Perimecturus

{{Short description|Fossil genus of mantis shrimp}} {{Automatic taxobox | fossil_range = Early Carboniferous (Viséan to Serpukhovian), {{Fossil range|345|324}} | image = Ar1050 Perimecturus rapax Unt Karbon Bear Gulch Montana USA.jpg | image_caption = Fossil of ''P. rapax'' from the Bear Gulch Limestone | taxon = Perimecturus | authority= Peach, 1908 | type_species = {{extinct}}'''''Anthrapalaemon parki''''' (= †'''''Perimecturus parki''''') | type_species_authority = Peach, 1882 | subdivision_ranks = Other species | subdivision = *{{extinct}}'''''P. rapax''''' Schram & Horner, 1978 | synonyms = {{collapsible list|bullets=true|title={{small|Synonyms of ''Perimecturus''}} |''Palaesquilla'' Peach & Horne, 1903 (''nomen nudum'') }} {{collapsible list|bullets=true|title={{small|Synonyms of ''P. parki''}} |''Anthrapalaemon parki'' Peach, 1882 |''Palaesquilla parki'' Peach & Horne, 1903 (''nomen nudum'') |''Perimecturus communis'' Peach, 1908 |''Perimecturus parki duplicicarinatus'' Peach, 1908 |''Perimecturus stocki'' Peach, 1908 }} }}

'''''Perimecturus''''' is an extinct genus of mantis shrimp that lived during the Early Carboniferous period in what is now Scotland and the United States. The first known specimens were collected near the River Esk in Glencartholm, Scotland, and the genus was named in 1908 by Ben Peach, making it the second genus of Paleozoic mantis shrimp to be described (only after ''Archaeocaris''). While many species have been classified in the genus since then, taxonomic revisions in the late 20th and 21st centuries have reassigned most of these to different genera, leaving two named species currently assigned to this genus. The type species, '''''P. parki''''', was first named in 1882 as a species of ''Anthrapalaemon'' and is known from the Viséan-aged Glencartholm Volcanic Beds of Scotland. Fossils of a later species, '''''P. rapax''''', have been found in the Bear Gulch Limestone of Montana and were first described by Frederick Schram.

Unlike other Paleozoic mantis shrimps which had narrow, shrimp-like bodies, ''Perimecturus'' had a wide and flattened body more closely resembling that of a lobster. This condition is also seen in modern mantis shrimps, but ''Perimecturus'' would have developed this shape separately from them in an example of parallel evolution. Members of this genus had a wide carapace with five ridges, in addition to six other ridges running down the abdomen. The two species differ primarily in the tail fan, with ''P. rapax'' having a longer telson spike and lacking the bristles seen in ''P. parki''. In addition, ''P. parki'' lacks the serrations on the telson and uropods that ''P. rapax'' has. ''Perimecturus'' is one of the largest Paleozoic mantis shrimps, with the largest known specimen of ''P. parki'' reaching a total length of {{convert|15|cm|abbr=on|in}}. However, most specimens are notably smaller than this.

Both ''Perimecturus'' species lived in fully marine habitats, and are believed to be intolerant of lower salinities. Like all other mantis shrimps, they would have been carnivores that handled prey with their raptorial thoracic appendages. Because the walking appendages are poorly preserved, it remains unclear whether ''Perimecturus'' would have been benthopelagic and swam just over the seabed like other early mantis shrimps.

==Discovery and naming== thumb|left|upright|Illustrations of the original ''Perimecturus parki'' fossils from Peach's 1882 paper, originally labeled as ''Anthrapalaemon parki'' The first fossil of ''Perimecturus'' known to science was discovered by A. Macconochie, with additional specimens found by Walter Park. These specimens were collected near the River Esk in Glencartholm, Scotland, and turned in to the Geological Survey of Scotland. In 1882, British paleontologist Ben Peach became the first person to study these fossils, which he believed represented a new species of ''Anthrapalaemon'', naming it ''Anthrapalaemon parki'' after Park.<ref>{{Cite journal |last=Peach |first=Ben N. |date=1882 |title=IV.—On some new Crustaceans from the Lower Carboniferous Rocks of Eskdale and Liddesdale |url=https://archive.org/details/transactionsofro301883roy/page/73/mode/1up |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=30 |issue=1 |pages=73–91 |doi=10.1017/S0080456800028982 |s2cid=129353541 |issn=2053-5945}}</ref> Later, Peach would work alongside J. Horne in 1903 to move this species to a separate genus which they called ''Palaesquilla'', however they did not formally rename it and thus ''Palaesquilla'' is deemed a ''nomen nudum''.<ref>{{Cite journal |last1=Peach |first1=B. N. |last2=Horne |first2=J. |date=1903 |title=The Canonbie Coalfield: its Geological Structure and Relations to the Carboniferous Rocks of the North of England and Central Scotland |url=https://archive.org/details/transactionsofro40roya/page/835/mode/1up |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=40 |issue=4 |pages=835–878 |doi=10.1017/S0080456800034815 |s2cid=128763435 |issn=2053-5945}}</ref> A formal reassignment would be published by Peach in 1908, in which he erected the new genus ''Perimecturus'' with this species (now renamed as ''Perimecturus parki'') as its type species. Furthermore, he also studied several other specimens which he named as a subspecies, ''P. parki duplicicarinatus'', and additional species which he assigned to the genus, including ''P. stocki'' and ''P. communis''.<ref name=":0">{{Cite book |last=Peach |first=B. N. |url=https://www.biodiversitylibrary.org/item/41415 |title=Monograph on the higher Crustacea of the Carboniferous rocks of Scotland |date=1908 |publisher=Printed for H.M. Stationery off., by J. Hedderwick & sons, ltd |location=Glasgow}}</ref>

{{multiple image | align = right | total_width = 275 | perrow = 2/2 | image1 = Perimecturus parki.jpg | alt1 = | image2 = Perimecturus parki duplicicarinatus.jpg | alt2 = | image3 = Perimecturus stocki.jpg | alt3 = | image4 = Perimecturus communis.jpg | alt4 = | footer = Illustrations of ''P. parki'' fossils from Peach's 1908 paper, originally named as (in clockwise order from the top left) ''P. parki'', ''P. parki duplicicarinatus'', ''P. communis'', and ''P. stocki'' respectively }} In 1979, a review of the Carboniferous-aged malacostracans of Britain written by American paleontologist Frederick Schram was published. The review found that ''P. parki'' was the only valid species of ''Perimecturus'' named by Peach, and that ''P. p. duplicicarinatus'' (which Schram misspelled as ''duplicarinatus''), ''P. stocki'' and ''P. communis'' were all junior synonyms of it. The specimen GSE 5896 was designated as the lectotype of this species. Schram stated that Peach's idea of the fossils as separate species was due to incorrect interpretation of the fossils preserved in different modes: the original ''P. parki'' holotype showed the animal in a top-down view, the ''P. p. duplicicarinatus'' specimen clearly preserved the longitudinal ridges, the ''P. stocki'' fossil is an individual in a slanted angle and the ''P. communis'' remains are displayed from the side.<ref name=":1">{{Cite book |last1=Schram |first1=Frederick R. |url=https://www.biodiversitylibrary.org/bibliography/3360 |title=British Carboniferous Malacostraca |date=1979 |publisher=Field Museum of Natural History |location=Chicago |language=}}</ref>

A second species of ''Perimecturus'' was erected by Schram in 1978 and named ''P. rapax'', the specific name being a Latin word meaning "to grasp" (in reference to the animal's predatory lifestyle and raptorial appendages). The holotype for this species, UM 6141, is held in the collection of the University of Montana and was discovered in the Bear Gulch Limestone of Fergus County, Montana.<ref name=":2">{{Cite journal |last1=Schram |first1=Frederick R. |last2=Horner |first2=John |date=1978 |title=Crustacea of the Mississippian Bear Gulch Limestone of Central Montana |journal=Journal of Paleontology |volume=52 |issue=2 |pages=394–406 |jstor=1303712 |issn=0022-3360}}</ref> In 1985, David Factor and Rodney Feldmann published a redescription of ''P. rapax'', after a detailed reanalysis of the fossils which found that Schram had misinterpreted some of their features.<ref name=":5">{{Cite journal |last1=Factor |first1=David F. |last2=Feldmann |first2=Rodney M. |date=1985 |title=Systematics and paleoecology of malacostracan arthropods in the Bear Gulch Lilmestone (Namurian) of central Montana |url=https://www.biodiversitylibrary.org/part/330776 |journal=Annals of the Carnegie Museum |volume=54 |pages=319–356 |doi=10.5962/p.330776 |issn=0097-4463|doi-access=free }}</ref>

===Reassigned species=== Because it was the second Paleozoic mantis shrimp genus to be named (after ''Archaeocaris'', which was named in 1872 but only recognized as one in 1962),<ref name=":7">{{Cite journal |last=Brooks |first=Harold Kelly |date=1962 |title=The Paleozoic Eumalacostraca of North America |url=https://www.biodiversitylibrary.org/page/10667554 |journal=Bulletins of American Paleontology |volume=44 |issue=202 |pages=163–338}}</ref> numerous species have been assigned to ''Perimecturus'' before better knowledge of early mantis shrimps was developed. The following species were formerly placed in ''Perimecturus'' but have since been moved to other genera:

* ''P. elegans'' was erected in 1908 by Peach based on fossils from the River Esk, Scotland.<ref name=":0" /> In 1979, Schram established the genus ''Bairdops'' to which this species was reassigned and became the type species of.<ref name=":1" />

* ''P. ensifer'' was named by Peach in 1908 from remains found in the Scottish localities of Liddel Water, Newcastleton and Glencartholm.<ref name=":0" /> Schram declared it to be a junior synonym of ''Bairdops elegans'' in 1979.<ref name=":1" />

* ''P. pattoni'' was described by Peach in 1908 based on a single fossil from the Top Hosie Limestone of the Lower Limestone Formation near East Kilbride, Scotland.<ref name=":0" /> It was first noted by Schram in 1979 to not properly belong to ''Perimecturus'', and in 2007 he moved it to the genus ''Daidal''.<ref name=":1" /><ref name=":3">{{Cite journal |last=Schram |first=Frederick R. |date=2007 |title=Paleozoic Proto-Mantis Shrimp Revisited |journal=Journal of Paleontology |volume=81 |issue=5 |pages=895–916 |doi=10.1666/pleo05-075.1 |issn=0022-3360 |jstor=4498847 |bibcode=2007JPal...81..895S |s2cid=85606671}}</ref>

* ''P. fraiponti'' was described in 1922 by Belgian carcinologist and paleontologist Victor van Straelen from pyritized remains found near Liège, Belgium.<ref>{{Cite journal |last=van Straelen |first=Victor |date=1922 |title=Quelques eumalacostracés nouveaux du Westphalien inférieur d'Argenteau près Liége |url=https://www.biodiversitylibrary.org/page/55548656 |journal=Annales de la Société Géologique de Belgique |language=fr |volume=45 |pages=35–40}}</ref> It was moved to the genus ''Gorgonophontes'' by German paleontologist Lothar Schöllmann in 2004.<ref>{{Cite journal |last=Schöllmann |first=Lothar |date=2004 |title=Archaeostomatopodea (Malacostraca, Hoplocarida) aus dem Namur B (höheres Marsdenium, Karbon) von Hagen-Vorhalle (NRW, Deutschland) und eine Neudefinition einiger Arten der Familie Tyrannophontidae |url=https://www.researchgate.net/publication/287448897 |journal=Geologie und Paläontologie in Westfalen |volume=62 |pages=111–141}}</ref>

==Description== The body of ''Perimecturus'' is distinctively flattened, appearing wide and almost rectangular when viewed from above, and its abdomen could be held straight.<ref name=":5" /> This makes its body partly lobster-like, differing from other Paleozoic mantis shrimps which have narrower, shrimp-like bodies with curved abdomens. While modern mantis shrimps also have a body shape more comparable to lobsters than to shrimp, ''Perimecturus'' would have evolved such an appearance separately from them, representing an example of parallel evolution.<ref name=":6">{{Cite journal |last1=Haug |first1=Carolin |last2=Haug |first2=Joachim T. |date=2021-04-16 |title=A new fossil mantis shrimp and the convergent evolution of a lobster-like morphotype |journal=PeerJ |volume=9 |article-number=e11124 |doi=10.7717/peerj.11124 |doi-access=free |issn=2167-8359 |pmc=8054755 |pmid=33959413}}</ref> With the largest specimen (GSE 5897) measuring {{convert|15|cm|abbr=on|in}} in total length, ''P. parki'' is among the biggest Paleozoic mantis shrimps, though most specimens measure just {{convert|1.28|-|3.37|cm|abbr=on|in}} in carapace length and {{convert|1.50|-|4.65|cm|abbr=on|in}} in abdomen length.<ref name=":1" /> ''P. rapax'' is a smaller species, reaching only {{convert|1.22|-|2.59|cm|abbr=on|in}} in carapace length and {{convert|1.45|-|2.83|cm|abbr=on|in}} in abdomen length.<ref name=":2" />

The rostrum is very broad and blunt, with a rounded tip in ''P. rapax'', though it is slightly more pointed in ''P. parki''. The antennae are short and flagellated, each with an elongated and pointed scaphocerite (exopod of the antenna). The compound eyes are stalked and oval in shape. The large, subrectangular carapace covers the entire thorax and has a marked furrow all around its margins, as well as short keels extending from the base of the antennae. The carapace has five prominent ridges (one down the middle of the carapace and two on either side) stretching across its latter half.<ref name=":5" /> Though Schram (1978) claims ''P. parki'' has only four such ridges and ''P. rapax'' has only three, detailed reanalysis by Factor and Feldmann (1985) and Jenner ''et al.'' (1998) confirms both species actually have five.<ref name=":2" /><ref name=":5" /><ref name=":4">{{Cite journal |last1=Jenner |first1=Ronald A. |last2=Hof |first2=Cees H.J. |last3=Schram |first3=Frederick R. |date=1998 |title=Palaeo- and archaeostomatopods (Hoplocarida, Crustacea) from the Bear Gulch Limestone, Mississippian (Namurian), of central Montana |url=https://brill.com/view/journals/ctoz/67/3/article-p155_1.xml |journal=Contributions to Zoology |volume=67 |issue=3 |pages=155–185 |doi=10.1163/18759866-06703001 |issn=1383-4517|doi-access=free }}</ref>

Like all mantis shrimps, ''Perimecturus'' had raptorial appendages attached to the thorax. Because the raptorial appendages of this genus are rather short and often retracted to overlap with each other, study of them has been difficult and their features often cannot be discerned. However, some ''P. parki'' specimens have shown that most segments of these appendages are approximately equal in length, except the fourth segment from the distal end which is notably shorter.<ref name=":1" />

Little is known about the thorax as it is completely covered by the carapace, though its hind segments at least are not fused with it. The abdomen is made up of six segments, each approximately the same length. A small backward-pointing spike is present at the edges of every abdominal segment. Schram (1978) wrongly stated that ''P. parki'' and ''P. rapax'' had four and three abdominal ridges respectively, believing they lined up with the carapace ridges.<ref name=":2" /> Reanalysis has found that both species have six keels on each abdominal segment, forming six continuous ridges down the abdomen (two median ridges and four lateral ridges). The ridges run parallel to each other in the first four segments and begin to converge with each other at the fifth segment. Two small wart-like bumps are present on each abdominal segment, one located in each space between the median ridges and innermost lateral ridges.<ref name=":5" /><ref name=":4" />

While both species have biramous (two-branched) uropods, spines near the end of the outer margin of the uropodal exopod (outer branch), a subtriangular telson that tapers into a pointed spike at the end and small furcae (spikes forming the tail fork) flanking the base of this spike, other aspects of the tail fan differs greatly between the two ''Perimecturus'' species. In ''P. parki'', this spike is less than half the length of the telson base, with delicate bristles around the edges of the telson and uropods. The exopod of the uropod and the hind part of the telson base are smooth.<ref name=":1" /> Meanwhile, the telson spike of ''P. rapax'' is over half the length of the telson base, no bristles are present on the tail fan, the outer margin of the uropodal exopod is serrated, and the telson is serrated near the furcae.<ref name=":5" />

==Classification== ''Perimecturus'' gives its name to the family Perimecturidae, of which it is the type genus. This family was established by Ben Peach in 1908, who placed it within the now defunct order Schizopoda, believing that perimecturids were intermediate forms between Lophogastridae and Anaspididae.<ref name=":0" /> In 1962, the Perimecturidae family was first recognized as a group of early mantis shrimps by H. K. Brooks, reassigning it to the order Palaeostomatopoda (now delisted as a suborder and named Palaeostomatopodea).<ref name=":7" /> With the advent of cladistic analyses, the palaeostomatopods as traditionally construed were first recovered as a paraphyletic grouping by Jenner ''et al.'' (1998), a finding later confirmed by Schram (2007).<ref name=":3" /><ref name=":4" /> Currently, Palaeostomatopodea is still used in a paraphyletic sense to refer to the evolutionary grade.<ref>{{Cite journal |last=Schram |first=Frederick |date=2008 |title=An adjustment to the higher taxonomy of the fossil Stomatopoda |journal=Crustaceana |volume=81 |issue=6 |pages=751–754 |doi=10.1163/156854008784513429 |issn=0011-216X |jstor=20111439}}</ref>

Several studies of conducted phylogenetic analyses on fossil mantis shrimps. While Jenner ''et al.'' (1998) found the genus to be monophyletic, some other authors have questioned its monophyly.<ref name=":4" /> Schram (2007) and Haug ''et al.'' (2010) both recovered ''Perimecturus'' to be paraphyletic, the former finding ''P. rapax'' to be the sister taxon to ''Bairdops elegans'' within a monophyletic family Perimecturidae, while the latter suggests the family is a paraphyletic grade in which ''P. parki'' is the sister taxon to all other mantis shrimps except ''Archaeocaris'' and ''Bairdops''.<ref name=":3" /><ref>{{Cite journal |last1=Haug |first1=Joachim T |last2=Haug |first2=Carolin |last3=Maas |first3=Andreas |last4=Kutschera |first4=Verena |last5=Waloszek |first5=Dieter |date=2010 |title=Evolution of mantis shrimps (Stomatopoda, Malacostraca) in the light of new Mesozoic fossils |journal=BMC Evolutionary Biology |language=en |volume=10 |issue=1 |page=290 |doi=10.1186/1471-2148-10-290 |doi-access=free |issn=1471-2148 |pmc=2955030 |pmid=20858249|bibcode=2010BMCEE..10..290H }}</ref> On the other hand, Smith ''et al.'' (2023) supports the idea that both ''Perimecturus'' and Perimecturidae are monophyletic. Their results are displayed in the cladogram below:<ref>{{Cite journal |last1=Smith |first1=C.P.A. |last2=Aubier |first2=P. |last3=Charbonnier |first3=S. |last4=Laville |first4=T. |last5=Olivier |first5=N. |last6=Escarguel |first6=G. |last7=Jenks |first7=J.F. |last8=Bylund |first8=K.G. |last9=Fara |first9=E. |last10=Brayard |first10=A. |date=2023-03-31 |title=Closing a major gap in mantis shrimp evolution – first fossils of Stomatopoda from the Triassic |url=https://www.researchgate.net/publication/369959650 |journal=Bulletin of Geosciences |language=en |pages=95–110 |doi=10.3140/bull.geosci.1864 |issn=1802-8225|doi-access=free }}</ref>

==Paleobiology== Possessing raptorial appendages on its thorax for grabbing prey like all other mantis shrimps, ''Perimecturus'' is believed to have occupied a low trophic level as an active carnivore in its habitat.<ref name=":5" /> It was proposed by Jenner ''et al.'' (1998) that palaeostomatopods like ''Perimecturus'' were scavengers that handled mostly dead prey since their raptorial appendages are small compared to those of extant mantis shrimps in the order Unipeltata, instead being closer in shape to the third to fifth pairs of thoracic appendages used by unipeltatans to manipulate food after it is caught.<ref name=":4" /> In addition, the appendages of palaeostomatopods lack the click-joint mechanism seen in unipeltatans, which is formed by a specialized joint and muscles and allows them to extend quickly and catch prey.<ref>{{Cite journal |last=Kunze |first=Janet C. |date=1981-05-12 |title=The functional morphology of stomatopod Crustacea |url=https://royalsocietypublishing.org/doi/10.1098/rstb.1981.0032 |journal=Philosophical Transactions of the Royal Society of London. B, Biological Sciences |language=en |volume=292 |issue=1059 |pages=255–328 |bibcode=1981RSPTB.292..255K |doi=10.1098/rstb.1981.0032 |issn=0080-4622|url-access=subscription }}</ref> Contrary to this, Haug and Haug (2021) suggest that at least some early mantis shrimps (namely ''Tyrannosculda'', ''Tyrannophontes'' and ''Gorgonophontes'') had posterior thoracic appendages (i.e. the walking appendages) which were incapable of the wide stance needed to attack prey from the seabed. Therefore, they proposed that these early forms were benthopelagic predators that grabbed prey from above while swimming just over the seabed, unlike modern mantis shrimps which are bottom-dwelling. However, because the walking appendages of ''Perimecturus'' are not well-preserved, it remains unclear whether this genus would have also had such a lifestyle.<ref name=":6" />

==Paleoenvironment== Based on the fact that both species are known exclusively from marine deposits, ''Perimecturus'' is believed to have been a fully marine animal with no adaptation towards lower salinity (unlike the related ''Bairdops'' which could tolerate a wider range of salinities). Remains of ''P. parki'' have only been collected from the Glencartholm Volcanic Beds, a site in Scotland that dates back to the Viséan stage of the Early Carboniferous period (around 345 million years ago), making it the older of the two known ''Perimecturus'' species. The Beds were deposited in a nearshore to fully marine environment, and ''P. parki'' is a commonly found crustacean in this locality, as are ''Bairdops'', ''Anthracocaris'', ''Belotelson'' and ''Anthracophausia''. The most abundant crustaceans found at this site are ''Crangopsis'', ''Pseudotealliocaris'' and ''Sairocaris'', being known from even more specimens than the aforementioned genera.<ref>{{Cite journal |last1=Briggs |first1=D. E. G. |last2=Clarkson |first2=E. N. K. |date=1989 |title=Environmental controls on the taphonomy and distribution of Carboniferous malacostracan crustaceans |url=https://www.cambridge.org/core/product/identifier/S026359330002873X/type/journal_article |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=80 |issue=3–4 |pages=293–301 |doi=10.1017/S026359330002873X |bibcode=1989EESTR..80..293B |s2cid=129228575 |issn=1755-6910|url-access=subscription }}</ref> Aside from crustaceans, fossils of other organisms are also known from the Beds. Fish are some of the most numerous, with over 200 specimens representing more than 30 species found in the area. Remains of plants, bivalves, xiphosurans and scorpions are also known from the deposits.<ref>{{Cite journal |last=Wood |first=Margaret |date=2017 |title=Glencartholm revisited: describing for the first time Stan Wood's discovery and excavation of Mumbie Quarry, adjacent to the important Palaeozoic fossil site of Glencartholm |url=https://www.cambridge.org/core/product/identifier/S175569101800018X/type/journal_article |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=108 |issue=1 |pages=47–54 |bibcode=2017EESTR.108...47W |doi=10.1017/S175569101800018X |issn=1755-6910 |s2cid=134352553|url-access=subscription }}</ref>

All known specimens of ''P. rapax'' originate from the Bear Gulch Limestone in Montana, which was deposited around 324 million years ago during the Serpukhovian stage of the Carboniferous period. This site is believed to have been a marine bay oriented from northwest to southeast, and would have been located 10 to 12 degrees north of the equator. The bay was positioned at the boundary between a tropical belt in the south and an arid belt in the north, and had a monsoonal climate like that of the modern African Sahel with distinct wet summer and dry winter seasons. A very high fossil diversity is recorded from the Bear Gulch Limestone, with some of the most famous fossils being the many types of chondrichthyan fish (including petalodonts, holocephalans, symmoriiforms, ''Squatinactis'' and ''Thrinacodus'') that make up close to 60% of the known fish species diversity.<ref>{{Cite journal |last1=Lund |first1=Richard |last2=Poplin |first2=Cécile |date=1999 |title=Fish diversity of the Bear Gulch Limestone, Namurian, Lower Carboniferous of Montana, USA |url=https://www.researchgate.net/publication/248616554 |journal=Geobios |language=en |volume=32 |issue=2 |pages=285–295 |doi=10.1016/S0016-6995(99)80042-4|bibcode=1999Geobi..32..285L }}</ref> Other types of fish like actinopterygians, coelacanths and acanthodians are also known from this site, with the coelacanths being the most abundant.<ref>{{Cite journal |last1=Lund |first1=Richard |last2=Greenfest-Allen |first2=Emily |last3=Grogan |first3=Eileen D. |date=2012-07-15 |title=Habitat and diversity of the Bear Gulch fish: Life in a 318 million year old marine Mississippian bay |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018212002209 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=342–343 |pages=1–16 |doi=10.1016/j.palaeo.2012.04.016|bibcode=2012PPP...342....1L |url-access=subscription }}</ref> Invertebrates represented in the area include various crustaceans, polychaete worms, cephalopods and bivalves.<ref name=":2" /><ref>{{Cite thesis |title=The taphonomy of a carboniferous lagerstätte: the invertebrates of the Bear Gulch Limestone Member |url=https://figshare.le.ac.uk/articles/thesis/The_taphonomy_of_a_carboniferous_lagerst_tte_the_invertebrates_of_the_Bear_Gulch_Limestone_Member/10164188/1 |publisher=University of Leicester |date=2004-01-01 |degree=thesis |language=en |first=Natalie |last=Thomas}}</ref><ref>{{Cite journal |last1=Klug |first1=Christian |last2=Landman |first2=Neil H. |last3=Fuchs |first3=Dirk |last4=Mapes |first4=Royal H. |last5=Pohle |first5=Alexander |last6=Guériau |first6=Pierre |last7=Reguer |first7=Solenn |last8=Hoffmann |first8=René |date=2019-07-31 |title=Anatomy and evolution of the first Coleoidea in the Carboniferous |journal=Communications Biology |language=en |volume=2 |issue=1 |page=280 |doi=10.1038/s42003-019-0523-2 |issn=2399-3642 |pmc=6668408 |pmid=31372519}}</ref><ref>{{Cite journal |last1=McRoberts |first1=Christopher A. |last2=Stanley |first2=George D. |date=1989 |title=A unique bivalve–algae life assemblage from the Bear Gulch Limestone (Upper Mississippian) of central Montana |url=https://www.cambridge.org/core/product/identifier/S0022336000041214/type/journal_article |journal=Journal of Paleontology |language=en |volume=63 |issue=5 |pages=578–581 |doi=10.1017/S0022336000041214 |bibcode=1989JPal...63..578M |s2cid=131030155 |issn=0022-3360|url-access=subscription }}</ref>

==References== {{reflist}}

==External links== {{Portal|Crustaceans|Paleontology}} {{Commons category|Perimecturus}} {{Wikispecies|Perimecturus}}

Category:Carboniferous animals of North America Category:Carboniferous arthropods of Europe Category:Stomatopoda Category:Fossil taxa described in 1908 Category:Prehistoric crustacean genera Category:Prehistoric mantis shrimps