''Platykotta akaina'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of decapod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

from the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

of the

United Arab Emirates The United Arab Emirates (UAE; ar, اَلْإِمَارَات الْعَرَبِيَة الْمُتَحِدَة ), or simply the Emirates ( ar, الِْإمَارَات ), is a country in Western Asia ( The Middle East). It is located at t ...

. It is the oldest known

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

from the infraorder

Anomura Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word ''crab'', all true crabs are in the sister group to the Anomura, the Brachyura (the two grou ...

, and is most closely related to '' Eocarcinus praecursor''.

Stratigraphy

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

of ''P. akaina'' was found in the

on the

Musandam Peninsula The Musandam Peninsula ( ar, جَزِيْرَة مُسَنْدَم \ رَأْس مُسَنْدَم, Jazīrat Musandam / Raʾs Musandam), locally known as Ruus Al Jibal ( ar, رُؤُوْس ٱلْجِبَال, ''Ruʾūs al-Jibāl'' Heads of the Mou ...

– the peninsula which separates the

Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a mediterranean sea in Western Asia. The bod ...

from the Gulf of Oman. From the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

, the area was near the shore of the

Tethys Sea The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

, which produced

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s. The strata that contained ''Platykotta'' were part of the Ghalilah Formation, of Norian– Rhaetian age. These rocks contain extensive networks of burrows, and various other fossils, including bivalves of the families Megalodontidae and Wallowaconchidae,

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...

s and

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s. The holotype was found at approximately and has been deposited in the

Natural History Museum of Geneva The Natural History Museum of Geneva (in French: ') is a natural history museum in Geneva, Switzerland. Louis Jurine’s collections of Hymenoptera, Coleoptera, Lepidoptera and Hemiptera are held by the museum. Other displays include a ...

, Switzerland.

Description

''Platykotta'' is characterised by a broad, triangular

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

, unlike the very narrow sternum seen in

Astacidea Astacidea is an infraorder of decapod crustaceans including lobsters (though not "lobsters" such as the spiny lobster etc.), crayfish, and their close relatives. Description The Astacidea are distinguished from most other decapods by the presen ...

(true lobsters and freshwater crayfish) and

Glypheoidea The Glypheoidea (containing the glypheoid lobsters), is a group of lobster-like decapod crustaceans which forms an important part of fossil faunas, such as the Solnhofen limestone. These fossils included taxa such as ''Glyphea'' (from which the ...

. A similar sternal form is seen in the

spiny lobster Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...

s and

slipper lobster Slipper lobsters are a family (Scyllaridae) of about 90 species of achelate crustaceans, in the Decapoda clade Reptantia, found in all warm oceans and seas. They are not true lobsters, but are more closely related to spiny lobsters and furry ...

s, and also several families of

, including

Galatheidae The Galatheidae are a family of squat lobsters. Genera There are 11 living genera and 7 extinct genera in the family Galatheidae: *† ''Acanthogalathea'' Müller & Collins, 1991 – Upper Eocene * '' Alainius'' Baba, 1991 * '' Allogalathea'' ...

and Chirostylidae (

squat lobster Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongsi ...

s), and Aeglidae. Unlike other anomurans, however, the carapace is considerably longer than wide. The pattern of grooves on the carapace indicates clear affinities with the Anomura.

Systematics

''Platykotta'' is placed in its own

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, Platykottidae, which sits alongside Eocarcinidae (containing only '' Eocarcinus'') in the superfamily

Eocarcinoidea Eocarcinoidea is a superfamily of fossil decapod crustaceans. Formerly thought to be the earliest true crabs, they are now thought to be the oldest members of the Anomura Anomura (sometimes Anomala) is a group of decapod crustaceans, includi ...

. ''Eocarcinus'' was previously treated as the earliest true crab, but is now thought, like ''Platykotta'', to show too little

carcinisation Carcinisation (or carcinization) is an example of convergent evolution in which a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced into evolutionary biology by L. A. Borradaile, who describe ...

to be a true crab, and is placed instead among the

References

{{Taxonbar, from=Q7202616 Anomura Triassic crustaceans Monotypic arthropod genera Triassic animals of Africa Norian first appearances Rhaetian extinctions