According to Wikipedia,
“Anomalocaris (“unlike other shrimp”, or “abnormal shrimp”) is an extinct genus of radiodont (anomalocaridid), an order of animals thought to be closely related to ancestral arthropods.”
That is confirmed below (Fig. 1). But where did Anomalocaris come from?
According to Wikipedia,
“Stephen Jay Gould cites Anomalocaris as one of the fossilized extinct species he believed to be evidence of a much more diverse set of phyla that existed in the Cambrian Period, discussed in his book Wonderful Life, a conclusion disputed by other paleontologists.”
That is not confirmed below. Based on phylogenetic bracketing, Anomalocaris evolved from flatworms and into trilobites. Thus, these do not increase the diversity of phyla in the Cambrian, but blend one into another.
Where else do we find such a mouth?
That’s the first clue to the origin of anomalocarids.
Evidently overlooked until now,
certain flatworms have a similar concentric ventral mouth (Fig. 1).
Anomalocarids apparently had the fluidity of motion
of a large swimming flatworm (see video below), combined with the segmentation of trilobites (= arthropod ancestors).
Distinct from flatworms, but like trilobites,
an anus appears posteriorly.
Like tentacled flatworms and trilobites with antennae,
two armored tentacles appear on anomalocarids,
Unlike flatworms, but like trilobites,
a pair of lateral eyes on short stalks appear.
A YouTube video
featuring Burgess Shale expert Professor Des Collins explains how the bits and pieces of Anomalocaris came together historically over several years as he holds a model of a large specimen.https://www.youtube.com/watch?v=xNbaHOJ7GGk
According to the Des Collins website:
“The fossil Anomalacaris was unlike any living animal and was misidentified over a period of 100 years revealing the false starts that can happen in scientific research. Collins set out to piece together the entire animal by looking at the vast trove of Burgess Shale fossils at the Royal Museum of Ontario where he worked. He discovered more pieces of the puzzle and realized that previous fossils that were described as separate organisms were, in fact, part of the animal Anomalacaris. Once he had assembled the entire animal, he had a model built to show what a fearsome predator it must have been.”
Or not. Anomalocaris was large, but its mouth was not ideally suited to crack open and attack the hard-shelled animals that were evolving in the Cambrian. According to the Wired.com article cited below, “We found that it’s extremely unlikely Anomalocaris could eat most trilobites,” said James Whitey Hagadorn, the research team’s leader and a paleontologist at the Denver Museum of Nature and Science. “It couldn’t close its mouth all of the way, its mouth was too soft to crush trilobite shells.”
Anomalocaris arising from large free-swimming flatworms
appears to be a novel hypothesis of interrelationships. If not, please provide a citation so I can promote it here.
This just in (March 11, 2021):
Tests show Anomalocaris was not a trilobite eater, but preferred mush, like modern flatworms do.
Daley AC, Paterson JR, Edgecombe GD, García-Bellido DC and Jago JB 2013. Donoghue P (ed.). New anatomical information on Anomalocaris from the Cambrian Emu Bay Shale of South Australia and a reassessment of its inferred predatory habits. Palaeontology: n/a. doi:10.1111/pala.12029
Whiteaves JF 1892. Description of a new genus and species of phyllocarid Crustacea from the Middle Cambrian of Mount Stephen, BC. The Canadian Record of Science. 5 (4).
Whittington HB and Briggs DE 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society B. 309 (1141): 569–609.