Exceptional basal-body preservation in some Early Triassic conodont elements from Oman

Souquet, Louise; Goudemand, Nicolas

doi:10.1016/j.palaeo.2019.01.028

Cited by 10 publications

(5 citation statements)

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“…The P 1 conodont element assemblage analysed here comes from the Wadi ad Daffah WAD‐2 block (samples F to I of Souquet & Goudemand (2019); GPS coordinates: 22°22′18.5″ N, 59°39′46.0″ E), in the governorate of Ash Sharqiyah South, Sultanate of Oman. WAD‐2 is part of the Hawasina nappes, which are described as allochthonous Permo‐Triassic material within Jurassic sediments (Baud et al .…”

Section: Methodsmentioning

confidence: 99%

“…We expect that the former species boundary might be blurred if the relative abundance of specimens with intermediate morphologies is high compared to those with unambiguous morphologies. Our material comprises hundreds of exceptionally well‐preserved conodont P 1 elements from the Wadi ad Daffah 2 section, Sultanate of Oman (Souquet & Goudemand 2019). This assemblage is from one rock horizon dated to early Smithian (earliest Olenekian, Early Triassic, c .…”

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When less is more and more is less: the impact of sampling effort on species delineation

et al. 2022

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Taxonomy is the very first step of most biodiversity studies, but how confident can we be in the taxa delineation? One may hypothesize that the more abundant the material, the more accurate the description of morphological variability and hence the better the taxonomic delineation. Yet, as we shall see, in the case of numerous transitional forms, this hypothesis may prove wrong. Similarly to rarefaction curves that assess the degree of knowledge on taxonomic diversity through sampling effort, we aim to test the impact of sampling effort on species delineation by subsampling a given assemblage. To do so, we use an abundant and morphologically diverse conodont fossil assemblage from the Smithian of Oman. We first recognize four well established morphospecies but about 80% of the specimens are transitional forms. We quantify the diagnostic characters in a sample of 159 P1 elements using geometric morphometrics and assess, via gradually subsampling the assemblage, the number of morphometric groups (i.e. morphospecies) using ordination and clustering analyses. Four morphospecies were detected when less than 20% of the specimens were considered. The number of detected clusters dropped to two when including more than 30% of the specimens. Such influence of sampling effort on species delineation highlights the complexity of taxonomic work, especially when transitional forms are more abundant than typical specimens. These results should encourage researchers to extensively illustrate, measure and quantitatively compare their material to better constrain the morphological variability and delineation of taxa.

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When less is more and more is less: the impact of sampling effort on species delineation

et al. 2022

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“…Euconodont (or “true conodonts”) elements consist of hypermineralized crown tissue and the dentine-like basal body ( Bengtson, 1976 ). The basal body is organic-rich, poorly mineralized and rarely preserved ( Lindström, 1965 ; Souquet & Goudemand, 2020 ). The crown tissue is composed of hyaline lamellar tissue and, in some conodont taxa, white matter, which is unique to conodonts ( Pander, 1856 ; Hass, 1941 ; Müller & Nogami, 1971 ).…”

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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“…2018), and are interpreted as seamount deposits reflecting open ocean conditions. In Oman, these offshore records yield large numbers of exceptionally well‐preserved and pristine Early Triassic conodont elements (Orchard 1995), even with occasionally preserved basal bodies (Souquet & Goudemand 2020). Such abundant and well‐preserved conodont elements are key to understanding the intra‐ and interspecies‐level variation of conodonts, on which a sound and robust taxonomy must be based.…”

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confidence: 99%

“…2019; Chen et al . 2019; Souquet & Goudemand 2020). However, relatively little is known from offshore records in Oman (Tozer & Calon 1990; Orchard 1995; Pillevuit et al .…”

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An expanded Smithian–Spathian (Lower Triassic) boundary from a reefal build‐up record in Oman: implications for conodont taxonomy, high‐resolution biochronology and the carbon isotope record

Leu¹,

Bucher²,

Baud

et al. 2023

Papers in Palaeontology

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Some 2.7 myr after the Permian-Triassic boundary mass extinction, a stepwise extinction of the nekton (ammonoids and conodonts) ended at the Smithian-Spathian boundary (SSB) during an episode of climate cooling. SSB records from continental shelves are usually affected by an unconformity, suggesting a forced regression of glacioeustatic origin. Here, we document a new 30-m-thick SSB section from Jebel Aweri (Batain Plain, Oman) that provides an exceptionally complete and expanded record preserved in an exotic block. Most of this SSB section consists of microbial boundstone build-ups with a framework of metazoan bioclasts that formed in shallow water on an offshore seamount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block records the SSB in a deeper water setting represented by Hallstatt-type facies. These two sections provide a unique perspective on the early Spathian rapid re-diversification of conodonts. They led to a thorough revision of conodont taxonomy around the SSB and to the construction of the highest resolution biochronological scheme for this time interval in the Tethys. A total of five SSB sections from Oman representing both offshore seamounts and lower slope deposits were included in a high-resolution, quantitative unitary associations (UA) analysis. The resulting 8 conodont biozones are intercalibrated with ammonoid zones and with the carbonate carbon isotope record ultimately placing the SSB in the interval of separation between UAZ 3 and UAZ 4 . Only the association of Novispathodus pingdingshanensis with Icriospathodus crassatus can be used to unambiguously characterize the base of the Spathian.

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Exceptional basal-body preservation in some Early Triassic conodont elements from Oman

Cited by 10 publications

References 43 publications

When less is more and more is less: the impact of sampling effort on species delineation

When less is more and more is less: the impact of sampling effort on species delineation

Growth and feeding ecology of coniform conodonts

An expanded Smithian–Spathian (Lower Triassic) boundary from a reefal build‐up record in Oman: implications for conodont taxonomy, high‐resolution biochronology and the carbon isotope record

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