Retifacies abnormalis is an extinct arthropod that lived in the lower Cambrian (about 518 million years ago). Its fossil remains have been found in the Maotianshan Shales of Yunnan, China. It is a member of the Artiopoda, and closely related to Pygmaclypeatus.
Retifacies abnormalis is an extinct arthropod that lived in the lower Cambrian (about 518 million years ago). Its fossil remains have been found in the Maotianshan Shales of Yunnan, China. It is a member of the Artiopoda, and closely related to Pygmaclypeatus.
== Description == left|thumb|Reconstruction in various views. E=uniramous cephalic appendages F=biramous appendages Key: exopod (exo) exite (exi) protopodite (pt) podomere (pd) spine/setae (s) terminal claw (tc) left|thumb|Two life restorations showing variation in carapace ornamentation Retifacies was relatively large sized, reaching a carapace length of , and a total length of , including the extended antennae and tailspine. The head shield was broad and short, and appears to have lacked eyes. The antennae had 17 segments, which telescoped into each other, with spines present on the underside of the antennae at the boundary between the segments. Also present on the head were four closely spaced pairs of appendages, the first three of which were uniramous (single branched), while the last was biramous (two branched). The three uniramous appendages had six segments (podomeres), each ending with a terminal claw, with the endopod (lower leg-like branch) of the fourth biramous limb having a similar morphology. The trunk was divided up into 10 segments (tergites), all of approximately equal length and width, each of which were associated with pairs of biramous appendages. The endopods of these limbs had 5/6 podomeres with terminal claws, while the exopod (upper limb branch) comprised a semicircular lobe that bore over 12 paddle-shaped lamellae, the last of which bore setae (hair-like structures) at its edge. These limbs also bore exites, consisting of lamellae borne from the basal segment (basipod) of the appendage. The pygidium segment at the end of the body was proportionally large, and bore 5-6 pairs of biramous appendages. The segmented tailspine emerged from the underside of the pygidium. The carapace was covered in polygonal reticulated (net-like) ornamentation, which varied between specimens, corresponding to two morphotypes. Due to one morphotype only being found among the largest specimens the differences may be due to ontogeny.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).