Thelodont Scales Research Articles

Thelodont scales from the Lower Devonian of Novaya Zemlya Archipelago, Arctic Russia.

Scales of a new thelodont species, Amaltheolepis terranovi sp. nov., are described from the upper Emsian, Lower Devonian Shevchenkinskaya Formation of Novaya Zemlya, Arctic Russia. The new species shows strong resemblance with the Emsian “Verdalen assemblage” from Spitsbergen, supporting an Emsian age for the upper part of the Shevchenkinskaya Formation. This conclusion in the context of the various Amaltheolepisassemblages from Spitsbergen allows for a more accurate comparison and correlation between assemblages from different regions in the Northern Hemisphere, suggesting that the type species, Amaltheolepis winsnesifrom Spitsbergen, is Eifelian in age

A phosphatised fossil Lagerstätte from the middle Cambrian (Wuliuan Stage) of North Greenland (Laurentia)

The upper Henson Gletscher Formation (Cambrian, Miaolingian Series, Wuliuan Stage) of southern Lauge Koch Land and Løndal, south-western Peary Land, North Greenland (Laurentia) yields diverse assemblages of phosphatised Small Shelly Fossils after treatment with weak acetic acid. The occurrence merits description as a fossil Lagerstätte on account of the exceptional preservation of soft parts in some specimens, although the phosphatisation itself is generally rather coarse. Bradoriid and phosphatocopid arthropods are common and display substantial variation in their preservational history. Some specimens retain traces of internal morphology, although details are generally obscured by indifferent preservation. Rare specimens extend the range of stem-group pentastomid arthropods back by more than 10 million years. A unique hatching larva demonstrates the same early developmental stage of a stem-group priapulan worm to that described in some present-day priapulans. The preservation of an in place operculum has demonstrated that the widespread, supposed mollusc Protowenella is actually an unusual, strongly coiled hyolith. Abundant coprolites and cololites provide additional evidence of early phosphatisation. In terms of morphology, Cambrocoryne lagenamorpha gen. et sp. nov. superficially resembles wiwaxiid and some annelid sclerites, thelodont scales and the foraminiferan Lagena, but its true identity is obscure.

Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U.S.A.

Intensive sampling of uppermost Silurian to lowermost Devonian levels of the marine sequence of the Roberts Mountains Formation exposed in the Birch Creek II section, Nevada has yielded assemblages of vertebrate microremains dominated by acanthodian scales. Taxonomic assessment of the vertebrates represented shows a suite and succession of taxa most similar to those recorded from contemporary circum-Arctic assemblages, with scales of the poracanthodid acanthodians Poracanthodes punctatus, P. canadensis, Radioporacanthodes porosus and ischnacanthid Gomphonchus sandelensis most abundant below the Silurian–Devonian (S–D) boundary (as previously determined by conodont and graptolite occurrences), and stem chondrichthyan ‘acanthodians’ Nostovicina laticristata and other Nostovicina spp. (order, family indet.) the most abundant above the boundary. Just one endemic acanthodian taxon, Funicristata nevadaensis nov. gen. nov. sp., was found, in the uppermost Silurian. Agnathan vertebrate remains are rare relative to acanthodian scales, with dermal fragments of heterostracans at fewer than 10 levels and scales of thelodonts from 12 levels scattered throughout the whole section. Thelodonts Apalolepis, Barlowodus spp., ?Boreania, Gonioporus alatus, Lanarkia, Loganellia, Nikolivia, Talivalia, Thelodus, ?Turinia sp. and Trimerolepis spp. are found below the purported S–D boundary. Rare thelodont scales including Boreania sp. cf. minima, N. gutta and a single scale of ?Amaltheolepis sp. are found above the S–D boundary level. The only identifiable gnathostome remains of groups other than acanthodians are from the putative osteichthyan Lophosteus sp. and chondrichthyans Ellesmereia schultzei and Polymerolepis sp., in the uppermost Silurian levels.

Revision of thelodonts, acanthodians, conodonts, and the depositional environments in the Burgen outlier (Ludlow, Silurian) of Gotland, Sweden

ABSTRACT Ludfordian strata exposed in the Burgen outlier in eastern Gotland, Sweden record a time of initial faunal recovery after a global environmental perturbation manifested in the Ludfordian Carbon Isotope Excursion (LCIE). Vertebrate microfossils in the collection of the late Lennart Jeppsson, hosted at the Swedish Museum of Natural History, hold the key to reconstruct the dynamics of faunal immigration and diversification during the decline of the LCIE, but the stratigraphic relationships of the strata have been debated. Historically, they had been placed in the Burgsvik Formation, which included the Burgsvik Sandstone and the Burgsvik Oolite members. We revise the fauna in the Jeppsson collection and characterize key outcrops of Burgen and Kapellet. The former Burgsvik Oolite Member is here revised as the Burgen Oolite Formation. In the Burgen outlier, back-shoal facies of this formation are represented and their position in the Ozarkodina snajdri Biozone is supported. The shallow-marine position compared to the coeval strata in southern Gotland is reflected in the higher δ13Ccarb values, reaching +9.2‰. The back-shoal succession includes high-diversity metazoan reefs, which indicate a complete recovery of the carbonate producers as the LCIE declined. The impoverishment of conodonts associated with the LCIE in southern Gotland might be a product of facies preferences, as the diverse environments in the outlier yielded all 21 species known from the formation. Fish diversity also returned to normal levels as the LCIE declined, with a minimum of nine species. In line with previous reports, thelodont scales appear to dominate samples from the Burgen outlier.

Late Silurian vertebrate microfossils from the Carnarvon Basin, Western Australia

Burrow, C.J., Turner, S., Trinajstic, K. & Young, G.C., 27 February 2019. Late Silurian vertebrate microfossils from the Carnarvon Basin, Western Australia. Alcheringa 43, 204–219. ISSN 0311-5518.A core sample from the offshore Pendock 1A well, Carnarvon Basin, Western Australia yielded microvertebrate residues at an horizon in the lower part of the Hamelin Formation, dated as late Silurian, ? Ludlow, based on associated conodonts. The fish fauna comprises loganelliiform thelodont scales, the ? stem gnathostome Aberrosquama occidens nov. gen. et sp., the acanthodian Nostolepis sp. aff. N. alta, and the ? stem osteichthyan Andreolepis sp. aff. A. petri. Because of the paucity of the material, and some differences between the Pendock scales and those of established species, a precise age can not be confirmed; however, the composition of the fauna at generic level most closely resembles that of late Silurian (Ludlow) assemblages from northern Eurasia.Carole J. Burrow* [carole.burrow@gmail.com], Geosciences, Queensland Museum, Hendra QLD 4011, Australia; Susan Turner [palaeoich@yahoo.com], Geosciences, Queensland Museum, Hendra QLD 4011, Australia; Kate Trinajstic [k.trinajstic@curtin.edu.au], School of Molecular and Life Sciences, Curtin University, Perth, WA 6102, Australia; Gavin C. Young [gavin.young@anu.edu.au], Research School of Physics and Engineering, Australian National University, Canberra, ACT 2000, Australia.

Microvertebrates from the Silurian–Devonian boundary beds of the Eastport Formation, Maine, eastern USA

Agnathan and gnathostome remains, associated with lingulid brachiopod fragments and distinctive ostracods, have been extracted from a small calcareous mudstone sample collected from the type section of the Eastport Formation on the northern shore of Moose Island, Maine. The vertebrate assemblage includes osteostracan, anaspid, and thelodont scales, and acanthodian scales, spines and teeth, which support a late Pridoli, or possibly earliest Lochkovian, age for the stratum. The thelodont Paralogania denisoni n. sp. is described, associated with a single thelodont scale referred tentatively to Talivalia? sp. indet., and acanthodians Nostolepis striata, Gomphonchus sandelensis, andPoracanthodes punctatus in a fauna that shows similarities to late Pridoli assemblages in Britain, parts of Europe, Russia, Greenland, and arctic Canada.

Early Frasnian thelodont scales from central Iran and their implications for turiniid taxonomy, systematics and distribution

ABSTRACTThe early Frasnian turiniid thelodont Neoturinia hutkensis gen. nov. is re-described on the basis of a new large scale set from the Chahriseh section in central Iran. Detailed morphological and histological information supports a new generic affinity for this species, which was previously assigned to Turinia. The generic affinity of other turiniid thelodonts from Gondwana is tested by a phylogenetic analysis based on scales, which proposes that most taxa from Gondwana form a clade separate from that comprising the first-studied Laurussian forms, including the type species Turinia pagei Powrie, 1870. This suggests that many of the Turinia species from Gondwana should be separated from this genus and need to be revisited. On the strength of the analysis, younger Gondwanan taxa in the mid–early Late Devonian should probably be referred to the new genus; one Late Silurian taxon from eastern Gondwana is removed. A biogeographic analysis, using a parsimony ancestral state method, is also conducted in order to discuss dispersal patterns in relation to the achieved model of interrelationships.http://zoobank.org/urn:lisd:zoobank.org:pub:03499C12-344D-4296-A633-201CDB982445SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Hairapetian, V., H. Blom, and S. Turner. 2016. Early Frasnian thelodont scales from central Iran and their implications for turiniid taxonomy, systematics and distribution. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1100632.

Palaeoenvironmental signatures revealed from rare earth element (REE) compositions of vertebrate microremains of the Vesiku Bone Bed (Homerian, Wenlock), Saaremaa Island, Estonia

Rare earth elements (REEs) have been analysed from fossil vertebrate microremains (thelodont scales) from the Vesiku Bone Bed, Saaremaa, Estonia, using in situ microsampling by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Well-preserved scales of three species of the genus Thelodus (T. carinatus, T. laevis and Thelodus sp.) show very uniform REE patterns with slightly lower overall REE concentrations in enameloid than in dentine, with enrichment in middle REEs, depletion in heavy REEs and pronounced negative europium anomaly, but no cerium anomaly. The results of this study suggest a similar diagenetic history and possibly contemporaneous habitats for all three Thelodus species, as well as possible suboxic to anoxic conditions of the bottom and pore waters during the formation of the Vesiku Bone Bed.

Early Devonian fishes from coastal De Long Strait, central Chukotka, Arctic Russia

ABSTRACT Calcareous and sandy deposits from the basal members of the Enmakaj and Pil'hikaj formations in coastal exposures along the De Long Strait in central Chukotka, Arctic far-eastern Russia, have yielded two assemblages of fossil fish comprising heterostracan plate fragments, turiniid and other thelodont scales, acanthodian scales and a partial tooth, typical of the Old Red Sandstone facies. Exceptional are acanthothoracid placoderm platelets characteristic of marine facies. In addition a sarcopterygian fragment have been found in Member 1 of the Enmakaj Formation. Some scale surfaces show an unusual, scoured preservation. A Lochkovian age, and most probably basal Lochkovian, is supported for the Enmakaj assemblage, and a somewhat later Lochkovian age is supposed for the Pil'hikaj assemblage. The palaeobiogeographic affinities of these assemblages based on the heterostracans and thelodonts are with other Lochkovian occurrences in Arctic regions such as Severnaya Zemlya, Spitsbergen and the northern a...

Endemic thelodonts (Vertebrata: Thelodonti) from the Lower Silurian of central Asia and southern Siberia

ABSTRACTNew fossil vertebrate microremains from the Lower Silurian of NW Mongolia, Tuva and S Siberia have been discovered, and previous collections of thelodonts (Vertebrata: Thelodonti) from this region re-studied, figured and described, following recent advances in morphology and systematics of thelodont scales. As a result, six thelodont species are described here and attributed to two families and three genera. An emended diagnosis is given for each species. Morpohological scale varieties of each species are revised, and the squamation types are introduced to the species descriptions, resulting in newly grouped morphological sets of scales. The previously monotypic genusTalimaalepisŽigaitė, 2004, is proposed to contain two different species; therefore, two new combinations of morphological scale sets of two species are described for the first time. Both of them show transitional scale structure between the generaLoganellia(family Loganellidae) andHelenolepis(family Phlebolepididae). Two of the thelodont genera,AngaralepisandTalimaalepis, as well as all the six species, are endemic and not known anywhere else in the world. They are accompanied by a variety of other peculiar early vertebrates, such as mongolepids, two endemic genera of acanthodians, and putative galeaspids. This work enhances our knowledge of early Silurian vertebrate diversity, and provides evidence of regional palaeoenvironmental conditions and palaeogeographical relationships of the Siberia and Tuva terranes.

Tissue diversity and evolutionary trends of the dermal skeleton of Silurian thelodonts

Previously described scale morphotypes of Silurian thelodonts, constrained by their representation as isolated dermal denticles are reassessed to provide a more robust character basis for their inclusion in future phylogenetic studies. As relatively common microfossils, thelodonts are important biostratigraphical markers, but their interrelationships with geologically younger species known by complete skeletons are still unresolved. We examined scales of 21 known morphotypes from north-eastern Europe, Siberia and central Asia and described their distinct tissue arrangements considering (1) thickness and direction of dentine tubules, (2) presence or absence of a pulp canal, (3) number and position of pulp canals, (4) the presence or absence of a distinct outer crown layer and (5) the extent of Sharpey's fibres penetrating the scale base. We correlated the traditional thelodont scale type morphologies with these distinct scale histologies, as found in Silurian thelodonts. In addition, a new histological type for thelodont scales, the Talimaalepis type, is described to represent a new taxon, from the Early-Mid Silurian. Our study suggests that, through time, there is a general trend of increasing complexity in thelodont dermal tissue structures. Three types of dentine and internal scale organisations were distinguished in Silurian species studied, namely (1) irregular, thin tubular dentine; (2) irregular, thick tubular dentine, with two subtypes as a function of pulp canal development and (3) regular, tubular dentine (orthodentine).

Thelodont scales from the Lower and Middle Devonian Andrée Land Group, Spitsbergen

Scales of six thelodont taxa are described from the Devonian of Spitsbergen. Numerous samples from localities widely dispersed on Spitsbergen yield several assemblages considered to represent different depositional phases of the late Lower lower Middle Devonian of the Andrée Land Group, but also support the view that certain lithostratigraphic units of the Andrée Land Group should be regarded as contemporaneous lithofacies subjected to different sedimentary environments, rather than as separate stratigraphic members. The description of Woodfjordia collisa gen. et sp. nov., Talivalia svalbardia sp. nov., Canonia cf. C. grossi, Amaltheolepis montiwatsonia sp. nov., Amaltheolepis winsnesi and Amaltheolepis austfjordia sp. nov. also allows for a comparison with similar faunas from other regions of the Northern Hemisphere and motivates further elaboration of Early-Middle Devonian thelodont biostratigraphy.

New observations on the squamation patterns of articulated specimens ofLoganellia scotica(Traquair, 1898) (Vertebrata: Thelodonti) from the Lower Silurian of Scotland

Articulated squamations of Loganellia scotica (Traquair, 1898) from the Lower Silurian Lesmahagow inliers of southern Scotland have been studied. They include seven articulated specimens, three of them representing complete thelodont fossils, and four partially preserved postpectoral, precaudal and caudal parts of the exoskeleton. All the five main types of thelodont scales that is rostral, cephalo-pectoral, postpectoral, precaudal and pinnal sacles, as well as respective squamation patterns have been observed on articulated specimens. The specific orbital, branchial, and bucco-pharyngeal scales, characteristic of L. scotica, have not been found due to the poor or non-preservation of these particular areas within the specimens studied. Tail morphology and squamation pattern of the caudal fin have been studied with particular attention, and the constitution of the caudal fin rays has been analyzed. The rostral squamation pattern is argued to be characteristic to L. scotica.

Silurian Thelodonts from the Niur Formation, Central Iran

Thelodont scales are described from the Silurian Niur Formation in the Derenjal Mountains, east central Iran. The material studied herein comes from four stratigraphic levels, composed of rocks formed in a shallow water, carbonate ramp environment. The fauna includes a new phlebolepidiform, Niurolepis susanae gen. et sp. nov. of late Wenlock/?early Ludlow age and a late Ludlow loganelliiform, Loganellia sp. cf. L. grossi, which constitute the first record of these thelodont groups from Gondwana. The phlebolepidiform Niurolepis susanae gen. et sp. nov. is diagnosed by having trident trunk scales with a raised medial crown area separated by two narrow spiny wings from the lateral crown areas; a katoporodid-type histological structure distinguished by a network of branched wide dentine canals. Other scales with a notch on a smooth rhomboidal crown and postero-laterally down-stepped lateral rims have many characters in common with Loganellia grossi. Associated with the thelodonts are indeterminable acanthodian scales and a possible dentigerous jaw bone fragment. This finding also provides evidence of a hitherto unknown southward dispersal of Loganellia to the shelves of peri-Gondwana.

A NEW EARLY DEVONIAN THELODONT FROM CELTIBERIA (SPAIN), WITH A REVISION OF SPANISH THELODONTS

Abstract: A revision of thelodont scales from the Lower Devonian of the Iberian Chains enables their grouping into two taxa: Turinia pagei and T. nachoi sp. nov. These taxa are clearly distinguishable by morphological and histological features; they also have a different stratigraphic range (T. pagei is restricted to Lochkovian strata, whereas T. nachoi sp. nov. occurs within lower–middle Pragian rocks). The new species is represented by head, transitional (cephalopectoral) and trunk scales.

Thelodonts and distribution of associated conodonts from the Llandovery–lowermost Lochkovian of the Welsh Borderland

Thelodont scales from the Middle Llandovery–lowermost Lochkovian of southern Britain are described with three new taxa, Loganellia? unispinata sp. nov., Nethertonodus prodigialis gen. et sp. nov. and Paralogania tarranti sp. nov. established, and Paralogania kaarmisensis Märss identified for the first time from Britain. Thelodonts are rare in the Llandovery and Wenlock series where predominantly Loganellia cf. aldridgei Turner, Loganellia scotica (Traquair) and Thelodus sp. are accompanied by coniform conodonts Panderodus Ethington, Decoriconus Cooper and Dapsilodus obliquicostatus (Branson and Mehl). The majority of the material has been recovered from the Ludlow and Přídolí series. Thelodus laevis (Pander) and Paralogania martinssoni (Gross) occur in the lower Gorstian. Paralogania kaarmisensis and Phlebolepis elegans Pander come from the Upper Gorstian–Lower Ludfordian and are associated with the zonal conodont Polygnathoides siluricus Branson and Mehl in the upper Gorstian. Thelodus parvidens Agassiz and T. trilobatus Hoppe dominate in the Upper Ludfordian in association with the rarer zonal conodonts Ozarkodina snajdri (Walliser), O. crispa (Walliser) and O. remscheidensis eosteinhornensis (Walliser). The basal Přídolí Series indicates a change to a thelodont fauna dominated by Paralogania ludlowiensis (Gross) and including Nethertonodus prodigialis. Higher in the Přídolí Series, a succession in faunas includes Katoporodus cf. timanicus (Karataju¯te‐Talimaa), Paralogania tarranti, Loganellia? unispinata and Goniporus alatus (Gross). In the highest Přídolí beds Paralogania kummerowi (Gross) and Loganellia cuneata (Gross) can be traced before the incoming of the lowermost Devonian taxon Turinia pagei (Powrie) along with Nikolivia gutta Karataju¯te‐Talimaa. Correlations with the Baltic are suggested from the Lower Ludlow, Upper Silurian, up to the Lower Lochkovian, Lower Devonian.

Thelodont Scales from the Lower Devonian Red Bay Group, Spitsbergen

Scales of nine thelodont taxa are described from the Red Bay Group of Spitsbergen, also characterized by its assemblage of other typical Early Devonian vertebrates. The four thelodont–bearing horizons of the lower Fraenkelryggen Formation yield typical Lochkovian thelodont assemblages, containing Boreania minima, Canonia grossi, Nikolivia depressa sp. nov., Nikolivia elongata, Nikolivia gutta and Turinia pagei. One horizon from the younger Ben Nevis Formation has a similar thelodont assemblage, except for two new taxa; Apalolepis angelica sp. nov. and Turinia barentsia sp. nov. The appearance of Turinia polita and the disappearance of Boreania minima is also characteristic for this assemblage. Comparison with similar faunas from the Northern Hemisphere supports this faunal change and allows further elaboration of Early Devonian thelodont biostratigraphy.

Thelodont fish and conodonts from the Early Devonian of Reefton, New Zealand

Thelodont scales and associated fragments of conodont elements identified as Turinia sp. cf. Turinia australiensis and Ozarkodina sp. cf. Ozarkodina buchanensis respectively are described for the first time from the Early Devonian Murray Creek Formation of Reefton, New Zealand. The conodont and thelodont components of the fauna suggest a late Pragian to early Emsian age for the assemblage.

Llandoverian thelodont scales from the Burnt Bluff group of Wisconsin and Michigan

Phosphatic microfossils including copious microvertebrates and conodont elements indicative of the upperIcriodella discreta–Icriodella deflectaZone (Aeronian) are found in a single bed of the Hendricks Formation, Burnt Bluff Group, Sturgeon Bay, Wisconsin. Scales of thelodonts, includingLoganelliasp. cf.Loganellia sibericaKarajute-Talimaa, 1978, and rareValyalepis cristaTurner (inTurner and Nowlan, 1995) predominate among the microvertebrate remains. Most scales are referred toZuegelepis potanusTurner new genus and species. Associated with the thelodont scales are rare phosphatic fragments of questionable dermal “bone” and scales, possibly of heterostracan origin. Thelodont scales are also found in the Hendricks Formation at Fayette State Park, Michigan and in the subsurface Byron Formation (Burnt Bluff Group) in Schoolcraft County, Michigan.

The Furcacaudiformes: a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and Devonian fossils from northern Canada

ABSTRACT A new order of “fork-tailed” agnathans (jawless vertebrates), the Furcacaudiformes, is described from Wenlockian (Silurian) and Lochkovian (Devonian) fossils from the Northwest Territories of Canada. Six new species are classified in five new genera and two new families. One Silurian species is in the genus Pezopallichthys, family Pezopallichthyidae. One Devonian species is described in each of the genera Cometicercus, Drepanolepis, and Sphenonectris. The Devonian genus Furcacauda includes two species, one new and another that was previously described as Sigurdia heintzae Dineley and Loeffler. Preliminary phylogenetic analysis suggests the following relationships within Furcacaudiformes: (Pezopallichthys (Cometicercus (Drepanolepis (Sphenonectris (Furcacauda)))). Furcacaudiforms resemble some previously described thelodonts in structure of their scales, which are of loganellid and nikoliviid types, but differ in having generally smaller scales, as well as in having laterally compressed, hump-backed bodies, large eyes, branchial openings in an oblique, condensed row, a prominent anal notch, and large, nearly symmetrical, forked and lobed tails. The distinctive tail may indicate a close relationship with Heterostraci. A large, barrel-shaped stomachlike chamber dominates the gut and is connected to the anal opening by a short, tapered intestine. Several Devonian species possess paired, ventral ‘fin-flaps’ and/or a dorsal fin; these structures are not universally present and may have been secondarily lost in some lineages.