Exceptionally Preserved Cambrian Fossils in the Genomic Era

Ortega‐Hernández, Javier

doi:10.1007/978-3-030-18202-1_3

Cited by 3 publications

(2 citation statements)

References 67 publications

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“…The Cambrian fossil record has produced fundamental insights into the morphology and initial diversification of animal phyla, with euarthropod evolution standing as a prime example of the impact of palaeontological data towards reconstructing the origin of major extant groups [1][2][3]. Our current understanding of the early history of euarthropods is made possible by the unusual abundance of exceptionally preserved biotas in Cambrian deposits [4][5][6][7][8], which capture details of the non-biomineralized anatomy that would normally be lost to decay, even under other pathways for exceptional preservation [9,10].…”

Section: Introductionmentioning

confidence: 99%

Proclivity of nervous system preservation in Cambrian Burgess Shale-type deposits

2019

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Recent investigations on neurological tissues preserved in Cambrian fossils have clarified the phylogenetic affinities and head segmentation in pivotal members of stem-group Euarthropoda. However, palaeoneuroanatomical features are often incomplete or described from single exceptional specimens, raising concerns about the morphological interpretation of fossilized neurological structures and their significance for early euarthropod evolution. Here, we describe the central nervous system (CNS) of the short great-appendage euarthropod Alalcomenaeus based on material from two Cambrian Burgess Shale-type deposits of the American Great Basin, the Pioche Formation (Stage 4) and the Marjum Formation (Drumian). The specimens reveal complementary ventral and lateral views of the CNS, preserved as a dark carbonaceous compression throughout the body. The head features a dorsal brain connected to four stalked ventral eyes, and four pairs of segmental nerves. The first to seventh trunk tergites overlie a ventral nerve cord with seven ganglia, each associated with paired sets of segmental nerve bundles. Posteriorly, the nerve cord features elongate thread-like connectives. The Great Basin fossils strengthen the original description—and broader evolutionary implications—of the CNS in Alalcomenaeus from the early Cambrian (Stage 3) Chengjiang deposit of South China. The spatio-temporal recurrence of fossilized neural tissues in Cambrian Konservat-Lagerstätten across North America (Pioche, Burgess Shale, Marjum) and South China (Chengjiang, Xiaoshiba) indicates that their preservation is consistent with the mechanism of Burgess Shale-type fossilization, without the need to invoke alternative taphonomic pathways or the presence of microbial biofilms.

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Section: Introductionmentioning

confidence: 99%

Proclivity of nervous system preservation in Cambrian Burgess Shale-type deposits

2019

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“…The Paleozoic Era contains spectacular examples of exceptionally preserved fossils that have produced critical insights into the origin, early evolution of complex animals and the Phanerozoic biosphere [1][2][3] (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Stuck in the mud: experimental taphonomy and computed tomography demonstrate the critical role of sediment in three-dimensional carcass stabilization during early fossil diagenesis

Waskom,

Losso,

Ortega-Hernández

2023

Preprint

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Exceptionally preserved fossils provide critical information on the morphology and ecology of extinct organisms, but their formation remains poorly understood. Experimental taphonomy has produced critical insights that allow us to better understand preservation biases, but they typically do not reflect realistic depositional environments, employ destructive sampling, and are restricted to a two-dimensional setting. Here, we utilize micro-computed tomography to non-invasively visualize the process of decay of carcasses of the branchiopod Triops longicaudatus for a year of post-burial decay. The earliest stages of post-burial diagenesis are dynamic and produce marked differences in relative density within each of the experimental replicates affecting both the carcass and the surrounding sediment. After 64 weeks, specimens are still detectable as three-dimensional voids that capture the body in life position and external morphological features. Sediment plays a critical role in carcass stabilization and the resulting voids provide sites for mineral precipitation needed for exceptional three-dimensional fossilization.

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Neuroanatomy in a middle Cambrian mollisoniid and the ancestral nervous system organization of chelicerates

et al. 2022

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Recent years have witnessed a steady increase in reports of fossilized nervous tissues among Cambrian total-group euarthropods, which allow reconstructing the early evolutionary history of these animals. Here, we describe the central nervous system of the stem-group chelicerate Mollisonia symmetrica from the mid-Cambrian Burgess Shale. The fossilized neurological anatomy of M. symmetrica includes optic nerves connected to a pair of lateral eyes, a putative condensed cephalic synganglion, and a metameric ventral nerve cord. Each trunk tergite is associated with a condensed ganglion bearing lateral segmental nerves, and linked by longitudinal connectives. The nervous system is preserved as reflective carbonaceous films underneath the phosphatized digestive tract. Our results suggest that M. symmetrica illustrates the ancestral organization of stem-group Chelicerata before the evolution of the derived neuroanatomical characters observed in Cambrian megacheirans and extant representatives. Our findings reveal a conflict between the phylogenetic signals provided by neuroanatomical and appendicular data, which we interpret as evidence of mosaic evolution in the chelicerate stem-lineage.

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Exceptionally Preserved Cambrian Fossils in the Genomic Era

Cited by 3 publications

References 67 publications

Proclivity of nervous system preservation in Cambrian Burgess Shale-type deposits

Proclivity of nervous system preservation in Cambrian Burgess Shale-type deposits

Stuck in the mud: experimental taphonomy and computed tomography demonstrate the critical role of sediment in three-dimensional carcass stabilization during early fossil diagenesis

Neuroanatomy in a middle Cambrian mollisoniid and the ancestral nervous system organization of chelicerates

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