Megarachne Servinei
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''Megarachne'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...
, an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
group of aquatic
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
s. Fossils of ''Megarachne'' have been discovered in deposits of
Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...
age, from the
Gzhelian The Gzhelian ( ) is an age in the ICS geologic time scale or a stage in the stratigraphic column. It is the youngest stage of the Pennsylvanian, the youngest subsystem of the Carboniferous. The Gzhelian lasted from to Ma. It follows the Ka ...
stage, in the Bajo de Véliz Formation of
San Luis, Argentina San Luis () is the capital city of San Luis Province in the Cuyo, Argentina, Cuyo region of Argentina. It is also the seat of the Juan Martín de Pueyrredón Department. City information Points of interest in the city include the Park of the Na ...
. The fossils of the single and
type species In International_Code_of_Zoological_Nomenclature, 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 spe ...
''M. servinei'' have been recovered from deposits that had once been a
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
environment. The generic name, composed of the
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
μέγας (''megas'') meaning "great" and Ancient Greek ἀράχνη (''arachne'') meaning "
spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...
", translates to "great spider"; because the fossil was misidentified as a large, prehistoric spider. With a body length of , ''Megarachne'' was a medium-sized eurypterid. If the original identification as a spider had been correct, ''Megarachne'' would have been the largest known spider to have ever lived. Eurypterids such as ''Megarachne'' are often called "sea scorpions", but the
strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
in which ''Megarachne'' has been found indicates that it dwelled in freshwater and not in marine environments. ''Megarachne'' was similar to other eurypterids within the Mycteropoidea, a rare group known primarily from South Africa and Scotland. The mycteropoids had evolved a specialized method of feeding referred to as sweep-feeding. This involved raking through the substrate of riverbeds in order to capture and eat smaller
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
s. Despite only two specimens having been recovered, ''Megarachne'' represents the most complete eurypterid discovered in
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
deposits in South America so far. Due to their fragmentary fossil record and similarities between the genera, some researchers have hypothesized that ''Megarachne'' and two other members of its family, '' Mycterops'' and '' Woodwardopterus'', represent different developmental stages of a single genus.


Description

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 ...
s of ''Megarachne'' indicate a body length of . While large for an arthropod, ''Megarachne'' was dwarfed by other
eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...
s, even relatively close relatives such as '' Hibbertopterus'' which could reach lengths exceeding . Though originally described as a giant
spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...
, a multitude of features support the classification of ''Megarachne'' as a eurypterid. Among them, the raised lunules (the vaguely moon-shaped ornamentation, similar to scales) and the cuticular sculpture of the mucrones (a dividing ridge continuing uninterrupted throughout 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 ...
, the part of the exoskeleton which covers the head) are especially important since these features are characteristic of eurypterids. ''Megarachne'' possessed blade-like structures on its appendages (limbs) which would have allowed it to engage in a feeding method known as sweep-feeding, raking through the soft sediment of aquatic environments in swamps and rivers with its frontal appendage blades to capture and feed on small
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
s. ''Megarachne'' also possessed a large and circular second opisthosomal tergite (the second
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...
segment of the abdomen), the function of which remains unknown. ''Megarachne'' was very similar to other mycteroptid eurypterids in appearance, a group distinguished from other mycteropoids by the parabolic shape of their
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 plate), hastate
telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
s (the hindmost part of the body being shaped like a ''
gladius ''Gladius'' () is a Latin word properly referring to the type of sword that was used by Ancient Rome, ancient Roman foot soldiers starting from the 3rd century BC and until the 3rd century AD. Linguistically, within Latin, the word also came t ...
'', a
Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of Roman civilization *Epistle to the Romans, shortened to Romans, a letter w ...
sword) with paired
keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...
-shaped projections on the underside, and heads with small
compound eye A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of a cornea, lens (anatomy), lens, and p ...
s that were roughly
trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...
al in shape.


History of research

''Megarachne servinei'' was originally described in 1980 by the Argentine
paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Mario Hünicken. The generic name, composed of the
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
μέγας (''megas'') meaning "great" and
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''arachne'' meaning "spider", translates to "great spider". 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 ...
(now stored at the Museum of Paleontology at the
National University of Córdoba The National University of Córdoba (), is a public university located in the city of Córdoba, Argentina. Founded in 1613, the university is the oldest in Argentina, the third oldest university of the Americas, with the first university being ...
) was recovered from the Pallero Member of the Bajo de Véliz 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 ...
, which has been dated to the Gzhelian age: to million years ago. The specimen preserves the carapace, the first two tergites, three partial
appendages An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
, and what is possibly a coxa (the
proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
-most limb segment). Hünicken wrongly identified the specimen as a mygalomorph spider (the group that includes
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although ...
e) based on the shape of the carapace; the wide, circular eye
tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...
(round outgrowth) located in the center of the head between the two eyes; and a circular structure behind the first body-segment - which he identified as the "moderately hairy" abdomen. Hünicken's identification relied heavily on
X-ray microtomography In radiography, X-ray microtomography uses X-rays to create cross-sections of a physical object that can be used to recreate a virtual model (3D model) without destroying the original object. It is similar to tomography and X-ray computed tomog ...
of the holotype. Additional hidden structures – such as a
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 ...
and labium, coxae and
cheliceral fang 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 as a type ...
s – were also extrapolated from the X-radiographs. With an estimated length of based on the assumption that the fossil was that of a spider, and with a leg-span estimated to be , ''Megarachne servinei'' would have been the largest spider to have ever existed; exceeding the
goliath birdeater The Goliath birdeater (''Theraphosa blondi'') belongs to the tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" ...
(''Theraphosa blondi''), which has a maximum leg-span of around . Because of its status as the "largest spider to have ever lived", ''Megarachne'' quickly became popular. Based on Hünicken's detailed description of the fossil specimen and various other illustrations and reconstructions made by him, reconstructions of ''Megarachne'' as a giant spider were set up in museums around the world. The identification of the specimen as a spider was doubted by some
arachnologist Arachnology is the scientific study of arachnids, which comprise spiders and related invertebrates such as scorpions, pseudoscorpions, harvestmen, ticks, and mites. Those who study spiders and other arachnids are arachnologists. More narrowly ...
s, such as Shear and colleagues (1989), who stated that while ''Megarachne'' had been assigned to the Araneae, it "may represent an unnamed order or a
ricinulei Ricinulei is a small order of arachnids. Like most arachnids, they are predatory; eating small arthropods. They occur today in west-central Africa ('' Ricinoides'') and the Americas ('' Cryptocellus'' and '' Pseudocellus'') from Brazil to southern ...
d". Even Hünicken himself acknowledged discrepancies in the morphology of the fossil that could not be accommodated with an
arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...
identity. These discrepancies included an unusual cuticular ornamentation, the carapace being divided into frontal and rear parts by a suture, and spatulate (having a broad, rounded end)
chelicerae The chelicerae () are the arthropod mouthparts, 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 ...
(already noted by Hünicken as a strange feature, as no known spider possesses spatulate chelicerae); all features unknown in other spiders. However, the holotype was by then deposited in a
bank vault A bank vault is a secure room used by banks to store and protect valuables, cash, and important documents. Modern bank vaults are typically made of reinforced concrete and steel, with complex locking mechanisms and security systems. This article ...
so other paleontologists only had access to
plaster cast A plaster cast is a copy made in plaster of another 3-dimensional form. The original from which the cast is taken may be a sculpture, building, a face, a pregnant belly, a fossil or other remains such as fresh or fossilised footprints – ...
s. In 2005, a second - more complete - specimen consisting of a part and counterpart (the matching halves of a
compression fossil A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way. The reason f ...
) was recovered. This specimen had preserved parts of the front section of the body, as well as coxae possibly from the fourth pair of appendages, and was recovered from the same locality and
horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...
. A research team led by the British paleontologist and arachnologist Paul A. Selden, and also consisting of Hünicken and Argentine arachnologist José A. Corronca, re-examined the holotype in light of the new discovery. They concluded that ''Megarachne servinei'' was a large eurypterid (a group also known as "sea scorpions"), not a spider. Although Hünicken had misidentified ''Megarachne'', his identification of it as an arachnid was not entirely absurd, as the two groups are closely related. A morphological comparison with other eurypterids indicated that ''Megarachne'' most closely resembled another large Permo-
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
eurypterid, the mycteroptid '' Woodwardopterus scabrosus'', which is known only from a single specimen. Selden and colleagues (2005) concluded that, despite only being represented by two known specimens, ''Megarachne'' is the most complete eurypterid discovered in Carboniferous
deposits A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below. ...
in South America so far.


Classification

''Megarachne'' was part of the stylonurine suborder, a relatively rare
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of eurypterids. Within the stylonurines, ''Megarachne'' is a member of the superfamily Mycteropoidea and its constituent
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 ...
Mycteropidae; which includes the close relatives ''Woodwardopterus'' and '' Mycterops''. Fossilized remains of the second tergite of the mycteroptid ''Woodwardopterus'' were compared to the fossil remains of ''Megarachne'' by Selden and colleagues (2005), which revealed that they were virtually identical; including features previously not noted in ''Woodwardopterus'', such as radiating lines covering the tergite. It was concluded that ''Megarachne'' and ''Woodwardopterus'' were part of the same family by Selden and colleagues (2005), with two primary differences: the tergites and the mucrones on the carapace are more sparsely packed in ''Megarachne'' and the protrusion of the anteroedian (i.e. before the middle) carapace, seen prominently in ''Megarachne'', does not occur in ''Woodwardopterus''. It has been suggested that three of the four
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
that constitute the Mycteroptidae, ''Mycterops'', ''Woodwardopterus'', and ''Megarachne'' might represent different ontogenetic stages (different developmental stages of the animal during its life) of each other based on their morphology and the size of the specimens. Should this interpretation be correct, the sparse mucrones of ''Megarachne'' might be because of its age; as ''Megarachne'' is significantly larger than ''Woodwardopterus''. The smallest genus, ''Mycterops'', has even more densely packed ornaments on its carapace and tergite; and thus might be the youngest, ontogenetic stage of the animal. Should ''Mycterops'', ''Megarachne'', and ''Woodwardopterus'' represent the same animal, the name-taking priority would be ''Mycterops''; as it was named first, in 1886.Dunlop, J. A., Penney, D. & Jekel, D. 2018
A summary list of fossil spiders and their relatives
In World Spider Catalog. Natural History Museum Bern, p. 19
The
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below is adapted from Lamsdell and colleagues (2010) and shows the relationship of ''Megarachne'' within the suborder Stylonurina.


Paleoecology

Both known specimens of ''Megarachne'' have been recovered from the Bajo de Véliz Formation of Argentina, dated to the Gzhelian stage of the Late Carboniferous. The environment of the Bajo de Véliz formation was, unlike the typical living environments of eurypterids (especially the swimming eurypterids of the suborder
Eurypterina Eurypterina is one of two suborders of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil depos ...
), a
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
environment in a
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
. Similar Late Carboniferous floodplains with fossilized remnants discovered in modern-day Australia suggest a flora dominated by different types of pteridosperms with pockets of isoetoid lycopsids. During ''Megarachne'' time, Argentina and the rest of South America was part of the ancient supercontinent
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
which was beginning to fuse with the northern continents of
Euramerica Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...
,
North China North China () is a list of regions of China, geographical region of the People's Republic of China, consisting of five province-level divisions of China, provincial-level administrative divisions, namely the direct-administered municipalities ...
,
Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
and
Kazakhstania Kazakhstania (), the Kazakh terranes, or the Kazakhstan Block, is a geological region in Central Asia which consists of the area roughly centered on Lake Balkhash, north and east of the Aral Sea, south of the Siberian craton and west of the Alta ...
to form
Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
. In addition to ''Megarachne'', the Bajo de Véliz Formation preserves a wide array of fossilized flying insects, such as '' Rigattoptera'' (classified in the order Protorthoptera), but as a freshwater predator, ''Megarachne'' would probably not have fed on them. Instead, the blades on the frontal appendages of ''Megarachne'' would have allowed it to sweep-feed, raking through the soft sediment of the rivers it inhabited in order to capture and feed on small invertebrates. This feeding strategy was common to other mycteropoids. In comparison to the comparatively warm climate of the earlier parts of the Carboniferous, the Late Carboniferous was relatively cold globally. This
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
likely occurred during the Middle Carboniferous due to falling levels in the atmosphere and high oxygen levels. The Southern Hemisphere, where Argentina was and still is located, may even have experienced
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
with large continental
ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
s similar to the modern glacial ice sheets of the
Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...
and
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, or smaller glaciers in dispersed centers. The spread of the ice sheets also affected sea levels, which would rise and fall throughout the period. Late Carboniferous flora was low in diversity but also developed uniformly throughout Gondwana. The plant life consisted of pteridosperm trees such as '' Nothorhacopteris'', '' Triphyllopteris'' and '' Botrychiopsis'', and lycopsid trees '' Malanzania'', '' Lepidodendropsis'' and '' Bumbudendron''. The plant fossils present also suggest that it was subject to
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
s during certain time intervals.


In popular culture

During the production of the 2005 British documentary '' Walking with Monsters'', ''Megarachne'' was slated to appear as a giant
tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although ...
-like spider hunting the cat-sized reptile ''
Petrolacosaurus ''Petrolacosaurus'' ("rock lake lizard") is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, long reptile, and one of the earliest known reptiles with two temporal fenestrae (holes at the rear part of the ...
'' in the segment detailing the Carboniferous, with the reconstruction closely following what was thought to be known of the genus at the time the series began production. The actual identity of the genus, as a eurypterid, was only discovered well into production and by then it was far too late to update the reconstructions. The scenes were left in, but the giant spider was renamed as an unspecified species belonging to the primitive spider suborder
Mesothelae The Mesothelae are a suborder of spiders (order Araneae). , two extant families were accepted by the World Spider Catalog, Liphistiidae and Heptathelidae. Alternatively, the Heptathelidae can be treated as a subfamily of a more broadly circum ...
, a suborder that actually exists but with genera much smaller than, and looking considerably different from, the spider featured in the program.


References


External links

* * {{Taxonbar, from=Q141230 Stylonurina Gzhelian genera Carboniferous eurypterids Carboniferous animals of South America Eurypterids of South America Carboniferous Argentina Fossils of Argentina Fossil taxa described in 1980