<i>Actinolepis spinosa</i>n. sp. (Arthrodira) from the Early Devonian of Latvia

Mark-Kurik, Elga

doi:10.1080/02724634.1985.10011866

Cited by 17 publications

(24 citation statements)

References 3 publications

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“…Supragnathals have been described for the actinolepid Actinolepis spinosa (Fig. 10D, ASG, PSG ;Mark-Kurik, 1985) including anterior and posterior ' dental fields '. Graded size sequences can be seen for the teeth included in these fields, and they conform best to the tooth rows described above.…”

Section: Placoderm Dentitions : Contribution Of Teeth and Denticlesmentioning

confidence: 99%

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Johanson¹,

Smith

2005

Biol. Rev.

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The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm dentition. A consensus view emerged that a dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crow...

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Section: Placoderm Dentitions : Contribution Of Teeth and Denticlesmentioning

confidence: 99%

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Johanson¹,

Smith

2005

Biol. Rev.

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“…A large PN plate is also known in Bryantolepis (Denison 1958(Denison , 1978. In Actinolepis the PN plates are wide but short and border the PrO and PtO plates anteriorly (Mark-Kurik 1973). An especially large PN plate is known in the rhenanid Brindabellaspis (Young 1980).…”

Section: Figures 2mentioning

confidence: 96%

“…3A), the Pi plate lies in a shallow embayment formed of the anterior margins of the PrO plates, and probably had its own ossification centre, marked with a protuberance. Similarly to the Actinolepis species (Mark-Kurik 1973) and Coccosteus cuspidatus (Miles & Westoll 1968, text- fig. 9e, f) there is no pineal opening.…”

Section: Figures 2mentioning

confidence: 96%

“…The Eukaia skull roof plate pattern is simple, resembling that of actinolepidoids, such as Baringaspis (Miles 1973) and Actinolepis (Mark-Kurik 1973), but the anterior part of the skull roof is only slightly narrower than the posterior part. It is significant that Eukaia has no dermal nasal capsule consisting of the R, Pi and PN plates, as known in many actinolepidoids: Kujdanowiaspis (Stensiö 1945), Erikaspis (Dupret et al 2007), Eskimaspis (Dineley & Liu 1984), Simblaspis (Denison 1958) and others.…”

Section: Figures 2mentioning

confidence: 97%

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A new Lower Devonian arthrodire (Placodermi) from the NW Siberian Platform

Mark-Kurik¹

2013

Estonian J. Earth Sci.

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A new genus and species of arthrodires, Eukaia elongata (Actinolepidoidei, Placodermi), is described from the Lower Devonian, ?Pragian of the Turukhansk region, NW Siberian Platform. A single specimen of the fish, a skull roof, comes probably from the lower part of the Razvedochnyj Formation. The occurrence of an actinolepidoid arthrodire in the Early Devonian of this area of Siberia is unexpected. Eukaia shows some distant relationship with the genus Actinolepis, but several features indicate similarity to representatives of other arthrodires

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“…Denison (1979) reinterpreted Helenacanthus incurvus as an ischnacanthid dentigerous jawbone; however, its resemblance to isolated placoderm gnathal bones from the Emsian Water Canyon Formation, Utah (Denison, 1958, fig. 101f) and the lower jaws of Actinolepis spinosa Mark-Kurik, 1985 from the Early Devonian of Latvia, indicate that the element is probably an actinolepid placoderm infragnathal (Burrow, 2004a). Denison (1960), in his description of the fish fauna from the Holland Quarry Shale, Ohio, regarded Machaeracanthus minor as a synonym of Onchus penetrans; he also referred spines from that locality to Onchus cf.…”

Section: Introductionmentioning

confidence: 96%

Early Devonian (Emsian) Acanthodian Faunas of the Western Usa

Burrow

2007

Journal of Paleontology

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Actinolepis spinosan. sp. (Arthrodira) from the Early Devonian of Latvia

Cited by 17 publications

References 3 publications

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

A new Lower Devonian arthrodire (Placodermi) from the NW Siberian Platform

Early Devonian (Emsian) Acanthodian Faunas of the Western Usa

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