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Complex axial growth patterns in an early Cambrian trilobite from South Australia

The exceptional fossil record of trilobites provides our best window on developmental processes in early euarthropods, but data on growth dynamics are limited. Here, we analyse post-embryonic axial growth in the Cambrian trilobite Estaingia bilobata from the Emu Bay Shale, South Australia. Using thr...

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Autores principales: Holmes, James D., Paterson, John R., García-Bellido, Diego C.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8670951/
https://www.ncbi.nlm.nih.gov/pubmed/34905705
http://dx.doi.org/10.1098/rspb.2021.2131
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author Holmes, James D.
Paterson, John R.
García-Bellido, Diego C.
author_facet Holmes, James D.
Paterson, John R.
García-Bellido, Diego C.
author_sort Holmes, James D.
collection PubMed
description The exceptional fossil record of trilobites provides our best window on developmental processes in early euarthropods, but data on growth dynamics are limited. Here, we analyse post-embryonic axial growth in the Cambrian trilobite Estaingia bilobata from the Emu Bay Shale, South Australia. Using threshold models, we show that abrupt changes in growth trajectories of different body sections occurred in two phases, closely associated with the anamorphic/epimorphic and meraspid/holaspid transitions. These changes are similar to the progression to sexual maturity seen in certain extant euarthropods and suggest that the onset of maturity coincided with the commencement of the holaspid period. We also conduct hypothesis testing to reveal the likely controls of observed axial growth gradients and suggest that size may better explain growth patterns than moult stage. The two phases of allometric change in E. bilobata, as well as probable differing growth regulation in the earliest post-embryonic stages, suggest that observed body segmentation patterns in this trilobite were the result of a complex series of changing growth controls that characterized different ontogenetic intervals. This indicates that trilobite development is more complex than previously thought, even in early members of the clade.
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spelling pubmed-86709512022-01-10 Complex axial growth patterns in an early Cambrian trilobite from South Australia Holmes, James D. Paterson, John R. García-Bellido, Diego C. Proc Biol Sci Palaeobiology The exceptional fossil record of trilobites provides our best window on developmental processes in early euarthropods, but data on growth dynamics are limited. Here, we analyse post-embryonic axial growth in the Cambrian trilobite Estaingia bilobata from the Emu Bay Shale, South Australia. Using threshold models, we show that abrupt changes in growth trajectories of different body sections occurred in two phases, closely associated with the anamorphic/epimorphic and meraspid/holaspid transitions. These changes are similar to the progression to sexual maturity seen in certain extant euarthropods and suggest that the onset of maturity coincided with the commencement of the holaspid period. We also conduct hypothesis testing to reveal the likely controls of observed axial growth gradients and suggest that size may better explain growth patterns than moult stage. The two phases of allometric change in E. bilobata, as well as probable differing growth regulation in the earliest post-embryonic stages, suggest that observed body segmentation patterns in this trilobite were the result of a complex series of changing growth controls that characterized different ontogenetic intervals. This indicates that trilobite development is more complex than previously thought, even in early members of the clade. The Royal Society 2021-12-22 2021-12-15 /pmc/articles/PMC8670951/ /pubmed/34905705 http://dx.doi.org/10.1098/rspb.2021.2131 Text en © 2021 The Authors. https://creativecommons.org/licenses/by/4.0/Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/ (https://creativecommons.org/licenses/by/4.0/) , which permits unrestricted use, provided the original author and source are credited.
spellingShingle Palaeobiology
Holmes, James D.
Paterson, John R.
García-Bellido, Diego C.
Complex axial growth patterns in an early Cambrian trilobite from South Australia
title Complex axial growth patterns in an early Cambrian trilobite from South Australia
title_full Complex axial growth patterns in an early Cambrian trilobite from South Australia
title_fullStr Complex axial growth patterns in an early Cambrian trilobite from South Australia
title_full_unstemmed Complex axial growth patterns in an early Cambrian trilobite from South Australia
title_short Complex axial growth patterns in an early Cambrian trilobite from South Australia
title_sort complex axial growth patterns in an early cambrian trilobite from south australia
topic Palaeobiology
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8670951/
https://www.ncbi.nlm.nih.gov/pubmed/34905705
http://dx.doi.org/10.1098/rspb.2021.2131
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