Oddity Ark #67 (247) Aegirocassis benmoulai

This week we’re heading back into deep time with a radiodontid request from @yejj. And remember if you want to request an issue on an amazing animal, fabulous fungus, perplexing plant or awesome paleofauna, don’t hesitate to leave a request in the comments.

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Oddity Ark #67 (#247)

Kingdom: Animalia

Phylum: Arthropoda

Class: Dinocaridida

Order: Radiodonta

Family: Hurdiidae

Genus: Aegirocassis

Species:benmoulai

Related Species:Aegirocassis benmoulai is the only named member of the genus Aegirocassis. Radiodonts, are a base group of arthropods that have no extant descendants (1).

Range: Fossils of Aegirocassis benmoulai are only known from the Fezouata Formation in Morocco.

IUCN Status: Aegirocassis benmoulai lived 490 million years ago (mya) in the Early Ordovician Period. and as such would be considered ‘Extinct’ by the International Union of the Conservation of Nature (IUCN).

Giant Swimmer

Aegirocassis benmoulai is a large radiodontid arthropod that reaches a body length of up to two meters. Like earlier radiodonts Anomalocaris, Aegirocassis has phalanges running down the top and bottom of its abdomen that allowed the radiodont to both move and ‘hover’ within the water course. At the front of Aegirocassis’s body was a large, armoured head with a pair of eyes positioned on the side of its body in comparison with the motile forward facing eye stalks of the Cambrian anomalocarids. Hanging below the head are two raptorial limbs that are used in feeding and could be moved to funnel caught prey into the radiodont’s mouth.

Aegirocassis is speculated to be a filter feeder due to the reduction of predatory features, such as the softening of the radial cone and movement of eye position, in comparison with species such as Anomalocaris. The raptorial feeding limbs of Aegirocassis were tipped with up to eighty bristle like setae that were analogous to the baleen found in baleen whales (2). These setae were curved inwards, allowing Aegirocassis to increase or decrease the gaps between the bristle, allowing it to feed on different sizes of the plankton it fed on. While Aegirocassis was the largest species found in the Fezouata Formation, its range was likely wider, causing it to overlap with large predators such as the nautiloid Endoceras giganteum. Increased predatory pressure likely caused Aegirocassis to grow large to reduce the risk of being targeted by these predators.

By the time Aegirocassis had evolved the large predatory members of the radiodonts had become extinct, their niche now filled by the eurypterids after evolving during the Great Ordovician Biodiversification Event at the beginning of the period (3). The radiodonts would endure into the Devonian period but had long since relinquished the niches of large predators and filter feeders, to become small, up to 10cm long, scavengers and predators (4).

Five Fossilised Filter Feeders

The filter feeding Devonian fish Titanichthys species still had small plates of sharpened bone found in its jaw, just like its placoderm relative Dunkleosteus (5).

Marine reptiles also evolved filter feeding, with the placodont Henodus usingrapid gulping movements to push water over baleen like denticles in the jaw.

An entire order of marine reptiles, the Hupehsuchia, were filter feeders, with plates in the body to allow them neutral buoyancy, while their body features were adapted for slow ram feeding on plankton.

The pterosaur Pterodaustro guinazui was a nocturnal filter feeder that sieved outsmall hard-shelled crustaceans (6) akin to modern flamingos and may have caused the animal to have pink pigmentation.

The Annaka short-winged swan (Annakacygna hajimei) was a flightless marine swan whose beak was lined with soft lamellae plates that allowed it to filter plankton out of the water as it dived.

References

1. www.arkive.com

2. Van Roy, Peter; Daley, Allison C.; Briggs, Derek E. G. (2015). "Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps". Nature. 522 (7554): 77–80

3. Servais, T.; Owen, A. W.; Harper, D. A. T.; Kröger, B. R.; Munnecke, A. (2010). "The Great Ordovician Biodiversification Event (GOBE): the palaeoecological dimension". Palaeogeography, Palaeoclimatology, Palaeoecology. 294 (3–4): 99–119

4. Gabriele Kühl; Derek E. G. Briggs & Jes Rust (2009). "A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany". Science. 323 (5915): 771–773.

5. Boyle, James; Ryan, Michael J. (March 2017). "New information on Titanichthys (Placodermi, Arthrodira) from the Cleveland Shale (Upper Devonian) of Ohio, USA". Journal of Paleontology. 91 (2): 318–336.

6. Codorniú, L., Chiappe, L.M., Arcucci, A., and Ortiz-Suarez, A. (2009). "First occurrence of gastroliths in Pterosauria (Early Cretaceous, Argentina)". XXIV Jornadas Argentinas de Paleontología de Vertebrados

Picture Credits

1. aegirocassis-prehistoric-marine-arthropod-jose-antonio-peasscience-photo-library.jpg (900×600) (fineartamerica.com)

2. R.033e3a9d4370aa05e83dcc9f4d27c630 (624×220) (bing.com)

3. two-henodus-swimming-deagostiniuigscience-photo-library.jpg (900×612) (fineartamerica.com)

4. Pterodaustro_guinazui.jpg (1024×771) (bp.blogspot.com)

5. annakacygna2-1030x686.jpg (1030×686) (swansg.org)

Next week we head into the scorching desert at midday to find the only other animal willing to head out under the blazing sun. And if you want to see more amazing animals and plants, please check out the Oddity Arkive or past issues. And if you want even more animals, please check out dearly departed Impurest Cheese’s Guide to Animals which can be found here, or on the blog of filter feeding fossil @ficopedia

If you still have a yearning for learning, please check out the master list of Mr Monster’s Martial Arts Journey.

@cbishop, @mrmonster, @lemillion, @spareheadone, @chino_xl, @goldpool, @whathappened, @yejj,@arranvid, @goodkarma, @jacdec, @steve40l, @cambatta, @arctika and @officialtopg

Anomalocaris 2: Electric Boogaloo - Filter Feeding Frenzy

Nice post ^. Hey that first post is that the ancestor for the sea turtle? Looks very similar.

@arctika: Thanks for the comment, and the excuse to talk about the Triassic Period, my favourite point of geological time.

So the short answer is Henodus and by extension the other placodonts are not closely related to modern day turtles and tortoises, outside the face they are both reptiles (which is a somewhat outdated taxonomic grouping in itself). What has happened to make Henodus look so turtle like is convergent evolution. The same evolutionary pressures that Henodus experienced in the mid-Triassic (237-227mya) will he the same ones the ancestors of sea turtles will experience in the Creataceous when they enter the ocean (110mya). Chief among these is the emergence and then persistence of large marine predators (sharks, nothosaurs and ichthyosaurs for Henodus and pliosaurs, marine crocodiles and sharks for marine turtles). A Because of this both groups independently evolved heavy shell like armour, as seen in this fossil of Henodus,

One of the ways to tell is Henodus or any other fossil is to look at the skulls. Placodonts are diapsids, along with lizards, snakes, crocodiles, plesiosaurs, pterosaurs and dinosaurs (technically birds too) which means they have a pair of temporal fenestrae at the back of the skull, typically on the side of the skull although they can migrate to the top of the skull in aquatic species, or seal shut such as in birds (hence them being technically diapsids). Turtles are anapsids which means they completely lack a temporal fenestrae. In the images below of the anapsid hawksbill turtle (Eretmochelys imbricata), the dinosaurs Allosaurus fragilis and the placodont Placodus species (the skull of Henodus show some crush damage) the temporal fenestrae is highlighted in blue.

While sea turtles would first appear in the Cretaceous Period, the wider group was already on the way to being recognisable tortoises and turtles by the time Henodys evolved and then went extinct. By the late Triassic, (aproximatley 210mya) we had an animal that we would recognise as being a tortoise (although it still had teeth in its mouth instead of a beak). Called Proganochelys quenstedi, this species is found in terrestrial and freshwater deposits suggesting it lived mostly lived on land but in close proximity to shallow ponds.

The actual oldest 'prototurtle' is a species from the Permian period (265-259mya) known as Eunotosaurus africanus which (judging from fossil finds) looked like...

But fear not because Eunotosaurus has skeletal features that betray where its descendants will go. Firstly there is the obvious fact that this animal has wide ribs. These ribs are already looking very plate like, and over time will fuse to form the carapace in modern turtle and tortoise shells. Additionally the number of back vertebrae is reduced to the point where Eunotosaurus only has nine of them, which is the amount some modern species of turtle have. And then there is the skull, Euotosaurus has no temporal fenestre, which at the very least mean its an anapsid.

Considering the presence of these features and a number of fossil proto turtles discovered in the geological column between Eunotosaurus and Proganochelys with those closer to the later species becoming more and more turtle like, it appears that turtles were well on their way to turtling when the placadonts began evolving into armoured marine forms line Henodus.

The Triassic period is, to be fair weird, I could show you a different fossil every day over the course of a month and you would still be finding the animals as weird at the end of the moth, as they were at the beginning of the month.

Picture Credits

1. OIP.lREE8w6z4r0QsyQKcT6QqAHaE7 (474×315) (bing.com)

2. OIP.nOE3mXHcuCYCHIj1SasF5gHaE0 (474×308) (bing.com)

3. image (960×1440) (bonhams.com)

4. placodus+skull.jpg (478×637) (bp.blogspot.com)

5. Proganochelys_Quenstedti.jpg (1518×709) (wikimedia.org)

6. Eunotosaurus_africanus.jpg (1280×996) (a-z-animals.com)

7. image_1119_2-eunotosaurus-africanus.jpg (580×653) (sci.news)

Aegirocassis.. my favorite prehistoric animal ever

@yejj: Glad you enjoyed it.

@sundown89: Nice! All good, I can tell you're heavily into this stuff. It's always interesting to see the evolution of these animals and various species.

@arctika: Thanks this is pretty much related to either my job or the stuff I had to learn for my job.

@sundown89: Oh that's cool, sounds interesting. You must enjoy zoos and animal exhibits I bet? I remember as a kid we'd go for school trips to both, it was definitely interesting but I also went to the zoo when my folks would take me.

@arctika: Zoos are a double edged sword, I understand that modern zoos are a lot better then they were and play an important part in conservation but I also feel a little sad when visiting because the animals should really be out in the wild.

That said the last zoo I went too was Parque de la Naturaleza de Cabárceno just outside of Santandere which had exhibits that were big enough to fit a small zoo into. It definitely was a big step up and was worth the 20km hike.

@sundown89: "Filter feeding fossil." lol

@ficopedia: Not my best work to be honest

@sundown89: Yeah I hear ya especially the bigger animals in the caged areas. Some no doubt now days are better than years ago for sure but yeah I hear ya. I've noticed smaller animals seem to have far more room to live and move around like the ground hogs in my local zoo hes kind of a celebrity where I'm from so he has his little house, alot of room to run around, treats, wood etc the natural stuff he needs.

@arctika: I have also noticed this but then this is sometimes due to their exhibits hosting multiple animals.

@sundown89: Yeah, in the case of my local groundhog at my zoo who's famous in my area and in the country one of the ones they use to judge early spring or longer winter, he has his own area no where near the other animals thankfully. It's pretty cool.

Not your worst either. ;)

@ficopedia: I’ll save those one for Shocktober

@arctika: I think I know what your referencing, that's pretty cool.

@sundown89: Yeah, I live in NYC, SI/NJ area. It's a neat tradition here for sure.