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Copyright of Spanish Journal of Palaeontology is the property of Socieadad Espanola de Paleontologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sparse fish microremains have been found in marine limestones from the Middle Devonian (Givetian) Skały Formation (Sitka Coral-Crinoid Limestone Member and Sierżawy Member), Świętomarz-Śniadka section, Bodzentyn Syncline, Łysogóry Region, northern Holy Cross Mountains, associated with conodonts of the hemiansatus to ansatus zones. Thelodont scales referred here to Australolepis sp. cf. A. seddoni come from near Śniadka village, from samples dated as hemiansatus to rhenanus/varcus zones. This increases the known range for the genus from its original find in Western Australia. The presence of a thelodont in the late Middle Devonian in Poland extends the known distribution of turiniids around the peri-Gondwana shorelines of Palaeotethys. [ABSTRACT FROM AUTHOR]

Abstract: Here we explore the spatial, temporal and phylogenetic patterns of ecological diversification for the entire clade of thelodonts, one of the earliest groups of vertebrates and longest lasting of the Palaeozoic agnathans in the fossil record. Parsimony and maximum‐likelihood methods are used to reconstruct ancestral states of their geographical distributions, habitats and lifestyles. Our results support the concept that thelodonts originated during the Middle?–Late Ordovician probably in marine open waters of Laurasia, with a demersal lifestyle on hard substrates being the ancestral condition for the whole clade. Later, thelodonts underwent a complex ecological diversification and palaeobiogeographical history, comparable in many aspects to those of some major groups of living fishes. Different modes of life evolved repeatedly and a wide range of habitats were colonized by distinct groups, including deep waters and brackish marine and/or freshwater environments. Diadromous strategies presumably appeared on nine different occasions. The palaeobiogeographical history of thelodonts reveals significant differences in the dispersal potential of some major groups. Dispersal of thelodontiforms entailed displacements over long distances and the crossing of deep‐water biogeographical barriers, whereas those of furcacaudiforms were always limited to areas interconnected by shallow platforms. We propose that the evolution of pelagic larval stages in thelodontiforms might explain this biogeographical pattern and could satisfactorily account for the greater evolutionary success of this group. [ABSTRACT FROM AUTHOR]

Thelodonts are an enigmatic group of Paleozoic jawless vertebrates that have been well studied from taxonomical, biostratigraphic and paleogeographic points of view, although our knowledge of their ecology and mode of life is still scant. Their bodies were covered by micrometric scales whose morphology, histology and the developmental process are extremely similar to those of extant sharks. Based on these similarities and on the well-recognized relationship between squamation and ecology in sharks, here we explore the ecological diversity and lifestyles of thelodonts. For this we use classic morphometrics and discriminant analysis to characterize the squamation patterns of a significant number of extant shark species whose ecology is well known. Multivariate analyses have defined a characteristic squamation pattern for each ecological group, thus establishing a comparative framework for inferring lifestyles in thelodonts. We then use this information to study the squamation of the currently described 147 species of thelodonts, known from both articulated and disarticulated remains. Discriminant analysis has allowed recognizing squamation patterns comparable to those of sharks and links them to specific ecological groups. Our results suggest a remarkable ecological diversity in thelodonts. A large number of them were probably demersal species inhabiting hard substrates, within caves and crevices in rocky environments or reefs, taking advantage of the flexibility provided by their micromeric squamations. Contrary to classical interpretations, only few thelodonts were placed among demersal species inhabiting sandy and muddy substrates. Schooling species with defensive scales against ectoparasites could be also abundant suggesting that social interactions and pressure of ectoparasites were present in vertebrates as early the Silurian. The presence of species showing scales suggestive of low to moderate speed and a lifestyle presumably associated with open water environments indicates adaptation of thelodonts to deep water habitats. Scale morphology suggests that some other thelodonts were strong-swimming pelagic species, most of them radiating during the Early Devonian in association with the Nekton Revolution. [ABSTRACT FROM AUTHOR]

In situ rare-earth element (REE) compositions have been measured in early vertebrate microremains from the Lower Devonian basin of Andrée Land (Svalbard), with the aim of obtaining information about their early depositional environment and potential reworking. Vertebrate microremains with different histology were used for the analyses, sourced from two different localities of marginal marine to freshwater sediments from geographically distant parts of the Grey Hœk Formation (Skamdalen and Tavlefjellet members). We selected thelodont and undescribed ?chondrichthyan scales, which allowed us to define potential taxonomic, histological, and taphonomic variables of the REE uptake. Results showed REE concentrations to be relatively uniform within the scales of each taxon, but apparent discrepancies were visible between the studied localities and separate taxa. The compilation of REE abundance patterns as well as REE ratios have revealed that thelodont and ?chondrichthyan originating from the same locality must have had different burial and early diagenetic histories. The shapes of the REE profiles, together with the presence and absence of the Eu and Ce anomalies, equally suggested different depositional and diagenetic environments for these two sympatric taxa resulting from either stratigraphical or long-distance reworking. The REE concentrations appear to have visible differences between separate dental tissues, particularly between enameloid and dentine of thelodonts, emphasizing the importance of in situ measurements in microfossil biomineral geochemistry. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

SUMMARY The role of teeth and jaws, as innovations that underpinned the evolutionary success of living jawed vertebrates, is well understood, but their evolutionary origins are less clear. The origin of teeth, in particular, is mired in controversy with competing hypotheses advocating their origin in external dermal denticles ('outside-in') versus a de novo independent origin ('inside-out'). No evidence has ever been presented demonstrating materially the traditional 'outside-in' theory of teeth evolving from dermal denticles, besides circumstantial evidence of a commonality of structure and organogenesis, and phylogenetic evidence that dermal denticles appear earlier in vertebrate phylogeny that do teeth. Meanwhile, evidence has mounted in support of 'inside-out' theory, through developmental studies that have indicated that endoderm is required for tooth development, and fossil studies that have shown that tooth-like structures evolved before dermal denticles (conodont dental elements), that tooth replacement evolving before teeth (thelodont pharyngeal denticles), and that teeth evolved many times independently through co-option of such structures. However, the foundations of 'inside-out' theory have been undermined fatally by critical reanalysis of the evidence on which it was based. Specifically, it has been shown that teeth develop from dermal, endodermal or mixed epithelia and, therefore, developmental distinctions between teeth and dermal denticles are diminished. Furthermore the odontode-like structure of conodont elements has been shown to have evolved independently of dermal and internal odontodes. The tooth-like replacement encountered in thelodont pharyngeal odontodes has been shown to have evolved independently of teeth and tooth replacement and teeth have been shown to have evolved late within the gnathostome stem lineage indicating that it is probable, if not definitive, that teeth evolved just once in gnathostome evolution. Thus, the 'inside-out' hypothesis must be rejected. The phylogenetic distribution of teeth and dermal denticles shows that these odontodes were expressed first in the dermal skeleton, but their topological distribution extended internally in association with oral, nasal and pharyngeal orifices, in a number of distinct evolutionary lineages. This suggests that teeth and oral and pharyngeal denticles emerged phylogenetically through extension of odontogenic competence from the external dermis to internal epithelia. Ultimately, internal and external odontodes appear to be distinct developmental modules in living jawed vertebrates, however, the evidence suggests that this distinction was not established until the evolution of jawed vertebrates, not merely gnathostomes. [ABSTRACT FROM AUTHOR]

A diverse microvertebrate fauna is described from the Virgin Hills and Napier formations, Bugle Gap Limestone Canning Basin, Western Australia. Measured sections at Horse Spring and Casey Falls (Virgin Hills Formation) and South Oscar Range (Napier Formation) comprise proximal to distal slope carbonates ranging in age from the Late Devonian Frasnian to middle Famennian. A total of 18 chondrichthyan taxa are identified based on teeth, including the first record of Thrinacodus tranquillus, Cladoides wildungensis, Protacrodus serra and Lissodus lusavorichi from the Canning Basin. A new species, Diademodus dominicus sp. nov. is also described and provides the first record of this genus outside of Laurussia. In addition, the upper range of Australolepis seddoni has been extended to Late Devonian conodont Zone 11, making it the youngest known occurrence for this species. The Virgin Hills and Napier formations microvertebrate faunas show close affinities to faunas recovered from other areas of Gondwana, including eastern Australia, Iran, Morocco and South China, which is consistent with known conodont and trilobite faunas of the same age. [ABSTRACT FROM AUTHOR]

Rare scales of agnathan thelodonts Paralogania ludlowiensis and Thelodus sp. cf. T. parvidens, or alternatively Thelodus macintoshi, and acanthodian fishes Nostolepis striata, Gomphonchus sp., Gomphonchoporus sp. aff. G. hoppei, and Machaeraporus stonehousensis (Legault) n. gen., plus acanthodian fin spines, teeth and tooth whorls have been identified from the upper Moydart and Stonehouse formations near Arisaig, Nova Scotia. The assemblage agrees well with the late Silurian (uppermost Ludlow--Pridoli) age assigned to these strata based on invertebrate assemblages, and the vertebrate taxa show affinity with British and Baltic faunas of this age. All vertebrate-bearing strata were deposited in various positions off the western shores of the Avalonia terrane during or after its collision with Laurentia. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM PUBLISHER]

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 ofWoodfjordia collisagen. et sp. nov.,Talivalia svalbardiasp. nov.,Canoniacf.C. grossi,Amaltheolepismontiwatsoniasp. nov.,AmaltheolepiswinsnesiandAmaltheolepisaustfjordiasp. 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. [ABSTRACT FROM PUBLISHER]

The Silurian thelodont Phlebolepis elegans Pander from Saaremaa, Estonia, is one of the most-often illustrated early vertebrates, yet its external morphology has remained poorly known and experts seldom agree about its probable body form. We examined hundreds of articulated specimens from the type locality (Himmiste Quarry) to reconstruct its morphological features. We found that a reconstruction published more than four decades ago by A. Ritchie was the best available till now. We disagreed mostly in that the mouth is not terminal, but subterminal, and there is a slight development of a rostrum dorsal to the mouth. The pectoral fin originates close behind the orbits, but is otherwise similar to Ritchie's reconstruction. We also found the caudal fin to be much larger, more flexible and more symmetrical (though not perfectly symmetrical) than earlier reconstructions, with a large dorsal lobe and an even larger ventral lobe, and a fin web supported by slender 'ray-like' scale-covered lobes. The shape, number and location of the branchial openings are notably still not certainly known. Our preferred morphological features are represented by an artist's restoration. With this revised understanding, future representations of Phlebolepis elegans can be based on more reliable information and its morphology can be compared more accurately with that of other early vertebrates. [ABSTRACT FROM AUTHOR]

A partly preserved squamation of Thelodus laevis (Pander) from the Himmiste outcrop (Saaremaa Island, Estonia) is described. Most of the trunk with a pectoral fin fragment and three fragments of posterior fins are present, while part of the head and the caudal fin are absent. Ontogenetic development of the scale cover of T. laevis is explained by comparing it with the squamation of Lanarkia horrida Traquair, Loganellia scotica (Traquair) and a modern fish. It is supposed that newly forming trunk scales of early juvenile Thelodus were smooth and rhomboidal. When the individual grew, ridged scales were added between smooth ones in irregular rows in the posterior part of the trunk. Adult individuals were covered with species-specific scales with particular morphology and sculpture of the crown. Co-occurrence of smooth and ridged scales on the trunk in the specimen studied corresponds to a young stage of ontogeny. [ABSTRACT FROM AUTHOR]

In the marine Přidolian to early Lochkovian environments of Podolia, vertebrates were rep- resented almost exclusively by thelodonts and acanthodians. Starting from the mid Lochko- vian (Chortkiv Formation), the heterostracans increased their abundance and diversity. Diverse macroscopic remains of the cyathaspidid heterostracans, the first small-size ptera- spidids and osteostracans appeared in the late Lochkovian (Ivanie Formation). The Old Red-type ecosystem of Podolia gradually emerged with retreat of the sea. Simultaneously, various agnathans, with ecological preferences to brackish or fresh waters, appeared. At the transition to the Pragian (red-bed Dniester Formation), when coarse terrigenous quartz sand gradually replaced fine carbonate silt and clay, the armoured vertebrate community reached its peak diversity, especially regarding the osteostracans and pteraspidid heterostracans. Many local lineages developed but some ties of the heterostracan faunas with those of west- ern European and the osteostracan faunas with Spitsbergen ones are traceable. Most evolu- tionary series recognised show increase in body size, both regarding the heterostracans and osteostracans. Taxonomic diversity decreased with coarsening of the sandy sediment and in- crease of sedimentation rate, culminating in complete disappearance of fish fossils before the Emsian. The sensory line system of the pteraspidids, with supraorbital commissures devel- oped on the rostral plate and arrangement of dorsomedial canals on the dorsal shield, is pro- posed to have high diagnostic value. Some 33 species, belonging to 20 genera of the hetero- stracans and 16 species of 9 genera of the osteostracans, are described. Althaspis tarloi sp. n., Djurinaspis secunda sp. n., Palanasaspis chekhivensis gen. et sp. n., Podolaspis danieli sp. n., Semipodolaspis slobodensis gen. et sp. n., and Zenaspis kasymyri sp. n. are proposed. [ABSTRACT FROM AUTHOR]

The article discusses the controversies in determining fin homologies among early vertebrates. It discusses molecular and developmental evidence for the evolution of paired fins. Early vertebrates such as euphaneropids, anaspida, thelodonti, and osteostraci are described. It is concluded that the fin or fin-like structures characterizing a variety of jawless vertebrates are developed from somites and are supported by fin radials.

Knowledge of the Thelodonti has improved greatly in recent years, but phylogenetic relationships remain poorly understood. We revised the data from an earlier phylogenetic study and added 15 scale-based species. Maximum parsimony analysis gives a well-resolved tree in which Archipelepis and Boothialepis form a basal clade, recognized here as the order Archipelepidiformes, sister group to two large clades also recognized as orders. The first is recognized as the order Furcacaudiformes, including Nikolivia, Lanarkia, Phillipsilepis, Pezopallichthys, Drepanolepis (in the new family Drepanolepididae), Barlowodus, Apalolepis, and Furcacaudidae. The second, here recognized as the Thelodontiformes, contains Turinia, Thelodus, Stroinolepis, Loganellia, Longodus, Helenolepis, Phlebolepis, Erepsilepis, Trimerolepis, Eestilepis, Valiukia, Paralogania, and Shielia. [ABSTRACT FROM AUTHOR]

The thelodont Loganellia cuneata (Gross) is redescribed and new thelodont taxa Paralogania perensae sp. nov., Nethertonodus laadjalaensis sp. nov., and Longodus acicularis gena. et sp. nov. are established. The last taxon belongs to the family Longodidae fam. nov. of Thelodonti but its order is uncertain. This assemblage comes from the Tahula Beds of the Kuressaare Stage, Ludlow, Upper Silurian of Estonia. [ABSTRACT FROM AUTHOR]

A thelodont Oeselia mosaica gen. et sp. nov. is described from the Upper Wenlock and Lower Ludlow (Silurian) of Estonia and Latvia. The species has very small to small scales and shows low variation in scale morphology, simple branching dentine tubules, and a specific ultrasculpture with polygons of irregular shape, separated by narrow grooves. [ABSTRACT FROM AUTHOR]

Sediments with the squamations of Phlebolepis elegans Pander at Himmiste-Kuigu were formed in a lagoon of the Palaeobaltic Sea, situated in the tropical realm during Himmiste time of the Paadla Age, Ludlow, late Silurian. From the micro- and macrolithological features of the rocks, and the distribution of facies during Himmiste time it is concluded that the thelodonts died in a shallow depression on the bottom of the lagoon behind the reef belt towards the land; the depression acted as a trap during low tide. Unfavourable conditions, primarily the lack of oxygen in warm and shallow water, caused the perishing of the Phlebolepis shoal. Very low wave activity prevented post-mortem disintegration of the squamation and rapid conservation in mud saved the exoskeletons from scattering. [ABSTRACT FROM AUTHOR]

Paralogania species in the Rootsiküla (Wenlock) and Paadla (Ludlow) stages from Saaremaa Island, Estonia, were re-studied. Extremely well preserved scales of P. martinssoni (Gross) were described from Silma Cliff (Himmiste Beds of the Paadla Stage) and compared with the scales from Vesiku Brook (Vesiku Beds of the Rootsiküla Stage), the type locality of the species. Paralogania kaarmisensis sp. nov. was established on the basis of relatively large, strongly elongate scales carrying a row of very fine spines laterally of the crown; the scales have one to two fine oblique ridges above the row of spines. The new species has a short range in the Phlebolepis elegans Biozone (Ludlow, Upper Silurian). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Describes the thelodont scales discovered in the Burnt Bluff Group of Wisconsin and Michigan. Sturgeon Bay thelodont occurrence; Other occurrences; Systematic paleontology.

The 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-A633-201CDB982445 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation 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. [ABSTRACT FROM AUTHOR]