View source for Bear Gulch Limestone

{{Infobox rockunit
| name           = Bear Gulch Limestone
| image          = File:†Echinochimaera meltoni Lund 1977.jpg
| imagesize      = 
| caption        = ''[[Echinochimaera|Echinochimaera meltoni]]'', one of many unusual [[chondrichthyan]]s found in the Bear Gulch Limestone
| type           = [[Lens (geology)|Lens]]
| age            = Late [[Serpukhovian]] ([[Namurian]] E2b),<br />{{Fossil range|324}}
| period         = Mississippian
| prilithology   = [[limestone]], [[shale]]
| otherlithology = [[siltstone]]
| namedfor       = Bear Gulch, Montana
| namedby        = 
| year_ts        = 
| region         = 
| country        = {{flag|United States}}
| coordinates    = {{coord|46.95|N|109|W|display=inline,title}}
| unitof         = [[Heath Formation]]
| subunits       = 
| underlies      =
| overlies       = 
| thickness      = 30-40 meters
| extent         = {{Flag|Montana}}
| area           = 
| map            = {{Location map+ | Montana
| relief = 1
| width   = 250
| float   = center
| places  =
  {{Location map~ | Montana
  | lat_deg = 46.95
  | lon_deg = -109
  | mark = Red pog.svg
  | marksize = 12
  }}
}}
| map_caption    = 
}}
The '''Bear Gulch Limestone''' is a [[limestone]]-rich [[Lens (geology)|geological lens]] in central [[Montana]], renowned for the quality of its late [[Mississippian (geology)|Mississippian]]-aged fossils. It is exposed over a number of outcrops northeast of the [[Big Snowy Mountains]], and is often considered a component of the more widespread [[Heath Formation]]. The Bear Gulch Limestone reconstructs a diverse, though isolated, marine ecosystem which developed near the end of the [[Serpukhovian]] age. It is a [[lagerstätte]], a particular type of rock unit with exceptional fossil preservation of both articulated skeletons and [[soft tissue]]s. Bear Gulch fossils include a variety of fish, invertebrates, and [[algae]] occupying a number of different habitats within a preserved shallow bay.<ref name=":4" /><ref name=":1" />

[[Fish]] include a high diversity of unusual [[Chondrichthyes|chondrichthyans]] (cartilaginous fish)<ref name=":3">{{Cite journal|last1=Lund|first1=Richard|last2=Poplin|first2=Cécile|date=1999-01-01|title=Fish diversity of the Bear Gulch Limestone, Namurian, Lower Carboniferous of Montana, USA|url=https://www.sciencedirect.com/science/article/pii/S0016699599800424|journal=Geobios|language=en|volume=32|issue=2|pages=285–295|doi=10.1016/S0016-6995(99)80042-4|issn=0016-6995}}</ref><ref name=":6" /> and one of the oldest known [[lamprey]]s,<ref name=":34" /> along with other [[vertebrate]]s.<ref name=":2" /> [[Invertebrate]]s include numerous fossils of [[crustacean]]s, [[worm]]s, [[cephalopod]]s, and [[Sponge|sea sponges]], which are concentrated in different parts of the bay basin. Shelled cephalopods are abundant, and the Bear Gulch Limestone also preserves some of the best early fossils of [[coleoid]] cephalopods.<ref name=":35" /><ref name=":36" /> Fossils of typical [[Benthos|benthic]] (seabed-attached) organisms are rare, and those that do occur are restricted to reef-like sponge patches in eastern exposures. This indicates that the conditions of the bay responsible for the Bear Gulch Limestone were at odds with other marine areas nearby.<ref name=":1" />

Some Bear Gulch fossils were preserved so rapidly and efficiently that mating behaviors,<ref name=":23" /><ref name=":32" /> internal organs,<ref name=":9" /> coloration patterns,<ref name=":25" /> gut content,<ref name=":23" /><ref name=":13" /> and even the pattern of blood vessels<ref name=":9" /> could be observed in fossils. This exceptional preservation may be a consequence of the prevailing warm [[monsoon]]al climate, as storms could frequently and rapidly cover the seabed with oxygen-poor organic runoff from shallower areas.<ref name=":1">{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=2002|title=The geological and biological environment of the Bear Gulch Limestone (Mississippian of Montana, USA) and a model for its deposition|url=https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2002n2a2.pdf|journal=Geodiversitas|volume=24|issue=2|pages=295–315}}</ref> Although up to 40 meters of sediment are found in the Bear Gulch Limestone, [[Biostratigraphy|biostratigraphic]] data suggests that the lens was emplaced in only 1000 years, a geological instant.<ref name=":2">{{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://www.researchgate.net/publication/248616554|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=342-343|pages=1–16|doi=10.1016/j.palaeo.2012.04.016|bibcode=2012PPP...342....1L|issn=0031-0182}}</ref>

== Geology ==

=== Geological setting ===
The Bear Gulch Limestone is commonly considered to be part of the [[Heath Formation]], the youngest formation in the [[Big Snowy Group]] of central [[Montana]].<ref name=":4">{{Cite journal|last=Williams|first=Loretta Ann|date=1983|title=Deposition of the Bear Gulch Limestone: a Carboniferous Plattenkalk from central Montana|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-3091.1983.tb00714.x|journal=Sedimentology|language=en|volume=30|issue=6|pages=843–860|doi=10.1111/j.1365-3091.1983.tb00714.x|bibcode=1983Sedim..30..843W|issn=1365-3091}}</ref><ref name=":5">{{Cite journal|last1=Feldman|first1=Howard R.|last2=Lund|first2=Richard|last3=Maples|first3=Christopher G.|last4=Archer|first4=Allen W.|date=1994-06-01|title=Origin of the Bear Gulch Beds (Namurian, Montana, USA)|url=https://www.sciencedirect.com/science/article/pii/S0016699594800456|journal=Geobios|language=en|volume=27|pages=283–291|doi=10.1016/S0016-6995(94)80045-6|issn=0016-6995}}</ref><ref name=":1" /><ref name=":0">{{Cite book|last=Hagadorn|first=James W.|title=Exceptional fossil preservation; a unique view on the evolution of marine life|publisher=Columbia University Press|year=2002|editor1-last=Bottjer|editor1-first=D.J.|location=New York|pages=167–183|chapter=Bear Gulch: An Exceptional Upper Carboniferous Plattenkalk|editor2-last=Etter|editor2-first=W.|editor3-last=Hagadorn|editor3-first=J.W.|editor4-last=Tang|editor4-first=C.M.|chapter-url=https://www.researchgate.net/publication/242175100}}</ref> Some authors instead consider the Bear Gulch Limestone to be an early member of the [[Tyler Formation]], a patchy but widespread unit of Carboniferous [[limestone]] and terrestrial sediments.<ref>{{Cite journal|last=Maughan|first=Edwin K.|date=1984-02-01|title=Paleogeographic Setting of Pennsylvanian Tyler Formation and Relation to Underlying Mississippian Rocks in Montana and North Dakota1|journal=AAPG Bulletin|volume=68|issue=2|pages=178–195|doi=10.1306/AD4609F9-16F7-11D7-8645000102C1865D|issn=0149-1423}}</ref><ref name=":8">{{Cite journal|last1=Singer|first1=Amy|last2=Stanley|first2=George D.|last3=Hinman|first3=Nancy W.|date=2019-02-24|title=Anatomy of the Book Canyon conglomerate: a sequence boundary at the top of the Bear Gulch Limestone in the Big Snowy Trough|journal=Facies|language=en|volume=65|issue=2|page=15|doi=10.1007/s10347-019-0557-4|s2cid=135197751|issn=1612-4820}}</ref> Most of the Heath Formation is represented by [[black shale]]s and [[marl]]s, indicative of [[Brackish water|brackish]] and salty [[Littoral zone|littoral]] environments. It developed along a [[Marine transgression|transgressive]] sequence in a narrow saltwater seaway, known as the [[Central Montana Trough]]<ref name=":3" /><ref name=":1" /><ref name=":6" /> or Big Snowy Trough.<ref name=":4" /><ref name=":0" /> This seaway flowed into the [[Williston Basin]], a shallow [[Inland sea (geology)|inland sea]] further east. The Central Montana Trough would have also been linked to fully marine basins on the western coastline of [[Laurussia]],<ref name=":4" /><ref name=":5" /><ref name=":0" /> but this connection may have been broken by the time of the Bear Gulch Limestone's deposition.<ref name=":3" /><ref name=":6" />

Many distinct limestone [[Lens (geology)|lenses]] (localized sediment packages) are developed in the Heath Formation. They overlap each other in an east-to-west sequence which extends over a distance of 160&nbsp;km in the Central Montana Trough. The only exposed portions of the sequence are found at Potter Creek [[Dome (geology)|Dome]], a small uplifted area northeast of the [[Big Snowy Mountains]].<ref name=":4" /><ref name=":1" /> The last few limestone lenses form a large portion of the Upper Heath Formation,<ref name=":5" /> which is sometimes termed the Bear Gulch Member in recognition of the most well-exposed and fossiliferous lens in the sequence.<ref name=":4" /><ref name=":7">{{Cite journal|last=Cox|first=Robt S.|date=1986|title=Preliminary report on the age and palynology of the Bear Gulch Limestone (Mississippian, Montana)|url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/preliminary-report-on-the-age-and-palynology-of-the-bear-gulch-limestone-mississippian-montana/555EDC346DDB615D3CA2741592F93383|journal=Journal of Paleontology|language=en|volume=60|issue=4|pages=952–956|doi=10.1017/S0022336000043092|s2cid=130548212 |issn=0022-3360}}</ref><ref name=":6" /> This lens, the Bear Gulch Limestone, was also one of the last in the sequence, only succeeded by the Surenough Beds immediately west of it.<ref name=":4" /><ref name=":1" /> The Bear Gulch Limestone can be observed in numerous outcrops, spread out over an area of more than 50 km2 in [[Fergus County, Montana]].<ref name=":1" /><ref name=":2" /><ref name=":6" />

The creation of limestone lenses in the Heath Formation has been linked to tectonic activity extending the seaway by excavating [[bay]]s out of the surrounding land. As old bays are filled in and buried by sediment, faulting and seismic events form new bays in a long eastward to westward succession.<ref name=":4" /><ref name=":5" /><ref name=":1" /> It may have taken a mere 1000 years for the bay responsible for the Bear Gulch Limestone lens to fill in completely, after only 25,000 years for the entire bay formation sequence to run its course across Montana.<ref name=":2" /><ref name=":6" /> The final limestone deposits in the area were succeeded by freshwater lake sediments of the [[Cameron Creek Formation]], the oldest unit of the early Pennsylvanian-age [[Amsden Group]].<ref name=":4" /><ref name=":1" />

=== Age ===
A wide variety of [[Biostratigraphy|biostratigraphic]] evidence places the Heath Formation in the upper part of the [[Chesterian]] stage, near the end of the Mississippian subperiod (early [[Carboniferous]] period). The upper Chesterian is the North American regional equivalent to the global Serpukhovian stage, as well as the lower part of the European [[Namurian]] stage. The Bear Gulch Limestone in particular is correlated with [[Ammonoidea|ammonoid]] zone E2b (middle Arnsbergian) of the Namurian,<ref name=":7" /> not far from the top of the Serpukhovian. Strata from zone E2b in [[England]] and the [[Czech Republic]] have been dated to around 324 million years ago.<ref>{{Cite journal|last1=Pointon|first1=Michael A.|last2=Chew|first2=David M.|last3=Ovtcharova|first3=Maria|last4=Sevastopulo|first4=George D.|last5=Crowley|first5=Quentin G.|date=2012-11-01|title=New high-precision U–Pb dates from western European Carboniferous tuffs; implications for time scale calibration, the periodicity of late Carboniferous cycles and stratigraphical correlation|journal=Journal of the Geological Society|volume=169|issue=6|pages=713–721|doi=10.1144/jgs2011-092|bibcode=2012JGSoc.169..713P|hdl=2262/79149|s2cid=129867190|issn=0016-7649|hdl-access=free}}</ref><ref>{{Cite journal|last1=Jirásek|first1=Jakub|last2=Opluštil|first2=Stanislav|last3=Sivek|first3=Martin|last4=Schmitz|first4=Mark D.|last5=Abels|first5=Hemmo A.|date=2018-02-01|title=Astronomical forcing of Carboniferous paralic sedimentary cycles in the Upper Silesian Basin, Czech Republic (Serpukhovian, latest Mississippian): New radiometric ages afford an astronomical age model for European biozonations and substages|journal=Earth-Science Reviews|volume=177|pages=715–741|doi=10.1016/j.earscirev.2017.12.005|bibcode=2018ESRv..177..715J|issn=0012-8252|doi-access=free}}</ref>

=== Climate ===
During the time of deposition, the area was about 10-12 degrees north of the [[equator]], on the boundary between the arid [[subtropics]] and tropical equatorial region. Cyclical deposition supports a climate model arguing that the overall climate was warm and [[monsoon]]al, with pronounced rainy and dry seasons. During the quiet [[dry season]], sedimentation was low and the basin would have been influenced by northeasterly [[trade winds]], [[Tide|tidal]] currents, and [[evaporation]]. Early in the [[Wet season|rainy season]], warmer temperatures and reduced trade winds would have isolated the basin and increased its overall [[salinity]]. As the rainy season progressed, heavy rainfall enhances the bay's horizontal salinity gradient, from the freshwater-influenced upper bay to the marine-influenced lower bay. Storms would also produce a shallow layer of freshwater, washing sediment and organic material from the basin margins down into deeper areas.<ref name=":1" />

=== Sedimentology and ecosystems ===
Fine-grained [[lithographic limestone]] ([[plattenkalk]]) is predominant in the Bear Gulch lens, though [[clay]] to [[silt]]-sized [[Siliciclastic|siliclastic]] material also forms a significant portion of rock in some areas. Several [[facies]] (sediment associations) are developed in different parts of the bay.<ref name=":4" /><ref name=":1" />

The thick and fossiliferous central basin facies develop along the main northwest-to-southeast axis of the bay, which is delimited by small [[dewatering]] [[Fault (geology)|microfaults]]. Well-preserved fish and other [[nekton]]ic (free-swimming) animals are common, but [[algae]] and typical [[Benthos|benthic]] (seabed-living) animals are very rare. Central basin sedimentation was cyclical, with thin beds of pale [[shale]] interbedded between thicker layers of dark, organic-rich [[limestone]] with a distinct oily smell.<ref name=":4" /><ref name=":0" /><ref name=":1" /> Each dark layer contains a sequence of sediments: dense, massive ([[homogenous]]) beds followed by [[Lamination (geology)|laminae]] with [[graded bedding]], which may be [[Bioturbation|bioturbated]] in the upper part of the layer. These small sequences, sometimes termed microturbidites, draw comparisons to the [[Bouma sequence]]s of deep marine [[turbidite]] deposits. The pale shale layers of the central basin were likely slowly accumulated during the dry season, while the darker layers correspond to settling bay margin sediments washed into the basin during the rainy season.<ref name=":1" /> Sedimentary [[Slump (geology)|slumps]] along the central basin axis have been used to reconstruct flow within the basin, indicating that it deepened and drained to the northeast.<ref name=":4" /><ref name=":5" /><ref name=":0" /><ref name=":1" /> The Bear Gulch Limestone reached a thickness of 30 meters at its eastern outlet,<ref name=":5" /><ref name=":1" /> and total basin depth was approximately 40 meters.<ref name=":4" /><ref name=":0" /><ref name=":2" />

At its eastern outlet and nearby sheltered alcoves, the central basin transitions into the lightly colored laminated sediments of the ''[[Arborispongia]]''-[[Productida|productid]] facies. They are characterized by reefs and patches of the arborescent (branching) [[sponge]] ''Arborispongia'', which is commonly covered with spiny productid [[brachiopod]]s. Marine benthic organisms, such as algae, [[Bivalvia|bivalves]], [[bryozoa]]ns, and [[crinoid]]s, make up a significant portion of the ecosystem in these few areas.<ref name=":0" /><ref name=":1" /> At the calm and shallow northwest rim of the basin, ''Arborispongia'' reefs, large [[stromatolite]]s, and plant debris can be observed. Salt crystal casts are abundant, indicative of [[Hypersaline lake|hypersalinity]] and high rates of evaporation in this area.<ref name=":2" /> As the bay was filled in by sediments, similar conditions extended into the center of the basin. This results in deposition of the "shallow" or "marly" facies, a collection of very pale [[micrite]]s with very little organic or siliciclastic material. They preserve various [[Microbialite|algal laminations]], diverse ''Arborispongia'' reefs, and local concentrations of [[chert]] and [[gypsum]] [[Nodule (geology)|nodules]].<ref name=":4" /><ref name=":5" /><ref name=":1" /> The end of the bay's lifespan was indicated by a sequence of layers with leaf fragments, limestone conglomerates,<ref name=":8" /> [[marl]]s, and finally fully freshwater sediments.<ref name=":1" />

When the bay was in its heyday, the south edge of the central basin axis saw the development of the filamentous algal facies. These are mostly dark, organic-rich limestones and shales, similar to the central basin facies though with more siliciclastic silt and fewer microturbidites. As the name indicates, strands of filamentous algae are abundant.<ref name=":0" /><ref name=":1" /> Further beyond the main basin axis, the rocks are even more silty, not clearly bedded, and have a very dark coloration. These sediments, the marginal facies, have a high content of [[Peloid (geology)|peloids]], plant debris, and other organic material. They likely correspond to shallow, brackish areas with an influx of freshwater. Fossils of fully saltwater taxa are rare and poorly preserved relative to other environments, though organisms with a wider range of salinity tolerance (''[[Acanthodes]]'', [[Gastropoda|gastropods]], filamentous algae) are fairly common.<ref name=":4" /><ref name=":0" /><ref name=":1" />

=== Preservation of fossils ===
The Bear Gulch Limestone is a [[Lagerstätte|konservat lagerstätte]], meaning that its fossils are uniquely well-preserved, including soft tissue details which offer rare insights into the biology of Carboniferous organisms.<ref name=":1" /> The fine-grained sediments common in the formation allow for fossilized structures to retain fine resolution, as seen in equivalent plattenkalk-based lagerstätten throughout geological history. Most fossils are isolated and flattened into very thin films between sheet-like layers. ''Arborispongia'' assemblages, [[cephalopod]] shells, and large vertebrate bones occasionally project through several thin layers, approaching three-dimensional preservation.<ref name=":5" /><ref name=":0" />

[[Vertebrate]]s typically come in the form of complete skeletons, and their fossils often preserve internal and external organic [[Biological pigment|pigments]]. Skin pigments can indicate color patterns and the extent of fins and other external structures, while internal pigments are used to outline the [[liver]], [[spleen]], eyes, and other organs. In rare cases, even the structure of fragile [[blood vessel]]s can be recognized from preserved blood pigments.<ref>{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=1995-01-01|title=Pigment patterns; soft anatomy and relationships of Bear Gulch Chondrichthyes (Namurian E2b; Lower Carboniferous; Montana; USA)|url=https://www.sciencedirect.com/science/article/pii/S0016699595801022|journal=Geobios|series=Premiers Vertandébrandés et Vertandébrandés Infandérieurs|language=en|volume=28|pages=145–146|doi=10.1016/S0016-6995(95)80102-2|issn=0016-6995}}</ref><ref name=":9">{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=1997|title=Soft tissue pigments of the Upper Mississippian chondrenchelyid, ''Harpagofututor volsellorhinus'' (Chondrichthyes, Holocephali) from the Bear Gulch Limestone, Montana, USA|url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/soft-tissue-pigments-of-the-upper-mississippian-chondrenchelyid-harpagofututor-volsellorhinus-chondrichthyes-holocephali-from-the-bear-gulch-limestone-montana-usa/E8F6AEF8F06E7F34DC79657BA4C0A311|journal=Journal of Paleontology|language=en|volume=71|issue=2|pages=337–342|doi=10.1017/S002233600003924X|s2cid=131227701 |issn=0022-3360}}</ref> Uncommon gut contents indicate the diet of some Bear Gulch animals,<ref name=":9" /><ref>{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=2008-12-12|title=A basal elasmobranch, ''Thrinacoselache gracia'' n. gen and sp., (Thrinacodontidae, new family) from the Bear Gulch Limestone, Serpukhovian of Montana, USA|url=https://www.researchgate.net/publication/213771568|journal=Journal of Vertebrate Paleontology|volume=28|issue=4|pages=970–988|doi=10.1671/0272-4634-28.4.970|s2cid=84735866|issn=0272-4634}}</ref> and [[phosphatized]] muscles have been found in very rare situations.<ref name=":0" /> Soft [[invertebrate]]s are indicated by a variety of [[Cast (geology)|molds, casts]], and organic discolorations on rocks.<ref name=":5" /><ref name=":0" /> In the central basin, fossils of invertebrates with [[calcareous]] shells are mostly dissolved, leaving only molds in the surrounding rock. On the other hand, invertebrates with [[chitinous]] or [[Phosphate mineral|phosphate]]-rich shells become more common in the central basin. This may have been a consequence of acidity in the pore fluids of sediments, with less acidic fluids favoring the preservation of calcareous fossils and more acidic fluids favoring phosphatized fossils.<ref name=":4" /><ref name=":0" />

There is some uncertainty over how this exceptional preservation was achieved. Most fossils are complete and undecomposed animals, with no signs of disturbance from [[scavenger]]s or strong currents. To prevent [[decomposition]] of fragile soft tissue in a warm environment, death and burial had to have been very rapid for the vast majority of articulated skeletons. Rare disarticulated fragments may correspond to large or buoyant carcasses which rise to the water surface to gradually decay and fall apart in a "bloat and float" [[Taphonomy|taphonomic]] process.<ref name=":5" /><ref name=":1" /> Fossils are dispersed throughout the Bear Gulch lens, rather than concentrated in specific fossil-rich beds (which would be expected if organisms were killed by [[algal bloom]]s).<ref name=":4" />

The cyclically deposited seabed of the central basin, though fossiliferous, is deprived of benthic invertebrates. Some authors have suggested that the deepest waters in the basin were too salty or oxygen-poor for most life.<ref name=":4" /> However, bottom-dwelling fish are common in the central basin, suggesting that [[Anoxic waters|anoxia]] (low oxygen) was not a persistent quality of bottom waters.<ref name=":5" /><ref name=":1" /> Nevertheless, many fish fossils are found with distended gills, favoring [[asphyxiation]] as a cause of death.<ref name=":9" /><ref name=":0" /><ref name=":1" /> One possible explanation for rapid asphyxiation and burial places blame on freshwater runoff during storms in the wet season. Heavy rainfall would bring a cascade of organic-rich marginal sediments into the central basin. As the sediments sink, they quickly absorb oxygen from the seawater, killing and burying basin organisms in only a matter of hours.<ref name=":1" />

==Paleobiota==
The [[ecosystem]] represented by the Bear Gulch Limestone was vibrant and well-represented by fossils, with many described and undescribed species of vertebrates and invertebrates among their ranks. Animals show a wide range of body types and show preferences to certain areas of the bay, indicating that the bay offered a wide range of habitats and [[Ecological niche|niches]] to be filled.<ref name=":6">{{Cite journal|last1=Lund|first1=Richard|last2=Greenfest-Allen|first2=Emily|last3=Grogan|first3=Eileen D.|date=2015-02-01|title=Ecomorphology of the Mississippian fishes of the Bear Gulch Limestone (Heath formation, Montana, USA)|journal=Environmental Biology of Fishes|language=en|volume=98|issue=2|pages=739–754|doi=10.1007/s10641-014-0308-x|s2cid=14850973|issn=1573-5133}}</ref> Many indicators of [[paleoecology]] and [[paleobiology]] have been preserved, from associations between encrusting shelled organisms and algae,<ref name=":31" /> to gut contents and other feeding traces,<ref name=":13" /> and even some animals fossilized while mating.<ref name=":23" /><ref name=":32" /> Fish are diverse and abundant, with thousands of specimens representing approximately 150 species (as of 2015).<ref name=":6" /> Many of these species are undescribed and unnamed, only mentioned through "code names"; unnamed species are not included in paleobiota lists here.

=== Chondrichthyans ===
The Bear Gulch Limestone is renowned for its unusual and ecologically diverse [[Chondrichthyes|chondrichthyans]], the group of cartilaginous fish containing modern [[shark]]s, [[Batoidea|rays]], and [[chimaera]]s. Over 80 species of chondrichthyans are known (as of 2012), representing close to 60% of the fish diversity (by species count) in the bay. This is a far cry from modern ecosystems, where chondrichthyans comprise only around 3% of fish species.<ref name=":2" /> In the Bear Gulch Limestone, chondrichthyans possess a wide range of ecologies and body types, including [[eel]]-like forms ("''[[Thrinacoselache]]''"), deep-bodied [[Durophagy|durophages]] ([[Petalodontiformes|petalodontiforms]]), small active swimmers (most [[Holocephali|holocephalans]]), ray-like [[Demersal fish|benthic]] forms (''[[Squatinactis]]'') and more typical shark-like predators ([[Symmoriiformes|symmoriiforms]] and [[Elasmobranchii|elasmobranchs]]).<ref name=":6" /> Chondrichthyan diversity and abundance patterns are correlated, with the highest number of species and fossils found in the central basin facies and the lowest in the marginal facies. Large predatory chondrichthyans such as ''[[Listracanthus]]'' and symmoriiforms (except ''Falcatus'') make up a higher portion of fossils in the hypersaline upper bay, while ''[[Falcatus]]'' and [[Holocephali|holocephalans]] are the most common fossils in the marginal and central basin facies. A sheltered reef habitat at the eastern edge of exposures has produced a high number of ''[[Heteropetalus]]'' fossils. Regardless, each habitat observes significant species overlap with other habitats, and "common" chondrichthyans (>3 specimens) are not abundant to the point that they outnumber more rare species (<3 specimens), in terms of total specimen count.<ref name=":2" />
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''Chondrichthyans of the Bear Gulch Limestone'''
|-
! Taxon !! Species !!  Notes !! Images
|-
|cf. ''[[Agassizodus]]''
|
|A [[Eugeneodontida|eugeneodont]] [[Euchondrocephali|euchondrocephalan]]<ref name=":23">{{Cite journal|last=Lund|first=Richard|date=1990-01-01|title=Chondrichthyan life history styles as revealed by the 320 million years old Mississippian of Montana|journal=Environmental Biology of Fishes|language=en|volume=27|issue=1|pages=1–19|doi=10.1007/BF00004900|s2cid=13249799|issn=1573-5133}}</ref><ref name=":2" /><ref name=":6" />
| rowspan="131" |
[[File:Belantsea montana.JPG|thumb|150px|''[[Belantsea|Belantsea montana]]'']]
[[File:Debeerius.png|thumb|150px|''[[Debeerius|Debeerius ellefseni]]'']]
[[File:Echinochimaera meltoni (fossil fish) (Bear Gulch Limestone, Upper Mississippian; Montana, USA) (33784748875).jpg|thumb|150px|''[[Echinochimaera|Echinochimaera meltoni]]'']]
[[File:Falcatus_falcatus_01.JPG|thumb|150px|''[[Falcatus|Falcatus falcatus]]'']]
[[File:Harpacanthus2DB.jpg|thumb|150px|''[[Harpacanthus|Harpacanthus fimbriatus]]'']]
[[File:Heteropetalus elegantulus Bear Gulch Montana USA.jpg|thumb|150px|''[[Heteropetalus|Heteropetalus elegantulus]]'']]
[[File:StethacanthusesDB 2.jpg|thumb|150px|''[[Stethacanthus|Stethacanthus altonensis ''and'' Stethacanthus productus]]'']]
[[File:Thrinacoselache gracia.jpg|thumb|150px|''[[Thrinacoselache|"Thrinacoselache" (Thrinacodus) gracia]]'']]
|-
|''[[Bealbonn]]<ref name="CA04">{{cite book|last1=Lund|first1=Richard|title=Recent Advances in the Origin and Early Radiation of Vertebrates|last2=Grogan|first2=Eileen D.|publisher=Verlag Dr. Friedrich Pfeil|year=2004|editor1=Arratia, G.|location=München|pages=505–531|chapter=Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA|editor2=Wilson, M.V.H.|editor3=Cloutier, R.|chapter-url=https://pfeil-verlag.de/wp-content/uploads/2015/05/3_52d24.pdf}}</ref>''
|''B. rogaire''
|A [[Gregoriidae|gregoriid]] euchondrocephalan<ref name=":20">{{cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=2008|title=A basal elasmobranch, ''Thrinacoselache gracia'' n. gen and sp., (Thrinacodontidae, new family) from the Bear Gulch Limestone, Serpukhovian of Montana, USA|url=https://www.researchgate.net/publication/213771568|journal=Journal of Vertebrate Paleontology|volume=28|issue=4|pages=970–988|doi=10.1671/0272-4634-28.4.970|s2cid=84735866}}</ref>
|-
|''[[Belantsea]]''<ref name=":21">{{Cite journal|last=Lund|first=Richard|date=1989-09-28|title=New petalodonts (Chondrichthyes) from the Upper Mississippian Bear Gulch Limestone (Namurian E2b) of Montana|journal=Journal of Vertebrate Paleontology|volume=9|issue=3|pages=350–368|doi=10.1080/02724634.1989.10011767|issn=0272-4634}}</ref>
|''B. montana''
|A [[Belantseidae|belantseid]] [[Petalodontiformes|petalodontiform]] euchondrocephalan<ref name=":22">{{Cite journal|last1=Lund|first1=R.|last2=Grogan|first2=E. D.|last3=Fath|first3=M.|date=2014-12-01|title=On the relationships of the Petalodontiformes (Chondrichthyes)|url=https://www.researchgate.net/publication/268149743|journal=Paleontological Journal|language=en|volume=48|issue=9|pages=1015–1029|doi=10.1134/S0031030114090081|s2cid=84617203|issn=1555-6174}}</ref>
|-
|''[[Carcharopsis]]''
|
|A putative [[Euselachii|euselachian]] shark<ref name=":6" />
|-
|''[[Cladodus]]''
|
|A "[[cladodont]]"<ref name=":23" /><ref name=":2" /><ref name=":6" />
|-
|''[[Cochliodus]]''
|''C. contortus''
|A "[[Cochliodontiformes|cochliodont]]" [[Holocephali|holocephalan]]<ref name=":24">{{Cite journal|last1=Lund|first1=R.|last2=Grogan|first2=E.D.|date=1997|title=Cochliodonts from the Mississippian Bear Gulch Limestone (Heath Formation; Big Snowy Group; Chesterian) of Montana and the relationships of the Holocephali|journal=Dinofest International Symposium, Proceedings|pages=477–492}}</ref>
|-
|''[[Damocles (genus)|Damocles]]''<ref name=":28">{{Cite journal|last=Lund|first=Richard|date=1986-03-07|title=On ''Damocles serratus'', nov. gen. et sp. (Elasmobranchii: Cladodontida) from the Upper Mississippian Bear Gulch Limestone of Montana|url=https://www.researchgate.net/publication/254313367|journal=Journal of Vertebrate Paleontology|volume=6|issue=1|pages=12–19|doi=10.1080/02724634.1986.10011594|issn=0272-4634}}</ref>
|''D. serratus''
|A large ''[[Falcatus]]''-like [[Symmoriiformes|symoriiform]]<ref name=":23" />
|-
|''[[Debeerius]]<ref name=":25">{{cite journal|author=Eileen D. Grogan & Richard Lund|year=2000|title=''Debeerius ellefseni'' (fam. nov., gen. nov., spec. nov.), an autodiastylic chondrichthyan from the Mississippian Bear Gulch Limestone of Montana (USA), the relationships of the chondrichthyes, and comments on gnathostome evolution|journal=[[Journal of Morphology]]|volume=243|issue=3|pages=219–245|doi=10.1002/(SICI)1097-4687(200003)243:3<219::AID-JMOR1>3.0.CO;2-1|pmid=10681469|s2cid=21466183 }}</ref>''
|''D. ellefensi''
|A [[Debeeriidae|debeeriid]] euchondrocephalan
|-
|''[[Delphyodontos]]''<ref>{{Cite journal|last=Lund|first=Richard|date=1980-08-08|title=Viviparity and Intrauterine Feeding in a New Holocephalan Fish from the Lower Carboniferous of Montana|url=https://www.researchgate.net/publication/6019589|journal=Science|volume=209|issue=4457|pages=697–699|doi=10.1126/science.209.4457.697|pmid=17821193|bibcode=1980Sci...209..697L|s2cid=36858963}}</ref>
|''D. dacriformes''
|An unusual holocephalan known from sharp-toothed fetuses<ref name=":23" />
|-
| rowspan="2" |''[[Echinochimaera]]''
|''E. meltoni''<ref>{{Cite journal|last=Lund|first=Richard|date=1977|title=''Echinochimaera meltoni'' new genus and species (Chimaeriformes) from the Mississippian of Montana|url=https://www.biodiversitylibrary.org/item/238343#page/229/mode/1up|journal=Annals of Carnegie Museum|volume=46|pages=195–221|doi=10.5962/p.330529 |s2cid=251525608 |doi-access=free}}</ref>
|An [[Echinochimaeridae|echinochimaerid]] holocephalan<ref name=":23" />
|-
|''E. snyderi''<ref>Lund, R. 1988. New Mississippian Holocephali (Chondrichthyes) and the evolution of the Holocephali. ''In'' Teeth Revisited: Proceedings of the VII Int. Symp. on Dental Morph., Paris, May 1986, Russell, D. E., Santoro, J. P. and Sigogneau‑Russell, D., Eds., Mem. Mus. Natn. Hist. Nat., Paris, (serie C) 53:195‑205.</ref>
|An echinochimaerid holocephalan<ref name=":23" />
|-
|cf. ''[[Erismacanthus]]''
|''E. maccoyanus''
|A putative "cochliodont"<ref name=":23" /><ref name=":6" />
|-
|''[[Falcatus]]''<ref name=":26">{{Cite journal|last=Lund|first=Richard|date=1985-03-01|title=The morphology of ''Falcatus falcatus'' (St. John and Worthen), a Mississippian stethacanthid chondrichthyan from the Bear Gulch Limestone of Montana|journal=Journal of Vertebrate Paleontology|volume=5|issue=1|pages=1–19|doi=10.1080/02724634.1985.10011842|issn=0272-4634}}</ref>
|''F. falcatus''
|A small and common symoriiform<ref name=":26" /><ref name=":28" />
|-
|''[[Fissodopsis]]<ref name=":22" />''
|''F. robustus''
|An [[Obruchevodidae|obruchevodid]] petalodontiform
|-
|''[[Gregorius (genus)|Gregorius]]''
|''G. rexi''<ref name="CA04" />
|A gregoriid<ref name=":20" />
|-
|''[[Harpacanthus]]''
|''H. fimbriatus''
|A euchondrocephalan with a tentaculated snout<ref name=":23" /><ref name="CA042">{{cite book|last1=Lund|first1=Richard|title=Recent Advances in the Origin and Early Radiation of Vertebrates|last2=Grogan|first2=Eileen D.|publisher=Verlag Dr. Friedrich Pfeil|year=2004|editor1=Arratia, G.|location=München|pages=171–187|chapter=Two tenaculum-bearing Holocephalimorpha (Chondrichthyes) from the Bear Gulch Limestone (Chesterian, Serpukhovian) of Montana, USA|editor2=Wilson, M.V.H.|editor3=Cloutier, R.|chapter-url=https://www.pfeil-verlag.de/wp-content/uploads/2015/05/3_52d09.pdf}}</ref>
|-
|''[[Harpagofututor]]''<ref>{{Cite journal|last=Lund|first=Richard|date=1982|title=''Harpagofututor volsellorhinus'' New Genus and Species (Chondrichthyes, Chondrenchelyiformes) from the Namurian Bear Gulch Limestone, ''Chondrenchelys problematica'' Traquair (Visean), and Their Sexual Dimorphism|url=https://www.researchgate.net/publication/285134505|journal=Journal of Paleontology|volume=56|issue=4|pages=938–958|issn=0022-3360|jstor=1304712}}</ref>
|''H. volsellorhinus''
|A long-bodied [[Chondrenchelyiformes|chondrenchelyiform]] holocephalan<ref name=":23" /><ref name=":9" />
|-
|''[[Heteropetalus]]''<ref>{{Cite journal|last=Lund|first=Richard|date=1977|title=A new petalodont (Chondrichthyes, Bradyodonti) from the Upper Mississippian of Montana|url=https://www.biodiversitylibrary.org/item/238343#page/157/mode/1up|journal=Annals of Carnegie Museum|volume=46|pages=129–155|doi=10.5962/p.330526 |s2cid=251529786 |doi-access=free}}</ref>
|''H. elegantulus''
|A slender debeeriid<ref name=":23" /><ref name=":25" />
|-
|''[[Janassa]]''
|''J. clarki<ref name=":21" />''
|A [[Janassidae|janassid]] petalodontiform<ref name=":23" /><ref name=":22" />
|-
|''[[Listracanthus]]''
|
|A spiny-backed chondrichthyan<ref name=":23" /><ref name=":3" /><ref name=":2" /><ref name=":6" />
|-
|''[[Obruchevodus]]''<ref>{{Cite journal|last1=Grogan|first1=E. D.|last2=Lund|first2=R.|last3=Fath|first3=M.|date=2014-12-01|title=A new petalodont chondrichthyan from the bear gulch limestone of montana, USA, with reassessment of Netsepoye hawesi and comments on the morphology of holomorphic petalodonts|url=https://www.researchgate.net/publication/268150219|journal=Paleontological Journal|language=en|volume=48|issue=9|pages=1003–1014|doi=10.1134/S0031030114090044|s2cid=84238164|issn=1555-6174}}</ref>
|''O. griffithi''
|An obruchevodid petalodontiform<ref name=":22" />
|-
|''[[Orestiacanthus]]''<ref name=":29">{{Cite journal|last=Lund|first=Richard|date=1984-01-01|title=On the spines of the Stethacanthidae (Chondrichthyes), with a description of a new genus from the Mississippian Bear Gulch limestone|url=https://www.academia.edu/48299587|journal=Geobios|language=en|volume=17|issue=3|pages=281–295|doi=10.1016/S0016-6995(84)80095-9|issn=0016-6995}}</ref>
|''O. fergusi''
|A [[Stethacanthidae|stethacanthid]] symoriiform<ref name=":23" />
|-
|''[[Orodus]]''
|
|An [[Orodontiformes|orodontiform]]<ref name=":23" />
|-
|''[[Netsepoye]]<ref name=":21" />''
|''N. hawesi''
|An obruchevodid petalodontiform<ref name=":22" />
|-
|''[[Papilionichthys]]''<ref name=":27">{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=2009|title=Two new iniopterygians (Chondrichthyes) from the Mississippian (Serpukhovian) Bear Gulch Limestone of Montana with evidence of a new form of chondrichthyan neurocranium|url=https://www.researchgate.net/publication/229951020|journal=Acta Zoologica|language=en|volume=90|issue=s1|pages=134–151|doi=10.1111/j.1463-6395.2008.00371.x|issn=1463-6395}}</ref>
|''P. stahlae''
|An [[Iniopterygians|iniopterygian]]
|-
|''[[Petalorhynchus]]''
|''P. beargulchensis<ref name=":21" />''
|A [[Petalorhynchidae|petalorhynchid]] petalodontiform<ref name=":22" />
|-
|''[[Polyrhizodus]]''
|''P. digitatus''
|A [[Petalodontidae|petalodontid]] petalodontiform<ref>{{Cite journal|last=Lund|first=Richard|date=1983-03-01|title=On a dentition of ''Polyrhizodus'' (Chondrichthyes, Petalodontiformes) from the Namurian bear gulch limestone of Montana|url=https://www.researchgate.net/publication/254313485|journal=Journal of Vertebrate Paleontology|volume=3|issue=1|pages=1–6|doi=10.1080/02724634.1983.10384478|issn=0272-4634}}</ref><ref name=":21" /><ref name=":23" /><ref name=":22" />
|-
|''[[Psephodus]]''
|
|A "cochliodont"<ref name=":23" /><ref name=":24" /><ref name=":3" /><ref name=":2" /><ref name=":6" />
|-
|''[[Rainerichthys]]<ref name=":27" />''
|''R. zangerli''
|An iniopterygian
|-
|''[[Siksika ottae|Siksika]]<ref name=":21" />''
|''S. ottae''
|A [[Basal (phylogenetics)|basal]] petalodontiform<ref name=":22" />
|-
|''[[Squatinactis]]''<ref>{{Cite journal|last1=Lund|first1=Richard|last2=Zangerl|first2=Rainer|date=1974|title=''Squatinactis caudispinatus'', a new elasmobranch from the Upper Mississippian of Montana|url=https://www.biodiversitylibrary.org/item/238300#page/59/mode/1up|journal=Annals of Carnegie Museum|volume=45|pages=43–54|doi=10.5962/p.330504 |s2cid=251537092 |doi-access=free}}</ref>
|''S. montanus''
|An unusual "cladodont" with broad [[pectoral fin]]s, reminiscent of modern [[Batoidea|rays]] or angelsharks (''[[Squatina]]'')<ref>{{Cite journal|last=Lund|first=Richard|date=1988|title=New Information on ''Squatinactis caudispinatus'' (Chondrichthyes, Cladodontida) from the Chesterian Bear Gulch Limestone of Montana|journal=Journal of Vertebrate Paleontology|volume=8|issue=3|pages=340–342|doi=10.1080/02724634.1988.10011718|issn=0272-4634|jstor=4523212}}</ref>
|-
| rowspan="3" |''[[Srianta (genus)|Srianta]]''<ref name="CA04" />
|''S. dawsoni''
|A gregoriid<ref name=":20" />
|-
|''S. iarlis''
|A gregoriid<ref name=":20" />
|-
|''S. srianta''
|A gregoriid<ref name=":20" />
|-
| rowspan="2" |''[[Stethacanthus]]''
|''S. altonensis''
|A stethacanthid<ref>{{Cite journal|last=Lund|first=Richard|date=1974|title=''Stethacanthus altonensis'' (Elasmobranchii) from the Bear Gulch Limestone of Montana|url=https://www.biodiversitylibrary.org/item/238300#page/181/mode/1up|journal=Annals of Carnegie Museum|volume=45|pages=161–178|doi=10.5962/p.330508 |s2cid=251532925 |doi-access=free}}</ref><ref name=":30">{{Cite journal|last=Lund|first=Richard|date=1985|title=Stethacanthid elasmobranch remains from the Bear Gulch Limestone (Namurian E2b) of Montana|url=https://digitallibrary.amnh.org/handle/2246/3554|journal=American Museum Novitates|language=en-US|issue=2828|pages=1–24|hdl=2246/3554}}</ref><ref name=":29" /><ref name=":26" /><ref name=":28" />
|-
|''S. productus''
|A stethacanthid<ref name=":30" /><ref name=":29" /><ref name=":26" /><ref name=":28" />
|-
|''[[Thrinacodus]]''
|''T. gracia<ref name=":20" />''
|An eel-like [[Thrinacodontidae|thrinacodontid]] elasmobranch, sometimes given its own genus, "''[[Thrinacoselache]]''"<ref name=":20" /><ref>{{Cite journal|last1=Ginter|first1=Michał|last2=Turner|first2=Susan|date=2010-12-02|title=The middle Paleozoic Selachian genus ''Thrinacodus''|journal=Journal of Vertebrate Paleontology|volume=30|issue=6|pages=1666–1672|doi=10.1080/02724634.2010.520785|s2cid=86058786|issn=0272-4634}}</ref><ref>{{Cite journal|last1=Frey|first1=Linda|last2=Coates|first2=Michael|last3=Ginter|first3=Michał|last4=Hairapetian|first4=Vachik|last5=Rücklin|first5=Martin|last6=Jerjen|first6=Iwan|last7=Klug|first7=Christian|date=2019-10-09|title=The early elasmobranch ''Phoebodus'': phylogenetic relationships, ecomorphology and a new time-scale for shark evolution|journal=Proceedings of the Royal Society B: Biological Sciences|volume=286|issue=1912|page=20191336|doi=10.1098/rspb.2019.1336|pmc=6790773|pmid=31575362}}</ref>
|-
| rowspan="3" |''[[Traquairius]]''
|''T. agkistrocephalus''
|A "cochliodont"<ref name=":24" />
|-
|''T. nudus''
|A "cochliodont"<ref name=":24" /><ref name="CA042" />
|-
|''T. spinosus''
|A "cochliodont"<ref name=":24" />
|-
|''[[Tristychius]]''
|
|A [[Tristychiidae|tristychiid]] elasmobranch<ref name=":23" /><ref name=":6" />
|-
|''[[Venustodus]]''
|''V. argutus''
|A broad-toothed euchondrocephalan<ref name=":23" />
|}

=== Actinopterygians ===
[[Actinopterygii|Actinopterygians]] (ray-finned bony fish) are also quite diverse, with about 50 described and undescribed species (as of 2012) making up more than a third of the Bear Gulch fish diversity. In terms of specimen count, they are the most abundant fish fossils in the Bear Gulch Limestone, representing approximately 80% of all fossil vertebrates.<ref name=":2" /> However, they are more restricted than chondrichthyans in terms of [[ecomorphology]]. Most have a small and generalized [[fusiform]] (smoothly tapering) body shape, with only a few deviations towards more elongated or deep-bodied forms.<ref name=":6" /> The most abundant actinopterygians include ''[[Wendyichthys]]'' and three closely related unnamed species (code names "Yogo", "Fub", and "Cop"). The relative abundance of actinopterygians drops off in the upper bay, though they are still fairly common. Schools of freshly hatched [[Fish larvae|larvae]] have been found in isolated reef habitats near the central basin.<ref name=":2" />
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''Ray-finned fish of the Bear Gulch Limestone'''
|-
! Taxon !! Species !!  Notes !! Images
|-
|''[[Aesopichthys]]''<ref name=":16">{{Cite journal|last1=Poplin|first1=Cécile|last2=Lund|first2=Richard|date=2000-09-25|title=Two new deep-bodied palaeoniscoid actinopterygians from Bear Gulch (Montana, USA, Lower Carboniferous)|journal=Journal of Vertebrate Paleontology|volume=20|issue=3|pages=428–449|doi=10.1671/0272-4634(2000)020[0428:tndbpa]2.0.co;2|s2cid=85632076 |issn=0272-4634}}</ref>
|''A. erinaceus''
|An [[Aesopichthyidae|aesopichthyid]] "[[palaeoniscoid]]"
| rowspan="140" |
[[File:†Discoserra pectinodon Unt Karbon Bear Gulch Montana USA Ch2431.jpg|thumb|150px|''[[Discoserra|Discoserra pectinodon]]'']]
[[File:†Paratarrasius hibbardi Carboniferous Bear Gulch, Montana.jpg|thumb|150px|''[[Paratarrasius|Paratarrasius hibbardi]]'']]
|-
|''[[Beagiascus]]<ref name=":17">{{Cite journal|last1=Mickle|first1=Kathryn E.|last2=Lund|first2=Richard|last3=Grogan|first3=Eileen D.|date=2009|title=Three new palaeoniscoid fishes from the Bear Gulch Limestone (Serpukhovian, Mississippian) of Montana (USA) and the relationships of lower actinopterygians|url=https://www.researchgate.net/publication/232691814|journal=Geodiversitas|volume=31|issue=3|pages=623–668|doi=10.5252/g2009n3a6|s2cid=128412802|issn=1280-9659}}</ref>''
|''B. pulcherrimus''
|A "palaeoniscoid"
|-
|''[[Cyranorhis]]''<ref name=":18">{{Cite journal|last1=Lund|first1=Richard|last2=Poplin|first2=Cécile|date=1997-09-04|title=The rhadinichthyids (paleoniscoid actinopterygians) from the Bear Gulch Limestone of Montana (USA, Lower Carboniferous)|journal=Journal of Vertebrate Paleontology|volume=17|issue=3|pages=466–486|doi=10.1080/02724634.1997.10010996|issn=0272-4634}}</ref>
|''C. bergeraci''
|A [[Rhadinychthyidae|rhadinychthyid]] "palaeoniscoid"
|-
|''[[Discoserra]]''<ref name=":19">{{Cite journal|last=Lund|first=Richard|date=2000|title=The new Actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA)|url=https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2000n2a2.pdf|journal=Geodiversitas|volume=22|issue=2|pages=171–206}}</ref>
|''D. pectinodon''
|A [[Guildayichthyiformes|guildayichthyiform]]
|-
|''[[Guildayichthys]]''<ref name=":19" />
|''G. carnegiei''
|A guildayichthyiform
|-
| rowspan="2" |''[[Kalops]]''<ref>{{Cite journal|last1=Poplin|first1=C. M.|last2=Lund|first2=R.|date=2002|title=Two Carboniferous fine-eyed palaeoniscoids (Pisces, Actinopterygii) from Bear Gulch (USA)|url=https://www.researchgate.net/publication/240776260|journal=Journal of Paleontology|volume=76|issue=6|pages=1014–1028|doi=10.1017/s002233600005784x|s2cid=232348836|issn=0022-3360}}</ref>
|''K. diophrys''
|A "palaeoniscoid"
|-
|''K. monophrys''
|A "palaeoniscoid"
|-
| rowspan="2" |''[[Lineagruan]]<ref name=":17" />''
|''L. judithi''
|A "palaeoniscoid"
|-
|''L. snowyi''
|A "palaeoniscoid"
|-
| rowspan="2" |''[[Paphosiscus]]''<ref>{{Cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|date=2015|title=Two new Actinopterygii (Vertebrata, Osteichthyes) with cosmine from the Bear Gulch Limestone (Heath Fm., Serpukhovian, Mississippian) of Montana USA|url=https://bioone.org/journals/proceedings-of-the-academy-of-natural-sciences-of-philadelphia/volume-164/issue-1/053.164.0114/Two-new-Actinopterygii-Vertebrata-Osteichthyes-with-cosmine-from-the-Bear/10.1635/053.164.0114.full|journal=Proceedings of the Academy of Natural Sciences of Philadelphia|volume=164|issue=1|pages=111–132|doi=10.1635/053.164.0114|s2cid=130093887|issn=0097-3157}}</ref>
|''P. circulocaudus''
|A [[Paphosisciformes|paphosisciform]] "palaeoniscoid"
|-
|''P. scalmocristus''
|A paphosisciform
|-
|''[[Paratarrasius]]''<ref>{{Cite journal|last1=Lund|first1=Richard|last2=Melton|first2=William G. Jr.|date=1982|title=A new actinopterygian fish from the Mississippian Bear Gulch Limestone of Montana|url=https://www.palass.org/publications/palaeontology-journal/archive/25/3/article_pp485-498|journal=Palaeontology|volume=25|issue=3|pages=485–498}}</ref>
|''P. hibbardi''
|A [[Tarrasiiformes|tarrasiiform]]<ref>{{Cite journal|last1=Lund|first1=Richard|last2=Poplin|first2=Cécile|date=2002-09-19|title=Cladistic analysis of the relationships of the Tarrasiids (Lower Carboniferous Actinopterygians)|journal=Journal of Vertebrate Paleontology|volume=22|issue=3|pages=480–486|doi=10.1671/0272-4634(2002)022[0480:caotro]2.0.co;2|s2cid=86148802 |issn=0272-4634}}</ref>
|-
|''[[Proceramala]]''<ref name=":16" />
|''P. montanensis''
|An aesopichthyid
|-
| rowspan="2" |''[[Wendyichthys]]''<ref name=":18" />
|''W. dicksoni''
|A rhadinychthyid
|-
|''W. lautreci''
|A rhadinychthyid
|}

=== Other fish ===
Non-actinopterygian and non-chondrichthyan fish make up a fairly small component of the overall diversity, though their fossils are still common in some habitats. Preserved [[Sarcopterygii|sarcopterygians]] (lobe-finned fish) include [[actinistia]]ns ([[coelacanth]]s) and the [[Rhizodontida|rhizodont]] ''[[Strepsodus]]'', which have very different habitat preferences. Coelacanths, particularly fossils of the genus ''[[Caridosuctor]]'', are abundant in the central basin and its margins, but are practically absent in the upper bay. ''Strepsodus'', on the other hand, is moderately common in the upper bay and very rare elsewhere. Neither are common in the sheltered eastern reef habitat. ''[[Acanthodes]]'', the only [[Acanthodii|acanthodian]] known from the Bear Gulch Limestone, has a similar distribution pattern to ''Strepsodus'': common in the upper bay and nowhere else. [[Lamprey]]s, represented by ''[[Hardistiella]]'', are too rare to estimate their habitat preference.<ref name=":2" /><ref name=":6" />
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''Fish of the Bear Gulch Limestone'''
|-
! Taxon !! Species !!  Notes !! Images
|-
|''[[Acanthodes]]''
|''A. lundi''<ref>{{Cite journal|last=Zidek|first=Jiri|date=1980|title=''Acanthodes lundi'', new species (Acanthodii) and associated coprolites from uppermost Mississippian Heath Formation of Central Montana|url=https://www.biodiversitylibrary.org/page/52334247#page/67/mode/1up|journal=Annals of Carnegie Museum|volume=49|issue=3|pages=49–78|doi=10.5962/p.214478 |s2cid=90673484 |doi-access=free}}</ref>
|An [[Acanthodii|acanthodian]]<ref name=":2" /><ref name=":6" />
| rowspan="145" |
[[File:†Allenypterus montanus Unt Karbon Bear Gulch Montana USA Ch927.jpg|thumb|150px|''[[Allenypterus|Allenypterus montanus]]'']]
[[File:†Caridosuctor populosum Unt Karbon Bear Gulch USA Ch1056.jpg|thumb|150px|''[[Caridosuctor|Caridosuctor populosum]]'']]
|-
|''[[Allenypterus]]''
|''A. montanus''
|An unusual [[Hadronectoridae|hadronectorid]] [[actinistia]]n (early [[coelacanth]])<ref name=":14">{{Cite journal|last1=Lund|first1=Richard|last2=Lund|first2=Wendy|date=1984|title=New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (U.S.A.)|journal=Geobios|volume=17|issue=2|pages=237–244|doi=10.1016/s0016-6995(84)80145-x|issn=0016-6995}}</ref><ref name=":15">{{Cite journal|last1=Lund|first1=Richard|last2=Lund|first2=Wendy Laurie|date=1985|title=Coelacanths from the Bear Gulch Limestone (Namurian) of Montana and the evolution of the Coelacanthiformes|url=https://www.biodiversitylibrary.org/page/52293861#page/219/mode/1up|journal=Bulletin of Carnegie Museum of Natural History|volume=25|pages=1–74|doi=10.5962/p.228604 |s2cid=251487945 |doi-access=free}}</ref>
|-
|''[[Caridosuctor]]''<ref name=":14" />
|''C. populosum''
|A [[Rhabdodermatidae|rhabdodermatid]] actinistian<ref name=":15" />
|-
|''[[Hadronector]]''<ref name=":14" />
|''H. donbairdi''
|A hadronectorid<ref name=":15" />
|-
|''[[Hardistiella]]''<ref name=":34">{{Cite journal|last1=Janvier|first1=Philippe|last2=Lund|first2=Richard|date=1983|title=''Hardistiella montanensis'' n. gen. et sp. (Petromyzontida) from the Lower Carboniferous of Montana, with remarks on the affinities of the lampreys|journal=Journal of Vertebrate Paleontology|volume=2|issue=4|pages=407–413|doi=10.1080/02724634.1983.10011943|issn=0272-4634}}</ref>
|''H. montanensis''
|One of the oldest known petromyzontiforms ([[lamprey]]s)<ref>{{Cite journal|last1=Janvier|first1=Philippe|last2=Lund|first2=Richard|last3=Grogan|first3=Eileen D.|date=2004-09-10|title=Further consideration of the earliest known lamprey, ''Hardistiella montanensis'' Janvier and Lund, 1983, from the Carboniferous of Bear Gulch, Montana, U.S.A.|journal=Journal of Vertebrate Paleontology|volume=24|issue=3|pages=742–743|doi=10.1671/0272-4634(2004)024[0742:fcotek]2.0.co;2|s2cid=131704031 |issn=0272-4634}}</ref>
|-
|''[[Lochmocercus]]''<ref name=":14" />
|''L. aciculodontus''
|An indeterminate actinistian<ref name=":15" />
|-
|''[[Polyosteorhynchus]]''<ref name=":14" />
|''P. beargulchensis''
|A hadronectorid<ref name=":15" />
|-
|''[[Squirmarius]]''
|''S. testai''
|A [[Cyclostomi|cyclostome]], named to replace ''Nemavermes'' after the holotype was found to be a proboscis of ''Tullimonstrum''. <ref name="Nemavermes">{{cite journal |last1=McCoy |first1=Victoria E. |last2=Wittry |first2=Jack |last3=Sadabadi |first3=Hamed |last4=Mayer |first4=Paul |title=A reappraisal of Nemavermes mackeei from the Mazon Creek fossil site expands Carboniferous cyclostome diversity |journal=Journal of Paleontology |date=September 2023 |volume=97 |issue=5 |pages=1116–1132 |doi=10.1017/jpa.2023.72 |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/reappraisal-of-nemavermes-mackeei-from-the-mazon-creek-fossil-site-expands-carboniferous-cyclostome-diversity/3DC5E415D26938218ECF81E411E2760D?utm_campaign=shareaholic&utm_medium=facebook&utm_source=socialnetwork |language=en |issn=0022-3360|doi-access=free }}</ref>
|-
|''[[Strepsodus]]''
|
|A [[Rhizodontida|rhizodont]]<ref name=":2" /><ref name=":6" />
|}

=== Arthropods ===
[[Arthropod]]s are diverse, the most abundant and speciose being various early [[Hoplocarida|hoplocarids]], relatives of modern stomatopods ([[mantis shrimp]]s).<ref name="FF85" /><ref name="J98" /> Other arthropods include an assortment of typical Carboniferous [[crustacean]]s,<ref name="SH78" /><ref name="FF85" /> rare [[xiphosura]]ns (horseshoe crabs),<ref name="S79Limulines" /> and a single "[[Synziphosurina|synziphosurine]]" (''[[Anderella]]'').<ref name=":33" /> [[Trilobite]]s, though common in adjacent formations, are practically absent in the Bear Gulch Limestone.
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''Arthropods of the Bear Gulch Limestone'''
|-
! Genus !! Species !!  Notes !! Images
|-
|''[[Aenigmacaris]]''<ref name="SH78" />
|''A. cornigerum''
|An [[Aeschronectida|aeschronectid]] hoplocarid<ref name="FF85" />
| rowspan="100" |
[[File:†Aenigmacaris cornigerum SCHRAM & HORNER 1979.jpg|thumb|150px|''[[Aenigmacaris|Aenigmacaris cornigerum]]'']]
[[File:20200924_Anderella_parva.png|thumb|150px|''[[Anderella|Anderella parva]]'']]
[[File:†Tyrannophontes acanthocercus Unt Karbon Bear Gulch Montana USA Ar886a.jpg|thumb|150px|''[[Daidal|Daidal (Tyrannophontes) acanthocercus]]'']]
[[File:†Dithyrocaris rolfei Unt Karbon Bear Gulch Montana USA Ar2547.jpg|thumb|150px|''[[Dithyrocaris|Dithyrocaris rolfei]]'']]
[[File:Ar1050 Perimecturus rapax Unt Karbon Bear Gulch Montana USA.jpg|thumb|150px|''[[Perimecturus|"Perimecturus" rapax]]'']]
|-
|''[[Anderella]]<ref name=":33">{{Cite journal|last1=Moore|first1=Rachel A.|last2=McKenzie|first2=Scott C.|last3=Lieberman|first3=Bruce S.|date=2007|title=A Carboniferous synziphosurine (Xiphosura) from the Bear Gulch Limestone, Montana, USA|url=https://mndi.museunacional.ufrj.br/aracnologia/Xiphosura/Moore%20et%20al%202007.pdf|journal=Palaeontology|language=en|volume=50|issue=4|pages=1013–1019|doi=10.1111/j.1475-4983.2007.00685.x|s2cid=59449700 |issn=1475-4983}}</ref>''
|''A. parva''
|The youngest known "[[Synziphosurina|synziphosurine]]" ( a group of [[xiphosura]]n-like [[Chelicerata|chelicerates]])
|-
|''[[Bairdops]]''
|''B. beargulchensis''<ref name="SH78">{{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>
|A possibly [[paraphyletic]] "[[Palaeostomatopoda|palaeostomatopod]]" (primitive hoplocarid), often considered a relative of ''[[Perimecturus]],<ref name="S79Archaeocaris">{{Cite journal|last=Schram|first=Frederick R.|date=1979|title=The genus ''Archaeocaris'', and a general review of the Paleostomatopoda (Hoplocarida: Malacostraca)|url=https://www.biodiversitylibrary.org/page/5784863#page/69/mode/1up|journal=Transactions of the San Diego Society of Natural History|volume=19|issue=5|pages=57–66}}</ref>''<ref name="J98">{{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><ref name="S07">{{Cite journal|last=SCHRAM|first=FREDERICK R.|title=Paleozoic Proto-Mantis Shrimp Revisited|date=2007-09-01|journal=Journal of Paleontology|volume=81|issue=5|pages=895–916|doi=10.1666/pleo05-075.1|s2cid=85606671|issn=0022-3360}}</ref> and at one point a [[junior synonym]] of ''[[Tyrannophontes]]''<ref name="FF85">{{Cite journal|last1=Factor|first1=David F.|last2=Feldmann|first2=Rodney M.|date=11 October 1985|title=Systematics and paleoecology of malacostracan arthropods in the Bear Gulch Limestone (Namurian) of Central Montana|url=https://www.biodiversitylibrary.org/page/52403449#page/343/mode/1up|journal=Annals of Carnegie Museum|volume=54|issue=10|pages=319–356|doi=10.5962/p.330776 |s2cid=251522559 |doi-access=free}}</ref>
|-
|''[[Belotelson]]''
|''B. magister''
|A [[Belotelsonidae|belotelsonid]] shrimp<ref name="SH78" /><ref name="FF85" />
|-
|[[Concavicarida]] indet.
|
|An indeterminate concavicarid, possibly referable to ''[[Ankitokazocaris]]'' or ''[[Concavicaris]]''<ref>{{Cite journal|last=Schram|first=Frederick R.|date=2014-01-01|title=Family level classification within Thylacocephala, with comments on their evolution and possible relationships|url=https://brill.com/view/journals/cr/87/3/article-p340_7.xml|journal=Crustaceana|language=en|volume=87|issue=3|pages=340–363|doi=10.1163/15685403-00003289|issn=1568-5403}}</ref>
|-
|''[[Crangopsis]]''
|''C. eskdalensis''
|A rare aeschronectid hoplocarid<ref name="FF85" />
|-
|''[[Daidal]]<ref name="S07" />''
|''D. acanthocercus''
|An "[[Archaeostomatopoda|archaeostomatopod]]" (hoplocarid closely related to modern mantis shrimps), previously referred to ''[[Tyrannophontes|Tyrannophontes theridion]]''<ref name="SH78" /><ref name="FF85" /> and sometimes considered its own species of ''Tyrannophontes''.
|-
|''[[Dithyrocaris]]''
|''D. rolfei''<ref name="SH78" />
|A large [[Phyllocarida|phyllocarid]] shrimp<ref name="FF85" />
|-
|''[[Euproops]]''
|''E''. sp.
|A rare xiphosuran (early horseshoe crab)<ref name="S79Limulines">{{Cite journal|last=Schrams|first=Frederick R.|date=1979|title=Limulines of the Mississippian Bear Gulch Limestone of Central Montana, USA|url=https://www.biodiversitylibrary.org/page/5784863#page/81/mode/1up|journal=Transactions of the San Diego Society of Natural History|volume=19|issue=6|pages=67–74}}</ref>
|-
|[[Ostracod]]a indet.
|
|Indeterminate and very rare ostracods<ref name=":4" />
|-
|"''[[Paleolimulus]]''"
|''"P". longispinus''<ref name="S79Limulines" />
|A xiphosuran with uncertain classification<ref>{{Cite journal |last=Bicknell |first=Russell D. C. |last2=Naugolnykh |first2=Serge V. |last3=Birch |first3=Sienna A. |date=2020-10-03 |title=A reappraisal of Paleozoic horseshoe crabs from Russia and Ukraine |url=https://doi.org/10.1007/s00114-020-01701-1 |journal=The Science of Nature |language=en |volume=107 |issue=5 |pages=46 |doi=10.1007/s00114-020-01701-1 |issn=1432-1904}}</ref>
|-
|''"[[Perimecturus]]"''
|''"P." rapax''<ref name="SH78" />
|A possibly [[polyphyletic]] "palaeostomatopod" (primitive hoplocarid), often considered a relative of ''Bairdops<ref name="S79Archaeocaris" />''<ref name="FF85" /><ref name="J98" /><ref name="S07" />
|-
|''[[Sairocaris]]''
|''S. centurion''<ref name="SH78" />
|A probable phyllocarid shrimp<ref name="FF85" />
|-
|''[[Schramine]]''
|''S. montanaensis<ref name="S06">{{Cite journal|last1=Schram|first1=Frederick R.|last2=Boere|first2=Arjan C.|last3=Thomas|first3=Natalie|date=2006-01-05|title=Cycloidea of the Mississippian Bear Gulch Limestone of central Montana|journal=Contributions in Science|volume=504|pages=1–8|doi=10.5962/p.210567|s2cid=160017485|issn=0459-8113|doi-access=free}}</ref>''
|One of the oldest of the crab-like [[Cyclida|cycloid]] crustaceans,<ref>{{Cite journal|last=Dzik|first=Jerzy|date=2008|title=Gill structure and relationships of the Triassic cycloid crustaceans|journal=Journal of Morphology|volume=269|issue=12|pages=1501–1519|doi=10.1002/jmor.10663|pmid=18690662|s2cid=17617567|issn=1097-4687|doi-access=free}}</ref> previously considered a species of ''[[Halicyne]]''<ref name="S06" />
|-
|''[[Titanoprosoma]]''<ref name=":37">{{Cite journal |last=Bicknell |first=Russell D.C. |last2=Kimmig |first2=Julien |last3=Smith |first3=Patrick M. |last4=Torsten |first4=Scheyer |date=1 February 2024 |title=An enigmatic euchelicerate from the Mississippian (Serpukhovian) and insights into invertebrate preservation in the Bear Gulch Limestone, Montana |url=https://digitallibrary.amnh.org/items/e992136b-e9b4-4e49-9ef6-408f64cfebe2 |journal=American Museum Novitates |volume=4008 |pages=1–14}}</ref>
|''T. edgecombei''
|A simplified arthropod tentatively identified as a [[Euchelicerata|euchelicerate]].<ref name=":37" />
|}


=== Molluscs ===
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''[[Mollusc]]s of the Bear Gulch Limestone'''
|-
! Taxon !! Species !!  Notes !! Images
|-
|[[Bivalvia]] sp.
|
|Several unnamed or undescribed species of [[Bivalvia|bivalves]], including [[scallop]]-like (''[[Aviculopecten]]''?) and [[mussel]]-like (''[[Myalina]]''?) forms.<ref name="SH78" /> Some encrusting [[Pterioidea|pterioid]] bivalves (''[[Caneyella]]'', ''[[Ptychopteria]]'') have been found attached to strands of ''[[sargassum]]''-like brown algae.<ref name=":31">{{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/journals/journal-of-paleontology/article/abs/unique-bivalvealgae-life-assemblage-from-the-bear-gulch-limestone-upper-mississippian-of-central-montana/A3CCEA3C99F10D7E5954426E3332074C|journal=Journal of Paleontology|language=en|volume=63|issue=5|pages=578–581|doi=10.1017/S0022336000041214|s2cid=131030155 |issn=0022-3360}}</ref>
| rowspan="99" |
[[File:Reticycloceras sp Carboniferous Bear Gulch Montana USA Mo1832b.jpg|thumb|150px|''[[Reticycloceras|Reticycloceras sp.]]'']]
|-
|[[Cephalopod]]a sp.
|
|Various [[cephalopod]]s, which are locally abundant in the Bear Gulch Limestone. They include coiled [[nautiloid]]s (''[[Anthracoceras]]'', ''[[Epistroboceras]], [[Tylonautilus]]''),<ref name=":7" /><ref name=":10">{{Cite journal|last=Mapes|first=Royal H.|date=1987|title=Upper Paleozoic cephalopod mandibles: frequency of occurrence, modes of preservation, and paleoecological implications|url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/upper-paleozoic-cephalopod-mandibles-frequency-of-occurrence-modes-of-preservation-and-paleoecological-implications/BF5BD4D6D61942B203D9B8D1882C59DA|journal=Journal of Paleontology|language=en|volume=61|issue=3|pages=521–538|doi=10.1017/S0022336000028687|s2cid=133533107 |issn=0022-3360}}</ref> [[Orthocone|orthoconic]] (straight-shelled) nautiloids (''[[Reticycloceras]]''),<ref name=":10" /> [[Ammonoidea|ammonoids]] (''[[Fayettevillea]]'', ''[[Eumorphoceras]]'', ''[[Metadimorphoceras]]''),<ref name=":7" /><ref name=":32">{{Cite journal|last1=Mapes|first1=Royal H.|last2=Landman|first2=Neil H.|last3=Klug|first3=Christian|date=2019-03-01|title=Caught in the act? Distraction sinking in ammonoid cephalopods|journal=[[Swiss Journal of Palaeontology]]|language=en|volume=138|issue=1|pages=141–149|doi=10.1007/s13358-018-0176-7|s2cid=135122075|issn=1664-2384}}</ref> [[Octopodiformes|vampyropods]] ([[Syllipsimopodi]]),<ref name="Whalen_Landman">{{Cite journal |last1=Whalen |first1=C. D. |last2=Landman |first2=N. H. |year=2022 |title=Fossil coleoid cephalopod from the Mississippian Bear Gulch Lagerstätte sheds light on early vampyropod evolution |journal=Nature Communications |volume=13 |issue=1 |pages=Article number 1107 |doi=10.1038/s41467-022-28333-5 |pmc=8904582 |pmid=35260548 |doi-access=free}}</ref> and [[Coleoidea|coleoids]] (''[[Gordoniconus]]'', etc.).<ref name=":35">{{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|pmid=31372519|pmc=6668408|issn=2399-3642}}</ref><ref name=":36">{{Cite journal |last1=Whalen |first1=Christopher D. |last2=Landman |first2=Neil H. |date=2022-03-08 |title=Fossil coleoid cephalopod from the Mississippian Bear Gulch Lagerstätte sheds light on early vampyropod evolution |journal=Nature Communications |language=en |volume=13 |issue=1 |page=1107 |doi=10.1038/s41467-022-28333-5 |pmid=35260548 |pmc=8904582 |issn=2041-1723}}</ref><ref>{{Cite journal |last1=Klug |first1=C. |last2=Stevens |first2=K. |last3=Hoffmann |first3=R. |last4=Zatoń |first4=M. |last5=Clements |first5=T. |last6=Košťák |first6=M. |last7=Weis |first7=R. |last8=De Baets |first8=K. |last9=Lehmann |first9=J. |last10=Vinther |first10=J. |last11=Fuchs |first11=D. |year=2023 |title=Revisiting the identification of ''Syllipsimopodi bideni'' and timing of the decabrachian-octobrachian divergence |journal=Nature Communications |volume=14 |issue=1 |at=8094 |doi=10.1038/s41467-023-42842-x |pmc=10703834 |pmid=38062003 |doi-access=free}}</ref><ref>{{Cite journal |last1=Whalen |first1=C. D. |last2=Landman |first2=N. H. |year=2023 |title=Reply to: Revisiting the identification of ''Syllipsimopodi bideni'' and timing of the decabrachian-octobrachian divergence |journal=Nature Communications |volume=14 |issue=1 |at=8228 |doi=10.1038/s41467-023-42843-w |pmc=10716472 |pmid=38086818 |doi-access=free}}</ref>
|-
|[[Gastropoda]] sp.
|
|Unnamed or undescribed species of [[Gastropoda|gastropods]] (sea snails), which are only common in marginal facies<ref name=":1" />
|}

=== Worms ===
{| class="wikitable" align="center"
|- 
! colspan="3" align="center" | '''Worms of the Bear Gulch Limestone'''
|-
! Genus !! Species !!  Notes 
|-
|''[[Archisymplectes]]''
|''A. rhothon''
|A [[Nemertea|nemertine]] (ribbon worm)<ref name=":11">{{Cite journal|last=Schram|first=Frederick R.|date=1979|title=Worms of the Mississippian Bear Gulch Limestone of Central Montana, USA|url=https://www.biodiversitylibrary.org/page/5784863#page/125/mode/1up|journal=Transactions of the San Diego Society of Natural History|volume=19|issue=9|pages=107–120}}</ref>
|-
|''[[Astreptoscolex]]''
|''A. anasillosus''
|A [[Nephtyidae|nephtyid]] [[polychaete]] worm<ref name=":11" />
|-
|''[[Brochosogenys]]''
|''B. reidiae''
|A [[Kielanoprionidae|kielanoprionid]] polychaete<ref name=":12">{{Cite thesis|last=Thomas|first=Natalie|date=2004|title=The Taphonomy of a Carboniferous Lagerstatte: the Invertebrates of the Bear Gulch Limestone Member|url=https://leicester.figshare.com/articles/thesis/The_taphonomy_of_a_carboniferous_lagerst_tte_the_invertebrates_of_the_Bear_Gulch_Limestone_Member/10164188/1|website=University of Leicester thesis|type=thesis}}</ref>
|-
|''[[Carbosesostris]]''<ref name=":11" />
|''C. megaliphagon''
|A [[Goniadidae|goniadid]] polychaete
|-
|''[[Deuteronectanebos]]''<ref name=":11" />
|''D. papillorum''
|An indeterminate worm
|-
|''[[Phiops]]''<ref name=":11" />
|''P. aciculorum''
|A [[Lumbrineridae|lumbrinerid]] polychaete
|-
|''[[Ramesses (genus)|Ramesses]]''<ref name=":11" />
|''R. magnus''
|An indeterminate polychaete
|-
|''[[Soris (genus)|Soris]]''<ref name=":11" />
|''S. labiosus''
|An indeterminate polychaete
|-
|''[[Symmetroprion]]''
|''S''. sp.
|A [[Symmetroprionidae|symmetroprionid]] polychaete<ref name=":12" />
|}

===Other invertebrates===
{| class="wikitable" align="center"
|- 
! colspan="4" align="center" | '''[[Invertebrate]]s of the Bear Gulch Limestone'''
|-
! Genus / Taxon !! Species !!  Notes !! Images
|-
|[[Brachiopod]]a sp.
|
|Several unnamed or undescribed species of brachiopods, including [[Productida|productids]], [[Spiriferida|spiriferids]], ''[[Orbiculoidea]]'', and ''[[Lingula (brachiopod)|Lingula]].''<ref name="SH78" /> Small and large spiny productids are common encrusters on other organisms.<ref name=":1" />
| rowspan="107" |
[[File:Bear gulch montana sea urchin.jpg|thumb|150px|An unnamed sea urchin]]
[[File:Typhloesus_fossils_2022.jpg|thumb|150px|''[[Typhloesus|Typhloesus wellsi]]'']]
|-
|[[Bryozoa]] sp.
|
|Very rare and undescribed encrusting bryozoans, including ''[[Pycnopora|Pycnopora regularis]]'' and ''[[Discretella|Discretella robusta]].''<ref name=":7" />
|-
|[[Conodont]]a sp.
|
|Various conodonts, only recovered from [[coprolite]]s or gut content of ''Typhloesus''. May include ''[[Lochriea]]'', ''[[Kladognathus]]'', ''[[Gnathodus]]'', and ''[[Cavusgnathus]].''<ref name=":13">{{Cite journal|last=Conway Morris|first=Simon|date=1990-04-12|title=''Typhloesus wellsi'' (Melton and Scott, 1973), a bizarre metazoan from the Carboniferous of Montana, U. S. A|url=https://royalsocietypublishing.org/doi/abs/10.1098/rstb.1990.0102|journal=Philosophical Transactions of the Royal Society of London. B, Biological Sciences|volume=327|issue=1242|pages=595–624|doi=10.1098/rstb.1990.0102|bibcode=1990RSPTB.327..595M}}</ref><ref>{{Cite journal|last=Purnell|first=Mark A.|date=1993-04-01|title=Feeding mechanisms in conodonts and the function of the earliest vertebrate hard tissues|url=https://doi.org/10.1130/0091-7613(1993)0212.3.CO;2|journal=Geology|volume=21|issue=4|pages=375–377|doi=10.1130/0091-7613(1993)021<0375:FMICAT>2.3.CO;2|bibcode=1993Geo....21..375P|issn=0091-7613}}</ref>
|-
|[[Echinoderm]]ata sp.
|
|Various rare echinoderms, including unnamed or undescribed species of [[crinoid]]s, [[echinoids]] (sea urchins), [[ophiuroids]] (brittle stars), and [[Asteroidea|asteroids]] (sea stars). The only moderately common echinoderm is ''[[Lepidasterella|Lepidasterella montanensis]]'', a many-armed sea star.<ref>{{Cite journal|last=Welch|first=James R.|date=1984|title=The Asteroid, ''Lepidasterella montanensis'' n. sp., from the Upper Mississippian Bear Gulch Limestone of Montana|journal=Journal of Paleontology|volume=58|issue=3|pages=843–851|jstor=1304921|issn=0022-3360}}</ref>
|-
|''[[Paraconularia]]''
|''P. subulata''
|A [[Conulariida|conulariid]]<ref>{{Cite journal|last1=Babcock|first1=Loren E.|last2=Feldmann|first2=Rodney M.|date=1986|title=Devonian and Mississippian conulariids of North America. part B. ''Paraconularia, Reticulaconularia,'' New Genus, and organisms rejected from Conulariida.|url=https://www.biodiversitylibrary.org/page/52460816#page/431/mode/1up|journal=Annals of Carnegie Museum|volume=55|pages=411–479|doi=10.5962/p.215204 |s2cid=251525208 |doi-access=free}}</ref>
|-
|[[Sponge|Porifera]] sp.
|
|Various rare to locally abundant sea sponges, including [[hexactinellid]]s, ''[[Norfordia]]'', and ''[[Belemnospongia]]''.<ref name=":12" /> By far the most abundant is ''[[Arborispongia|Arborispongia delicatula]]'', a ramose (branching) sponge which serves as the foundation for complex reef-like ecosystems.<ref name=":1" />
|-
|''[[Sphenothallus]]''
|
|A common but enigmatic organism with a strand-like tubular shape, possibly represented by multiple species. May be related to [[cnidaria]]ns or conulariids.<ref>{{Cite journal|last1=Iten|first1=Heyo Van|last2=Cox|first2=Robt S.|last3=Mapes|first3=Royal H.|date=1992|title=New data on the morphology of ''Sphenothallus'' Hall: implications for its affinities|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1502-3931.1992.tb01378.x|journal=Lethaia|language=en|volume=25|issue=2|pages=135–144|doi=10.1111/j.1502-3931.1992.tb01378.x|hdl=2027.42/73676|issn=1502-3931|hdl-access=free}}</ref>
|-
|"Square objects"
|
|Very common but enigmatic barrel-shaped [[plankton]]ic organisms, possibly [[salp]]s or cnidarians
|-
|''[[Typhloesus]]''<ref name=":13" />
|''T. wellsi''
|An unusual swimming invertebrate originally mistaken for large conodonts ("''Lochriea wellsi''", "''Scottognathus elizabethi''") with complex jaws. Conodont elements are now understood to be gut content.<ref name=":13" /> Often interpreted as a [[deuterostome]], but recently reinterpreted as a [[heteropod]]-like [[Gastropoda|gastropod]].<ref>{{Cite journal |last1=Conway Morris |first1=Simon |last2=Caron |first2=Jean-Bernard |title=A possible home for a bizarre Carboniferous animal: is Typhloesus a pelagic gastropod? |journal=Biology Letters |year=2022 |volume=18 |issue=9 |page=20220179 |doi=10.1098/rsbl.2022.0179 |pmc=9489302 |pmid=36126687}}</ref>
|}

==See also==
*[[List of types of limestone]]
{{Commons category|Bear Gulch Limestone|position=left}}

==External links==
*[https://web.archive.org/web/20120204055726/http://www.sju.edu/research/bear_gulch/  Personal website of Richard Lund and Eileen Grogan, exhibiting the Bear Gulch Limestone and its fossils]
*[https://archive.org/details/prehistoric-sharks-2007-discovery-channel 1998 Discovery Channel documentary "Prehistoric Sharks", featuring a segment on Bear Gulch (4:36-16:13)]
*[https://www.youtube.com/watch?v=l2i6sbNimf0&t=737s&ab_channel=wttwchicago Segment of the 2020 PBS documentary "Prehistoric Road Trip", focusing on the Bear Gulch fossils (12:16-22:53)]

==References==
{{reflist}}

[[Category:Carboniferous Montana]]
[[Category:Carboniferous paleontological sites]]
[[Category:Lagerstätten]]
[[Category:Limestone formations of the United States]]
[[Category:Mississippian United States]]
[[Category:Serpukhovian]]
[[Category:Paleontology in Montana]]
[[Category:Carboniferous System of North America]]