Alkenopterus

Last updated

Alkenopterus
Temporal range: Late Pragian-Early Emsian, 409–402.5  Ma
Alkenopterus brevitelson holotype drawing.png
SMF VIII 150, the holotype of Alkenopterus brevitelson
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Order: Eurypterida
Superfamily: Onychopterelloidea
Family: Onychopterellidae
Genus: Alkenopterus
Størmer, 1974
Type species
Alkenopterus brevitelson
Størmer, 1974
Species
  • A. brevitelsonStørmer, 1974
  • A. burglahrensisPoschmann & Tetlie, 2004

Alkenopterus is a genus of prehistoric eurypterid classified as part of the family Onychopterellidae. The genus contains two species, A. brevitelson and A. burglahrensis, both from the Devonian of Germany.

Contents

Description

Restoration of A. burglahrensis. The second to fourth pair of appendages (limbs) are based on a close relative, Onychopterella augusti, while the fifth one is based on A. brevitelson. Alkenopterus burglahrensis restoration.png
Restoration of A. burglahrensis. The second to fourth pair of appendages (limbs) are based on a close relative, Onychopterella augusti , while the fifth one is based on A. brevitelson.

Like the other onychopterellids, Alkenopterus was a small eurypterid. The largest species was A. brevitelson, being 7.5 centimetres (3.0 inches) long. [1] The other species, A. burglahrensis, represents in fact the smallest species of eurypterid known as far, only measuring 2.03 cm (0.80 in). [2]

The prosoma (head) was large, with a subquadrate (almost square) to semielliptic (nearly elliptic), horseshoe-like outline. It was anteriorly surrounded by a broad and flat marginal rim that reached its posterior corners. The carapace (the exoskeleton part covering the prosoma) was rounded in the front. Its surface was somewhat inflated, being distinguished several narrow grooves and ridges, most of them wrinkle-like. The prominent lateral eyes were placed in the center of the carapace. They were reniform (bean-shaped), with a strongly arcuate visual surface (a "half moon" in the eye). Between the eyes was located a tubercle or node carrying the ocelli (simple eye-like sensory organs). [1] [2] A. brevitelson also had between the eyes, behind the tubercle, certain grooves resembling the reversed V-shaped structure found in some stylonurines. [1]

The appendages (limbs) of Alkenopterus are not known in much detail. A pair of poorly preserved appendages of A. brevitelson representing the sixth (and last) pair of them is known. [2] The podomeres (leg segments) were more or less rectangular and constant in width. In the end there was a spine about as long as the podomeres which was slightly curved, with a long longitudinal groove. [1] The third to fifth appendages are also known, but they are not exceptionally preserved. Nevertheless, in all of them a distal spine can be identified. Regarding A. burglahrensis, only an appendage belonging to the sixth pair with five distal podomeres (podomeres that were not underneath the prosoma) is known. The seventh and eighth podomeres (and perhaps more of them) were somewhat prolonged outwards [2] and flattened. They featured spine-like immovable spurs on their anterior margins. On the posterior margin of the seventh podomere was the movable spine-like podomere 7a, characteristic of the eurypterines. [3] All the podomeres had similar proportions, except the distal spine which was slightly curved and probably had a pointed tip. [2]

The opisthosoma (abdomen) suffered a strong to moderate first order differentiation, that is, it was divided into a preabdomen (body segments 1 to 7) and a postabdomen (segments 8 to 12). The preabdomen had lateral convex margins and was quite short and broad, with the first tergite (dorsal half of the segment) being less wide than the subsequent ones. The postabdomen was narrow, had a constant width and did not have epimera (lateral "extensions" of the segment), like the preabdomen. The segments of the whole body were hardly distinguishable from each other. The integument of the body lacked ornamentation [2] and was very smooth. [3] The main difference between A. brevitelson and A. burglahrensis was the length of the telson (the posteriormost division of the body). [2] The one of A. brevitelson was short, measuring only 0.55 cm (0.22 in) in a 7.5 cm (3.0 in) long specimen. The ratio between the total body length and telson of this specimen is around 13.6. It was slightly subtriangular (almost triangular) and had a median "keel" (ridge), with an expanded anterior base articulated to the pretelson (segment that preceded the telson). [1] In the other hand, the telson of A. burglahrensis was long, measuring 0.35 cm (0.14 in) in a specimen with 2.03 cm (0.80 in) in total, with a ratio significantly small of 5.8. It had an expanded anterior portion as well. The telson of both species had, however, the same styliform shape. [2]

History of research

Size comparison of both species of Alkenopterus Alkenopterus Scale.svg
Size comparison of both species of Alkenopterus

In 1974, paleontologist Leif Størmer described two specimens of a new eurypterid. SMF VIII 150 (the holotype) is a relatively complete and well preserved fossil with almost all the appendages missing, while SMF VIII 241 (the paratype) is a smaller, little preserved and strongly telescoped (with segments overlapping each other, a defect product of the fossilization of the organism) specimen. Both were collected in the Nellenköpfchen Formation near the municipality of Alken in Rhineland-Palatinate, Germany (then West Germany). Currently, they are located in the Naturmuseum Senckenberg. This new eurypterid was named Alkenopterus brevitelson, with the generic name composed by Alken [1] and the Ancient Greek suffix πτερόν (pteron, "wing"), commonly used in eurypterids. [4] On the other hand, the specific name brevitelson derives from the Latin word brevis (short) and the Ancient Greek word τέλσον (literally "terminal", but here referring to the telson). Størmer also compared Alkenopterus with Drepanopterus and Moselopterus , placing them in the stylonuroid family Drepanopteridae doubtfully alongside Onychopterella . [1]

In 2004, paleontologists Markus Poschmann and Odd Erik Tetlie described a series of new fossils found in the Nellenköpfchen Formation, in the center of the Rhenish Massif, Germany. Among them were two new specimens of A. brevitelson from Alken, 624-D (a well-preserved prosoma with remains of appendages) and 697-D (a fragmentary specimen with the prosoma, appendages, preabdomen, the last two postabdominal segments and telson). They also redescribed the holotype of A. brevitelson. Further, a specimen of a new species of Alkenopterus was found in another locality in the Nellenköpfchen Formation, near Burglahr (in the same state as Alken). PWL 2002/5011 LS is almost complete and well-preserved but somewhat distorted; it is the only known find of this species. It was named A. burglahrensis, the specific name coming from Burglahr due to the proximity of its type locality with this municipality. A. burglahrensis was very similar to A. brevitelson, the former having a longer and broader telson and more strongly expanded distal podomeres in appendage VI than the latter. [2]

Poschmann and Tetlie claimed to find no evidence of a podomere 7a in the sixth appendage of Alkenopterus, determining that it could no longer be classified as part of Drepanopteridae, thus erecting the new family Alkenopteridae for it. This family was not assigned to any superfamily due to the poor knowledge of the second to fourth appendages of its only genus, Alkenopterus. Alkenopteridae was distinguished by the Drepanopterus-type B (with no podomere 7a) fifth appendage and an "Alkenopterus-type" sixth appendage, this one having podomeres almost equal in length (except the distal spine) and moderately flattened. Both pairs of appendages lacked spines. The Alkenopterus-type leg was introduced as a new standard type of non-spiniferous eurypterid appendage. [2] Alkenopterus (as well as Drepanopteridae, now monotypic) would be subsequently included in the Stylonurina suborder [5] for not possessing the podomere 7a. However, in 2014, Poschmann reexamined the holotype of A. burglahrensis by carefully removing some of the matrix of the fossil and using light microscopy with a higher magnification. This resulted in the detection of a movable podomere 7a instead of a simple projection as previously thought. Therefore, Poschmann assigned it to the family Onychopterellidae, with whom it shared several characteristics. It is assumed that in the fossils of A. brevitelson, this podomere was not preserved, but if this is not the case, A. brevitelson should be reassigned to Stylonurina and A. burglahrensis to a new onychopterellid genus. [3]

See also

Related Research Articles

Eurypterid Order of arthropods (fossil)

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 likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during the Ordovician, eurypterids became major components of marine faunas during the Silurian, from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event. They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event 251.9 million years ago.

Stylonurina Extinct suborder of arthropods

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 deposits primarily in Europe and North America, but also in Siberia.

<i>Hughmilleria</i> Genus of extinct arthropods

Hughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Hughmilleria have been discovered in deposits of the Silurian age in China and the United States. Classified as part of the basal family Hughmilleriidae, the genus contains three species, H. shawangunk from the eastern United States, H. socialis from Pittsford, New York, and H. wangi from Hunan, China. The genus is named in honor of the Scottish geologist Hugh Miller.

Chasmataspidida Order of arthropods

Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest that they form a clade (Dekatriata) with Eurypterida and Arachnida. Chasmataspidids are known sporadically in the fossil record through to the mid-Devonian, with possible evidence suggesting that they were also present during the late Cambrian. Chasmataspidids are most easily recognised by having an opisthosoma divided into a wide forepart (preabdomen) and a narrow hindpart (postabdomen) each comprising 4 and 9 segments respectively. There is some debate about whether they form a natural group.

<i>Jaekelopterus</i> Extinct Devonian species of the Eurypterida (sea scorpions)

Jaekelopterus is a genus of predatory eurypterid, a group of extinct aquatic arthropods. Fossils of Jaekelopterus have been discovered in deposits of Early Devonian age, from the Pragian and Emsian stages. There are two known species: the type species J. rhenaniae from brackish to fresh water strata in the Rhineland, and J. howelli from estuarine strata in Wyoming. The generic name combines the name of German paleontologist Otto Jaekel, who described the type species, and the Greek word πτερόν (pteron) meaning "wing".

<i>Bassipterus</i> Extinct genus of arthropods

Bassipterus is a genus of eurypterid, an extinct group of aquatic arthropods. Bassipterus is classified as part of the family Adelophthalmidae, the only clade within the derived ("advanced") Adelophthalmoidea superfamily of eurypterids. Fossils of the single and type species, B. virgnicus, have been discovered in deposits of the Late Silurian age in West Virginia and Maryland, United States. The genus is named after Bass, where most of the fossils have been recovered.

<i>Drepanopterus</i> Extinct genus of sea scorpions

Drepanopterus is an extinct genus of eurypterid and the only member of the family Drepanopteridae within the Mycteropoidea superfamily. There are currently three species assigned to the genus. The genus has historically included more species, with nine species associated with the genus Drepanopterus, however five of these have since been proven to be synonyms of pre-existing species, assigned to their own genera, or found to be based on insubstantial fossil data. The holotype of one species proved to be a lithic clast.

<i>Nanahughmilleria</i> Extinct genus of arthropods

Nanahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Nanahughmilleria have been discovered in deposits of Devonian and Silurian age in the United States, Norway, Russia, England and Scotland, and have been referred to several different species.

<i>Onychopterella</i> Extinct genus of arthropods

Onychopterella is a genus of predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Onychopterella have been discovered in deposits from the Late Ordovician to the Late Silurian. The genus contains three species: O. kokomoensis, the type species, from the Early Pridoli epoch of Indiana; O. pumilus, from the Early Llandovery epoch of Illinois, both from the United States; and O. augusti, from the Late Hirnantian to Early Rhuddanian stages of South Africa.

<i>Tylopterella</i> Extinct genus of arthropods

Tylopterella is a genus of eurypterid, a group of extinct aquatic arthropods. Only one fossil of the single and type species, T. boylei, has been discovered in deposits of the Late Silurian period in Elora, Canada. The name of the genus is composed by the Ancient Greek words τύλη, meaning "knot", and πτερόν, meaning "wing". The species name boylei honors David Boyle, who discovered the specimen of Tylopterella.

<i>Parahughmilleria</i> Extinct genus of arthropods

Parahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Parahughmilleria have been discovered in deposits of the Devonian and Silurian age in the United States, Canada, Russia, Germany, Luxembourg and Great Britain, and have been referred to several different species. The first fossils of Parahughmilleria, discovered in the Shawangunk Mountains in 1907, were initially assigned to Eurypterus. It would not be until 54 years later when Parahughmilleria would be described.

<i>Unionopterus</i> Genus of eurypterid

Unionopterus is a genus of eurypterid, an extinct group of aquatic arthropods commonly known as "sea scorpions". Fossils have been registered from the Early Carboniferous period. The genus contains only one species, U. anastasiae, recovered from deposits of Tournaisian to Viséan stages in Kazakhstan. Known from one single specimen which was described in a publication of Russian language with poor illustrations, Unionopterus' affinities are extremely poorly known.

Megalograptidae Family of arthropods (fossil)

Megalograptidae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions".

Mycteroptidae Extinct family of arthropods

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, which in turn is one of four superfamilies classified as part of the suborder Stylonurina.

Kokomopteroidea Extinct superfamily of arthropods

Kokomopteroidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina. Kokomopteroids have been recovered from deposits of Early Silurian to Late Devonian age in the United States and the United Kingdom.

Hibbertopteridae Extinct family of arthropods

Hibbertopteridae is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Mycteropoidea. Hibbertopterids were large, broad and heavy animals unlike virtually every other group of eurypterids, which are commonly streamlined and lightweight. Their bizarre morphology is so unusual that they in the past have been thought to represent an entirely distinct order of chelicerates. Fossils of the family first appear in deposits of Middle Devonian age and the last known fossils representing hibbertopterids are known from deposits of Late Permian age. The hibbertopterids represent the last known living eurypterids, going extinct during the Permian–Triassic extinction event or shortly before.

Waeringopteridae Extinct family of arthropods

Waeringopteridae is a family of eurypterids, an extinct group of aquatic arthropods. The Waeringopteridae is the only family classified as part of the superfamily Waeringopteroidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina. The earliest known member of the group, Orcanopterus, has been recovered from deposits of Katian age and the latest known surviving member, Grossopterus, has been recovered from deposits of Siegenian age. The name Waeringopteridae is derived from the type genus Waeringopterus, which is named in honor of eurypterid researcher Erik N. Kjellesvig-Waering.

Adelophthalmidae Family of eurypterids, an extinct group of aquatic arthropods

Adelophthalmidae is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina.

<i>Herefordopterus</i> Extinct genus of arthropods

Herefordopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Herefordopterus is classified as part of the family Hughmilleriidae, a basal family in the highly derived Pterygotioidea superfamily of eurypterids. Fossils of the single and type species, H. banksii, have been discovered in deposits of Silurian age in Herefordshire and Shropshire, England. The genus is named after Herefordshire, where most of the Herefordopterus fossils have been found. The specific epithet honors Richard Banks, who found several well-preserved specimens, including the first Herefordopterus fossils.

<i>Borchgrevinkium</i> Extinct genus of arthropods

Borchgrevinkium is an extinct genus of chelicerate arthropod. A fossil of the single and type species, B. taimyrensis, has been discovered in deposits of the Early Devonian period in the Krasnoyarsk Krai, Siberia, Russia. The name of the genus honors Carsten Borchgrevink, an Anglo-Norwegian explorer who participated in many expeditions to Antarctica. Borchgrevinkium represents a poorly known genus whose affinities are uncertain.

References

  1. 1 2 3 4 5 6 7 Størmer, Leif (1974). "Arthropods from the Lower Devonian (Lower Emsian) of Alken an der Mosel, Germany. Part 4: Eurypterida, Drepanopteridae, and other groups". Senckenbergiana Lethaea. 54: 359–451.
  2. 1 2 3 4 5 6 7 8 9 10 Poschmann, Markus; Tetlie, Odd Erik (2004). "On the Emsian (Early Devonian) arthropods of the Rhenish Slate Mountains: 4. The eurypterids Alkenopterus and Vinetopterus n. gen. (Arthropoda: Chelicerata)". Senckenbergiana Lethaea. 84 (1–2): 173–193. doi:10.1007/BF03043470. S2CID   127313845.
  3. 1 2 3 Poschmann, Markus (2014). "Note on the morphology and systematic position of Alkenopterus burglahrensis (Chelicerata: Eurypterida: Eurypterina) from the Lower Devonian of Germany". Paläontologische Zeitschrift . 88 (2): 223–226. doi:10.1007/s12542-013-0189-x. S2CID   132432538.
  4. Erik Tetlie, O; Poschmann, Markus (2008-06-01). "Phylogeny and palaeoecology of the Adelophthalmoidea (Arthropoda; Chelicerata; Eurypterida)". Journal of Systematic Palaeontology. 6 (2): 237–249. doi:10.1017/S1477201907002416. S2CID   59488956.
  5. Lamsdell, James C.; Braddy, Simon J.; Tetlie, O. Erik (2010). "The systematics and phylogeny of the Stylonurina (Arthropoda: Chelicerata: Eurypterida)". Journal of Systematic Palaeontology . 8 (1): 49–61. doi:10.1080/14772011003603564. S2CID   85398946.