Devonian Taxa Research Articles

Traquair's lungfish from Loanhead: dipnoan diversity and tooth plate growth in the late Mississippian

ABSTRACTRamsay Heatley Traquair, the eminent Victorian Scottish palaeoichthyologist and museum curator, procured an extensive collection of Palaeozoic fishes from across Scotland with the help of local miners and quarrymen. One very productive locality near Edinburgh was Loanhead. Traquair described numerous fossil fish from this Serpukhovian site, including four lungfish taxa:Ctenodus interruptus,Sagenodus quinquecostatus,Uronemus splendensandCtenodus angustulus. The first three are now quite well known, but the fourth was only briefly described and never figured. It is based entirely on tooth plates, which are unusual both in their very small size and the arrangement of the tooth ridges. They lack the diagnostic characters ofCtenodustooth plates and are here renamedClackodus angustulus. A further taxon,Conchopomasp., has recently been identified. Represented by a spade-shaped parasphenoid and denticulated jaw elements, it is the earliest known occurrence of the genus, extending its range into the Mississippian. A sixth taxon may be represented by an isolated parasphenoid bearing an anterior process, previously only seen in Devonian lungfish. The presence of up to six lungfish taxa at a single locality is unprecedented in the Carboniferous and indicates that the high level of lungfish diversity encountered in the Tournaisian of the Scottish Borders continued throughout the Mississippian, adding to the growing evidence that post-Devonian lungfish evolution was not as limited as previously proposed. This may have been due to changes in tooth plate growth, enabling greater variation in dentition and diet. In most Devonian taxa, tooth plate growth can be explained by comparison with that in extant forms, but analysis of Carboniferous tooth plates suggest growth was different in many taxa, possibly based on more than one pioneer tooth, allowing for novel patterns of tooth ridges and different types of teeth to develop on the same plate.

A primitive actinopterygian braincase from the Tournaisian of Nova Scotia.

The vertebrate fossil record of the earliest Carboniferous is notoriously poorly sampled, obscuring a critical interval in vertebrate evolution and diversity. Recent studies of diversity across the Devonian–Carboniferous boundary have proposed a vertebrate mass extinction at the end-Devonian, and recent phylogenies suggest that the origin of the actinopterygian crown may have occurred in the earliest Carboniferous, as part of a broader recovery fauna. However, the data necessary to test this are limited. Here, we describe a partial actinopterygian skull, including diagnostic elements of the posterior braincase, from the Tournaisian Horton Bluff Formation of Blue Beach, Nova Scotia. The braincase surprisingly shows a confluence of characters common in Devonian taxa but absent in Mississippian forms, such as an open spiracular groove; lateral dorsal aortae that pass through open broadly separated, parallel grooves in the ventral otoccipital region, posterior to the articulation of the first infrapharyngobranchial and an intertemporal–supratemporal complex. Phylogenetic analysis places it deep within the actinopterygian stem, among Devonian moythomasiids and mimiids, suggesting more phylogenetically inclusive survivorship of stem group actinopterygians across the end-Devonian mass extinction. With a high lineage survivorship in tetrapods and lungfish across the Devonian–Carboniferous boundary and high vertebrate diversity at Tournaisian localities, this hints at a more gradual turnover between Devonian and Carboniferous vertebrate faunas.

A redescription of the Middle Devonian dipnoanPentlandia macropteraTraquair, 1889, and an assessment of the Phaneropleuridae

During the Devonian Period, lungfishes underwent rapid diversification. Such rapid diversification has marred phylogenetic analyses and is suspected as being responsible for reducing phylogenetic hypotheses to large polytomies. This problem is exacerbated by poor morphological understanding of key Devonian taxa comprising loosely defined, paraphyletic lungfish families. Pentlandia macroptera Traquair, 1888, is one such taxon that has not received a detailed assessment since it was first discovered nearly 130 years ago. A detailed redescription of P. macroptera demonstrates that it resides in the monophyletic crown group of Devonian lungfish comprising phaneropleurids, fleurantiids, and scaumenacids but, at this stage, establishment of a new family based on this clade is not warranted. It is considered to be the most derived Middle Devonian lungfish. Several previously unrecognized structures for this taxon are described including the circumorbital bones, the cheek bones, cranial ribs, the lower jaw, and tooth plates, all of which show the derived condition. Pentlandia macroptera is also considered derived in possessing an unossified snout and neurocranium and represents the first occurrence of these conditions that were later to become prevalent in Carboniferous dipnoans. Of greatest significance, P. macroptera demonstrates the presence of the oldest pelvic girdle seen in the Dipnoi, which is conserved in form through to the Upper Devonian and even modern lungfish. The current work indicates that many of the derived characteristics of Late Devonian and Carboniferous dipnoans had their origin in the Middle Devonian.

An enigmatic echinoid spine from south Devon, UK: Devonian or Cretaceous?

Echinoids are poorly known from the Devonian of SW England. This report records an external mould of a solitary primary spine in a chert cobble collected from near the site of Wolborough Quarry, SW Devon, a well-known Middle Devonian palaeontological site. However, cherts are rare in Devonian limestones of south Devon and the spine is unusually robust in comparison with those of other Devonian taxa. The cobble is here interpreted as an erratic, most probably an Upper Cretaceous flint, and the spine is identified as Prionocidaris sp. cf. P. vendocinensis (Agassiz & Desor). This is another illustration of the high fidelity possible in fossils preserved in cherts even after reworking.

Vetupraeca n. gen. and Mucopraeca n. gen. (Cryptodonta, Bivalvia): A reappraisal of Late Devonian bivalves from the Hercynian Facies

Bivalves from the Late Devonian pelagic or Hercynian Facies of classical regions such as eastern North America and Europe have not been investigated for almost a century.A group of small, radially ribbed bivalves frequently occurs in association with ammonoids and conodonts in pelagic cephalopod limestones and shales of the latest Frasnian and early Famennian. These bivalves have traditionally been assigned to the Late Silurian genus Praecardium Barrande, 1881. Re-studying the types of the Late Devonian taxa, Cardium? vetustum Hall, 1843, Cardiola duplicata Münster, 1840, Praecardium clymeniae Beushausen, 1895, Praecardium melletes Clarke, 1904, and Praecardium multicostatum Clarke, 1904 shows that they differ significantly from Praecardium.As a result, two new genera, Vetupraeca n. gen. and Mucopraeca n. gen, are established. Furthermore, neotypes are designated for Cardiola nehdensis, Kayser, 1873 and Vetupraeca clymeniae (Beushausen, 1895), and lectotypes are chosen for Mucopraeca multicostata (Clarke, 1904) and Vetupraeca duplicata (Münster, 1840). These bivalve taxa were widely distributed in the subtropical to tropical, latest Frasnian/early Famennian outer shelf habitats of Laurussia and Gondwana.

Vetupraeca n. gen. and Mucopraeca n. gen. (Cryptodonta, Bivalvia): A reappraisal of Late Devonian bivalves from the Hercynian Facies

Bivalves from the Late Devonian pelagic or Hercynian Facies of classical regions such as eastern North America and Europe have not been investigated for almost a century. A group of small, radially ribbed bivalves frequently occurs in association with ammonoids and conodonts in pelagic cephalopod limestones and shales of the latest Frasnian and early Famennian. These bivalves have traditionally been assigned to the Late Silurian genus Praecardium Barrande, 1881. Re-studying the types of the Late Devonian taxa, Cardium? vetustum Hall, 1843, Cardiola duplicata Münster, 1840, Praecardium clymeniae Beushausen, 1895, Praecardium melletes Clarke, 1904, and Praecardium multicostatum Clarke, 1904 shows that they differ significantly from Praecardium. As a result, two new genera, Vetupraeca n. gen. and Mucopraeca n. gen, are established. Furthermore, neotypes are designated for Cardiola nehdensis, Kayser, 1873 and Vetupraeca clymeniae (Beushausen, 1895), and lectotypes are chosen for Mucopraeca multicostata (Clarke, 1904) and Vetupraeca duplicata (Münster, 1840). These bivalve taxa were widely distributed in the subtropical to tropical, latest Frasnian/early Famennian outer shelf habitats of Laurussia and Gondwana.

ORIGIN, EVOLUTION AND CLASSIFICATION OF THE NEW SUPERORDER NEPIOMORPHIA (MOLLUSCA, BIVALVIA, LOWER PALAEOZOIC)

Abstract: A number of bivalve taxa defined in the past as ‘Cryptodonten’ by Neumayr, 1884 were grouped together in the high‐level taxon Palaeoconchae Neumayr, 1884. Cox (1969) noted that Palaeoconchae and Cryptodonta were synonymous and Newell (1969) used Cryptodonta as a subclass of bivalves. However, for the past 120 years, the Cryptodonta has been poorly conceptualized and the name was used for poorly understood genera or those lacking dentition. As used by Newell, Cryptodonta included taxa now placed in the subclasses Protobranchia Pelseneer and Autolamellibranchiata Grobben, and to the class Rostroconchia Pojeta, Runnegar, Morris and Newell. The bulk of Newell's use of Cryptodonta was made up of Silurian and Devonian taxa first described by Barrande (1881) from Bohemia; Newell placed these in the order Praecardioida Newell. In effect, Cryptodonta became a ‘wastebasket’ grouping for what, at the time, were poorly understood taxa. Many of the formerly poorly understood praecardioids are now better known and are herein placed in the new superorder Nepiomorphia. The Nepiomorphia contains two orders: (1) order Praecardioida that includes the families Slavidae Kříž, Cardiolidae Hoernes, Praecardiidae Hoernes and Buchiolidae Grimm; and (2) new order Antipleuroida that includes the families Stolidotidae fam. nov., Spanilidae fam. nov. and Antipleuridae Neumayr. The Nepiomorphia originated probably in the early Silurian as result of r‐selection progenesis. When the marine current system became re‐established after the late Ordovician glaciation and in the early Silurian, an at least temporary ventilation of the shallow waters by surface currents was renewed in higher latitudes of peri‐Gondwana and Siberia, producing acceptable sea‐bottom environments. Larvae were distributed by surface currents from the warm tropical regions of Laurentia and Baltica and were among the first benthic organisms to colonize the new environments. Temporary ventilation created frequent density‐independent catastrophic mortalities of early ontogenetic stages, with no competitors and with super‐abundant resources. During the Silurian and early Devonian, the Nepiomorphia underwent several diversifications in the recurring cephalopod limestone biofacies characteristic of peri‐Gondwana, and evolved infaunal, semi‐infaunal and epifaunal modes of life in several lineages. The Nepiomorphia most probably became extinct during the early Carboniferous and had no role in the future evolution of the Bivalvia.

Late Silurian or Early Devonian corals from the continental slope off southern New South Wales

Latest Silurian or Early Devonian tabulate corals have been recovered in a dredge haul from submarine bedrock at a water depth of 2620 – 2155 m on the continental slope off southern New South Wales 45 km east of Tuross Heads from the submerged and unexplored part of the eastern Lachlan Orogen. The corals have been identified as latest Silurian to Early Devonian taxa, Favosites gothlandicus and Squameofavosites squamuliferus forma nitidus. The presence of shallow water deposits containing these forms indicates that a crustal thickening event or events took place near the end of Silurian or early in Devonian time in the eastern Lachlan Orogen east of the present coastline. This occurred well after the end of subduction in Early Silurian time which is marked by the welding of the Cambrian — Late Ordovician Wagonga Group accretionary wedge or collided terrain on to the eastern margin of the orogen and significantly earlier than the emplacement of the Moruya Suite granites in Middle Devonian time.

Systematic revision of the middle and late devonian brachiopods Schizophoria (Schizophoria) and ‘Schuchertella’ from North America

Synopsis Schizophoria and ’Schuchertella’, two common genera of Devonian brachiopods from North America, are systematically revised based on cladistic analysis. Several Early Devonian schizo‐phoriid species are placed within S. (Eoschuchertella), while all other North American Devonian and Mississippian species studied are placed within S. (Schizophoria). Schizophoria meeki Fenton & Fenton is synonymised with S. macfarlanii Meek. Ancestral forms of Schizophoria (Schizophoria) were present in Europe and the Appalachian basin and inhabited outer platform environments through the Frasnian. Several independent lineages of S. (Schizophoria) persisted through the Late Devonian biodiversity crisis and subsequently colonised nearshore environments. Most cladogenetic events within North American species of S. (Schizophoria) occurred via dispersal mechanisms, while vicariant speciation was rare. Cladistic analysis of North American species assigned to ’Schuchertella’ revealed that all species through the Frasnian belong to Floweria, an impunctate genus, while Famennian and later species belong to Schuchertella. The generic placement of the Devonian ‘schuchertellids’ is revised accordingly. Schuchertella and Floweria are superficially similar and exhibit an analagous (albeit temporally offset) evolutionary transition from free‐resting ancestors to descendants with attached pedicle valves. Floweria also exhibits reduced rates of vicariant speciation compared to speciation by dispersal. The relative reduction in vicariant speciation has been documented for other Devonian taxa (bivalves, phyllocarids and trilobites) and may be an important control on faunal dynamics in North America during the Late Devonian biodiversity crisis.

Reworked miospores in the upper paleozoic and Lower Triassic of the northern circum‐polar area and selected localities

Reworking of Devonian, Carboniferous and Permian palynomorphs into the Lower Triassic of western Canada, Yukon, the Canadian Arctic Archipelago and Alaska has been documented by a number of workers. The phenomenon occurs in other northern circumpolar localities, such as East Greenland and the Barents Sea, and was probably widespread. Examples are given from western and eastern Europe, Russia, the Middle East, Pakistan, China, Brazil and Australia. The abundance and diversity of reworked palynomorphs from a number of stratigraphic units of different ages into the Lower Triassic is an important palynostratigraphic phenomenon of chronostratigraphic value. It may be the result of a major regional regression in the late Permian, followed by a widespread marine transgression in the Early Triassic, or it may be due to tectonic activity resulting in eustatic sea‐level rise. Whatever the mechanism, the advancing transgression resulted in erosion of exposed Devonian, Carboniferous and Permian rocks, but by Mid‐Triassic times most pre‐Triassic rocks had been covered by sediment, and the supply of reworked material much reduced. Reworked Devonian taxa belong to a variety of suprageneric groups including cavate trilete spores (lycopsids), acavate trilete spores (ferns) and monolete spores; Lower Carboniferous taxa include cingulate trilete spores. Possibly reworked Upper Carboniferous and Permian pollen includes that of Gymnosperms—Cordaites, conifers, pteridosperms (taeniate bisaccate and polyplicates), and cycads and gnetophytes. Lower Triassic palynomorphs, possibly in situ, may include (sometimes abundant) acanthomorph acritarchs such as Micrhystridium breve, M. setasessitante, M. fragile and Wilsonastrum colonicum. Lack of recognition of reworking has many implications concerning chronostratigraphy, palynostratigraphy, paleoenvironments, paleoclimates, coal petrography, thermal maturity, geochemistry, and chemostratigraphy. For example, if the Upper Permian and Lower Triassic Densoisporites playfordii, D. complicatus, D. nejburgii, Lundbladispora obsoleta and Aculeisporites variabilis are not in situ, but reworked specimens of the Devonian progymnosperm cavate morphon Geminospora lemurata, one has to question the commonly held view that a lycopsid dominated macroflora, with a large biomass, recolonised the land in the Early Triassic. Lower Triassic assemblages in which reworking occurred but has not been recognised may give the impression of palynofloral diversity, whereas low diversity and low abundance would be more consistent with the hostile arid environment of the Lower Triassic. One Upper Permian and Lower Triassic plant entity, well‐adapted to harsh conditions, was the algal cyst Chordecystia chalasta. Nevertheless, some higher plants must have survived the Permian‐Triassic crisis as witnessed by the presence of gymnosperm pollen in the Mesozoic. This is Geological Survey of Canada (Calgary), Contribution no. 2004237.

A redescription of Chasmataspis laurencii Caster & Brooks, 1956 (Chelicerata: Chasmataspidida) from the Middle Ordovician of Tennessee, USA, with remarks on chasmataspid phylogeny

ABSTRACTThe type material of Chasmataspis laurencii Caster & Brooks, 1956 (Chelicerata: Chasmataspidida) from the Middle Ordovician (Tremadoc to Caradoc) of Sevier County, Tennessee, USA, is redescribed, and comparisons are drawn with recently discovered Devonian chasmataspids from Scotland, Germany and Russia. The depositional setting of the C. laurencii fossils is reinterpreted as an ash fall into shallow marine/tidal sediments. Chasmataspis laurencii confirms the presence of 13 opisthosomal segments in Chasmataspidida, a character of unresolved polarity. The phylogenetic position ofC. laurencii is difficult to resolve. A monophyletic Chasmataspidida has one convincing autapomorphy in the nine-segmented postabdomen, but C. laurencii shares a number of characters with xiphosurans (i.e. cardiac lobe, pre-abdomen with axial region, biramous and chelate limbs), while the Devonian taxa more closely resemble eurypterids (i.e. through pediform limbs and a genital appendage). Earlier interpretations of the respiratory system in C. laurencii appear unconvincing in the light of new evidence from Devonian forms with opisthosomal opercula. Resting impressions of a Chasmataspis-like animal from the Upper Cambrian Hickory Sandstone of Texas, USA, also appear to show evidence of opercula. These Texan fossils could represent the oldest record of Euchelicerata. Two chasmataspid families are recognised, and C. laurencii is placed in the monotypic Chasmataspididae Caster & Brooks, 1956, redefined here on the fused pre-abdominal buckler with an axial region and the narrow, elongate post-abdomen ending in a long, lanceolate telson.

A new Late Famennian lungfish from New South Wales, Australia, and its bearing on Australian-Asian terrane relations

A new genus and species of lungfish with toothplates, Adelargo schultzei, is described from the Hunter Siltstone (Devonian, Late Famennian) near Grenfell, New South Wales. Materials assigned to Adelargo schultzei gen. et sp. nov., include a portion of the left side of the skull comprising B, I (postparietal) and J (parietal) bones, pterygoid and prearticular toothplates, a parasphenoid with a long posterior stalk, vertebrae, ribs, anal fin supports and scales. Toothplates are similar to Dipterus, although morphology of the skull, parasphenoid and postcranial elements is more derived. Biogeographic relationships of the Grenfell fauna were based on the presence of the antiarch group Sinolepidoidei, also present on Asian terranes during the Late Devonian. A small number of lungfish scales have been described from Asian sinolepid localities of this age, but differ from those of Adelargo schultzei, and other faunal similarities between these areas appear limited. Paucity of eastern Australian Devonian taxa on the North and South China blocks implies that strong biogeographic relationships between eastern Australia and Euramerican localities during the Late Devonian were not the result of Asian migration routes, but the closer proximity of these areas.

Actinopterygians from the Namurian of Bearsden, Scotland, with comments on early actinopterygian neurocrania

Two new stem-actinopterans,Melanecta anneaegen.etsp. nov.andWoodichthys bearsdenigen.etsp. nov., are described from the Manse Burn Formation (basal Namurian) of Bearsden, Glasgow.Melanectaresembles Devonian taxa such asHowqualepisandMimia. Significant features include a large head, long gape, well preserved otoliths, micromeric squamation, broad-based fins, and fringing fulcra restricted to the extended leading pectoral edge. New data onErpetoichthysotoliths are presented for comparison with those ofMelanectaand other early actinopterygians. The primitive actinopterygian condition probably includes partly vateritic otoliths, with a small sagitta and large asteriscus contained within a single chamber. The small scales ofMelanectamay be a primitive characteristic, but the apparent independence of factors such as size, histology, and scale row to somite ratios, obscures clear evolutionary trends.WoodichthysresemblesMoythomasiaandKentuckia, and includes a flattened but detailed neurocranium. A new neurocranial specimen ofPteronisculus magnusexamined for comparison reveals new data on the otic labyrinth, lateral cranial canals, and postorbital wall. Haemopoietic organ accommodation is considered insufficient explanation for lateral cranial canal elaboration. Several new basisphenoidal and postorbital wall characters are identified which are associated with early stages in posterior myodome evolution. Most of these characters are present inMoythomasia durgaringa.

Vincular furrows in some Early Silurian and Devonian Phacopidae (Trilobita), predominantly from North America

The vincular furrow morphology of 19 species of Phacopidae is critically examined. The anterior part of the vincular furrow is much less variable than the posterior part of the vincular furrow, but it can be absent, shallow, deep, or have a slightly ventrally elongated boss. The posterior part of the vincular furrow can have pleurovincular pits (for reception of the thoracic pleural tip processes) or indentations for these processes, plus bounding walls that are variably indented laterally and very variable in vertical elongation. The functional morphology of the various elements of the vincular furrow is best explained by a paradigm of resistance to lateral shearing.All elements of the vincular furrow in Devonian taxa had already appeared in the Early Silurian, but Early Silurian taxa are richer in diversity of elements. Some Devonian subspecies, essentially based on dorsal morphologies, show distinctly different vincular furrows. Cluster analysis of the data gathered on the vincular furrow complexes regroups the distinctly different Devonian subspecies and some Silurian subgenera. Other vincular furrows within the Phacopidae suggest that Reedops is near the Phacops logani complex and that the Phacopidellinae is a valid subfamily, but formal emendations within the family are not suggested because of incomplete data, notably on our knowledge of the distribution of vincular furrows. The use of the widely conceived genus Phacops Emmrich, 1839, over more recently described taxa such as Paciphacops Maximova, 1972, is presently favored, as this reflects more clearly current understanding of the systematics within the family Phacopidae.Primary types of the North American taxa Phacops cristata, P. cristata gaspensis, and Acernaspis (Acernaspis) orestes are critically reviewed; significant changes of previous interpretations are suggested. Phacops cristata vitrea n. subsp. is erected. Thoracic pleural tip processes and anterolateral ventral pygidial processes are described in detail within Phacops rana rana and Acernaspis (Acernaspis) orestes. A pathological specimen of Phacops rana rana, with an injured eye, demonstrates that the individual did not revert to a primitive type of lens packing.