Name: Naraoiidae;
Naraoia spinosa
Geological
Time: Early Cambrian Qiongzhusi Section, Yu'anshan Member, Heilinpu
Formation (~525 million years ago)
Size: 5 mm
Fossil
Site: Chengjiang Maotianshan Shale, Qiongzhusi Section, Yu'anshan
Member, Heilinpu Formation, Mafang Village, Haikou County, Kunming, Yunnan
Province, China
The
exact taxonomic status of the arthropod Naraoia
is in dispute. It has been termed a “trilobitomorpha”
by some researchers, indicating their beliefs in its close affinity
with the trilobites. While the Trilobitoorpha is listed in the Treatise,
most now consider that this subphylum is invalid, a catchall much
like some of the dustbin terms used by Walcott for a number of the
Burgess Shale fauna. Whittington termed Naraioa a “soft-bodied
trilobite”’ but that belief is not supported at present.
Their similarity in appearance to the Agnoistida is purely a result
of convergence. Two large groupings of the Paleozoic arthropods
are currently in favor: the Crustaceomorpha (which includes Waptia)
and the Arachnomorpha, dominated by the trilobites. The Naraoiidae
are arachnomorphs and include Misszhouia and Naraoia. The species
is one found in several locations within Yunnan Province. 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. This
one shows many of the classic features of the taxon. Even the central
gut is in evidence, as is the soft cuticle that betrays the outline
of the body. Naraoia
spinosa is only known from the Chengjiang
Biota. This is a most unusual juvenile example (I have included
a photo of an adult for scale) with exceptional soft tissue preservation
for which Chengjiang is famous.
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