Carole J. Burrow

False teeth: conodont-vertebrate phylogenetic relationships revisited

ABSTRACT An evidence-based reassessment of the phylogenetic relationships of conodonts shows that they are not “stem” gnathostomes, nor vertebrates, and not even craniates. A significant group of conodont workers have proposed or accepted a craniate designation for the conodont animal, an interpretation that is increasingly becoming established as accepted “fact”. Against this prevailing trend, our conclusion is based on a revised analysis of traditional morphological features of both discrete conodont elements and apparatuses, histological investigation and a revised cladistic analysis modifying that used in the keystone publication promoted as proof of the hypothesis that conodonts are vertebrates. Our study suggests that conodonts possibly were not even chordates but demonstration of this is beyond the scope of this paper. To summarize, in conodonts there is low cephalization; presence of simple V-shaped trunk musculature and unique large-crystal albid material in the elements; lack of a dermal skeleton including characteristic vertebrate hard tissues of bone, dentine and enamel; lack of odontodes with bone of attachment and a unique pulp system; lack of segmentally-arranged paraxial elements and dermal elements in median fins, all of which supports neither a vertebrate nor a craniate relationship for conodonts.

A review of placoderm scales, and their significance in placoderm phylogeny

An historical review of the literature relating to placoderm scales preserved in association with articulated dermal plates, or as isolated units in microvertebrate assemblages, is followed by a discussion of their relevance in phylogenetic analyses of the Placodermi. The dentinous tissue forming the tubercles of Early Devonian acanthothoracid scales and dermal bone is similar to that of the dermal bone ornament of some osteostracans, and denticles of the vertebrate Skiichthys from the Ordovician Harding Sandstone. This similarity supports the proposition that the gnathostomes are the sister-group of the Osteostraci, with the Placodermi branching earliest within the gnathostomes, and the Acanthothoraci branching earliest within the Placodermi. The meso-semidentine in acanthothoracid tubercles, rather than semidentine (sensu stricto), is most likely to be synapomorphic for the Placodermi.

A REDESCRIPTION AND REINTERPRETATION OF GYRACANTHIDES MURRAYI WOODWARD 1906 (ACANTHODII, GYRACANTHIDAE) FROM THE LOWER CARBONIFEROUS OF THE MANSFIELD BASIN, VICTORIA, AUSTRALIA

Abstract The articulated acanthodian Gyracanthides murrayi Woodward from the Lower Carboniferous of Mansfield, Victoria, Australia, is redescribed from original and newly aquired material. It includes the only known head region from a member of the Gyracanthidae. A new reconstruction and interpretation of the pectoral area are proposed, incorporating the elements from the original description as well as a new bone interpreted as a procoracoid attached to a prepectoral spine. The posterior free pectoral spine described by Woodward is reinterpreted as a scapulocoracoid. A subsequent reconstruction of the pectoral girdle which synonymised the anterior and posterior prepectoral spines is rejected. A clear difference in size and shape of the pectoral and pelvic fin spines is established. The morphology of the tubercular ornament of the paired fin spines is used to distinguish species of Gyracanthides. Gyracanthides murrayi had a covering of dermal polyodontodia with spinose crowns and a concave base with a central vascular canal opening. The systematic position of the Gyracanthidae remains unclear, with the family retained within the Climatiiformes only on the basis of the broad-based, fin spines with nodose ornament.

Devonian placoderm scales from Australia

The morphology and histology of Australian placoderm scales which were found associated with dermal plates are described and compared. The specimens include the arthrodire Buchanosteus confertituberculatus from the Early Devonian (Emsian) of Buchan, Victoria, the arthrodires Goodradigbeeon australianium and Buchanosteidae gen. et sp. indet., the acanthothoracid Murrindalaspis wallacei from the Emsian of Taemas, New South Wales, and the antiarch Wurungulepis denisoni from the Emsian of the Broken River Group of northern Queensland. Isolated scales from Emsian limestones of Taemas-Wee Jasper, N.S.W., and Tyers, Victoria, and Lochkovian/Pragian assemblages from New South Wales and Queensland are also reviewed, to indicate the potential biostratigraphical value of placoderm scales in microvertebrate faunal assemblages, and their relevance to phylogenetic analysis.

GNATHOSTOME MICROREMAINS FROM THE LOWER DEVONIAN JAWF FORMATION, SAUDI ARABIA

Abstract Calcareous horizons in the Qasr and Hammamiyat members (Lower Devonian, ?Pragian and lower Emsian) of the Jawf Formation, northwestern Saudi Arabia, yielded a rich assemblage of microremains from acanthodian, placoderm, chondrichthyan, and sarcopterygian vertebrates. The most abundant elements are scales from acanthodians Nostolepis spp., Milesacanthus ancestralis n. sp., Canadalepis? sp., and Gomphonchus? fromensis, scales and dermal bone fragments from acanthothoracid and ?rhenanid placoderms, and teeth from onychodontids. Rarer occurrences include ?chondrichthyan scales of several different morphotypes, and petalichthid and ?ptyctodontid placoderm elements. The Qasr Member assemblage shows a close resemblance to slightly older faunas from the Lochkovian of Brittany and Spain. The Hammamiyat Member microvertebrate fauna shows closest affinity with that of the stratigraphically lower Qasr Member, with similarities also to coeval faunas from southeastern Australia, late Emsian/Eifelian faunas from west-central Europe, and the Givetian Aztec Siltstone fauna from Antarctica.

EARLY DEVONIAN (EMSIAN) ACANTHODIAN FAUNAS OF THE WESTERN USA

Abstract Isolated spines and scales from acanthodian fishes are common elements in vertebrate assemblages from the Early Devonian (Emsian) of Arizona, Idaho, Nevada, Utah, and Wyoming. The material described here is from the Sevy Dolomite and lower Grassy Flat Member, Water Canyon Formation, and includes one partially articulated specimen plus isolated fin spines and dermal plates of a new ?climatiid Sevyacanthus elliotti n. gen. and sp.; spines and shoulder girdle elements of a ?climatiid Nodocosta denisoni n. sp.; dentigerous jawbones from at least two ischnacanthiform taxa Ischnacanthus sp. and Cacheacanthus utahensis n. gen. and sp.; fin spines from a ?diplacanthiform Bryantonchus peracutus n. gen.; and scales of Ptychodictyon americanum n. sp. Most of the species appear endemic, although some show a close relationship with older Euramerican taxa (Ischnacanthus, Climatiidae sensu stricto) and younger Baltic taxa (Ptychodictyon rimosum, Nodocosta pauli).

Disarticulated acanthodian and chondrichthyan remains from the upper Middle Devonian Aztec Siltstone, southern Victoria Land, Antarctica

Abstract Well-preserved vertebrate microremains are abundant in the residues from a calcareous grey siltstone in the karawaka biozone (?late Givetian) of the Aztec Siltstone at Mount Crean, Lashly Mountains, Antarctica. Acanthodians are represented by scales of acritolepid Pechoralepis juozasi sp. nov., climatiid Nostolepis sp. cf. N. gaujensis Valiukevičius, diplacanthid Milesacanthus antarctica Young & Burrow, and an undetermined acanthodiform. The acanthodian assemblage resembles those from early Frasnian carbonates of central Iran. Chondrichthyan elements in the fauna include rare teeth of Aztecodus harmsenae Long & Young and Antarctilamna prisca Young, ctenacanthoid-type scales and branchial denticles which are possibly from Antarctilamna, and scales of an indeterminate chondrichthyan. An isolated set of acanthodid acanthodiform jaws from the uppermost ‘phyllolepid’ biozone of the Aztec Siltstone at Mount Ritchie, Warren Range, Antarctica is also described.

Redescription of the gnathostome fish fauna from the mid-Palaeozoic Silverband Formation, the Grampians, Victoria

Gnathostome vertebrate remains from fine-grained sandstones of the Silverband Formation in the Grampians, Victoria include dissociated fin spines, scales and teeth. These elements are assigned herein to the acanthodians Sinacanthus? micracanthus (fin spines) and Radioporacanthodes sp. cf. R. qujingensis (scales and tooth whorls). This fauna indicates a Late Silurian (?late Ludlow) age for the vertebrate-bearing stratum. Under current systematic groupings, the two gnathostome taxa from the Silverband Formation belong to two different families, the Sinacanthidae and the Poracanthodidae. However, the preserved association could indicate that the three element types derived from the same biological species. The possibility that the Sinacanthidae is a sister group to the Climatiidae and the Poracanthodidae is raised by this scenario. The Sinacanthidae is tentatively reassigned to the Acanthodii, as it is considered to lack diagnostic chondrichthyan characters.

Early Devonian putative gyracanthid acanthodians from eastern CanadaInternational Geoscience Programme (IGCP) Contribution 491, Middle Palaeozoic Vertebrate Biogeography, Palaeogeography, and Climate.

In 1890, Traquair assigned isolated fin spines from the Early Devonian of eastern Canada to a new gyracanthid acanthodian Gyracanthus incurvus, based on the similarity of the distinctive oblique ridges on the spines to the ornament on the large robust fin spines of Gyracanthus spp. from the British Carboniferous Coal Measures. Other similarly ornamented spines from the Early Devonian of Germany were tentatively assigned in 1933 by Gross to the same genus as a new species Gyracanthus? convexus. Based on examination of the type material, as well as newly collected specimens from Emsian sandstones and mudstones of the Gaspe Peninsula, Quebec and the Atholville beds, New Brunswick, we erect a new genus Ankylacanthus gen. nov. for these two species. Spines of the new genus are distinguished by being laterally flattened and thin-walled, with a single row of denticles along one side of the posterior groove, and having thin spine ridges ornamented with low smooth nodes. Other Early to Middle Devonian specimens in...

Redescription of Parexus recurvus, an Early Devonian acanthodian from the Midland Valley of Scotland

Parexus Agassiz was one of the first Early Devonian ‘spiny sharks’ to be described. The genus is readily recognized by the large size and ornament of its anterior dorsal fin spine. Although two species were erected, reappraisal of all known specimens indicate they should be synonymized in the type species Parexus recurvus. Farnellia tuberculata Traquair, originally described as a vertebral column, is actually tooth rows of jaw dentition, and is also now considered to be a junior synonym of P. recurvus. Parexus has a perichondrally ossified scapulocoracoid of typical acanthodian shape, and diagnostic features of the family Climatiidae, but has distinctive scales comprising appositional growth zones that closely resemble those of the putative stem chondrichthyan Seretolepis elegans Karatajute-Talimaa.