''Pulmonoscorpius'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always en ...

from the Mississippian (Early Carboniferous) of

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

. It contains a single named

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 ...

, ''Pulmonoscorpius kirktonensis''. It was one of the largest scorpions to have ever lived, with the largest known individual having an estimated length exceeding 70 cm (28 inches). ''Pulmonoscorpius'' retains several general arthropod features which are absent in modern scorpions, such as large lateral eyes and a lack of adaptations for a burrowing lifestyle. It was likely an active diurnal predator, and the presence of

book lungs A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnids, such as scorpions and spiders. Each of these organs is located inside an open ventral abdominal, air-filled cavity (atrium) and con ...

indicate that it was fully terrestrial.

Discovery

East Kirkton Quarry in West Lothian in Scotland 1

Fossils of ''Pulmonoscorpius kirktonensis'' have been found at the

East Kirkton Quarry East Kirkton Quarry is a former limestone quarry in West Lothian, Scotland (East Kirkton Limestone), now better known as a fossil site known for terrestrial fossils from the fossil-poor Romer's gap, a 15 million year period at the beginning of th ...

, West Lothian in

. Rock layers exposed at the quarry date back to the Carboniferous, specifically the

Viséan The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Ma. It follow ...

and

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed b ...

stages of the Mississippian (Early Carboniferous) subperiod, around 336.0 – 326.4 million years ago. The name derives from "

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''pulmonis'', a lung, and

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''skorpios'', a scorpion." The species name "kirktonensis" refers to the East Kirkton Quarry. ''Pulmonoscorpius'' was described in 1994 based on 16 complete specimens and over 300 additional fragments from East Kirkton. In each specimen, only the outer layer of hyaline cuticle is preserved, estimated to only be 15-18 μm thick in the largest specimen. Scorpion cuticle is present in the

East Kirkton Limestone The East Kirkton Limestone is a rock unit in the West Lothian Oil-Shale Formation in Scotland. It preserves fossils of the Carboniferous period. The limestone outcrops at East Kirkton Quarry. See also * '' Kirktonecta'' * List of fossiliferou ...

(lower exposed unit) and Little Cliff Shale (middle exposed unit), but not the Geikie Tuff (upper exposed unit). Although cuticle could be found in a variety of shale and

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 ...

facies, it is most easily prepared out of finely-laminated

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, which can be dissolved away with dilute

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

while leaving the organic cuticle unharmed. Almost all material is completely flattened, so three-dimensional reconstructions are mostly hypothetical.

Description

The

diet Diet may refer to: Food * Diet (nutrition), the sum of the food consumed by an organism or group * Dieting, the deliberate selection of food to control body weight or nutrient intake ** Diet food, foods that aid in creating a diet for weight loss ...

of ''Pulmonoscorpius'' is not known directly, but it is probable that it preyed on smaller

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s, and small

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s (new arrivals). Most complete specimens were in length, while a large, fragmentary specimen is estimated to have been long when alive. The only portions preserved were the outer portions of the cuticle.

Dorsal surface

''Pulmonoscorpius'' possess two pairs of eyes on the

prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

(the head and legs segment, also known as a cephalothorax). These include a pair of anterior-positioned median eyes (near the center of the prosoma) and a pair of

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

lateral eyes (on the edge of the prosoma), with each lateral eye bearing between 40 and 60 lateral

ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

. In modern scorpions, lateral eyes are strongly reduced, but those of ''Pulmonoscorpius'' are large, similar to other basal scorpions and most other arthropods. The prosoma is covered by a carapace (a large plate). The prosoma is followed by a

mesosoma The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings. In hymenopterans of ...

(the broad portion of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...

-like

opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma ( cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to ...

), which has seven segments each covered by a

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

(smaller, broad plate). The surface of the carapace and tergites are relatively smooth in juveniles, while tuberculated in larger individual. The

metasoma The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circul ...

(tail) has five segments, not counting the bulbous

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

(stinging segment) at the end. The last (5th) metasomal segment does not exceed the length of the preceding (4th) metasomal segment. Metasomal segments are boxy and ornamented by paired carinae (tuberculated ridges) in adults. The strongest carinae are the dorsal (upper) pair, and superior lateral (upper part of the side), inferior lateral (lower part of the side), and inferior median (underside) carinae are also present.

Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

may be present in ''Pulmonoscorpius'', as some specimens (females?) have wider metasomal segments. In ''Pulmonoscorpius kirktonensis'', the vesicle (venom-bearing portion of the telson) has pair of strong carinae on its underside. One unique juvenile specimen is observed to lack these carinae, and may belong to a separate species (''Pulmonoscorpius'' sp. A).

Ventral structures

20210110 Pulmonoscorpius juvenile ventral

The coxae of each leg (the shortest segment, closest to the body) converge along the underside of the prosoma. The

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 ...

(ventral plate between the bases of legs 3 and 4) is characteristically elongated, with a Y-shaped sulcus at the rear. The underside of the mesosoma possessed a bilobed and laterally elongated genital operculum (a covering of the

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 t ...

), followed by pectines (comb-like sensory appendages) with 150-160 narrow teeth, and finally ventral plates (3 in juveniles and 4 in adults). In juveniles, the first ventral plate has a unique median lobation. As with modern scorpions, four pairs of

were present at the corresponding ventral plates.

Appendages

Like other scorpions, ''Pulmonoscorpius'' had four pairs of walking legs as well as larger pincer-like

pedipalps Pedipalps (commonly shortened to palps or palpi) are the second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and ...

and smaller pincer-like

chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as " jaws", chelicerae may be shaped as either articulated fangs, or similarl ...

(mouthparts). One characteristic trait of ''Pulmonoscorpius'' is the presence of a long spur on each of the apophyses (an extension of the coxa). The chelicerae and legs were noted be to be similar to those of extant scorpions, except that the coxa and

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

(first and third segments) in legs 3 and 4 are less elongated, and the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

(fifth segment) of these legs are elongated to about the same length as their femur. In the pedipalps, the femur and patella (fourth segment) are lined with carinae.

Setae In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

(hairs) are sparse and clustered, particularly in larger individuals. Setae density is highest on the large (fixed) finger of the pedipalps. One juvenile specimen has 30% more setae on its fixed finger than any other ''Pulmonoscorpius kirktonensis'' specimen. This specimen may belong to a separate species (''Pulmonoscorpius'' sp. B). Aside from the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

, two other specimens were noted to possibly be distinct, one with "juvenile pedipalp fingers with 30% more

seta In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

l follicles" than ''P. kirktonensis'' and one "lacking tuberculateventral carinae on vesicle of

References

External links

* https://web.archive.org/web/20061023072618/http://www.langsfossils.com/museum/pages/m-scld-002.htm * http://dml.cmnh.org/1999Jun/msg00432.html
Images of the holotype fossil at GB3D
{{Taxonbar, from=Q612611 Prehistoric scorpions Paleozoic arachnids Carboniferous arthropods of Europe Carboniferous arachnids Viséan life Carboniferous Scotland Fossils of Scotland Fossil taxa described in 1994