Aegirocassis

Aegirocassis
	Reconstruction drawing
Temporal occurrence
	Under ordovician
	485.4 to 470 million years
Locations
	Morocco (Fezouata Formation);
Systematics
	Arthropod ( arthropoda )
	Radiodonta
	Anomalocaridida
	Hurdiidae
	Aegirocassis
Scientific name
	Aegirocassis
	Van Roy , Daley & Briggs , 2015
Art
	Aegirocassis benmoulai ; Van Roy, Daley & Briggs, 2015 ;

Aegirocassis is an extinct arthropod that lived in the seas of the Lower Ordovician . Its fossil remains are in the Fezouata Formation in southeastern Morocco . It belongs to the family of the Hurdiidae from the parent group of the Anomalocarididae . With Aegirocassis benmoulae , only one species of the genus is known. The species name benmoulae is a tribute to the fossil collector Ben Moula, who discovered a particularly well-preserved specimen. In 2015, a three-dimensional specimen in outstanding preservation enabled new insights into the morphology , systematics and ecology of these animals: They had a long, segmented body and moved through the ocean with two-branch swimming appendages. The head appendages formed a filtering apparatus and provide important information about their diet and the marine ecosystem in the Lower Ordovician.

Ben Moula discovered the three-dimensional fossil in 2011 , recognized its importance and informed the paleontologist Peter Van Roy. Van Roy and his group prepared the find in more than 500 hours and were able to describe the fossil scientifically in a comprehensive manner.

features

Aegirocassis was a sea creature almost 2 meters tall with a three-part front carapace . The long, flat trunk is divided into 11 segments . Each body segment has lateral, wing-like structures (flaps), two each dorsal and two ventral . With its two-branched wing-like fins (flaps), Aegirocassis is a missing link on the way to modern crustaceans : The recent crustaceans have multifunctional extremities for swimming, running, breathing, grasping and for sperm transfer. This find confirms the idea that the crustaceans' two-branched body appendages developed from a fusion of these dorsal and ventral fin structures (flaps). The Anomalocarididen these appendages are not yet fused together - it arranges Van Roy this group of animals in an early stage of Euarthropoden - Evolution one. A band of bristles runs across the trunk segment between the two dorsal fins. Aegirocassis has a filtering apparatus under the head, which consists of 7 head appendages (podomeres) of different lengths. The podomeres vary in length and are covered with thorn-like spines and finer bristles. Despite good soft tissue preservation, none of the Aegirocassis benmoulai specimens has a tail fan . Eyes have not yet been found on any specimen. Then there is its size: it was about twice the size of the next smallest sea creature.

ecology

Aegirocassis , like all of her relatives, lived in the sea. While swimming, she stretched her mouth appendages so that they formed a filtering apparatus in front of the mouth opening. She used it to filter plankton from the seawater. This filtering diet is unusual because almost all other anomalocarids were predators and hunted larger prey. Apart from the Moroccan fossil, only one other filtering anomalocaridid is known, Tamisiocaris borealis from the lower Cambrian of Greenland. With this feeding strategy and its size, Aegirocassis has taken on a similar ecological niche in the Ordovician Sea as today's baleen whales and whale sharks . The evolution of large, filtering marine animals is an indication of highly developed plankton communities during the Great Ordovician Biodiversification Event .

Systematics

Aegirocassis benmoulai is the only known species of the genus Aegirocassis . It belongs to the family of the Hurdiidae and thus to the relationship of the Anomalocarididae , which are classified in the stem group of the early arthropods. Their fossils have been found in North America (USA / Canada), China, Europe (Germany and Poland), Morocco and Australia to date. However, due to the large gaps in the fossil record, the relationships have not yet been conclusively clarified.

Note on taxonomy

The original name of the fossil aegirocassis benmoulae was 2015 in accordance with the requirements of the International Rules for Zoological Nomenclature in aegirocassis benmoulai changed.

Location

The Fezouata Formation in south-east Morocco is a conservative deposit from the Lower Ordovician and was discovered in 1990 by the Moroccan fossil collector Ben Moula. This taphocenosis gives a unique insight into the biodiversity and ecology of the sea between the Cambrian and the Upper Ordovician. The fossil-bearing layers were deposited in calm, deep water. Most of the fossils of the Fezouata Formation are flattened, some have been preserved in three dimensions. In some cases, non-mineralized body appendages are also fossilized. This preservation of soft tissues is typical for conservatory deposits. All three-dimensional preserved specimens in Fezouata come from two sites on the eastern flank of the Jbel Tigzigzaouine. The carapace , bristles (setal blades) and ventral thorns of the head appendages come from various fossil specimens from several other sites.

Importance of the find

Fezouata is a famous fossil site from the Paleozoic . Several new species of Anomalocarididae have been discovered in these marine deposits, along with a large number of other marine life . For more than 30 million years they were important elements of the marine communities there. Fezouata Biota closes a knowledge gap between the Cambrian fossil deposits and the late Ordovician Soom schists . The large number of fossils and their excellent preservation make this Konservatlagerstätte as significant as the Canadian Burgess Shale or the German Bundenbach - slate . The discovery of this three-dimensional Aegirocassis benmoulai specimen is particularly significant because this preservation enables new insights into the anatomy , ecology and evolution of the anomalocaridids .

etymology

Ægir is a giant of Norse mythology and the god of the sea.
Cassis (Latin helmet ) refers to the size of the head shield.
benmoulai : Mohamed 'Ou Said' Ben Moula is the fossil collector who discovered the Fezouata biota and the fossil.
Gender Female.

Web links

Commons : Aegirocassis - collection of images, videos and audio files

Aegirocassis benmoulae. Peabody Museum of Natural History . YouTube, March 11, 2015.

Individual evidence

↑ ^a ^b ^c ^d ^e ^f Peter Van Roy, Allison C. Daley and Derek EG Briggs: Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps. In: Nature (Nature Publishing Group). March 11, 2015, doi: 10.1038 / nature14256 .
↑ Van Roy, Peter; Briggs, Derek EG; Gaines, Robert R. (2015): The Fezouata fossils of Morocco; an extraordinary record of marine life in the Early Ordovician . Journal of the Geological Society: 2015-017. doi: 10.1144 / jgs2015-017 .
↑ Martin, Lefebvre et al .: The Fezouata Biota (Central Anti-Atlas, Morocco): Biostratigraphy and Associated Environmental Conditions of an Ordovician Burgess Shale. In: STRATI 2013. Springer Geology 2014, pp. 419–423. doi: 10.1007 / 978-3-319-04364-7_81 , ISBN 978-3-319-04363-0 .
↑ Peter van Roy, Derek Briggs: Anomalocaridid Diversity In The Early Ordovician Fezouata Biota Of Southeastern Morocco. 2014. GSA Annual Meeting in Vancouver, British Columbia (October 19-22, 2014).

[nat-150311-1] ↑ ^a ^b ^c ^d ^e ^f Peter Van Roy, Allison C. Daley and Derek EG Briggs: Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps. In: Nature (Nature Publishing Group). March 11, 2015, doi: 10.1038 / nature14256 .

[2] Van Roy, Peter; Briggs, Derek EG; Gaines, Robert R. (2015): The Fezouata fossils of Morocco; an extraordinary record of marine life in the Early Ordovician . Journal of the Geological Society: 2015-017. doi: 10.1144 / jgs2015-017 .

[3] Martin, Lefebvre et al .: The Fezouata Biota (Central Anti-Atlas, Morocco): Biostratigraphy and Associated Environmental Conditions of an Ordovician Burgess Shale. In: STRATI 2013. Springer Geology 2014, pp. 419–423. doi: 10.1007 / 978-3-319-04364-7_81 , ISBN 978-3-319-04363-0 .

[4] Peter van Roy, Derek Briggs: Anomalocaridid Diversity In The Early Ordovician Fezouata Biota Of Southeastern Morocco. 2014. GSA Annual Meeting in Vancouver, British Columbia (October 19-22, 2014).