#stanleycaris

[technician-the]

Just got some new pets! still learning how to take care of them ^^

Stanleycaris was a small cambrien radiodont, notable for having three eyes, and a fully fossilized brain. According to a 2022 paper, it is the best preserved radiodont, with 268 specimens, including the aforementioned fossilized brain

some images on the fish food label are cc from wikipedia, tank decorations are old projects and the background is made from real photos taken in my living room wrapped onto 3d models

[alphynix]

Radiodonts were early arthropods with specialized frontal appendages, disc-like mouths, complex compound eyes, and swimming flaps along the sides of their bodies. Once considered to be bizarre "weird wonders" of the Cambrian Explosion that represented a failed evolutionary experiment, we now know that they were actually a highly diverse and successful lineage that lasted for at least 120 million years.

While some radiodonts were the largest animals of their time periods, Stanleycaris hirpex here was one of the smallest known members of the group – although at around 10cm long (~4") it was still respectably big compared to most other Cambrian animals.

Discovered in the Canadian Burgess Shale deposits (~508 million years ago), it was originally known only from isolated frontal appendages and mouthparts, and had been assumed to be a fairly typical member of the hurdiid family. But the recent discovery of over 200 new fossils, including some exceptionally well-preserved full body specimens, has catapulted it directly from being poorly-known into now being one of the most completely known of all radiodonts.

And it had a very big surprise for us, right in the middle of its face.

It turns out that Stanleycaris had a huge third eye, unlike anything ever seen in a radiodont before. A large unpaired eye was also part of the five-eyed arrangement in opabiniids and Kylinxia, and finding a similar example in radiodonts too raises the possibility that this sort of well-developed "median eye" may have been more widespread in early arthropods than previously thought.

Along with the third eye, some of the Stanleycaris specimens preserve fine internal details of its nervous system and show that its brain was made up of two segments instead of the three seen in modern arthropods. It also had gills positioned on its underside, unlike most other radiodonts which had them on their backs.

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[mus-paleo]

My favorite guys!! the radiodonts :)

Alt versions under read more 👁

3-eyed Peytoia version and also a transparent one!

[ready-set-fish]

The Stanleycaris Parable. Is this anything

[extinctworld-ua]

Stanleycaris

Stanleycaris — вимерлий монотипний рід радіодонтів хурдиїд, який існував у Канаді в середньому кембрії. Типовим видом є Stanleycaris hirpex. Stanleycaris був описаний з формації Стівен поблизу льодовика Стенлі сланців Берджес, були також неофіційні повідомлення про знахідки на горі Одарай. Тварина мала три ока, що раніше не зустрічалось в інших родів радіодонтів.

Повний текст на сайті "Вимерлий світ":

https://extinctworld.in.ua/stanleycaris/

[trigonodus]

Hi saw your peytoia reconstructions!!

could you explain more about how peytoia could’ve had 3 eyes? Tried reading the article but paywall 😧

it’s gotta in my top 3 favorite animals so knowing more is always cool

Hi, thanks for asking! I must say I approve your excellent choice in favorite animals.

So, it's not uncommon for arthropods, both fossil and extant, to have an eye (or several) in the middle, called the median eye! On the stem-group side, Opabinia is a nice case of a head with five well-developed eyes, and there are many example in the crown group, including (but not limited to) horseshoe crabs and a wide variety of insects. As opposed to the regular pair of lateral eyes, which can be simple or compound, median eyes are typically simple.

(A robber fly [Holcocephala fusca] with three small median eyes, right behind the antennae. Photo by Thomas Shahan on flickr)

Now, for radiodonts specifically:

In body fossils of Peytoia, the head tends to be not so nicely preserved, so it can be hard to interpret features, especially without a strong anatomical baseline to refer to. From their conclusions on the anatomy of Stanleycaris (which is better preserved and appears to have had 3 eyes), Moisyuk & Caron made comparisons with a few other stem-group arthropods, including the closely related Peytoia. What they interpret as a third eye in Peytoia is a reflective patch near the front of the head (labelled 'me'):

(Part of fig. S3 from the supplementaries of Moisyuk & Caron 2022. Abbreviations: fl = flaps, le = lateral eye, me = median eye, Pe = P-element, sc = preocular sclerite, sg = supraesophageal ganglion. Scale bar = 5 mm)

I'm no authority on Burgess fossils, but the preservation seems consistent with what's known for eye tissue in this locality, and a median eye is certainly not surprising (though somewhat unexpected) given how many arthropods in either direction on the family tree seem to have one, so I can definitely stand by this proposition.

Not only is the idea of a third eye in radiodonts pretty cool, it also shows that median eyes have a deep evolutionary origin (possibly derived from the simple eyes of lobopodians) and are a quite continuous feature throughout the arthropod lineage!

Hope this answers it!

[trigonodus]

Updated version of my previous reconstruction of Peytoia nathorsti, the somewhat lesser-known relative and contemporary of Anomalocaris canadensis.

Now with 2 pairs of flaps (proposed by Van Roy et al. 2015 based on comparison with Aegirocassis) and a median third eye (proposed by Moysiuk & Caron 2022 based on comparison with Stanleycaris).

The shape and 3-part structure of the head carapace complex is still quite speculative, and might get invalidated by potential future discoveries, as Stanleycaris has shown us (with its 3 eyes and single-part carapace) that the head of radiodonts was more variable (and weirder, if such a thing can be) than previously thought!