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Mycteropoidea is an extinct superfamily of
Mycteropoids are diagnosed as stylonurines with a posterior cleft on the metastoma and rounded lenses overlaying the lateral eyes as well as having anterior prosomal appendages modified for sweep-feeding.
Sweep-feeding strategies evolved independently in two of the four stylonurine superfamilies, the Stylonuroidea and the Mycteropoidea. In both superfamilies, the adaptations to this lifestyle involves modifications to the spines on their anterior prosomal appendages for raking through the substrate of their habitats. Stylonuroids have fixed spines on appendages II-IV which could have been used as dragnets to rake through the sediments and thus entangling anything in their way. Mycteropoids show even more extreme adaptations towards a sweep-feeding lifestyle.
They possess blades on prosomal appendages II-III (and IV within the Hibbertopteridae), highly distinct from flattened spines such as in the kokomopteroid '' Hallipterus'', being laterally expanded with a blunt and rounded termination that has sensory setae. The tactile function of these might have allowed mycteropoids to select prey from the sediments in a way that stylonuroids could not.
In the mycteroptids, appendages II and III were used for prey capture, whilst hibbertopterids also used appendage IV, while also retaining its use as a leg for walking. The coxae in '' Hibbertopterus'' are reduced, leading to part of the food masticatory process being assumed by the laden (plates overlaying the coxae). Some species of ''Hibbertopterus'' have even further adaptations towards sweep-feeding than other mycteropoids, with its blades modified into comb-like rachis that could entrap smaller prey or other organic food particles. With its coxae being large, it is likely that some species of ''Hibbertopterus'' would also feed on relatively large invertebrates when able to.
Mycteropoids are so derived and unusual that their unique morphology on occasion has prompted researchers to place them as an order separate to
eurypterid
Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...
s, an extinct group of chelicerate 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 commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina
Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from ...
. Mycteropoids have been recovered from Europe, Russia, South America and South Africa. Mycteropoid specimens are often fragmentary, making it difficult to establish relationships between the included taxa. Only two mycteropoid taxa are known from reasonable complete remains, '' Hibbertopterus scouleri'' and ''H. wittebergensis''.
Mycteropoids were large bizarre Eurypterid
Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...
s found from the Early Silurian to the end of 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 ...
period. They were sweep feeders, inhabiting freshwater swamps and rivers, feeding by raking through the soft sediment with blades on their anterior appendages to capture small invertebrates. Their morphology was so unusual that they have been thought to be an order separate to Eurypterida
Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...
. Recent work however confirms them to be derived members of the suborder Stylonurina
Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from ...
, with the 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 ...
'' Drepanopterus'' being a basal member of their superfamily.
The mycteropoids are important within eurypterid evolutionary history as the last group of eurypterids to experience a significant radiation in diversity at the genus level (during the Late Devonian and Carboniferous) as well as being the latest known surviving members of the group, going extinct during the Permian-Triassic extinction event.
Description
Mycteropoids are diagnosed as stylonurines with a posterior cleft on the metastoma and rounded lenses overlaying the lateral eyes as well as having anterior prosomal appendages modified for sweep-feeding.
Sweep-feeding strategies evolved independently in two of the four stylonurine superfamilies, the Stylonuroidea and the Mycteropoidea. In both superfamilies, the adaptations to this lifestyle involves modifications to the spines on their anterior prosomal appendages for raking through the substrate of their habitats. Stylonuroids have fixed spines on appendages II-IV which could have been used as dragnets to rake through the sediments and thus entangling anything in their way. Mycteropoids show even more extreme adaptations towards a sweep-feeding lifestyle.
They possess blades on prosomal appendages II-III (and IV within the Hibbertopteridae), highly distinct from flattened spines such as in the kokomopteroid '' Hallipterus'', being laterally expanded with a blunt and rounded termination that has sensory setae. The tactile function of these might have allowed mycteropoids to select prey from the sediments in a way that stylonuroids could not.
In the mycteroptids, appendages II and III were used for prey capture, whilst hibbertopterids also used appendage IV, while also retaining its use as a leg for walking. The coxae in '' Hibbertopterus'' are reduced, leading to part of the food masticatory process being assumed by the laden (plates overlaying the coxae). Some species of ''Hibbertopterus'' have even further adaptations towards sweep-feeding than other mycteropoids, with its blades modified into comb-like rachis that could entrap smaller prey or other organic food particles. With its coxae being large, it is likely that some species of ''Hibbertopterus'' would also feed on relatively large invertebrates when able to.
Systematics and genera
Mycteropoids are so derived and unusual that their unique morphology on occasion has prompted researchers to place them as an order separate to Eurypterida
Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...
. Recent research however resolve them as a sister group to Kokomopteroidea, united by a median ridge on the carapace between the lateral eyes and a distal thickening to the podomeres of the prosomal appendages, within the Stylonurina
Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from ...
suborder of eurypterids.
'' Drepanopterus'', the only member of the family Drepanopteridae, was resolved as a sister taxon to all other mycteropoids and is also the earliest known member of the group, occurring from the Lower Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
to the Upper Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
. ''Drepanopterus'' also shares certain characteristics with the kokomopteroids (such as having a clavate telson) and other mycteropoids (a posteriorly cleft metastoma and having blades on the anterior prosomal appendages). Other mycteropoids are classified within one of two families, the Hibbertopteridae or the Mycteroptidae
Mycteroptidae are a family of eurypterids, a group of extinct chelicerate arthropods commonly known as "sea scorpions". The family is one of three families contained in the superfamily Mycteropoidea (along with Hibbertopteridae and Drepanopte ...
. The Hibbertopteridae and Mycteropidae are united by the possession of a hastate telson with paired ventral keels and a cuticular ornament consisting of scales or mucrones.
It is worth noting that it is thought that several genera within the Mycteropoidea may represent different ontogenic stages. Though further work is required to either confirm or disprove such hypotheses, one example is the suggestion that almost all the members of the Mycteroptidae
Mycteroptidae are a family of eurypterids, a group of extinct chelicerate arthropods commonly known as "sea scorpions". The family is one of three families contained in the superfamily Mycteropoidea (along with Hibbertopteridae and Drepanopte ...
(''Megarachne
''Megarachne'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Megarachne'' have been discovered in deposits of Late Carboniferous age, from the Gzhelian stage, in San Luis, Argentina. The fossils of the single and ...
'', '' Mycterops'' and '' Woodwardopterus'') might represent ontogenic stages of a single genus, ''Mycterops''.
Superfamily Mycteropoidea Cope, 1886
* Family Drepanopteridae Kjellesvig-Waering, 1966
** '' Drepanopterus'' Laurie, 1892
* Family Hibbertopteridae Kjellesvig-Waering, 1959
** '' Hibbertopterus'' Kjellesvig-Waering, 1959
** '' Campylocephalus'' Eichwald, 1860
** '' Vernonopterus'' Waterston, 1957
* Family Mycteroptidae
Mycteroptidae are a family of eurypterids, a group of extinct chelicerate arthropods commonly known as "sea scorpions". The family is one of three families contained in the superfamily Mycteropoidea (along with Hibbertopteridae and Drepanopte ...
Cope, 1886
** '' Mycterops'' Cope, 1886
** '' Woodwardopterus'' Kjellesvig-Waering, 1959
** ''Megarachne
''Megarachne'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Megarachne'' have been discovered in deposits of Late Carboniferous age, from the Gzhelian stage, in San Luis, Argentina. The fossils of the single and ...
'' Hünicken, 1980
** '' Hastimima'' White, 1908
References