:en:Aegirocassis

{{Speciesbox

| image = YPM 237172 Aegirocassis benmoulae.jpg

| image_caption = Fossil holotype

| image2 = 20191205 Aegirocassis benmoulai Aegirocassis benmoulae.png

| image2_caption = Reconstruction of Aegirocassis benmoulai

| fossil_range = Late Tremadocian, {{Fossil Range|480}}

| genus = Aegirocassis

| species = benmoulai

| authority = Van Roy, Daley, & Briggs, 2015{{cite journal|last1=Van Roy|first1=Peter|last2=Daley|first2=Allison C.|last3=Briggs|first3=Derek E. G.|title=Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps|journal=Nature|volume=522|issue=7554|year=2015|pages=77–80|issn=0028-0836|doi=10.1038/nature14256|pmid=25762145|s2cid=205242881 }}

(nom. corr. Van Roy et al. {{cite journal|last1=Van Roy|first1=Peter|last2=Briggs|first2=Derek E. G.|last3=Gaines|first3=Robert R.|title=The Fezouata fossils of Morocco; an extraordinary record of marine life in the Early Ordovician|journal=Journal of the Geological Society|year=2015|pages=2015–017|issn=0016-7649|doi=10.1144/jgs2015-017|volume=172|issue=5|hdl=1854/LU-8714212|s2cid=129319753 |hdl-access=free}})

}}

Aegirocassis is an extinct genus of giant radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician in the Fezouata Formation of Morocco. It is known by a single species, Aegirocassis benmoulai.{{refn|group=note|name=namenote|The species was originally termed A. benmoulae, but was corrected to A. benmoulai to comply with the terms of the ICZN.}} Van Roy initiated scientific study of the fossil, the earliest known of a "giant" filter-feeder discovered to date. Aegirocassis is considered to have evolved from early predatory radiodonts.{{cite web|url=https://theconversation.com/fossils-of-huge-plankton-eating-sea-creature-shine-light-on-early-arthropod-evolution-38520#comment_619451|title=Fossils of huge plankton-eating sea creature shine light on early arthropod evolution|website=The Conversation|author=Van Roy, Peter|date=12 March 2015|accessdate=2024-05-12|archive-url=https://web.archive.org/web/20231011112228/https://theconversation.com/fossils-of-huge-plankton-eating-sea-creature-shine-light-on-early-arthropod-evolution-38520#comment_619451|archive-date=2023-10-11|url-status=live}} This animal is characterized by its long, forward facing head sclerite, and the endites on its frontal appendages that bore copious amounts of baleen-like auxiliary spines. This animal evolving filter-feeding traits was most likely a result of the Great Ordovician Biodiversification Event, when environmental changes caused a diversification of plankton, which in turn allowed for the evolution of new suspension feeding lifeforms.{{Cite journal |last1=Servais |first1=T. |last2=Owen |first2=A. W. |last3=Harper |first3=D. A. T. |author-link3=David Harper (palaeontologist) |last4=Kröger |first4=B. R. |last5=Munnecke |first5=A. |year=2010 |title=The Great Ordovician Biodiversification Event (GOBE): the palaeoecological dimension |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=294 |issue=3–4 |pages=99–119 |doi=10.1016/j.palaeo.2010.05.031}}{{Cite journal |last=Stigall |first=A.L |display-authors=etal |date=December 2016 |title=Biotic immigration events, speciation, and the accumulation of biodiversity in the fossil record |journal=Global and Planetary Change |volume=148 |pages=242–257 |bibcode=2017GPC...148..242S |doi=10.1016/j.gloplacha.2016.12.008}} Alongside the closely related Pseudoangustidontus,{{cite journal |last1=Potin |first1=G. J.-M. |last2=Gueriau |first2=P. |last3=Daley |first3=A. C. |year=2023 |title=Radiodont frontal appendages from the Fezouata Biota (Morocco) reveal high diversity and ecological adaptations to suspension-feeding during the Early Ordovician |journal=Frontiers in Ecology and Evolution |volume=11 |at=1214109 |doi=10.3389/fevo.2023.1214109 |doi-access=free}} an unnamed hurdiid from Wales,{{Cite journal| doi = 10.1098/rsos.200459| volume = 7| issue = 6| pages = 200459| last1 = Pates| first1 = Stephen| last2 = Botting| first2 = Joseph P.| last3 = McCobb| first3 = Lucy M. E.| last4 = Muir| first4 = Lucy A.| title = A miniature Ordovician hurdiid from Wales demonstrates the adaptability of Radiodonta| journal = Royal Society Open Science| date = 2020| pmid = 32742697| pmc = 7353989| bibcode = 2020RSOS....700459P| doi-access = free}} the middle Ordovician dinocaridid Mieridduryn,{{cite journal |last1=Pates |first1=S. |last2=Botting |first2=J. P. |last3=Muir |first3=L. A. |last4=Wolfe |first4=J. M. |year=2022 |title=Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution |journal=Nature Communications |volume=13 |issue=1 |at=6969 |doi=10.1038/s41467-022-34204-w |pmid=36379946 |pmc=9666559 |doi-access=free}} and the Devonian hurdiid Schinderhannes, this radiodont is one of the few dinocaridids known from post-Cambrian rocks.{{cite journal |author=Gabriele Kühl |author2=Derek E. G. Briggs |author3=Jes Rust |name-list-style=amp |year=2009 |title=A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany |journal=Science |volume=323 |issue=5915 |pages=771–773 |bibcode=2009Sci...323..771K |doi=10.1126/science.1166586 |pmid=19197061 |s2cid=47555807}}

Description

{{gallery |width=200

|File:20210221 Aegirocassis size.png|Size estimation (regions in light grey are inferred)|File:YPM 527123 Aegirocassis benmoulai frontal appendage.png|Fossil of frontal appendage

|File:20191229 Radiodonta frontal appendage Aegirocassis benmoulai Aegirocassis benmoulae.png|Reconstruction of frontal appendage

|File:20210516 Radiodonta head sclerites Aegirocassis benmoulai Aegirocassis benmoulae.png|Head sclerite complex

}}

File:Aegirocassis scale.svg

A. benmoulai was the largest known radiodont and the largest known animal that existed in this period, and the length was described as exceeding {{convert|2.0|m|ft}}.

The fossil was preserved with exceptional three-dimensional detail, unlike most other radiodont fossils, in which the animals are flattened. The quality of three-dimensional preservation has shed light on the nature of radiodont trunk flaps. Each trunk segment of the Aegirocassis benmoulai specimen has both a ventral and a dorsal pair of flaps. Several details seen clearly in the specimen led to a review and reassessment of research of existing specimens and, most importantly, to the conclusion that the ventral pair are homologous with arthropod endopods (limb-like inner branches) and lobopodian limbs (lobopods), and the dorsal pair are homologous with the flaps of gilled lobopodians and exites (gill-like outer branches) of the arthropod biramous limb.{{cite web | last = Perkins | first = S.

| title = Newly discovered sea creature was once the largest animal on Earth

| publisher = AAAS

| date = 2015-03-11

| url = https://www.science.org/content/article/newly-discovered-sea-creature-was-once-largest-animal-earth

| accessdate = 2024-05-12 |archive-url=https://web.archive.org/web/20230813181050/https://www.science.org/content/article/newly-discovered-sea-creature-was-once-largest-animal-earth|archive-date=2023-08-13|url-status=live}} This discovery also found that other hurdiid radiodonts like Peytoia and Hurdia had a dorsal pair of flaps as well.

Frontal appendages of Aegirocassis had five endites, and each endites had around 80 setae-like auxiliary spines. These spines are estimated to have been used as a mesh for filter feeding. It was probably able to consume mesozooplankton roughly the same size as the other filter feeding radiodont, Tamisiocaris, was able to catch. However, the spines on the frontal appendages of Aegirocassis are inward-angled, which allowed the spines to overlap to a degree, allowing more control over the size of the filtering mesh. This has led to the estimation that Aegirocassis may have fed on larger size ranges of zooplankton than Tamisiocaris could. In addition, the large carapace (H-element) may have helped to guide the feeding current to the frontal appendages. Eyes and mouthpart (oral cone) are not known from Aegirocassis. Since it was probably a filter feeder, Aegirocassis probably lacked a hard mouthpart and had a flexible one, explaining why mouth structures are not preserved.

File:Fezouata Biota.jpg

Discovery

A fossil of A. benmoulai from the Fezouata biota, Morocco was discovered by and named after Mohamed Ben Moula, a fossil collector who recognized its rare characteristics and brought it to the notice of a professional paleontologist, Peter Van Roy, at the Ghent University in Belgium.{{Cite journal |last1=Van Roy |first1=Peter |last2=Briggs |first2=Derek E. G. |date=2011 |title=A giant Ordovician anomalocaridid |url=https://www.nature.com/articles/nature09920 |journal=Nature |language=en |volume=473 |issue=7348 |pages=510–513 |doi=10.1038/nature09920 |pmid=21614078 |s2cid=205224390 |issn=1476-4687}}

Phylogeny

Phylogenetic position of Aegirocassis within Panarthropoda, according to Pates et al. (2022).{{Cite journal| doi = 10.1098/rspb.2021.2093| volume = 289| issue = 1968| last1 = Pates| first1 = Stephen| last2 = Wolfe| first2 = Joanna M.| last3 = Lerosey-Aubril| first3 = Rudy| last4 = Daley| first4 = Allison C.| last5 = Ortega-Hernández| first5 = Javier| title = New opabiniid diversifies the weirdest wonders of the euarthropod stem group| journal = Proceedings of the Royal Society B: Biological Sciences| date = 2022-02-09| pmid = 35135344| pmc = 8826304| doi-access = free}}

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|1={{clade

|1=Aysheaia

|2=Onychodictyon

|3=Tardigrada

|4=Onychophora

|label5=Euarthropoda

|5={{clade

|1={{clade

|1=Megadictyon

|2=Jianshanopodia

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