bathyuriscus is an extinct genus of cambrian trilobite .

it was a nektobenthic predatory carnivore .

the genus bathyuriscus is endemic to the shallow seas that surrounded laurentia .

its major characteristics are a large forward-reaching glabella , pointed pleurae or pleurae with very short spines , and a medium pygidium with well-impressed furrows .

complete specimens have never reached the size of 7 cm predicted by the largest pygidium found .

bathyuriscus is often found with the free cheeks shed , indicating a moulted exoskeleton .

an average specimen will in addition have a furrowed glabella , crescent-shaped eyes , be semi-circular in overall body shape , have 7 to 9 thoracic segments , and a length of about 1.5 inches .

bathyuriscus

bathyuriscus <EOT> burgess shale and vicinity : bathyuriscus adaeus walcott , 1916 , from several localities higher in the bathyuriscus - elrathina zone on mount stephen , mount odaray , and park mountain .

bathyuriscus rotundatus ( figures 4 and 5 ) illustrated by rominger ( 1887 ) as embolimus rotundata .

other deposits : other species of bathyuriscus have been described from numerous localities elsewhere in the cambrian of north america .

species of elrathina , along with those of the corynexochid bathyuriscus , were found to be very abundant in a narrow interval of middle cambrian rocks throughout western north america , forming the basis of the bathyuriscus - elrathina zone erected by charles deiss ( 1940 ) .

bathyuriscus rotundatus was first described in the same 1887 publication as several other important mount stephen trilobites . carl rominger initially used the name embolimus rotundata for partial specimens of this trilobite , and named a second similar species in his collection embolimus spinosa ( now known as zacanthoides romingeri ) . in 1908 , walcott revised rominger ' s original species name to yield the combination bathyuriscus rotundatus , still in use today ( walcott , 1908 ) . along with the co - occurring elrathina cordillerae , b . rotundatus is a signature fossil for the middle cambrian bathyuriscus - elrathina zone in the southern canadian rockies .

bathyuriscus – a variation of the earlier trilobite genus name bathyurus , originally based on the greek bathys , “deep , ” and the greek oura , “tail , ” thus , a trilobite with a deep tail .

bathyuriscus rotundatus was a mobile epibenthic trilobite . because we have no direct evidence of limb structure , its feeding habits are uncertain . it may have been a deposit feeder and opportunistic scavenger . like ogygopsis , bathyuriscus may occur as fully intact individuals ( probably carcasses ) , with the free cheeks missing , inverted , or rotated ( presumed moults ) , and as scattered pieces . some show evidence of healed injuries that may be predation scars ( rudkin , 2009 ) .

trilobite ( bathyuriscus rotundatus ) found in the burgess shale . this fossil dates from the middle cambrian period , about 505 million years ago . burgess pass . yoho national park . british columbia , canada . ( collection of the colorado school of mines geology museum . golden , colo . )

this is a large , 3 inch long bathyuriscus fimbiatus trilobite from the marjum formation of utah . it ' s a molt like about 99 . 9 % of them , but it ' s in about the top 1 % size wise . i collected this from a private lease in the house range , several years ago .

description : this is a rare treat for the spence shale and utah specialist trilobite collector , a bathyuriscus brighamensis . this one is complete and in good condition . the only flaw is a bit of the pygidium is missing . it is the first one to i have ever encountered . considering what a hard place it is to collect , i don’t expect to see another soon .

elrathina has been used as an index fossil for a medial middle cambrian interval termed the bathyuriscus - elrathina zone , and despite its unsettled synonymization with ptychoparella and the discovery of one species of elrathina in the distinctly older albertella zone ( see palmer , 1968 ; palmer and halley , 1979 ; and discussion under elrathina below ) , this itagnostus - elrathina - elrathia assemblage indicates an interval widely correlatable within laurentia in the upper part of the as yet unnamed cambrian stage 5 . however , the occurrence of the assemblage in north greenland is problematic in that it overlies strata that have been assigned to the bolaspidella zone , which generally overlies the bathyuriscus - elrathina zone . however , these zones appear to be partly coeval , and differences in the stratigraphic assignment can be explained by different biofacies .

all material referred to this taxon was collected from the talus of slopes of the tulip beds locality ( formerly s7 [ 19 ] ) , mount stephen , yoho national park , british columbia , canada . the lithology indicates that these specimens come from the campsite cliff shale member of the burgess shale formation , bathyuriscus – elrathina biozone ( cambrian , series 3 , stage 5 ) [ 20 ] .

this is a little plate of agnostid trilobites . it ' s both the posative and negative sides of the plate . on this plate , the largest agnostid is 7 mm ( just over 1 / 4 " ) , the smallest is 2 mm ( . 08 " ) . on the plate is also a cephalon of a bathyuriscus fimbriatus trilobite formation : wheeler shale age : cambrian location : house range , utah

specimen count 1 site number 145 record last modified 5 jul 2018 geological age paleozoic - cambrian - upper / late stratigraphy stephen fm nmnh - paleobiology dept . common name trilobite taxonomy animalia arthropoda trilobita collector walcott burling see more items in paleogeneral types : arthropoda arthropoda trilobita type paleobiology place sauk county , british columbia , canada collection date 1907 type citation walcott . 1916 . smithsonian misc . colln . 64 ( n . 5 ) : 346 , unfig . usnm number pal339012 published name bathyuriscus rotundatus ( rominger )

numerous specimens of this new , undescribed species are known from the burgess shale of the walcott quarry on fossil ridge in the yoho national park , british columbia , where is it known from mass assemblages such as a cluster with more than 40 specimens reposited as rom 59549 ( burgess shale fossil gallery , < urltoken > [ accessed october 2016 ] ) . these occurrences are from the bathyuriscus - elrathina zone in the stephen formation . however , the same species is also known from the trilobite beds at mount stephen , which belongs to the glossopleura zone of the stephen formation , so that a distinct stratigraphic separation from e . cordillerae does not exist .

itagnostus subhastatus n . sp . is closely related to the well - known species itagnostus interstrictus ( white , 1874 ) , which is primarily distributed in the bathyuriscus fimbriatus and bolaspidella contracta subzones of the bolaspidella zone of utah ( robison , 1964 ) . subsequently , i . interstrictus was described from the p . atavus zone of alaska and the ptychagnostus punctuosus zone in the cow head group , newfoundland , with material assigned to the species from the tomagnostus fissus and liostracus allachjunensis zones of the lena river basin , siberia ( palmer , 1968 ; egorova et al . , 1982 ; young and ludvigsen , 1989 ; westrop et al . , 1996 ) . itagnostus subhastatus is distinguished from i . interstrictus , however , by a set of minor differences that particularly include the slightly more slender posterior glabellar lobe ; differences in the morphology of the thoracic segments ; a narrower and distinctly more pointed pygidial axis ; smaller and almost rudimentary spines on the pygidial border ; and a wider doublure ( compare robison 1964 , pl . 82 , figs . 1–15 , 18 ) .

palmer and peel ( 1979 ) noted that the occurrence of the ekspedition bræ formation fauna with elrathina was problematic because a bolaspidella fauna is present in stratigraphically older strata in north greenland . this latter fauna occurs in the uppermost beds of the henson gletscher formation in lauge koch land and has been assigned to the ptychagnostus gibbus zone ( cambrian stage 5 ) ( robison , 1988 , 1994 ; babcock , 1994 ; blaker and peel , 1997 ; ineson and peel , 1997 ) . palmer and peel ( 1979 ) also recorded an apparent bolaspidella zone fauna of peronopsis , olenoides , bolaspidella , bathyuriscus , elrathina , ehmania , and alokistocare from the base of the ekspedition bræ formation at the head of henson gletscher ( eastern side ) . robison ( in peel and streng , 2015 ) dated an equivalent horizon in freuchen land , about 35 km to the west , to the ptychagnostus atavus zone , which is the basal zone of the drumian stage ( cambrian series 3 , stage 6 ) . the latter zone is equivalent to the lower part of the bolaspidella zone ( babcock et al . , 2007 ) .

other similar species include peronopsis ( p . ) scutalis ( salter in hicks , 1872 ) from scandinavia , p . ( svenax ) egenus ( resser and endo , 1937 ) from manchuria , and quadragnostus columbiensis ( rasetti , 1951 ) from the bathyuriscus - elrathina zone of the canadian rockies . peronopsis ( p . ) scutalis and p . ( s . ) egenus are best distinguished by posterolateral thickenings on the pygidial border , which appear similar to short spines . in addition to the absence of distinct spines on the border , they are differentiated by a decidedly thickened pygidial border , a more strongly extended posterior glabellar lobe , and in a narrowly incised cephalic border furrow . by contrast , p . columbiensis has a slightly bent transglabellar furrow , small basal lobes , marginal structures in the relatively narrow pygidial rhachis , and short postaxial space . itagnostus subhastatus is furthermore distinguished from these species by the more hastate shape of its pygidial rhachis , more subcircular cephala and pygidia , and a relatively longer glabella . it should be noted that the studied material from the ekspedition bræ formation is preserved in full relief or almost full relief , whereas material of the siberian and manchurian species is often flattened . these differences in the preservation , however , do not affect the discussed differences .

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trilobites are extinct euarthropods , probably stem lineage representatives of the mandibulata , which includes crustaceans , myriapods , and hexapods ( scholtz and edgecombe , 2006 ) .

rotundatus – from the latin rotundus , “round , ” presumably alluding to the rounded outline of the dorsal shield .

type status under review – ummp 4884 ( 9 specimens ) , university of michigan museum of paleontology , ann arbor , michigan , usa .

the trilobite beds and other localities on mount stephen . fossil ridge in sections stratigraphically below the walcott quarry .

hard parts : adult dorsal exoskeletons may be up to 5 cm long and are narrowly oval in outline , with a semicircular cephalon , a thorax of nine segments ending in blade - like tips with short spines , and a semicircular pygidium without spines .

the long glabella reaches almost to the anterior cephalic border ; the posterior portion is narrow and parallel - sided , while the anterior third expands rapidly forward . there are four pairs of lateral glabellar furrows , with the two front pairs angled forward and the posterior pair directed obliquely back . the eyes are relatively long and lie close to the glabella . broad free cheeks are extended back into short genal spines . the pygidium is slightly smaller than the cephalon , with a well - defined narrow axial lobe of five rings and a terminal piece ; four pairs of pygidial ribs are usually visible . the exoskeleton is mostly smooth externally , but very well preserved specimens may show faint anastomosing ridges on the free cheeks .

extremely common in the mount stephen trilobite beds , where it rivals ogygopsis klotzi in abundance .

rasetti , f . 1951 . middle cambrian stratigraphy and faunas of the canadian rocky mountains . smithsonian miscellaneous collections , 116 ( 5 ) : 1 - 277 .

rominger , c . 1887 . description of primordial fossils from mount stephens , n . w . territory of canada . proceedings of the academy of natural sciences of philadelphia , 1887 : 12 - 19 .

rudkin , d . m . 2009 . the mount stephen trilobite beds , pp . 90 - 102 . in j . - b . caron and d . rudkin ( eds . ) , a burgess shale primer - history , geology , and research highlights . the burgess shale consortium , toronto .

scholtz , g . and edgecombe , g . d . 2006 . the evolution of arthropod heads : reconciling morphological , developmental and palaeontological evidence . development genes and evolution , 216 : 395 - 415 .

walcott , c . d . 1888 . cambrian fossils from mount stephens , northwest territory of canada . american journal of science , series 3 : 163 - 166 .

walcott , c . d . 1908 . mount stephen rocks and fossils . canadian alpine journal , 1 : 232 - 248 .

walcott , c . d . 1916 . cambrian geology and paleontology iii . cambrian trilobites . smithsonian miscellaneous collections , 64 ( 5 ) : 303 - 456 .

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description : coming from the cambrian marjum formation deposits of millard county , utah this is a fine example of bathyuruiscus fimbriatus . unlike many seen , the librigenae are tightly attached , and this one has both the part and counterpart preserved in fine detail .

description : coming from the cambrian spence shale of utah this is a fine example of the trilobite bathyuruiscus wasatchensis . resser described this and numerous other species from the locality in 1939 ; walcott also described many in the early part of the 20th century .

description : coming from the cambrian marjum formation deposits of millard county , utah this is a fine example of bathyuruiscus fimbriatus . unlike many seen , the librigenae are tightly attached , and this one misses only a small portion of the glabella .

size : trilobite is 7 / 8” in length on a 5 ½ x 3 ¾” plate .

this fossil comes from the george lee collection of southern california . mr . lee accumulated an entire warehouse full of fossils over thirty - five years of self - collecting and purchasing . most of the fossils were acquired during the 1960s through the mid 1990s . unfortunately , for we collectors , many of these sites and areas are no longer available for collecting . therefore , many of my offerings are of special importance , as they are now rarely available to the public . since mr . lee’s death , a few years ago , the collection has slowly been liquidated . this fossil came from one of the last available batches sold .

elrathina cordillerae ( figure 7 ) illustrated by rominger ( 1887 ) as conocephalites cordillerae .

cordillerae – in reference to the western cordillera ( canadian rocky mountain ranges ) , derived from the spanish cordilla , the diminutive of cuerda , meaning “cord . ”

type status under review – ummp 4883 ( 6 specimens ) , university of michigan museum of paleontology , ann arbor , michigan , usa .

burgess shale and vicinity : elrathina parallela , e . brevifrons , e . spinifera , and e . marginalis have been described from similar stratigraphic horizons at nearby sites on mount field , mount stephen , and mount odaray .

other deposits : other species of elrathina have been reported from the cambrian of north america and greenland .

the walcott quarry on fossil ridge . the trilobite beds and additional localities on mount stephen .

e . cordillerae was originally described under the genus name conocephalites in rominger ' s 1887 publication on trilobites from mount stephen . in 1888 walcott reallocated the species to ptychoparia where it remained until charles resser , walcott ' s former assistant at the united states national museum , established the new replacement genus elrathina ( resser , 1937 ) . other workers have subsequently suggested that elrathina is indistinguishable from ptychoparella ( see blaker and peel , 1997 ) .

hard parts : adult dorsal exoskeletons average about 2 cm long . the semicircular cephalon is about one - third the length of the entire dorsal shield , bordered by a well - defined narrow rim , and with rounded genal angles . weak transverse eye ridges extend to the small eyes , which are located just forward of cephalic mid - length . the slightly anteriorly narrowing glabella is rounded in front and exhibits three pairs of shallow lateral furrows ; the pre - glabellar field is about the same width as the narrow anterior rim . the long , tapering thorax with a narrow axial lobe contains between 17 and 19 straight - sided segments , flexed gently downwards a short distance from the rounded tips . the tiny elliptical pygidium usually features two segments .

unmineralized anatomy : rare specimens from the walcott quarry on fossil ridge retain tantalizing evidence of soft parts , including a pair of slender uniramous antennae , followed by very delicate looking biramous limbs beneath the cephalon , thorax and pygidium . these and other individuals of e . cordillerae are occasionally associated with a dark stain adjacent to the exoskeleton , presumably representing fluidized decay products .

relatively common on fossil ridge and locally very abundant in the walcott quarry , where it represents about 25 % of all trilobites collected ( caron and jackson , 2008 ) .

like similar - looking ptychoparioid trilobites , e . cordillerae may be interpreted as a fully mobile , epibenthic deposit ( particle ) feeder adapted to very low oxygen levels .

blaker , m . r . and j . s . peel . 1997 . lower cambrian trilobites from north greenland . meddeleser om grønland , geoscience , 35 , 145 p .

caron , j . - b . and d . a . jackson . 2008 . paleoecology of the greater phyllopod bed community , burgess shale . palaeogeography , palaeoclimatology , palaeoecology , 258 : 222 - 256 .

deiss , c . 1940 . lower and middle cambrian stratigraphy of southwestern alberta and southeastern british columbia . bulletin of the geological society of america , 51 : 731 - 794 .

rasetti , f . 1951 . middle cambrian stratigraphy and faunas of the canadian rocky mountains . smithsonian miscellaneous collections , 116 ( 5 ) : 277 p .

resser , c . e . 1937 . third contribution to nomenclature of cambrian trilobites . smithsonian miscellaneous collections , 95 ( 22 ) : 29 p .

rudkin , d . m . 1989 . trilobites with appendages from the middle cambrian stephen formation of british columbia . 28th international geological congress , washington , d . c . july 9 - 19 , 1989 . abstracts : 2 - 729 .

scholtz , g . and g . d . edgecombe . 2006 . the evolution of arthropod heads : reconciling morphological , developmental and palaeontological evidence . development genes and evolution , 216 : 395 - 415 .

walcott , c . 1918 . cambrian geology and paleontology iv . appendages of trilobites . smithsonian miscellaneous collections , 67 ( 4 ) : 115 - 216 .

walcott , c . d . 1924 . cambrian and lower ozarkian trilobites . smithsonian miscellaneous collections , 75 ( 2 ) : 53 - 60 .

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this article has been cited by the following publications . this list is generated based on data provided by crossref .

zeng , han zhao , fangchen yin , zongjun and zhu , maoyan 2017 . appendages of an early cambrian metadoxidid trilobite from yunnan , sw china support mandibulate affinities of trilobites and artiopods . geological magazine , vol . 154 , issue . 06 , p . 1306 .

peel , john s . 2017 . the oldest pelmatozoan encrusted hardground and holdfasts from laurentia ( cambrian series 2–3 ) . gff , vol . 139 , issue . 3 , p . 195 .

) north america with the framed outcrop area in north greenland ( enlarged in fig . 1 . 3 ) ; (

) henson gletscher / j . p . koch fjord and løndal areas showing sample localities ( ggu 225501 and ggu 255720 ) of the ekspedition bræ formation .

fauna from the ekspedition bræ formation . composition of the entire fauna ( top ) and composition of the trilobite species for exoskeletons only ( bottom ) .

) mguh 30906 , pygidium . dorsal views if not stated otherwise . scale bars = 1 mm .

resser , 1937b , plaster cast of holotype in the museum of comparative zoology , cambridge , mass . , usnm 65009 , carapace without librigenae , parker slate , parker quarry , georgia . scale bars = 5 mm .

zone , stephen formation , trilobite beds , mount stephen , british columbia ; length of specimen 19 . 5 mm ; (

zone , stephen formation , trilobite beds , mount stephen , b . c . ; (

) usnm 65518a , incomplete dorsal carapace ; stephen formation , mount stephen , b . c . ( original of walcott , 1918 , pl . 21 , fig . 4 ) ; (

) usnm 65518g , incomplete dorsal carapace with detached librigenae ; stephen formation , mount stephen , b . c . ; (

) usnm 65518f , incomplete dorsal carapace with detached librigenae ; stephen formation , mount stephen , b . c . ; note strongly curved posterior branch of suture ; ×2 . 7 ; (

) under lot usnm 17831 , posterior part of thorax and pygidium ; stephen formation , mount stephen , b . c . ; original specimen stored with plaster and gutta - percha casts with the collection number provided by resser ( 1937a ) as characterizing the “holotype ; ” ×2 . 3 ; (

rasetti , 1951 ; usnm 116279 , holotype ( rasetti , 1951 , pl . 33 , fig . 20 ) , incomplete dorsal carapace without librigenae ; stephen formation , mount stephen , b . c . all scale bars = 5 mm .

) paratype , mguh 30913 , latex cast of late meraspid cranidium , slightly oblique view . all scale bars = 1 mm , except in fig . 7 . 1 .

n . sp . distribution of the larger tubercles on the cranidium marked by dots . note the roughly bilaterally symmetrical arrangement . magnification approximately×10 .

) close - up of fig . 9 . 8 , showing minute wrinkles in the occipital furrow and surface ornamentation ; (

) paratype , mguh 30932 , cranidium with fractures . dorsal views . scale bars = 1 mm .

) close - up of fig . 11 . 1 showing muscle scars on the glabella and eye ridge ; (

) close - up of fig . 11 . 5 , with muscle scars on the glabella , radial caeca on frontal area , bifid eye ridge , and punctate surface of the internal mold ; (

) paratype , mguh 30942 , dorsal carapax without librigenae , dorsal view ; scale bar = 5 mm . (

) paratype , mguh 30948 , incomplete pygidium , dorsal view . scale bars = 1 mm , except for fig . 11 . 9 and 11 . 13 .

n . sp . reconstruction of the muscle scar pattern seen on the glabella .

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the richly fossiliferous ekspedition bræ formation of north greenland yields a typical oligospecific fossil assemblage with well - preserved trilobites , helcionelloids , and lingulate brachiopods . the trilobites include

zone as known from the cordilleran regions of laurentia . excellent preservation allows a detailed assessment of the prosopon and elucidates aspects of the ontogenetic development of

the ekspedition bræ formation forms part of the northward prograding brønlund fjord group and was deposited during a lowstand of sea level ( surlyk and ineson , 1987 ; higgins et al . , 1991 ; ineson and peel , 1997 ) . it was named after a small glacier flowing east into the head of j . p . koch fjord in lauge koch land and crops out in southern freuchen land , lauge koch land , and western peary land , north greenland ( fig . 1 ) . the formation consists mainly of pale - weathering , thin - bedded , dark - gray lime mudstones and skeletal wackestones , interbedded with gray - green calcareous mudstones that form distinctive recessive , gray - weathering slopes between cliff - forming formations below and above ( ineson and peel , 1997 ) . it attains a thickness of 82 m at its type locality south of the snout of ekspedition bræ , but thins to the west and east , being only 30 m thick on the eastern side of j . p . koch fjord and in løndal ( fig . 1 ) . despite the considerable thinning , the lithological composition remains constant , although the argillite content decreases to the south and increases to the west ( ineson and peel , 1997 ) .

most of the available material was picked from the talus - covered outcrops . preservation of the fossils is generally excellent , but usually affected by subrecent diagenesis and weathering . ggu sample 225501 ( collected on 20 june 1979 ) consists of slabs of thin ( several millimeters to 3 cm thick ) , platy , dark - gray lime mudstone with occasional fossil shells or sclerites floating in the matrix without grain support . the planar surfaces are pale and often weathered to show the typical epikarstic rough exterior of rocks exposed for some time under arctic climate . the sample was collected from the middle part of the formation at its type section . ggu sample 225720 ( collected on 16 july 1979 ) is very similar lithologically to ggu sample 225501 , but from the western side of løndal . the slabs are from talus lying on the surface of the formation and originate from the middle part of the formation .

the trilobites preserved in the samples belong to only three genera and in total six species . all of the genera ( itagnostus , elrathina , and elrathia ) are well known and widely distributed over laurentia , whereas all of the species , perhaps except for itagnostus sp . cf . i . gaspensis , are new . all three genera co - occur , for example , in the pentagon shale–pagoda limestone interval in northwestern montana , u . s . a . ( deiss , 1939 ) , and the presence of two of the genera in association has been noted from most well - known coeval middle cambrian localities of laurentian north america , such as utah ( robison , 1964 ) , idaho ( resser , 1939 ) , the grand canyon region ( mckee and resser , 1945 ) , british columbia ( rasetti , 1951 ) , pennsylvania ( rasetti , 1965 ) , georgia ( schwimmer , 1989 ) , new york ( bird and rasetti , 1968 ) , and alaska ( palmer , 1968 ) .

macrofossils in the studied samples are typically concentrated on bedding planes . leaching of calcareous beds from several horizons within the formation has produced insoluble residues of small shelly fossils ( peel and streng , 2015 ) . articulated remains of trilobites form a high percentage of the species’ remains in the samples ( more than one - third for itagnostus subhastatus n . sp . , about two - thirds for elrathina aphrodite n . sp . , about four - fifths for elrathina athena n . sp . , slightly more than one - third for elrathina hera n . sp . , and only about 5 % for elrathia groenlandica n . sp . ) . most of the nearly complete exoskeletons lack librigenae and are thus carcasses that record the “olenid mode” of molting ( e . g . , clarkson et al . , 2003 ) , in which the librigenae separate from the cranidium to release the trilobite through the thus - generated anterior opening , leaving a carcass of attached sclerites on the sea floor . scattered isolated sclerites are sometimes vaguely accumulated into small clusters and then include fragmented remains ; they may result from the activities of scavengers , which , however , are not recorded by body or trace fossils . however , isolated librigenae are rare in close proximity to the rest of the exuviae .

the studied samples record a low - diversity assemblage of comparable composition with six trilobite , two acrotretoid , and one helcionelloid species in the macrofossil record . the composition , based on 109 specimens , is illustrated in figure 2 where the dominance of the three elrathina and the single elrathia species suggests their ecological fitness for the particular habitat conditions . in this respect , it should be emphasized that the unusual preservation and abundance of the well - known elrathia kingii in the wheeler formation of the house range , utah , has been interpreted as result of an opportunistic ecological strategy for living in an exaerobic zone ( gaines and droser , 2003 ) . a similar , but probably less strongly restricted habitat may be assumed for the sample horizons of the ekspedition bræ formation described herein , which may have forced the trilobites to similar strategies .

the abbreviation ggu indicates collections from greenland made under the auspices of grønlands geologiske undersøgelse ( geological survey of greenland , now a part of the geological survey of denmark and greenland ) . individual type or figured specimens are identified by mguh numbers and this material is deposited in the geological museum , copenhagen , part of the natural history museum of denmark . additional figured material is housed in the royal ontario museum ( rom ) , the university of michigan museum ( ummp ) , and the u . s . national museum of natural history ( usnm ) under the numbers given in the figure captions .

agnostus elkedrensis etheridge , 1902 ; from the middle cambrian of australia and siberia ( by original designation ) .

the comprehensive reappraisal of the peronopsis clade by naimark ( 2012 ) clarified a number of problems within the complex evolutionary group and demonstrated evolutionary pathways , but also illustrated deficiencies in the knowledge of morphology and the difficulties in the correct weighting of characters . these problems particularly affect the genus itagnostus , which was introduced by öpik ( 1979a , b ) as a subgenus of peronopsis hawle and corda , 1847 . laurie ( 2004 ) raised itagnostus to generic level , dramatically emending the concept and diagnosis , and placing the genus within the family spinagnostidae and subfamily doryagnostinae . naimark ( 2012 ) amply discussed the case and re - emended the genus . in addition , she discussed in detail problems resulting from both the inclusion of species such as peronopsis interstricta ( white , 1874 ) , and the unstable concept of itagnostus in respect to its phylogenetic relationship with euagnostus whitehouse , 1936 .

we follow herein the general concept of itagnostus sensu naimark ( 2012 ) and suggest that peronopsis interstricta should be placed within naimark’s morphogroup xiva , under itagnostus . the new species described below is similar to i . interstrictus , which has slightly larger pygidial spines . this character reinforces the placement among the species of itagnostus , although i . interstricta can be regarded as a transitional species between peronopsis ( svenax ) öpik , 1979a , b and itagnostus .

together with a number of other species of the peronopsidae , species of itagnostus have a median postaxial furrow on the pygidium . kobayashi ( 1939 ) erected the genus acadagnostus for such species , which westergård ( 1946 ) subsequently placed in peronopsis . as explained by shergold and laurie ( 1997 ) , and in detail by naimark ( 2012 ) , acadagnostus ( type species : a . acadicus [ hartt in dawson , 1868 ] [ not “ acadica ” as used in some publications such as naimark , 2012 ] ) is a valid genus , which is taxonomically distinguished from itagnostus .

mguh 30893 ( fig . 3 . 3 ) . western side of henson gletscher , lauge koch land , north greenland , middle part of the ekspedition bræ formation , ggu sample 225501 .

western side of henson gletscher , lauge koch land , ggu sample 225501 : five fairly complete exoskeletons ( figured specimens under mguh 30903 and 30892 ) , three cephala with attached thoracic segments ( mguh 30896 , 30897 , 30895 ) ; western side of løndal , ggu sample 255720 : one fairly complete carapace ( under mguh 30891 ) , four cephala ( figured specimen under mguh 30894 ) , two pygidia ( figured specimen under mguh 30902 ) . tentatively assigned to i . subhastatus : ggu sample 255720 : two pygidia ( mguh 30899 and mguh 30901 ) .

species of itagnostus with a comparatively slender posterior glabellar lobe ; anterior lobe of the glabella completely defined by furrow ; preglabellar furrow absent ; pygidial rhachis narrow , subtriangular to hastate , subacute posteriorly , with laterally developed transaxial furrows ; postaxial furrow developed ; small to rudimentary spines on the pygidial border ; doublure comparatively wide .

cephalon moderately convex , subcircular to subquadrate , with distinctly curved lateral margins and well - rounded anterior angles ; length / width ratio ~ 0 . 9 . glabella bilobate , tapering forward . posterior lobe with length about equal to width , slightly longer than 1 . 5 times length of anterior lobe , highest elevation about one - third from well - rounded posterior end ; without tubercle or with extremely faint , narrow longitudinal node ( fig . 3 . 3 ) . anterior lobe evenly rounded in front . transverse furrow straight . anterior lobe well defined by moderately deep dorsal furrow . occipital ring very narrow , continuous with the simple , triangular , slightly inequilateral basal lobes , which are somewhat oblique to axis .

genae convex , preglabellar median furrow absent . border moderately convex , growing in width from genal angles anteriorly , but subequal in width anteriorly between anterolateral corners ; posterolateral corners with well - developed , highly raised thorn - shaped spines . border furrow narrow , rather deep posterolaterally , moderately deep anteriorly .

thorax of two segments . axial rings laterally tripartite , strongly oblique furrow demarcates raised , oblique lateral nodes , which are smaller on anterior than on posterior segment . axial furrow chevron shaped along axial rings . pleurae on anterior segment a subangular bulb traversed by a shallow pleural furrow that curves strongly forward to demarcate a swollen subcircular anterior pleural band ; with a small node - like thorn in a posterolateral position ( fig . 3 . 2 ) ; stout pleural tip strongly ventrally deflected . pleurae on posterior segment short , but distinctly longer than in anterior segment , ventrally deflected and with obliquely forward - directed , acute pleural tip ; pleural furrow slightly s - shaped , anterior to midline of pleura , swinging anteriorly in distal portion ; with fairly well - developed socket on posterior pleural band close to axial furrow ( fig . 3 . 3 ) .

pygidium moderately convex , subcircular to subquadrate , with weakly curved lateral and distinctly curved posterior margins ; length / width ratio ~ 0 . 85 . rhachis variably of 68–77 % pygidial length , 41–45 % pygidial maximum width across anterior segment , which is defined by a broad constriction and a faint and wide depression instead of a distinct lateral furrow ; lateral axial furrows obscure ; posterior two - thirds or almost three - fourths of rhachis hastate in dorsal view , with variably developed and slightly broadened m3 , narrowing into a pointed tip ; median tubercle elliptical in outline , approximately one - third from anterior end .

postaxial median furrow present , slit - like or developed as a triangular , posteriorly broadened depression ( fig . 3 . 3 ) that joins the dorsal and marginal furrows . pleural lobes moderately convex . border moderately convex , growing in breadth from anterolateral corners to a maximum of approximately twice this breadth on sagittal line ; wider than on the cephalon ; with somewhat variably developed , small and short marginal spines located slightly posterior to a transverse line drawn at tip of axis . anterior border confluent with lateral border at distinct anterolateral corners , swinging forward and raised while slightly growing in width up to well - developed fulcral points that fit into sockets of posterior thoracic segment . border furrow well developed , moderately deep , subequal in width throughout . doublure slightly wider than border .

lengths of cranidia in the present material 2 . 3–3 . 7 mm ; lengths of pygidia 1 . 6–3 . 5 mm . entire surface of carapace smooth .

from the latin hastatus , lance - shaped ; an allusion to the shape of the pygidial rhachis .

cephalon subcircular to subquadrate , with distinctly curved lateral margins , anterior margin tends to have an almost straight median section ; length / width ratio ~ 0 . 85 . posterior lobe of glabella with weakly curved sides , greatest slightly behind midlength , with width ~ 85 % length , slightly longer than 1 . 5 times length of anterior lobe , highest elevation about one - third from well - rounded posterior end ; without faint , narrow longitudinal node . anterior lobe evenly rounded or with slightly narrower curvature in front . occipital ring very narrow , continuous with the simple , triangular , slightly inequilateral basal lobes .

border growing in width from genal angles anteriorly , but subequal in width anteriorly between anterolateral corners .

thoracic axial rings laterally tripartite , strongly oblique furrow demarcates raised , oblique lateral nodes , which are subequal in size on anterior as on posterior segment . pleurae on anterior segment consist of a bulb - like anterior pleural band defined by a well - marked shallow pleural furrow that curves strongly forward and fades close to the arcuate pleural tips ( fig . 3 . 11 ) ; posterior pleural band on anterior segment with narrow and low proximal and elevated and slightly broader , obliquely forward directed distal portions . pleurae on posterior segment distinctly longer than in anterior segment , ventrally deflected , with obliquely forward - directed , acute pleural tip ; with socket on posterior pleural band close to axial furrow ( fig . 3 . 11 ) .

pygidium subsemicircular to subquadrate , with weakly curved lateral and distinctly curved posterior margins ; length / width ratio ~ 0 . 80–0 . 85 ( n = 4 ) . rhachis of 75–82 % pygidial length , 40–43 % pygidial maximum width across anterior segment , which is defined by a distinct constriction and a shallow , but well - marked pair of lateral furrows , the branches of which curve forward from the axial furrows and demarcate bulb - like swellings of the first segment of the rhachis ; second pair of axial furrows obscure ; posterior two - thirds of rhachis ogival in dorsal view , with slightly broadened m3 , narrowing into a pointed tip ; median tubercle a longitudinal crest , most prominent point close to posterior end ( fig . 3 . 14 ) . postaxial median furrow developed as posteriorly broadened depression .

lengths of cranidia in the present material 2 . 7–3 . 7 mm , lengths of pygidia 3 . 2–4 . 2 mm . entire surface of carapace smooth .

western side of henson gletscher , lauge koch land , north greenland , ggu sample 225501 : two fairly complete exoskeletons ( under mguh 30904 and 30905 ) ; western side of løndal , north greenland , ggu sample 255720 : single pygidium ( mguh 30906 ) . material tentatively assigned to itagnostus sp . cf . i . gaspensis : ggu sample 255720 : two cephala .

the material treated here resembles the type material of itagnostus gaspensis ( rasetti , 1948 ) from middle cambrian limestone boulders within the so - called lévis conglomerate at grosses roches , quebec . differences exist in the slightly narrower glabella , the more tapering and slightly longer pygidial rhachis , the narrower pygidial border , and an apparently broader ( sag . ) articulating half - ring . unfortunately , rasetti ( 1948 , pl . 45 , figs . 1–3 ) figured only one cephalon and two pygidia . at least the pygidium assigned by rasetti ( 1948 , pl . 45 , fig . 5 ) is not closely related to the species and belongs to a different genus in the concept of naimark ( 2012 ) .

a similar species , peronopsis taitzuhoensis lu , 1957 was described from the middle cambrian tangshih formation ( abandoned , now hsuchuang formation ) and thus hsuchuangia - ruichengella through bailiella - lioparia zones of the taizihe ( earlier spelled “taitzuhe” ) valley , benxi , liaoning province , and from the henan province ( lu , 1957 ; lu et al . , 1965 ; pei , 1991 ) . this species has been regarded as a subspecies of itagnostus gaspensis by naimark ( 2012 ) , but we regard it as an independent , although closely related species within itagnostus . itagnostus sp . cf . i . gaspensis from greenland differs from this species from south china in having a cephalon with an almost straight median sector of the anterior margin rather than being well rounded . in addition , the pygidial rachis is generally narrower and particularly in the posterior portion clearly narrower and more strongly tapering with less clearly impressed lateral furrows ; the marginal spines are distinctly smaller . a similar form was described as peronopsis sp . cf . i . taitzuhoensis from the heicigou group of the north qilian district , tarim platform , northwest china ( zhou and dean , 1996 ) .

the material of itagnostus sp . cf . i . gaspensis from the ekspedition bræ formation clearly differs from i . subhastatus n . sp . , which appears in the same samples , in a number of characters : a shorter and nearly subparallel rather than tapering glabella with a relatively longer posterior lobe ; a narrower anterior and lateral cephalic border ; a distinctly longer pygidial rhachis with an ogival rather than hastate posterior portion and two constrictions as well as a longitudinal , crest - like median tubercle ; a short depression connecting dorsal and border furrows ; a less strongly broadening border ; and marginal spines that are short and thorn - like .

itagnostus interstrictus ( white , 1874 ) has a posteriorly broadened posterior lobe and thus a clearly tapering glabella . naimark ( 2012 ) assigned specimens from the malokuonamka “horizon” of the siberian platform described as peronopsis aff . gaspensis ( egorova et al . , 1982 , pl . 51 , figs . 1 , 3 ) to itagnostus interstrictus . specimens described as euagnostus aff . interstrictus by laurie ( 2004 , p . 245 , figs . 18a–18n ) , however , were assigned by naimark ( 2012 ) to i . gaspensis . laurie ( 2004 ) stated that they differ from itagnostus interstrictus only by having a posteriorly displaced glabellar tubercle ; this was interpreted by naimark ( 2012 ) as being a characteristic feature of i . gaspensis . the present specimens from the ekspedition bræ formation are not well enough preserved to permit an unequivocal assessment based on this character ; they appear to show a faint tubercle in a more central position on the posterior glabellar lobe and thus to indicate another character difference from i . gaspensis .

the similar species peronopsis ( p . ) scutalis ( salter in hicks , 1872 ) from scandinavia ( typical specimens figured by westergård , 1946 ) lacks true pygidial spines . it is also very similar to acadagnostus acadica ( hartt , 1868 ) , from which it can be separated by the same character .

conocephalites cordillerae rominger , 1887 ; stephen formation , british columbia , canada ( by original designation ) .

elrathina is one of the genera with a fairly generalized morphology , and since resser’s ( 1937b ) rudimentary introduction and the rapid emendation by deiss ( 1939 ) , it has grown into one of the frequent taxonomic waste baskets among the alokistocaridae , with at least 23 validly described species , or subspecies . the difficulties that result from the attempt to perfectly characterize the species’ morphology when based on imperfectly preserved material have been addressed by rasetti ( 1951 , p . 221 ) in a surprisingly plain style .

the type species , elrathina cordillerae , was introduced as conocephalites cordillerae by rominger ( 1887 ) and shown in a single figure ( rominger 1887 , pl . 1 , fig . 7 ) , which provides an utterly erroneous impression of its morphology ; it is discussed below . its bilobate terminal axial piece in the pygidium could even be used as a criterion to separate it from the vast majority of species assigned to elrathina . however , as long as the morphologic plasticity of this character is not fully understood , we suggest retention of the traditional generic concept .

solov’ev and grikurov ( 1978 ) described material from the ptychagnostus praecurrens zone of the shackleton range , antarctica , as elrathina parallela longa , and their naming suggested a new variety of e . parallela . the available material consisted of only two moderately well - preserved carapaces ( one of them an external mold ) , which do not present details of the pygidium and the glabella . solov’ev and grikurov ( 1978 , p . 197–198 ) emphasized the similarity with e . parallela , from which the specimens from the shackleton range were distinguished by a more slender glabella with subparallel sides and a narrow frontal lobe . in fact , this interpretation is based on the fact that the anterior part of the glabella in both specimens appears to be transversely compressed and therefore has a ridge that connects the glabella with the anterior border as a taphonomic artifact . we thus regard the type material of e . parallela longa as insufficient to characterize a taxon .

elrathina antiqua palmer in palmer and halley , 1979 from the carrara formation of the belted range , nevada , is characterized by a pygidium with an unusually short axis , a thorax of only 15 or 16 segments , and librigenae with an angular thorn , but otherwise shares the diagnostic characters of the genus ( fig . 4 . 2 ) . it is derived from the albertella zone and is thus the oldest known species of the genus .

, plaster cast of holotype in the museum of comparative zoology , cambridge , mass . , usnm 65009 , carapace without librigenae , parker slate , parker quarry , georgia . scale bars = 5 mm .

elrathina spinifera rasetti , 1951 from the stephen formation of the mt . odaray section , british columbia , has a glabella with an almost flat front , a fairly narrow preglabellar field , a distinct swelling of the anterior border such that the anterior border furrow describes a rearward swing and is shallower on the sagittal line , and a short obliquely backward directed occipital spine . the thorax , pygidium , and librigenae are unknown .

summarized , the species from the stephen formation indicate that specific differences include variation of the preglabellar field , the breadth and possible swelling of the anterior cephalic border , the size of the occipital node or spine , the position of the geniculation of the thoracic segments , and the length and width of the pygidial rhachis , all of which appear to be constant within the species . therefore , these characters are regarded as a blueprint for taxonomic distinction within the elrathina clade .

the most conspicuous taphonomic effect in elrathina is the absence of librigenae even in the nearly complete carapaces . these therefore qualify as carcasses that record the “olenid mode” of molting .

a common feature in larger sclerites is the presence of cracks . their frequency depends on the size and morphology of the sclerites . isolated thoracic segments are generally preserved as fragments only , which is interpreted as an effect of the narrow and brittle nature of the segments . their fractures are concentrated at or adjacent to the axial furrow .

) usnm 65518a , incomplete dorsal carapace ; stephen formation , mount stephen , b . c . ( original of walcott ,

) under lot usnm 17831 , posterior part of thorax and pygidium ; stephen formation , mount stephen , b . c . ; original specimen stored with plaster and gutta - percha casts with the collection number provided by resser (

, pl . 33 , fig . 20 ) , incomplete dorsal carapace without librigenae ; stephen formation , mount stephen , b . c . all scale bars = 5 mm .

1887 conocephalites cordilleræ rominger , p . 17 , pl . 1 , fig . 7 .

? 1899 ptychoparia cordilleræ ; matthew , p . 44 , pl . 1 , fig . 7a , 7b .

1902 ptychoparia cordilleræ ; woodward , p . 536 , text - fig . 4 .

1908 ptychoparia cordilleræ ; walcott , p . 243 , pl . 3 , fig . 5 .

? 1912 ptychoparia cordilleræ ; walcott , p . 190 , pl . 24 , fig . 2 .

1918 ptychoparia cordilleræ ; walcott , p . 144 , pl . 21 , fig . 4 .

? 1918 ptychoparia cordilleræ ; walcott , pl . 21 , fig . 3 , 5 .

? 1950 elrathina cordillerae ; mclaughlin and enbysk , p . 469 , pl . 65 , figs . 12 , 15–17 .

non 1950 elrathina cordillerae ; mclaughlin and enbysk , pl . 65 , fig . 14 .