Growth and patterning in the conodont skeleton

Donoghue, Philip C. J.

doi:10.1098/rstb.1998.0231

Cited by 108 publications

(158 citation statements)

References 75 publications

(139 reference statements)

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“…The immediate oral subsurface of the platform in the Palmatolepis P 1 element is composed of surface-normal crystallites (¢gure 2b^d ) and the overhanging underside of the platform is Microstructural variation in conodont enamel P. C. J. Donoghue 1693 composed of crystallites that are orientated subperpendicular to the surface. The crown tissue also includes vacuities and areas of hypomineralization (¢gure 2c) (Donoghue 1998) and there is poor crystallographic continuity between the increments of growth, as evidenced by prominent incremental growth lines (¢gure 2b^d ). There is no evidence of any di¡erentiation of the crown microstructure within the platform.…”

Section: (B) Palmatolepismentioning

confidence: 99%

“…This implies that the characteristic mineralized feeding apparatus of conodonts represents the ¢rst vertebrate experiment in skeletonization. Furthermore, comparison of the histology and morphogenesis of conodont and vertebrate hard tissues indicates that the developmental basis for the vertebrate dermal and visceral skeleton was already established in the latest common ancestor of conodonts and all more derived vertebrates (Donoghue 1998;Donoghue & Aldridge 2001). Thus, conodonts provide a unique insight into the plesiomorphic condition of the vertebrate skeleton.…”

Section: Introductionmentioning

confidence: 99%

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Microstructural variation in conodont enamel is a functional adaptation

Donoghue

2001

Proc. R. Soc. Lond. B

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Recognition that conodonts were the earliest vertebrate group to experiment with skeletal biomineralization provides a window in which to study the origin and early evolution of this developmental system. It has been contended that the conodont skeleton comprised a classic suite of vertebrate hard tissues, while others suggest that conodont hard tissues represent divergent specializations within the early diversi¢cation of vertebrate hard tissues, supporting a view that the hard tissues of conodonts, particularly enamel, exhibit a range of microstructural variation beyond that seen in vertebrates. New evidence reveals that, although variable, conodont enamel microstructure is consistent between homologous portions of homologous dentitions. Although there is a correlation between morphology and microstructure, this belies a stronger correlation between the commonality of microstructure and dental function. The enamel of conodonts evolved in response to changes in dental function and di¡erentiation of the microstructural layer into a number of enamel types and can be linked to dental occlusion, heterodonty, a permanent dentition, enamel thickness and, probably above all, the small size of the dental elements.

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Section: (B) Palmatolepismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microstructural variation in conodont enamel is a functional adaptation

Donoghue

2001

Proc. R. Soc. Lond. B

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“…Little is known about the endoskeleton of fossil jawless vertebrates [e.g., fossil cyclostomes (hagfishes and lampreys) and "ostracoderms"]. Although the view is still debated (2), euconodonts would have possessed the very first vertebrate mineralized skeleton in the form of their oral denticles (3,4).…”

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confidence: 99%

Synchrotron-aided reconstruction of the conodont feeding apparatus and implications for the mouth of the first vertebrates

Goudemand

Orchard

Urdy

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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The origin of jaws remains largely an enigma that is best addressed by studying fossil and living jawless vertebrates. Conodonts were eel-shaped jawless animals, whose vertebrate affinity is still disputed. The geometrical analysis of exceptional three-dimensionally preserved clusters of oro-pharyngeal elements of the Early Triassic Novispathodus, imaged using propagation phase-contrast X-ray synchrotron microtomography, suggests the presence of a pulley-shaped lingual cartilage similar to that of extant cyclostomes within the feeding apparatus of euconodonts ("true" conodonts). This would lend strong support to their interpretation as vertebrates and demonstrates that the presence of such cartilage is a plesiomorphic condition of crown vertebrates.apical cartilage | conodont oral skeleton | early vertebrates | homology H ow the transition from "agnathans" to gnathostomes ("jawed" vertebrates) occurred is one of the most intriguing problems of evolutionary biology (1). Little is known about the endoskeleton of fossil jawless vertebrates [e.g., fossil cyclostomes (hagfishes and lampreys) and "ostracoderms"]. Although the view is still debated (2), euconodonts would have possessed the very first vertebrate mineralized skeleton in the form of their oral denticles (3, 4).The general architecture of the conodont oral skeleton is a bilaterally symmetrical array of usually 15 phosphatic elements, which generally becomes disarticulated after the decay of the supporting tissues. Hence most conodonts are known only as isolated elements. From the detailed study of hundreds of articulated "natural assemblages" and photographic simulation of their collapse, Purnell and Donoghue (5) constructed a 3D model of the Idiognathodus apparatus [presumably a template for all ozarkodinid apparatuses (6)] in which one pair of obliquely pointed M elements are located rostrally and, behind them, one unpaired S 0 (subscript number indicates distance ordering from the symmetry axis) element lying on the axis of bilateral symmetry and four pairs of elements (S 1-4 ) located on both sides of the S 0 would have grasped food and, more caudally, two pairs of pectiniform elements (P 1 , P 2 ) would have processed this food by crushing and/or slicing (5, 7, 8) ( Fig. 1 A-B) (for "standard" orientation of single elements, see Fig. S1). Purnell and Donoghue's reconstruction of a generalized resting (dead) position is very well supported and in most aspects very convincing. It is therefore adopted here as a basis upon which we build our dynamic reconstruction of the feeding apparatus at work.How could these elements actually grasp or cut prey tissues? Purnell and Donoghue's functional model (section 6 of ref. 5) was based chiefly on analogies with extant agnathans. Indeed, the "quite simple" geometry of the Idiognathodus elements does not provide much indication of what motions are possible or not [except for uncommon natural assemblages (see below)]. Thus, hypotheses were inferred from extant putative closest relatives. In our view, the more "compli...

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“…These elements formed an oropharyngeal feeding array at the anterior of an eel-like animal, and were used to capture and process prey. Despite being the earliest vertebrates with mineralized tissues [3,4], and a notable component of marine ecosystems from the Cambrian to the Triassic [5], the range in feeding ecology of this group is virtually unknown. In the 'complex' conodonts (prioniodontids, sensu [5]), the apparatus can be divided broadly into two suites of morphologically distinct elements: an array of rostral food acquisition ramiform elements (bearing a number of more or less elongate processes); and pairs of caudal 'platform' (blade-like and molar-like) elements proposed to perform a role in food processing [6].…”

Section: Introductionmentioning

confidence: 99%

Cutting the first ‘teeth’: a new approach to functional analysis of conodont elements

2013

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The morphological disparity of conodont elements rivals the dentition of all other vertebrates, yet relatively little is known about their functional diversity. Nevertheless, conodonts are an invaluable resource for testing the generality of functional principles derived from vertebrate teeth, and for exploring convergence in a range of food-processing structures. In a few derived conodont taxa, occlusal patterns have been used to derive functional models. However, conodont elements commonly and primitively exhibit comparatively simple coniform morphologies, functional analysis of which has not progressed much beyond speculation based on analogy. We have generated high-resolution tomographic data for each morphotype of the coniform conodont Panderodus acostatus. Using virtual cross sections, it has been possible to characterize changes in physical properties associated with individual element morphology. Subtle changes in cross-sectional profile have profound implications for the functional performance of individual elements and the apparatus as a whole. This study has implications beyond the ecology of a single conodont taxon. It provides a basis for reinterpreting coniform conodont taxonomy (which is based heavily on cross-sectional profiles), in terms of functional performance and ecology, shedding new light on the conodont fossil record. This technique can also be applied to more derived conodont morphologies, as well as analogous dentitions in other vertebrates and invertebrates.

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Growth and patterning in the conodont skeleton

Cited by 108 publications

References 75 publications

Microstructural variation in conodont enamel is a functional adaptation

Microstructural variation in conodont enamel is a functional adaptation

Synchrotron-aided reconstruction of the conodont feeding apparatus and implications for the mouth of the first vertebrates

Cutting the first ‘teeth’: a new approach to functional analysis of conodont elements

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