Conodont anatomy, chordate phylogeny and vertebrate classification

Donoghue, Philip C. J.; Purnell, Mark A.; Aldridge, Richard J.

doi:10.1111/j.1502-3931.1998.tb00509.x

Cited by 37 publications

(8 citation statements)

References 44 publications

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“…Until the discovery of some specimens with elements of the soft anatomy preserved (Aldridge, 1987;Aldridge et al, 1986;Briggs et al, 1983;Gabbott et al, 1995), they had been interpreted as belonging to a number of invertebrate and vertebrate groups (see for a review of previously hypothesized conodont interrelationships), or assigned to a separate phylum (Sweet, 1988). Current suggestions include (a) that they are chordates lying outside of craniates/vertebrates (Aldridge, 1987;Aldridge & Briggs, 1990;Aldridge et al, 1986;Blieck et al, 2010;Pridmore et al, 1997;Turner et al, 2010), (b) that they occupy a basal position among crown vertebrates (Aldridge & Purnell, 1996;Aldridge & Theron, 1993;Briggs, 1992;Briggs & Kear, 1994;Donoghue et al, 2000;Donoghue, Purnell, & Aldridge, 1998;Gabbott et al, 1995;Purnell, 1995;Schubert, Escriva, Xavier-Neto, & Laudet, 2006;Sweet & Donoghue, 2001) or (c) that they are stem cyclostomes (Miyashita et al, 2019).…”

Section: Conodontamentioning

confidence: 99%

A critical appraisal of appendage disparity and homology in fishes

2019

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Fishes are both extremely diverse and morphologically disparate. Part of this disparity can be observed in the numerous possible fin configurations that may differ in terms of the number of fins as well as fin shapes, sizes and relative positions on the body. Here, we thoroughly review the major patterns of disparity in fin configurations for each major group of fishes and discuss how median and paired fin homologies have been interpreted over time. When taking into account the entire span of fish diversity, including both extant and fossil taxa, the disparity in fin morphologies greatly complicates inferring homologies for individual fins. Given the phylogenetic scope of this review, structural and topological criteria appear to be the most useful indicators of fin identity. We further suggest that it may be advantageous to consider some of these fin homologies as nested within the larger framework of homologous fin‐forming morphogenetic fields. We also discuss scenarios of appendage evolution and suggest that modularity may have played a key role in appendage disparification. Fin modules re‐expressed within the boundaries of fin‐forming fields could explain how some fins may have evolved numerous times independently in separate lineages (e.g., adipose fin), or how new fins may have evolved over time (e.g., anterior and posterior dorsal fins, pectoral and pelvic fins). We favour an evolutionary scenario whereby median appendages appeared from a unique field of competence first positioned throughout the dorsal and ventral midlines, which was then redeployed laterally leading to paired appendages.

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Section: Conodontamentioning

confidence: 99%

A critical appraisal of appendage disparity and homology in fishes

2019

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“…Conodonts are a large clade of stem gnathostomes, possessing a skeleton com posed of phosphatic elements that formed a bilaterally symmetrical feeding apparatus (Aldridge and Purnell 1996;Donoghue et al 1998). They have an excellent fossil record (Foote and Sepkoski 1999), unrivalled among vertebrates (Sweet and Donoghue 2001;Pur nell and Donoghue 2005).…”

Section: Introductionmentioning

confidence: 99%

Directional evolution in the conodontPterospathodus

Jones¹

2009

Paleobiology

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The excellent fossil record of conodonts represents an ideal, yet underutilized, resource for resolving fundamental issues of pattern and process in evolutionary theory. However, this potential has not been exploited because the quantitative understanding of the evolution of conodont element morphology is limited. This work applies standardized morphometric protocols to skeletal elements belonging to the conodontPterospathodus, derived from a densely sampled section from Estonia. It has established a robust quantitative framework for morphological variation inPterospathodus, permitting statistical analysis of the current qualitative hypotheses of evolutionary pattern within this genus for the first time. Apparent directional trends were statistically compared with patterns expected for directional evolution, an unbiased random walk and stasis, using maximum-likelihood model fitting, rescaled range analysis, and the runs test. Results confirmed the presence of trends in size and shape change through time, providing an example of convincing directional morphological change in a fossil lineage. The morphometric analyses have also allowed quantitative investigation of ontogenetic processes inPterospathodus, suggesting that allometric repatterning was the proximal mechanism responsible for mediating the observed shifts in morphology through time. The results have demonstrated that conodonts represent an important resource for understanding evolutionary pattern and process in the fossil record.

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“…Furthermore, conodonts provide a great resource to identify general functional principles of the evolution of dental tools at the biomechanical, morphological and histological level ( Jones, 2009 ; Jones et al, 2012a , 2012b ; Martínez-Pérez et al, 2014 ; Dzik, 2015 ; Martínez-Pérez et al, 2016 ; Guenser et al, 2019 ; Petryshen et al, 2020 ). Multiple modes of feeding have been proposed in the past, but only the macrophagous predator or scavenger ( Aldridge et al, 1986 ; Purnell, 1993 ) and filtering as a microphagous active suspension feeder ( Nicoll & Rexroad, 1987 ) are compatible with the conodont body plan ( Purnell & Donoghue, 1997 ; Donoghue, Purnell & Aldridge, 1998 ). These interpretations have been established in quantitative studies on growth dynamics ( Armstrong & Smith, 2001 ; Zhan, Aldridge & Donoghue, 1997 ), histology (Donoghue, 1997) and chemical composition ( Shirley et al, 2018 ; Balter et al, 2019 ) carried out mostly on “complex” conodonts.…”

Section: Introductionmentioning

confidence: 99%

Growth and feeding ecology of coniform conodonts

Leonhard

Shirley

Murdock

et al. 2021

PeerJ

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Conodonts were the first vertebrates to develop mineralized dental tools, known as elements. Recent research suggests that conodonts were macrophagous predators and/or scavengers but we do not know how this feeding habit emerged in the earliest coniform conodonts, since most studies focus on the derived, ‘complex’ conodonts. Previous modelling of element position and mechanical properties indicate they were capable of food processing. A direct test would be provided through evidence of in vivo element crown tissue damage or through in vivo incorporated chemical proxies for a shift in their trophic position during ontogeny. Here we focus on coniform elements from two conodont taxa, the phylogenetically primitive Proconodontus muelleri Miller, 1969 from the late Cambrian and the more derived Panderodus equicostatus Rhodes, 1954 from the Silurian. Proposing that this extremely small sample is, however, representative for these taxa, we aim to describe in detail the growth of an element from each of these taxa in order to the test the following hypotheses: (1) Panderodus and Proconodontus processed hard food, which led to damage of their elements consistent with prey capture function; and (2) both genera shifted towards higher trophic levels during ontogeny. We employed backscatter electron (BSE) imaging, energy-dispersive X-ray spectroscopy (EDX) and synchrotron radiation X-ray tomographic microscopy (SRXTM) to identify growth increments, wear and damage surfaces, and the Sr/Ca ratio in bioapatite as a proxy for the trophic position. Using these data, we can identify whether they exhibit determinate or indeterminate growth and whether both species followed linear or allometric growth dynamics. Growth increments (27 in Pa. equicostatus and 58 in Pr. muelleri) were formed in bundles of 4–7 increments in Pa. equicostatus and 7–9 in Pr. muelleri. We interpret the bundles as analogous to Retzius periodicity in vertebrate teeth. Based on applied optimal resource allocation models, internal periodicity might explain indeterminate growth in both species. They also allow us to interpret the almost linear growth of both individuals as an indicator that there was no size-dependent increase in mortality in the ecosystems where they lived e.g., as would be the case in the presence of larger predators. Our findings show that periodic growth was present in early conodonts and preceded tissue repair in response to wear and damage. We found no microwear and the Sr/Ca ratio, and therefore the trophic position, did not change substantially during the lifetimes of either individual. Trophic ecology of coniform conodonts differed from the predatory and/or scavenger lifestyle documented for “complex” conodonts. We propose that conodonts adapted their life histories to top-down controlled ecosystems during the Nekton Revolution.

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Conodont anatomy, chordate phylogeny and vertebrate classification

Cited by 37 publications

References 44 publications

A critical appraisal of appendage disparity and homology in fishes

A critical appraisal of appendage disparity and homology in fishes

Directional evolution in the conodontPterospathodus

Growth and feeding ecology of coniform conodonts

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