''Apankura'' is an extinct genus of
Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
euthycarcinoids from the
Santa Rosita Formation of
Argentina
Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
. The genus contains a
single species, ''Apankura machu''.
It was at one point the only Cambrian euthycarcinoid. However, ''
Mosineia'' and ''
Mictomerus'' are likely older.
Description
''Apankura'' is roughly long, and has large
mandibles
In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla).
The jawbone i ...
, a trait previously unknown from euthycarcinoids. The
antennae are uniramous like other euthycarcinoids, with a possible buccal complex present behind the mandibles. No post-mandibular oral appendages are present. The pre-abdomen is composed of five
tergites, with 11 uniramous limb pairs, with the tergites showing "segment decoupling" where there are more limbs than tergites. The pre-abdomen also has 11
sternite
The sternum (: sterna) is the ventral portion of a segment of an arthropod thorax or abdomen.
In insects, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the su ...
s, each roughly 3 times wider than long. The pre-abdominal limbs match other euthycarcinoids, although they taper distally and lack setae. The
apodemes are preserved as several dark rods. The post-abdomen is incomplete but composed of at least six segments, all lacking limbs, with the gut preserved as a dark line in the centre. A circular structure on the second post-abdominal segment is of unclear function, although it may be a
gonopore
A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects, have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female, it is ...
. ''Apankura'' is unique among euthycarcinoids due to the reduced anterior pre-abdominal limbs, a longer post-abdomen and relatively few limb podomeres.
[
]
Etymology
''Apankura'' derives from a Quechua word meaning "crab", whilst ''machu'' derives from a word meaning "grandfather" in reference to the age of the fossils.[
]
References
{{Taxonbar, from=Q131382433
Fossils of Argentina
Fossil taxa described in 2004
Paleozoic arthropods of South America
Paleontology in Argentina
Cambrian genus extinctions