Morphology of the covers of Proarticulata (Ediacaran metazoa)

Ivantsov, A.Y., Zakrevskaya, M., Nagovitsyn, A.

First paleontological Virtual Congress, December 2018

Estremamente interessante analisi su strutture che sarebbero andate perse durante i processi tafonomici, ma che rendono un'idea della complessità degli organismi del Precambriano. Al momento si ha un semplice abstract (che copio sotto). Se riesco ad avere ulteriori info, le mettero' sotto.

Proarticulata, which include well-known genus Dickinsonia, were the largest mobile animals of the Ediacaran Period. Body fossil impressions, classified as Proarticulata, were formed by bilateral objects, divided in transverse direction into two rows of "half-segments". It has been previously thought that the body of the animal was isomeric, consisting of either a special organ located on its dorsal side or a solid shield forming a dorsal cover. The results of recent studies allow us to amend these views. Our observations show that objects that formed the majority of imprints did not represent the whole body of Proarticulata, but only a part, that was resistant to decomposition. This structure, divided into transverse elements, extended both to dorsal and ventral sides of the body. This structure was dense and probably served as an internal support. The study of some rare exceptionally preserved specimens suggests that a cover tissue was located over the segmented structure. On the dorsal side, it created a continuous shield that showed no signs of segmentation. The outer surface of the dorsal side of several genera of Proarticulata (Dickinsonia, Yorgia, Archaeaspinus, Lossinia, Onega) was covered with numerous evenly distributed tubercles. In Onega, the dorsal tissue at the posterior end formed a pair of long filamentous outgrowths. Ichnofossils attributed to Proarticulata consist of shallow pits created by ingestion of the microbial mat. Based on these traces, the ventral side of the body was segmented externally similarly to the supporting structure. The cover tissue on the ventral side probably bore cilia; furrows from presumed ciliary movement are preserved on the traces. The newly obtained data are in accord with the concept of a relatively high level of organization of Proarticulata.