Taphonomy and sedimentology of an echinoderm obrution bed in the Lower Devonian Voorstehoek Formation (Bokkeveld Group, Cape Supergroup) of South Africa

Reid, Mhairi; Bordy, Emese M.; Taylor, Wendy L.

doi:10.1016/j.jafrearsci.2015.04.009

Cited by 15 publications

(5 citation statements)

References 48 publications

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“…) and Early Devonian fossil ophiuroids of South Africa (Reid et al. ). The present study, however, is the first to use digital models based on micro‐CT scans for mobility analysis of the brittle star skeleton.…”

Section: Discussionmentioning

confidence: 99%

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

et al. 2018

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Brittle stars (Phylum Echinodermata, Class Ophiuroidea) have evolved rapid locomotion employing muscle and skeletal elements within their (usually) five arms to apply forces in a manner analogous to that of vertebrates. Inferring the inner workings of the arm has been difficult as the skeleton is internal and many of the ossicles are sub‐millimeter in size. Advances in 3D visualization and technology have made the study of movement in ophiuroids possible. We developed six virtual 3D skeletal models to demonstrate the potential range of motion of the main arm ossicles, known as vertebrae, and six virtual 3D skeletal models of non‐vertebral ossicles. These models revealed the joint center and relative position of the arm ossicles during near‐maximal range of motion. The models also provide a platform for the comparative evaluation of functional capabilities between disparate ophiuroid arm morphologies. We made observations on specimens of Ophioderma brevispina and Ophiothrix angulata. As these two taxa exemplify two major morphological categories of ophiuroid vertebrae, they provide a basis for an initial assessment of the functional consequences of these disparate vertebral morphologies. These models suggest potential differences in the structure of the intervertebral articulations in these two species, implying disparities in arm flexion mechanics. We also evaluated the differences in the range of motion between segments in the proximal and distal halves of the arm length in a specimen of O. brevispina, and found that the morphology of vertebrae in the distal portion of the arm allows for higher mobility than in the proximal portion. Our models of non‐vertebral ossicles show that they rotate further in the direction of movement than the vertebrae themselves in order to accommodate arm flexion. These findings raise doubts over previous hypotheses regarding the functional consequences of ophiuroid arm disparity. Our study demonstrates the value of integrating experimental data and visualization of articulated structures when making functional interpretations instead of relying on observations of vertebral or segmental morphology alone. This methodological framework can be applied to other ophiuroid taxa to enable comparative functional analyses. It will also facilitate biomechanical analyses of other invertebrate groups to illuminate how appendage or locomotor function evolved.

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Section: Discussionmentioning

confidence: 99%

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

et al. 2018

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“…According to Brett et al (1997), echinoids can be transported still articulated in few hours after their death. Fragments in these coquinas indicate the influence of mixed taphonomic processes, related to energy events that would have carried remains of fossil from other areas and incorporated them into the bottom sediment for longer periods (Speyer & Brett 1991, Reid et al 2015. Therefore, part of the fauna preserved in these coquinas would have represented para-autochthonous and or allochthonous individuals.…”

Section: Typementioning

confidence: 99%

Tafonomy of macroinvertebrates and Albian marine ingression as recorded by the Romualdo Formation (Cretaceous, Araripe Basin, Brazil)

2018

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The Romualdo Formation, Araripe Basin, crops out in the municipality of Exu, Pernambuco State, exposing coquinas. Fauna survey, taphonomic analysis of the macrobenthos, and identification of sedimentary facies of the outcrop were carried out to contribute to paleoenvironmental understanding of the Romualdo Formation. The association of molluscs (Cerithium sp., Tylostoma ranchariensis, Aguileria dissita, Brachidontes araripensis and unidentified cassiopids) and echinoids of the species Bothryopneustes araripensis suggests sedimentation in the marine environment. The taphonomic similarities made possible the grouping of coquinas into two types. Coquinas type 1 exhibit characteristics of transport and reworking of bioclast generated by storms in proximal setting. Coquinas type 2 demonstrates echinoids in situ and articulated with spines connected to shells, suggesting a fast sedimentation by distal tempestite. Regarding sedimentary facies, the concentrations of invertebrates would have been formed in the transitional offshore zone of siliclastic platform. The results presented here evidence a broader distribution of echinoids and expand the geographic limits of the shallow marine environment in the Romualdo Formation.

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“…The initial discovery of the Karbonaatjies bed occurred during a preliminary study in 2014, when collected samples revealed rare, well-preserved individuals of an undescribed taxon of ophiuroid and stylophorans [22]. The study area is located within the Cape Fold Belt, and the exposed rocks lithostratigraphically belong to the Lower Devonian (Emsian ∼400 Ma) Voorstehoek Formation, Bokkeveld Group in South Africa [23].…”

Section: Data Descriptionmentioning

confidence: 99%

A micro X-ray computed tomography dataset of fossil echinoderms in an ancient obrution bed: a robust method for taphonomic and palaeoecologic analyses

et al. 2018

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Background Taphonomic and palaeoecologic studies of obrution beds often employ conventional methods of investigation such as physical removal and extraction of fossils from their host rock (matrix) by mechanical preparation. This often-destructive method is not suitable for studying mold fossils, which are voids left in host rocks due to dissolution of the original organism in post-depositional processes. Findings Microcomputed tomography (µCT) scan data of 24 fossiliferous rock samples revealed thousands of Paleozoic echinoderms. Digitally "stitching" together individually µCT scanned rock samples within three-dimensional (3D) space allows for quantifiable taphonomic data on a fossil echinoderm-rich obrution deposit from the Devonian (Emsian) of South Africa. Here, we provide a brief step-by-step guide on creating, segmenting, and ultimately combining sections of richly fossiliferous beds to create virtual models suited for the quantitative and qualitative taphonomic analyses of fossil invertebrate assemblages. Conclusions Visualizing the internal features of fossiliferous beds in 3D is an invaluable taphonomic tool for analyzing delicate fossils, accounting for all specimens irrespective of their preservation stages and with minimal damage. This technique is particularly useful for analyzing fossiliferous deposits with mold fossils that prove to be difficult to study with traditional methods, because the method relies on the large density contrast between the mold and host rock.

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Taphonomy and sedimentology of an echinoderm obrution bed in the Lower Devonian Voorstehoek Formation (Bokkeveld Group, Cape Supergroup) of South Africa

Cited by 15 publications

References 48 publications

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

Tafonomy of macroinvertebrates and Albian marine ingression as recorded by the Romualdo Formation (Cretaceous, Araripe Basin, Brazil)

A micro X-ray computed tomography dataset of fossil echinoderms in an ancient obrution bed: a robust method for taphonomic and palaeoecologic analyses

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