Trilobites: latest complete fossils (Introduction)

by David Turell , Friday, June 28, 2024, 16:27 (148 days ago) @ David Turell
edited by David Turell, Friday, June 28, 2024, 16:37

Volcanic ash entombment:

https://www.sciencemagazinedigital.org/sciencemagazine/library/item/28_june_2024/420430...

"Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.

"Trilobites are arguably the most familiar of fossil invertebrates, known from over 22,000 species and millions of specimens spanning the Paleozoic. Their calcite exoskeleton confers high fossilization potential, providing a tool for early Paleozoic biostratigraphy and informing on their ontogeny and developmental evolution (2-4); and through their calcified eye lenses, it has been possible to gain insights into the vision of early arthropods. (my bold)

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"In this study, we were able to establish that the labrum is distinct from the hypostome, the labrum being attached to the dorsal doublure at the posterior end of the hypostome, with the same relationship that the labrum has to the epistome in chelicerates. Similar to the robustly sclerotized epistome in Xiphosura, the trilobite hypostome is biomineralized—with the labrum being relatively soft in both clades—and the hypostome accommodates the antennal insertion, just as the xiphosuran epistome accommodates the chelicerae. Furthermore, we were able to identify the mouth opening in front of the dorsal platform of the labrum, which is consistent with the position of the start of the esophagus, demonstrating that the hypostome covered the mouth.

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"Although the soft-bodied anatomy of trilobites has been known for over 100 years, the Tatelt specimens reveal critical details at a level not previously observed, despite the long stratigraphic range and abundance of this iconic group of Paleozoic fossils. The extraordinary preservation of fine anatomical detail in the ash deposit of a pyroclastic event is unexpected but points to the great potential of ashdeposits inmarine settings to yield further discoveries."

Comment: hopefully the website address will allow a look at the amazing illustrations. I would remind the reader this large population has no predecessors. They represent the Cambrian Gap. This article has the illustrations:

https://www.sciencealert.com/never-before-seen-trilobite-anatomy-preserved-by-pompeii-l...

"'Although the soft-bodied anatomy of trilobites has been known for over 100 years, the Tatelt specimens reveal critical details at a level not previously observed, despite the long stratigraphic range and abundance of this iconic group of Paleozoic fossils," the researchers write.

"The extraordinary preservation of fine anatomical detail in the ash deposit of a pyroclastic event is unexpected but points to the great potential of ash deposits in marine settings to yield further discoveries.'"