| Urokodia Temporal range: | |
|---|---|
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| Fossil specimen with preserved appendages | |
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| Reconstruction of Urokodia | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| (unranked): | † Artiopoda |
| Genus: | † Urokodia Hou et al, 1989 |
| Type species | |
| Urokodia aequalis Hou et al, 1989 | |
Urokodia is an extinct genus of marine arthropod from the early Cambrian. The only known species is Urokodia aequalis from the Maotianshan Shales of China based on some 15 specimens. [1]
Urokodia is an elongated arthropod measuring up to 3.5 cm. The dorsal exoskeleton (tergite) is composed of a cephalon (head) and a pygidium (tail shield) of subequal size. Both were initially thought to be nearly identical, possessing 4 pairs of large lateral spikes. However, subsequent studies revealed that the pygidium had a distinct triangular shape and a parallel row of tiny posterior spikes. Between the cephalon and pygidium was an elongated thorax of 14 or 15 segments. [2] It possesses a pair of stalked eyes and stubby antennae below the front of its head. The remaining ventral region possesses subequal appendages with annulated bases and lamellar (lobe-like) outer branches, 3 pairs under both cephalon and pygidium and 1 pair under each thoracic segment. All but the pygidial appendages bore segmented, stenopodous (leg-like) inner branches. [3]
The ventral appendages of Urokodia had been unknown for a long time, and its dorsal features resemble Mollisoniidae (e.g. Mollisonia , Thelxiope , and Corcorania ) at first glance. This lead to the previous classification of Urokodia as a member of the order Mollisoniida with other mollisoniids. Based on the discovery of Mollisonia appendages in 2019, the group is suggested to be stem-chelicerates. [4] However, a redescription published in July 2024 discovered the appendages of Urokodia to differ markedly from those of mollisoniids or any other chelicerates. Phylogenetic analysis based on the new discovery instead places Urokodia as the most basal member of Artiopoda, an extinct group which includes trilobites and their relatives. [3]
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