plus enamel in the paraconodont/euconodont feeding apparatus. Bone appeared later, co‐ordinate with the development of a dermal skeleton, and it appears to have been primitively acellular. Atubular dentine is more primitive than tubular dentine. However, the subsequent distribution of the different types of dentine (e.g. mesodentine, orthodentine), suggests that these tissue types are homoplastic. The topology of relationships and known stratigraphic ranges of taxa in our phylogeny predict the existence of myxinoids and petromyzontids in the Cambrian.

Fossil fishes from the Cenomanian (Upper Cretaceous) of Namoura, Lebanon

Synopsis A new fish fauna is described from the middle Cenomanian of Namoura, Lebanon. Thirty species are described of which 13 are new. Six new genera are erected to contain seven of these new species. These new taxa include the teleosts Ctenodentelops striatus gen. et sp. nov. (Elopidae), Lebonichthys namourensis sp. nov. (Albulidae), Triplomystus noorae gen. et sp. nov. and Triplomys‐tus oligoscutatus gen. et sp. nov. (Paraclupeidae), Armigatus namourensis sp. nov. and Armigatus alticorpus sp. nov. (Clupeomorpha incertae sedis), Scombroclupea diminuta sp. nov. (Clupeiformes incertae sedis), Enchodus mecoanalis sp. nov. (Enchodontidae), Serrilepis prymnostrigos gen. et sp. nov. and Serrilepis minor gen. et sp. nov. (Halecidae), Paracentrus lebanonensis gen. et sp. nov. (Holocentroidea) and Gigapteryx lebanonensis gen. et sp. nov. (Euacanthopterygii incertae sedis). Two new species of the aspidorhynchid genus Belonostomus are recognised but left un‐named awaiting better material, as is one newspecies of pycnodont. Comparison of taxic composition of the faunas at Hakel, Hajula and Namoura suggests that at both species and generic level there is considerably more similarity between Hakel and Hajula than between either and Namoura. Furthermore, counts of actual specimens belonging to individual clades reveals a poverty of aulopiforms and myctophiforms at Namoura and may add to the evidence from non‐fish taxa that Namoura was much nearer to the contemporaneous land than was either Hakel or Hajula and may be of a slightly different age. Wider comparisons with other Cenomanian localities surrounding central Tethys suggest a phenetically closer relationship between Morocco, Lebanon and Slovenia than between any of these localities and Southeast England.

87Sr/86Sr, Na, F, Sr, and La in skeletal fish debris as a measure of the paleosalinity of fossil-fish habitats

Forty-six samples of apatite from lower vertebrates (ostracoderms, placoderms, elasmobranchs, actinopterygians, and crossopterygians), ranging in age from Silurian to Recent, were analyzed to determine each specimen9s 87 Sr/ 86 Sr isotopic ratio and content of the elements Na, F, Sr, and La. Our aim was to determine whether these chemical parameters can yield reliable information about the paleosalinity conditions of the ancient fish habitats. In recent times, the uniform 87 Sr/ 86 Sr isotopic ratio and Na, F, and Sr abundances of sea water in general differ characteristically from the corresponding ratios and abundances of fresh waters and low-saline brackish waters. For evaluation of the data on fossils, analyses were made on recent skeletal-fish apatite derived from different waters with known Sr-isotopic ratio and salinity. Salinity interpretations based on our chemical analyses are generally congruent with the salinity conditions indicated by other paleoenvironmental parameters inherent in the fossil-bearing strata. Some fossil specimens, however, gave signals seemingly incompatible with prevailing opinions regarding the environment in which the embedding strata formed. In some cases, the divergences could be accounted for by erratic occurrences of reworked material. Other cases, such as ostracoderm and placoderm remains from the Old Red Sandstone, are less easy to unravel. The method tested in this study may be a useful tool, clarifying, for example, salinity conditions during formation of various Old Red Sandstone deposits.

Latimeria: A Paradoxical Fish

The traditional view of the phylogenetic position of Latimeria is based on osteological details and states that coelacanths are derivatives of rhipidistians and hence are the nearest living relatives of tetrapods. However, recent studies of the soft anatomy ofLatimeria have highlighted many similarities with chondrichthyans. These similarities have led to the hypothesis that coelacanths are most closely related to cartilaginous fishes. The evidence for this hypothesis is questioned and the view that Latimeria is a bony fish is reaffirmed, with the suggestion that, among Recent fishes, it is the cousin of tetrapods.

Yet more reflections on agnathan-gnathostome relationships

ABSTRACT Evidence for two competing theories of relationships between Recent agnathans (hagfishes and lampreys) and gnathostomes is reviewed. The hypothesis that lampreys and gnathostomes are sister-groups is favored. The more obvious structures (fins, gill chambers, skeleton) seen in fossil agnathans are discussed and conclusions about their distribution are used in an attempt to include the fossil groups within a classification of Recent craniates. It is concluded that heterostracans are the sister-group of lampreys + gnathostomes; that anaspids are the sister-group of lampreys; and that galeaspids are the sister-group of osteostracans + gnathostomes.

Latimeria chalumnae and its pedigree

Latimeria is the product of a long coelacanth lineage, usually viewed as having changed very little. In this paper a classification of better known coelacanth genera is proposed based on a cladistic computer analysis of 56 morphological characters. Biometrical data are then matched with the classification to explore the possibility of identifying subtle change. It is concluded that throughout coelacanth history there have been changes in the structure of the vertebral column involving an overall increase in the number of vertebral elements, and a consequent crowding of these elements within the abdominal region. These changes may be associated with increasing lobation of the second dorsal and anal fins. In the skull, parameters involving the intracranial joint have also changed in such a way that the anterior part of the skull has lengthened in relation to the posterior part and this may be associated with an increase in length of the basicranial muscle.

Using ghost lineages to identify diversification events in the fossil record

Observed rises in taxic diversity could reflect bias of the fossil record or a genuine diversification. Here we outline a new method that attempts to differentiate between these two possible explanations. The method is based on the calculations of average ghost lineage duration through successive intervals of time. Biases due to variation in preservational conditions affect taxa independently from their position in the tree of life. A genuine radiation event will affect some parts of the tree of life more than others. During periods of rapid diversification, there will be a high proportion of new taxa showing short ghost lineages and therefore the average ghost lineage duration will drop as diversity rises, allowing us to distinguish such events from preservational bias during which ghost lineage duration remains unchanged. We test the method on Aptian–Maastrichtian (Cretaceous) ray-finned fish diversity. The result shows that a peak of diversity in the Cenomanian is associated with a drop in average ghost lineage duration, indicating that a genuine biological radiation occurred at that time.

Methods for Preparing Dry, Partially Articulated Skeletons of Osteichthyans, with Notes on Making Ridewood Dissections of the Cranial Skeleton

Abstract We describe methods for preparing dry skeletons of virtually any osteichthyan species with a well-ossified skeleton, including very large specimens (e.g., > 1 m Megalops atlanticus). Our approach differs from those conventionally used to prepare skeletons of tetrapods in that (1) fairly complete dissection of the specimen is required at the outset of processing; and (2) we use an alcohol dehydration step to rapidly dry the specimen. Similar techniques can be used to prepare well-calcified chondrichthyan skeletons. We also outline the steps for making Ridewood dissections of the skull. Dry, partially articulated skeletons prepared by these methods can be stored indefinitely in acid-free containers in an environmentally controlled space (21 C ± 3 C; Rh = 40% ± 5%) in pest-proof specimen cases. Although a truism of anatomical research is that you cannot learn everything from studying one specimen or one type of preparation, partially articulated dry skeletons are useful for research ranging from phylogenetic investigations to age and growth analyses to functional morphology, making them of great and lasting value to any collection.

A NEW COELACANTH FROM THE MIDDLE DEVONIAN OF LATVIA

Abstract We describe a new species of coelacanth, Miguashaia grossi sp. nov., recognized from isolated cranial, shoulder girdle bones and scales from the Upper Givetian Gauja and Lode Formations of two Latvian localities. This coelacanth, together with comparisons with other Devonian coelacanths, allows a more precise description of the plesiomorphic condition of the lower jaw, shoulder girdle, and palate. These plesiomorphic conditions are as follows. The dentary is shallow throughout, the articular-retroarticular is deep posteriorly where it is developed as two processes—one for the symplectic articulation and the other demarcating the posteroventral angle of the jaw. In the shoulder girdle plesiomorphic attributes include the large triangular clavicle, a cleithrum which is directed anterodorsally and possibly a large and polygonal extracleithrum. In the palate the pterygoid shows a dorsal process of unknown function mid-way along the dorsal margin and this is also a plesiomorphic feature of coelacanths.

Evolution of myosin filament arrangements in vertebrate skeletal muscle

A survey of skeletal muscles throughout craniates shows basic kinds of myosin filament arrangement, simple‐lattice and superlattice, within the A‐band of each sarcomere. Distribution of simple‐ and superlattice arrangements across a phylogeny of craniates suggests that the superlattice arrangement is primitive and that Amia and teleosts are derived in showing simple‐lattice arrangements. Two taxa examined (Scyliorhinus and Acipenser) show both lattice types within the same organism implying that there is not a simple evolutionary transformation of one to the other fiber arrangement. We discuss the possible functional significance of the different lattice types. We believe that the crossbridges may have greater competition for actin binding sites in simple‐lattice muscles compared to the superlattice types.