Extinct crustacean with fins

In the photo - the upper part of the shell of the extinct crustacean Pseudoarctolepis sharpi with two spiky processes on the sides. These crustaceans swam in the seas in 3–3–333. Cambrian period 3-3-33200. and reminded their species of the Devonian shell-fish of arctolepis (3-3-3325. Arctolepis 3-3-33200.), which is reflected in the name of the genus.

Pseudoarctolepises belong to subclass 3-3-3329. phyllocaride class higher crayfish whose representatives flourished from Cambrian by Devonian period 3-3-33200. , they left one modern detachment - thin shell . Phyllocarids were the earliest animals that began to use minerals to build hard shells that protected them from predators.

The carapace covered the front of the body, consisted of two cusps and reached a length of 11 cm. Two lateral processes were most likely stabilizers during active swimming (crustaceans were 3–3–341. Nektonic 3–3–3200 animals). Pseudoarctolepis residues are found in the Cambrian 3-3-3373. clay shales 3-3-33200. ridge House ( House Range ) US state Utah and for the first time were 3-33200 are described. in 1956. Mostly paleontologists find only fossilized shells, but occasionally samples with soft-body prints come across.

Photo (3-3-3203. On the left 3-3-3204.) And a diagram of the structure of 3-3-3203. Pseudoarctolepis sharpi [/i] from Cambrian clay shales 3-3-33200. House Ridge in the US state of Utah . 1 - paired structures protruding in front of the shell: part of the forelimbs or eyes, 3-3-3387. 2 [/b] - shell, 3 - armored processes, 4 - tail processes, B - abdominal segments (six segments are distinguishable). Image from article R. Lerosey-Aubril et al., 2020.3-3r389. New exceptionally preserved panarthropods from the Drumian Wheeler Konservat-Lagerstatte of the House Range of Utah

Since the discovery of pseudoarctolepises, their family ties have remained controversial. For example, they were indicated to have no moving rostrum characteristic of phyllocarids. It was assumed 3-3-33200. possible connection of these Cambrian animals with thylakocephalus (3-3-33101. Thylacocephala 3-3-33200.), a later group of marine predatory arthropods (see picture of the day 3-3-3103. Mysterious thilacocephalous with large eyes 3-3-33200.). In addition, repeatedly 3-3-3105. indicated 3-3-33200. the similarity in the structure of the shells Pseudoarctolepis and other "bivalve" arthropods, especially 3-3-3203. Isoxys [/i] and Tuzoia , but the absence of residues of other parts of the body did not allow us to verify the reliability of this similarity. Therefore, a specimen found in Utah with the remains of soft parts of the body provides a good opportunity for more detailed comparisons. In the meantime, pseudoarctolepis is classified as phyllocarides.

Carapace of different specimens Pseudoarctolepis sharpi , right - only the left half of the shell. Photo from sites flickr.com , fossilera.com , commons.wikimedia.org

Why pseudoarctolepises are common in the clay shales of the House ridge, but are not found in the Canadian clay 3-3-3151. Burgess Shale the same period (see 3–3–3153. The Burgess shale fauna 3–3–3200.), as well as in other Cambrian 3–3–3155. lagerstett Utah, unclear. But on the other hand, pseudoarctolepises are found in more distant places. In 2011 in the South China Formation of Kaili (3–3–3157. Kaili Formation 3–3–3200.) Of the Middle Cambrian layers 3–3–3191. found related species - Pseudoarctolepis semicircularis , which was distinguished by flap-like extensions of the carapace, rather than spiky processes. And in 2019 in the Valongu Formation ( Valongo Formation ) In northern Portugal found poorly preserved fossil of the crustacean Ordovician period supposedly belonging to the same genus.

Fingerprint 3-3-3203. Pseudoarctolepis semicircularis [/i] and his scheme. Image from an article by J. Yuan et al., 2011.3-3r3203. [/i] New Bivalved Arthropods from Mid-Cambrian Kaili Biota of Southeastern Guizhou, Southwest China

Photo from the site fossilmuseum.net .

Andrey Petrov