Posterior Process Of Anomalocaris, Largest Member of Chengjiang Biota
"Terror Of The Cambrian"

Anomalocaris saron

Phylum Uncertain, Anomalocarididae

Geological Time: Early Cambrian (~525 million years ago)

Size (25.4mm=1 inch): 150 mm and 130 mm long on a 165 mm by 58 mm matrix

Fossil Site: Chengjiang Maotianshan Shales - Quiongzhusi Section, Yu’anshan Member, Heilinpu Formation, Mafang Village, Anning, Kunming, Yunnan Province, China

Anomalocaris saronThis is the proximal base of the bifurcated“rooster tail” of the “Terror Of The Cambrian”, Anomalocaris saron, seen here in the first example I have had. The members of this group of enigmatic creatures are known from Asia, Australia, Europe, and North America, and are thought by many to be closely allied with the Arthropda, as position not held by all researchers. As of the publication of Hou’s book in 2004, some 20 examples were known, most being grasping arms. The last decade has show that A. Canadensis of the younger Burgess Shale, A. saron, Amplectobelua from Chengjiang all sported an elongated process at the posterior. This is not a structure homologous to the telson (tailfan) of Arthropods. It is not certain whether this structure was fixed or movable, but I favor the movable theory as an aid in maneuvering. Known only from the Chengjiang biota, this species is closely related to A. canadensis, the type Anomalocarisspecies, from the younger Burgess Shale. The genus derives its name from “anomalous shrimp” which was what the describer thought the appendage was.

The discovery of the Chengjiang Biota by Hou Xian-guang in 1984 opened a window onto a remarkable array of lifeforms from what is termed the Cambrian Explosion. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

click fossil pictures to enlarge

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