''Platykotta akaina'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

decapod The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and p ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

from the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

of the

United Arab Emirates The United Arab Emirates (UAE), or simply the Emirates, is a country in West Asia, in the Middle East, at the eastern end of the Arabian Peninsula. It is a Federal monarchy, federal elective monarchy made up of Emirates of the United Arab E ...

. 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 preserve ...

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 groups ...

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

Stratigraphy

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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

on the

Musandam Peninsula The Musandam Peninsula (), locally known as Ruus Al Jibal ( Capes of the Mountains), is a peninsula that forms the northeastern point of the Arabian Peninsula. Geography The peninsula lies to the south of the Strait of Hormuz, between the Persia ...

– the peninsula which separates the

Persian Gulf The Persian Gulf, sometimes called the Arabian Gulf, is a Mediterranean seas, mediterranean sea in West Asia. The body of water is an extension of the Arabian Sea and the larger Indian Ocean located between Iran and the Arabian Peninsula.Un ...

from the

Gulf of Oman The Gulf of Oman or Sea of Oman ( ''khalīj ʿumān''; ''daryâ-ye omân''), also known as Gulf of Makran or Sea of Makran ( ''khalīj makrān''; ''daryâ-ye makrān''), is a gulf in the Indian Ocean that connects the Arabian Sea with th ...

. 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 251.902 Mya. It is the s ...

to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

, the area was near the shore of the

Tethys Sea The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

, which produced

carbonate A carbonate is a salt of carbonic acid, (), 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 group ...

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

s. The strata that contained ''Platykotta'' were part of the Ghalilah Formation, of

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

–

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

age. These rocks contain extensive networks of

burrow file:Chipmunk-burrow (exits).jpg, An eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of Animal lo ...

s, and various other fossils, including

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

of the families

Megalodontidae Megalodontidae is an extinct family of bivalve molluscs that reportedly lived from the Devonian to the Jurassic period. Nomenclature A family of insects was also previously called "Megalodontidae", containing the sawfly genus '' Megalodontes''. ...

and Wallowaconchidae,

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of 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 e ...

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

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s and

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

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 coll ...

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

Description

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

sternum The sternum (: sternums or sterna) 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 bl ...

, unlike the very narrow sternum seen in

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

(true

lobster Lobsters are Malacostraca, malacostracans Decapoda, decapod crustaceans of the family (biology), family Nephropidae or its Synonym (taxonomy), synonym Homaridae. They have long bodies with muscular tails and live in crevices or burrows on th ...

s and freshwater

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

) and

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

. A similar sternal form is seen in the spiny lobsters and

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

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, alongs ...

s), and Aeglidae. Unlike other anomurans, however, the

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

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 ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

, 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, includ ...

. ''Eocarcinus'' was previously treated as the earliest true

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

, but is now thought, like ''Platykotta'', to show too little

carcinisation Carcinisation (American English: carcinization) is a form of convergent evolution in which non-crab crustaceans evolve a crab-like body plan. The term was introduced into evolutionary biology by Lancelot Alexander Borradaile, who described it a ...

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

References

{{Taxonbar, from1=Q20899239, from2=Q7202616, from3=Q20899240 Anomura Triassic crustaceans Monotypic decapod genera Triassic animals of Africa Norian genus first appearances Rhaetian genus extinctions Fossil taxa described in 2011 Paleontology in the United Arab Emirates