Cécile Poplin

The rhadinichthyids (paleoniscoid actinopterygians) from the Bear Gulch Limestone of Montana (USA, Lower Carboniferous)

ABSTRACT Three new fusiform Namurian paleoniscoids are described: Wendyichthys dicksoni, gen. et sp. nov., Wendyichthys lautreci, sp. nov. and Cyranorhis bergeraci, gen. et sp. nov. Their most unique features consist of their snout anatomy (with a rostropostrostral, reverse-L shaped antorbitals, a rostral notch, and the lack of premaxillaries) and the presence of extralateral gulars in addition to normal median and lateral gulars. These supplementary gulars and the rostral notch were probably mechanical adaptations for a greater widening of the mouth cavity during abduction of the mandible: as a result these fishes probably fed by suction, either at the bottom of the water column or by intake of floating nutritive particles. Prior to a phylogenetic analysis of the relationships of these and other Bear Gulch actinopterygians, these three new taxa are placed into the Rhadinichthyidae. A revised definition of this family, including new features recognized during this study, is given after a reappraisal of th...

TWO NEW DEEP-BODIED PALAEONISCOID ACTINOPTERYGIANS FROM BEAR GULCH (MONTANA, USA, LOWER CARBONIFEROUS)

Abstract Two new species of deep-bodied Paleozoic actinopterygians, Aesopichthys erinaceus gen. nov., sp. nov. and Proceramala montanensis gen. nov., sp. nov., are described from the Upper Chesterian, Upper Mississippian (Namurian E2b, Lower Carboniferous) Bear Gulch Limestone of Montana, USA, and the new family Aesopichthyidae is erected for them. These two fishes share features usually associated with deep body and deep head specializations, particularly in Palaeoniscimorpha, such as a shortened gape, tall maxilla, vertical suspensorium, deepened flank scales and an elongate dorsal fin. Aesopichthys in particular, for which more complete information is known, also possessed a suite of very specialized adaptations in feeding mechanism, ganoine sculpturing, fin form, and cranial defensive structures that have strong ethological implications. These features include small mobile premaxillae, a spinous and apparently rotatable posteroventral infraorbital, lobed pectoral base, and partially webbed pectoral, dorsal, anal and caudal fins. Within a general scheme of interrelationships of primitive actinopterygians, these two new taxa pertain to Palaeoniscimorpha, i.e., basal Actinopteri. Then, from a cladistic analysis limited, beside these two new taxa, to Wendyichthys and Cyranorhis (two other already described actinopterygians from Bear Gulch), Platysomus, and Cheirolepis, it appears that the Aesopichthyidae display no close relationship to the Platysomidae but should be the sister group of the Rhadinichthyid-group i.e., [Cyranorhis + [Rhadinichthyidae + Wendyichthys]].

The Braincase Anatomy of Lawrenciella schaefferi, Actinopterygian from the Upper Carboniferous of Kansas (USA)

Abstract A full description and diagnosis are given of Lawrenciella schaefferi Poplin 1984, from the Pennsylvanian (Late Carboniferous) of Kansas, U.S.A. This taxon is only known by braincases and associated parasphenoids, which are exceptionally well preserved as phosphatic nodules. The external and internal morphology of the endocrania were studied from serial sectionings which allowed detailed three-dimensional reconstructions. The study shows that, besides synapomorphies inherent to basal actinopterans, L. schaefferi displays a set of very peculiar features such as prespiracular fossae, intracranial ossicles, and paired anterior myodomes for nonocular eye muscles. Another conspicuous feature, the notochordal canal ending blindly anteriorly, has been observed until now only in more advanced Triassic actinopterans. The anatomical characters of L. schaefferi indicate, in the light of recent cladistic analyses, that this Carboniferous taxon is a relatively advanced actinopteran compared to basal forms such as Kentuckia, Mimia, or Moythomasia.

CLADISTIC ANALYSIS OF THE RELATIONSHIPS OF THE TARRASIIDS (LOWER CARBONIFEROUS ACTINOPTERYGIANS)

Abstract Revised diagnoses of the family Tarrasiidae and of Tarrasius (Visean of Scotland) and Paratarrasius (Namurian of North America) are presented. These are used in a phylogenetic analysis also comprising one theoretical outgroup, three sarcopterygians as part of the outgroup, and eleven Palaeozoic, Triassic, and Recent actinopterygians, and based on a matrix of 75 characters of head and body. The results are that: (1) Polypterus is the sister group of the other Actinopterygii (=Actinopteri); (2) the analysed Actinopteri are a monophyletic group (Palaeoniscimorpha); and (3) Tarrasiids are monophyletic and are the sister group of the other analysed Actinopteri. This scheme supports the most recent studies in indicating that Tarrasiidae are close to stem actinopterygians.

Fish diversity of the Bear Gulch Limestone, Namurian, Lower Carboniferous of Montana, USA

Quarrying operations for fossil fish from the Bear Gulch Limestone (Heath Formation, Namurian, Montana, USA) have occurred from 1968 to 1997 and continue. The Bear Gulch Limestone lens (14 x 9 km) thins to a shore line on all edges except the buried eastern boundary, and contains an entirely marine flora and fauna. Eighty outcrops have been sampled, and 4 547 identifiable fish of 113 taxa have been recorded. This study details aspects of the diversity and distribution of the fishes of the Bear Gulch Bay analyzed on the basis of geographic areas, following facies and sedimentary criteria. The total diversity of the fish fauna is 21.08 (Simpson index) and 12.07 (Margalef index). Diversity decreases from east to west and towards the southern margin. These trends mask dramatic differences in species occurrences and dominant species in each area. The high diversity of the Depocenter area can be accounted for by its proximity to the mouth of the bay and access to the epicontinental seaway to the east. The southeast region is comprised of the Blacktail, Allen, and Buchek areas. Diversity declines greatly from the algae - and sponge - rich Blacktail area southwestward to the marginal Buchek area. This region contains several dominant species that are adapted to lurk in or maneuver among plants, feed from the bottom, or burrow. High numbers of larval paleoniscoids and the coelacanth Caridosuctor lower the diversity of the near-shore North Shore area. The western end of the bay is dominated by Acanthodes, scales of Listracanthus and Strepsodus, and large cladodont sharks. Fish distributions, preliminary assessments of morphological adaptations, and facies all support the concept of a heterogeneous set of habitats within this fossil bay.

Un Myxinoı̈de (Craniata, Hyperotreti) dans le Konservat-Lagerstätte Carbonifère supérieur de Montceau-les-Mines (Allier, France)

Abstract Several fossils from the Late Carboniferous of Montceau-les-Mines, France, are referred to a new taxon of fossil hagfish. Two specimens display impressions of two pairs of tooth rows that are strikingly similar in shape and organization to the horny teeth of modern hagfish. In addition, by its slender body shape, this new taxon is more suggestive of modern hagfish than the only previously known fossil form from the Carboniferous of the USA. Living hagfish being exclusively marine, this discovery raises the question of the reputedly freshwater environment of the Montceau-les-Mines ‘Konservat-Lagerstatte’.

Preliminary analysis of theinterrelationships of some paleozoic actinopterygii

Abstract A cladistic analysis of 20 actinopterygian species; including several new taxa from the Lower Carboniferous Bear Gulch Limestone of Montana; USA; is presented. This analysis is based upon 74 dermal cranial and shoulder girdle characteristics. The results strongly support several classical groupings such as that of Paleoniscimorpha. On the basis of these cranial data; there is some relationships between Rhadinichthys canobiensis and two of the Bear Gulch actinopterygians; all characterized by the lack of premaxillae. This analysis will later be expanded with other characters such as postcranial ones.

Le genre Bourbonnella (Actinopterygii, Aeduellidae) : révision et description d'une nouvelle espèce du Stéphanien (Carbonifère supérieur) de Montceau-les-Mines (Massif Central, France)

The genus Bourbonnella (Actinopterygii, Aeduellidae): revision and description of a new species from the Stephanian (Upper Carboniferous) of Montceau-les-Mines (Massif Central, France). After a revision of the diagnosis of the family Aeduellidae, the previously known species of the genus Bourbonnella have been briefly recorded from a systematic point of view with, in particular, a reappraisial of their diagnoses and, consequently, that of the genus: B. guilloti, type species from the Autunian of Buxieres-les-Mines, B. sottyi from the Stephanian of Montceau-les-Mines (both from Massif Central) and B. sp. indet. from the Virgilian (= Stephanian) of New Mexico (USA). An other undetermined Autunian species from Germany is finally attributed to the genus Aeduella. Bourbonnella fourrieri n. sp., from a new fossiliferous Stephanian level of Montceau-les-Mines, is described. It differs from the three other species by its deeper body, the greater area of small scales supporting the dorsal fin, the proportions of the head in regards to the body and the meristics of fin rays. Its scales are devoid of dentine. According to our present knowledge, Bourbonnella seems to be a euryhaline, equatorial and tropical genus at the Carboniferous - Permian turnover.

Fates of the rostral;postrostral and premaxillary in the early history of actinopterygians

Abstract The three bones studied here have various patterns in the different primitive fossil actinopterygian groups: theyare either separate; or fused in many ways; lastly postrostral and premaxillary disappear in some lineages. Fusion and disparition probably occurred many times. The disappearance of the premaxillary leads either to the lenghtening of the maxillary which contacts that of the other side anteriorly; or to an anterior median notch of the dermal snout. Taxa lacking premaxillaries cannot be related to neopterygians.

Paleohistological study of the scales of Amia Robusta Priem, 1901, Amiidae from the Thanetian (Paleocene) of Cernay (France)

Abstract The paleohistological study of scales belonging to the Thanetian amiid Amia robusta shows that their structure ispractically like that of the scales of the living A. calva scales. The osseous superficial layer houses osteocytes. The basal plate is a complex plywood of collagenous fibrils that mineralised by means of Mandls corpuscles.