Chondrichthyans from the Lower Permian of Mechetlino, South Urals

Ivanov, Alexander

doi:10.3140/bull.geosci.1645

Cited by 4 publications

(2 citation statements)

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“…The second most common tooth histotype, orthodonty, evolved three times independently in modern sharks: in the frilled shark C. anguineus (Hexanchiformes), in carpet sharks (Orectolobiformes), and in ground sharks (Carcharhiniformes). Orthodont teeth were also reported for other Chondrichthyes in †Xenacanthimorpha (Hampe & Ivanov, 2007;Ivanov, 2016) and †Hybodontiformes (Maisey et al 2004). This indicates that the orthodont tooth histotype is a highly plastic feature that evolved several times independently in cartilaginous fishes and, therefore, makes phylogenetic interpretations of this histology pattern difficult.…”

Section: Eulermentioning

confidence: 84%

Evolutionary trajectories of tooth histology patterns in modern sharks (Chondrichthyes, Elasmobranchii)

Jambura

Türtscher

Kindlimann³

et al. 2019

Journal of Anatomy

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During their evolutionary history, modern sharks developed different tooth mineralization patterns that resulted in very distinct histological patterns of the tooth crown (histotypes). To date, three different tooth histotypes have been distinguished: (i) orthodont teeth, which have a central hollow pulp cavity in the crown, encapsulated by a prominent layer of dentine (orthodentine); (ii) pseudoosteodont teeth, which have their pulp cavities secondarily replaced by a dentinal core of porous dentine (osteodentine), encased by orthodentine; and (iii) osteodont teeth, which lack orthodentine and the whole tooth crown of which consists of osteodentine. The aim of the present study was to trace evolutionary trends of tooth mineralization patterns in modern sharks and to find evidence for the presence of phylogenetic or functional signals. High resolution micro-computed tomography images were generated for the teeth of members of all nine extant shark orders and the putative stem group †Synechodontiformes, represented here by three taxa, to examine the tooth histology non-destructively. Pseudoosteodonty is the predominant state among modern sharks and represents unambiguously the plesiomorphic condition. Orthodonty evolved several times independently in modern sharks, while the osteodont tooth histotype is only developed in lamniform sharks. The two shark orders Heterodontiformes and Pristiophoriformes showed highly modified tooth histologies, with Pristiophorus exhibiting a histology only known from batomorphs (i.e. rays and skates), and Heterodontus showing a histological difference between anterior and posterior teeth, indicating a link between its tooth morphology, histology and durophagous lifestyle. The tooth histotype concept has proven to be a useful tool to reflect links between histology, function and its taxonomic value for distinct taxa; however, a high degree of variation, especially in the pseudoosteodont tooth histotype, demonstrates that the current histotype concept is too simplistic to fully resolve these relationships. The vascularization pattern of the dentine might offer new future research pathways for better understanding functional and phylogenetic signals in the tooth histology of modern sharks.

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Section: Eulermentioning

confidence: 84%

Evolutionary trajectories of tooth histology patterns in modern sharks (Chondrichthyes, Elasmobranchii)

Jambura

Türtscher

Kindlimann³

et al. 2019

Journal of Anatomy

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“…The Symmoriiformes show a range of both low and high completeness value distributions. This is not surprising given the prominent members of this group such as Symmorium [125], Akmonistion [95], Cobelodus [126] or Falcatus [127] which are all known from at least partially articulated skeletons, while the low completeness levels stem from species described from isolated remains alone such as Kungurodus [128] or Denaea williamsi [129].…”

Section: Completeness Variation Between Chondrichthyan Taxonomic Groupsmentioning

confidence: 99%

The skeletal completeness of the Palaeozoic chondrichthyan fossil record

Schnetz,

Butler,

Coates

et al. 2024

R. Soc. Open Sci.

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Chondrichthyes (sharks, rays, ratfish and their extinct relatives) originated and diversified in the Palaeozoic but are rarely preserved as articulated or partly articulated remains because of their predominantly cartilaginous endoskeletons. Consequently, their evolutionary history is perceived to be documented predominantly by isolated teeth, scales and fin spines. Here, we aim to capture and analyse the quality of the Palaeozoic chondrichthyan fossil record by using a variation of the skeletal completeness metric, which calculates how complete the skeletons of individuals are compared to estimates of their original entirety. Notably, chondrichthyan completeness is significantly lower than any published vertebrate group: low throughout the Silurian and Permian but peaking in the Devonian and Carboniferous. Scores increase to a range similar to pelycosaurs and parareptiles only when taxa identified solely from isolated teeth, scales and spines are excluded. We argue that environmental influences probably played an important role in chondrichthyan completeness. Sea level significantly negatively correlates with chondrichthyan completeness records and resembles patterns already evident in records of ichthyosaurs, plesiosaurs and sauropodomorphs. Such observed variations in completeness highlight the impact of different sampling biases on the chondrichthyan fossil record and the need to acknowledge these when inferring patterns of chondrichthyan macroevolution.

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