Topic
Ischnacanthus
About: Ischnacanthus is a research topic. Over the lifetime, 9 publications have been published within this topic receiving 153 citations.
Papers
TL;DR: The Tillywhandland fish bed of the Lower Old Red Sandstone in the Strathmore area of the Scottish Midland Valley accumulated in a lake, here called Lake Forfar, which was created suddenly following a period of fluvial deposition as mentioned in this paper.
Abstract: The Tillywhandland fish bed of the Lower Old Red Sandstone in the Strathmore area of the Scottish Midland Valley accumulated in a lake, here called Lake Forfar, which was created suddenly following a period of fluvial deposition. Lake creation may have been due to basin faulting or the disruption of drainage patterns by contemporaneous volcanic activity. The fish bed laminites accumulated in a hydrologically open lake under a seasonal climatic regime. When fully developed, laminites comprise repeated quadruplets of clastic silt/carbonate/organic/green clay–shale laminae averaging 0·5 mm in thickness. Following 2000 years of laminite deposition an increasingly silty succession with thin current-rippled sandstones provided the lake-fill.The fish fauna is dominated by Mesacanthus and Ischnacanthus with rare Euthacanthus, Parexus, Climatius, Vernicomacanthus and Cephalaspis. Most fish carcasses were partially decayed before deposition in the laminites on the poorly oxygenated lake floor. Abundant coprolites are the result of predation on Mesacanthus and small Ischnacanthus, probably by larger Ischnacanthus. Arthropods present include eurypterids (Pterygotus), washed in as near complete exuviae and fragments, and millipeds which were washed in from surrounding terrestrial environments along with plants, of which Parka and Zosterophyllum are common. Bioturbation indicates that conditions were not permanently anoxic during deposition of the laminites.Comparison of our collections with the Mitchell Collection accumulated in the 19th century indicates that Tillywhandland Quarry was the main source of specimens in laminite lithologies labelled ‘Turin Hill’.
60 citations
1 Jan 2004
TL;DR: A change in biting mode from a vertically occluding, cog-like action in Silurian-Early Devonian fish to a shearing action in Middle-Late DevonianFish is indicated by a change in the layout, shape and wear of the teeth on the jaw bones.
Abstract: Within the early gnathostome group Acanthodii, several different types of dentition are exhibited. Of the Siluro-Devonian acanthodians, some of the Climatiidae and the Brochoadmonidae have rows of small tooth whorls lining their jaws, while the Ischnacanthidae and Poracanthodidae have dermally derived dentigerous jaw bones, with some taxa also having a large symphysial tooth whorl and smaller tooth whorls and teeth within the mouth cavity. A change in biting mode from a vertically occluding, cog-like action in Silurian-Early Devonian fish to a shearing action in Middle-Late Devonian fish is indicated by a change in the layout, shape and wear of the teeth on the jaw bones. Acanthodopsis, a Carboniferous genus of the Acanthodidae, also has dentigerous jaw bones. A revised generic diagnosis of this form is presented, and isolated jaws of a new Australian species, Acanthodopsis russelli sp. nov., give further evidence that these dentigerous elements are not homologous with those of ischnacanthiforms. Some new examples of Ischnacanthus gracilis jaws are illustrated, and compared with those of Acanthodopsis, in which the bone is a perichondral ossification that covers the entire jaw cartilage, without a separate, toothed dermal bone forming the biting surface.
32 citations
TL;DR: 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.
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).
27 citations
Journal Article•
TL;DR: Ischnacanthus gracilis (Egerton, 1861), the only ischnacanthiform acanthodian from the Lochkovian Lower Red Sandstone of Scotland, is known from hundreds of specimens in institutional collections worldwide as discussed by the authors.
Abstract: Ischnacanthus gracilis (Egerton, 1861), the only ischnacanthiform acanthodian from the Lochkovian Lower Old Red Sandstone of Scotland, is known from hundreds of specimens in institutional collections worldwide. Despite this relative abundance, morphology and histology of its skeletal elements have rarely been investigated. Surface details of spines, dental elements, and scales are often not visible in specimens because they are usually split through the middle. We have examined a broad size range of fish, from 35 mm to 250 mm long. Several intact (not split) specimens have been collected in recent years and acid-prepared to show fine details of the dermal and dental elements. We have also used scanning electron microscopy of scales, jaws and dental elements, denticles and fin spines, and serial thin sectioning of articulated specimens, to document their structure. Some of our notable observations include: identification of ventral lateral lines, double-layered subtessellate calcified cartilage forming the jaws, and the probable occurrence of extraoral tricuspid denticles on the jaws of most fish. Examination of the size range, body proportions and dentition of institutional specimens gives no support for recognising more than one species in the Midland Valley localities.
26 citations
TL;DR: The first full description of the Lochkovian acanthodian Euthacanthus gracilis shows that the species shares many characters with the type species EUTHacanthus macnicoli supporting its retention in this genus.
Abstract: Synopsis The first full description of the Lochkovian acanthodian Euthacanthus gracilis , presented here, shows that the species shares many characters with the type species Euthacanthus macnicoli supporting its retention in this genus. Euthacanthus elegans is deemed to be a junior synonym of E. gracilis . E. gracilis differs from E. macnicoli in having large ‘umbellate’ scales edging the main lateral line canal, and small body scales. The crown morphology of the enlarged lateral line scales are similar to isolated ‘umbellate’ scales described world-wide in the Siluro-Devonian. They have the same general morphology as the sensory line scales on some other acanthodians including the sensory line scales on the head of Ischnacanthus gracilis and the lateral lines in Brochoadmones milesi . Neither of these articulated forms is closely related to Euthacanthus . The crown morphology of the normal flank scales is similar to that of the type species, and also the acritolepid acanthodian Acritolepis urvantsevi . Acritolepids are ischnacanthiform acanthodians, and are not closely related to Euthacanthus . This similarity indicates that scale crown morphology without histology is not always a useful tool in identifying species or genera from isolated remains.
17 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2018 | 1 |
| 2017 | 1 |
| 2015 | 1 |
| 2013 | 1 |
| 2011 | 1 |
| 2007 | 1 |