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| Orygmaspis (Parabolinoides) contracta with gut structure |
And what is most exciting about this specimen is that there is clear preservation of some of the gut structures preserving this trilobite's last meal.
Documentation of non- or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification of metazoans during the early Palaeozoic.
Biomineralization, biologically controlled mineralization, occurs when crystal morphology, growth, composition, and location is completely controlled by the cellular processes of a specific organism. Examples include the shells of invertebrates, such as molluscs and brachiopods. The soft bits of those same animals tend to rot or be scavenged long before mineralization or fossilization can occur — hence, we find less of them.
So, not surprisingly, the fossil record of soft-bodied metazoans is particularly scarce for this critical time interval. To date, the fossils we do have are relatively rare and scattered at a dozen or so localities worldwide.
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| Location and stratigraphy of the Fossil Locality |
This specimen was found in Upper Cambrian exposures in the Clay Creek section at the top of the left fork of the ravine below Tanglefoot Mountain, 20 km northeast of Fort Steele.
It was the keen eyes of Chris Jenkins who noticed the interesting structures worthy of exploration.
Lerosey-Aubril along with colleagues, Patterson, Gibb and Chatterton, published a great study on this trilobite in Gondwana Research, February 2017.
Their work looked at this new occurrence of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. Their study followed up on the work of Chatterton et al. studying trilobites with phosphatised guts in this same 10-m-thick interval.
Lerosey-Aubril et al.'s paper looked at two stratigraphically higher horizons with soft-tissue preservation. One yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens.
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| Undetermined ctenophore |
The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow ‘tailspine’. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson.
They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatite) outer layer.
Macro imagery of the trilobite reveals previously unknown gut features — medial fusion of digestive glands — possibly related to enhanced capabilities for digestion, storage, or the assimilation of food.
These new fossils show that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section is ongoing by Chris New, Chris Jenkins and Don Askey. There work and collaboration will likely result in more continued discoveries of exceptional fossils.
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| Glypharthrus magnoculus sp. |
Photo One: Orygmaspis (Parabolinoides) contracta (Trilobita) from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A–D, specimen RBCM.EH2016.031.0001.001, complete dorsal exoskeleton preserved dorsum-down and showing ventral features, such as the in situ hypostome and phosphatised digestive structures.
A, general view, specimen immersed under ethanol; B, detail of the digestive structures, specimen under ethanol; C, same as B, electron micrograph; D, same as B and C, interpretative drawing with digestive tract in blue-purple and digestive glands in pink.
Abbreviations: Dc 1 and 2, cephalic digestive glands 1 and 2, Dt1 and 5, thoracic digestive glands 1 and 5, hyp, hypostome, L2, glabellar lobe 2, LO, occipital lobe, T1 and 5, thoracic segments 1 and 5. Scale bars represent 2 mm (A) and 1 mm (B–D). For interpretation of the references to the colours in this figure legend, you'll want to read the full article in the link below.
Photo Two: Undetermined ctenophore from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A, B, specimen UA 14333, flattened body fragment with oral-aboral axis oriented parallel to bedding; specimen photographed immersed under dilute ethanol with presumed oral region facing to the bottom. A, general view. B, detailed view showing comb rows and ctene. Scale bars represent 1 cm (A) and 5 mm (B). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Photo Three: Glypharthrus magnoculus sp. nov. from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A–H, holotype, UA 14332, almost complete dorsal exoskeleton; photographs (A–C) and electron micrographs (D, backscattered; E–H, secondary) of the specimen in dorsal view with anterior facing to the top. A, B, general view in normal (A) and inverted (B) colours; C, D, detail of posterior trunk region, showing T12 and its contacts with T11 and the spiniform telson (arrows); the core of the fossil is made of a clay mineral and was initially entirely covered by an apatitic thin layer (white areas on D); E, left eye; F, right posterolateral glabellar lobe; G, rounded tubercles on right posterior border of cephalon; H, triangular tubercles pointing backwards (bottom right corner) on trunk axial region. Scale bars represent 5 mm (A, B), 1 mm (C, D), 500 μm (E, F), and 100 μm (G, H).
Link to the paper: https://www.researchgate.net/publication/309549546_Exceptionally-preserved_late_Cambrian_fossils_from_the_McKay_Group_British_Columbia_Canada_and_the_evolution_of_tagmosis_in_aglaspidid_arthropods
