today , deep - water benthic habitats , i.e. those areas below the euphotic zone at a water depth of more than c. 200  m , account for more than 65% of the earth 's surface .
however , these regions are much more difficult to access than shallow waters and thus , despite considerable effort during the past decades , they remain much less explored .
usually , major tectonic movements are needed to expose ancient deep - water sediments at the surface . because of deposition at great water depths and tectonic displacement , the fossil record in these sediments often suffers from significant diagenetic loss and deformation . furthermore , due to low primary productivity , nutrients in deep - water settings mostly are scarce and macrobenthic organisms do not form dense populations . as a result ,
fossils of deep - water organisms commonly occur scattered and in low abundance , and collecting representative samples requires detailed investigation of large rock exposures . during the mesozoic ,
because they evolved comparatively rapidly , ammonites are used widely as biostratigraphic markers and many outcrops of mesozoic deep - water sediments have thus been sampled extensively .
this careful collecting has often yielded representative samples of the rare autochthonous benthic deep - water organisms , which is the case for the bivalves detailed herein .
the lower cretaceous deposits of the puez area in the dolomites ( southern calcareous alps , south tyrol , italy ) were first sampled for fossils during the late nineteenth century , and the geologists victor uhlig ( 1888 ) and haug , 1888 , haug , 1889 published initial descriptions of the geology and fauna of these sediments . during the last decade
( 20032012 ) , the puez cretaceous strata were re - sampled intensively by italian and austrian scientists , mostly bed by bed .
in addition to an impressive number of more than 1200 ammonites , these workers also collected rare echinoids , solitary corals , brachiopods , and bivalves ( lukeneder and aspmair , 2006 , lukeneder , 2008 , lukeneder , 2010 ) .
these bivalves , comprising allochthonous epibionts as well as autochthonous deep - water inhabitants , are described in detail and illustrated herein , and their palaeoecological requirements are discussed .
today , the lower cretaceous sediments of the higher dolomites are preserved as relics , either in pure limestone facies ( biancone formation ; e.g. , mayer and appel , 1999 ) or in marl to marly limestone facies ( puez formation ; lukeneder , 2010 ) .
the puez formation , preserved predominantly on the puez - odle - gardenaccia plateau ( fig .  1 ) , was deposited on triassic hauptdolomit or lower cretaceous rosso ammonitico puezzese limestones ( lukeneder and aspmair , 2006 , lukeneder , 2010 , lukeneder , 2011 ) . in the puez area , cone - shaped hills up to 150  m high are formed by the puez formation and are overlain by tectonically emplaced slivers of triassic dachstein limestone up to 10  m thick , that have acted as a protection against erosion ( lukeneder and aspmair , 2006 , lukeneder , 2010 ) .
as described in detail by lukeneder ( 2010 ) , the section of the puez formation at puez comprises marls and ( marly ) limestones that are approximately 120  m thick .
the puez formation can be subdivided into three members that were deposited during a time span from the late valanginian to the early cenomanian ( fig .  2 ) .
the first , the puez limestone member , consists of approximately 50  m of marly limestones , which are late valanginian to late barremian in age .
the second , the puez redbed member , is only 9  m thick and comprises foraminiferal wackestones to packstones of aptian age , while the third , the puez marl member , consists of approximately 57  m of alternating marl and limestone beds , dated as early aptian to early cenomanian .
biostratigraphic data were obtained from ammonoids ( lukeneder , 2012 ) and nannofossils ( e. halsov , pers .
the dolomites ( permian to late cretaceous in age ) comprise an integral , inner part of the fold - thrust belt ( backthrust belt ) of the southern alps in northern italy , and emerged as a result of the deformation of the tethyan passive continental margin of adria ( bosellini et  al . , 2003 , castellarin et  al . , 2006 ) . during the early cretaceous , the dolomites formed part of the trento plateau which was situated on the eastern flank of the lombardian basin ( bosellini et  al . , 2003 ,
lukeneder , 2008 ) , at a palaeolatitude of 2030 n ( muttoni et  al . , 2005 ) .
the puez area is located within the dolomites in the northernmost part of the trento plateau .
the cretaceous sediments of the puez area formed on a submarine plateau , the puez - odle - gardenaccia plateau . for a more detailed geological overview of the puez area ,
most of the specimens described herein derive from systematic bed - by - bed collection of fossils at the puez locality in the years between 2003 and 2012 . with the exception of oysters , which originate from the late aptian part of the puez marl member ,
all specimens have been collected from the puez limestone member and are dated as early to late barremian ( fig .  2 ) .
a few additional individuals of parvamussium are available from old , stratigraphically unconstrained nhmw collections and from the holdings of the naturmuseum sdtirol ( bolzano , south tyrol , italy ) . a single large parvamussium from correlative deposits of the barremian puez limestone member at the ra stua locality north of cortina d'ampezzo , province of belluno
altogether , only 30 rock samples with bivalves from piz de puez have been studied , although some samples contain multiple inoceramidae and dimyidae .
due to poor preservation , oysters could not be counted ( see details below ) .
class bivalvia linnaeus , 1758subclass pteriomorphia beurlen , 1944 ( emend . boss , 1982)order myalinida h. paul , 1939superfamily inoceramoidea c. giebel , 1852family inoceramidae c. giebel , 1852genus inoceramus j. sowerby , 1814  type species .
inoceramidae have only been mentioned twice , in open nomenclature , in previous studies on the puez formation ( haug , 1888 , lukeneder and aspmair , 2006 ) .
class bivalvia linnaeus , 1758 subclass pteriomorphia beurlen , 1944 ( emend . boss , 1982 ) order myalinida h. paul , 1939 superfamily inoceramoidea c. giebel , 1852 family inoceramidae c. giebel , 1852 genus inoceramus j. sowerby , 1814   type species .
inoceramidae have only been mentioned twice , in open nomenclature , in previous studies on the puez formation ( haug , 1888 , lukeneder and aspmair , 2006 ) .
inoceramids from the early half of the early cretaceous are generally poorly known and illustrated , and are commonly described from relatively limited , deformed and incompletely preserved material .
interpretation of many specimens is hampered further by the impact of taphonomic artifacts , whereby different modes of preservation interact with shell structures to produce taxonomically misleading morphologies ( crampton , 2004 ) .
for all these reasons , the taxonomy of early cretaceous inoceramidae remains problematic and the large number of nominal taxa is in need of revision .
some important and relevant publications that review or figure hauterivian to aptian inoceramids include pergament , 1965 , pokhialainen , 1969 , pokhialainen , 1972 , pokhialainen , 1985 , glazunova , 1973 , crame , 1985 , dhondt , 1992 and lazo ( 2006 ) .  
nine adult specimens derived from a single rock sample ( nhmw 2013/0292/00010009 ) , and a single juvenile right valve ( nhmw 2013/0292/0010 ) . preserved as flattened internal moulds with patches of the external , prismatic calcite shell layer retained .
complete specimens : l ( max )  =  55  mm ; h ( max )  =  52  mm ; most specimens are fragmentary ; the largest fragment measures approximately 90  mm in height .  description
. inequivalved ; juvenile left valve probably moderately inflated ( as judged from flattened material ) and becoming weakly inflated with growth ; right valve uniformly weakly inflated .
outline obliquely elliptical to ovate , with height exceeding length ( descriptive terminology follows crampton , 1996 , fig . 30 ; crampton and gale , 2009 , fig .
2 ) . moderately prosocline ; growth axis infracrescent in early growth stages and becoming weakly retrocrescent in adult stages . adult sculpture of irregularly and widely spaced , very low , rounded , and indistinct commarginal folds . a single juvenile individual ( fig . 
3a ) has weak but regularly spaced folds restricted to the earliest growth stage ( < 10  mm ) .
outer prismatic shell thin and nowhere more than 1  mm thick .  remarks . on present evidence
it is not possible to identify the material from the puez formation described here to species level .
these specimens , although rather nondescript and imperfectly preserved , can be distinguished from most described , elliptical , hauterivian to early aptian taxa by their combination of apparently weakly inflated left valves and lack of  pronounced commarginal sculpture .
thus , for example , coloniceramus colonicus ( anderson , 1938 ) and heteropteria heteropterus ( pokhialainen , 1969 ) ( generic assignments of pokhialainen , 1972 ) from the hauterivian to barremian of far east russia and the pacific coast of north america , have the weak sculpture seen in the puez formation material , but possess highly inflated , gryphaeoid umbones in the left valve that project above the hingeline and , in the case of c.  colonicus , a comparatively thick shell .
 inoceramus aucella ( trautschold , 1865 ) is recorded widely from hauterivian and barremian strata of northern mid- to high latitudes and is , again , relatively highly inflated in the left valve and has moderately developed and regularly spaced commarginal folds . 
: lukeneder & aspmair , pl . 8 , fig . 10 .  for a more complete synonymy of n.  neocomiensis , refer to dhondt and dieni ( 1988 ) .  material .
a single internal mould of a left valve ( nhmw 2005z0245/0007 ) .  measurements .
l  =  32  mm ; h  =  29  mm .  description . left valve moderately weakly inflated .
faint radial striations inferred to mark tracks of adductor and/or pallial muscle scars on the internal mould .  remarks .
haug , 1888 , haug , 1889 and reithofer ( 1928 ) , who presumably adopted haug 's identification , reported pholadomya barremensis matheron from the puez formation .
corresponding specimens have not been located in the nhmw collections nor collected during extensive excavations during the last decade .
neocomiensis and pholadomya barremensis are superficially similar in outline and sculpture , with distinct commarginal ribs .
however , the latter species has an additional set of less prominent but distinct radial ribs ( not merely faint striations ) , and it remains unclear whether haug , 1888 , haug , 1889 confused the two species or not .
nine adult specimens derived from a single rock sample ( nhmw 2013/0292/00010009 ) , and a single juvenile right valve ( nhmw 2013/0292/0010 ) . preserved as flattened internal moulds with patches of the external , prismatic calcite shell layer retained .
complete specimens : l ( max )  =  55  mm ; h ( max )  =  52  mm ; most specimens are fragmentary ; the largest fragment measures approximately 90  mm in height .   description .
inequivalved ; juvenile left valve probably moderately inflated ( as judged from flattened material ) and becoming weakly inflated with growth ; right valve uniformly weakly inflated .
outline obliquely elliptical to ovate , with height exceeding length ( descriptive terminology follows crampton , 1996 , fig .
moderately prosocline ; growth axis infracrescent in early growth stages and becoming weakly retrocrescent in adult stages . adult sculpture of irregularly and widely spaced , very low , rounded , and indistinct commarginal folds . a single juvenile individual ( fig . 
3a ) has weak but regularly spaced folds restricted to the earliest growth stage ( < 10  mm ) .
growth lines very weakly expressed , if at all . outer prismatic shell thin and nowhere more than 1  mm thick .   remarks .
on present evidence it is not possible to identify the material from the puez formation described here to species level .
these specimens , although rather nondescript and imperfectly preserved , can be distinguished from most described , elliptical , hauterivian to early aptian taxa by their combination of apparently weakly inflated left valves and lack of  pronounced commarginal sculpture .
thus , for example , coloniceramus colonicus ( anderson , 1938 ) and heteropteria heteropterus ( pokhialainen , 1969 ) ( generic assignments of pokhialainen , 1972 ) from the hauterivian to barremian of far east russia and the pacific coast of north america , have the weak sculpture seen in the puez formation material , but possess highly inflated , gryphaeoid umbones in the left valve that project above the hingeline and , in the case of c.  colonicus , a comparatively thick shell .
 inoceramus aucella ( trautschold , 1865 ) is recorded widely from hauterivian and barremian strata of northern mid- to high latitudes and is , again , relatively highly inflated in the left valve and has moderately developed and regularly spaced commarginal folds .  
8 , fig . 10 .   for a more complete synonymy of n.  neocomiensis , refer to dhondt and dieni ( 1988 ) .  
l  =  32  mm ; h  =  29  mm .   description . left valve moderately weakly inflated .
faint radial striations inferred to mark tracks of adductor and/or pallial muscle scars on the internal mould .   remarks .
haug , 1888 , haug , 1889 and reithofer ( 1928 ) , who presumably adopted haug 's identification , reported pholadomya barremensis matheron from the puez formation .
corresponding specimens have not been located in the nhmw collections nor collected during extensive excavations during the last decade .
neocomiensis and pholadomya barremensis are superficially similar in outline and sculpture , with distinct commarginal ribs .
however , the latter species has an additional set of less prominent but distinct radial ribs ( not merely faint striations ) , and it remains unclear whether haug , 1888 , haug , 1889 confused the two species or not .
the specimen illustrated here shows the characteristic shape and sculpture of the n.  neocomiensis group , although in the absence of preserved prismatic shell , this identification must be regarded as uncertain . as noted by others ,
there are a number of widely distributed valanginian to aptian species that are apparently closely allied to n.  neocomiensis ( crame , 1985 , dhondt and dieni , 1988 , lazo , 2006 ) , and the group may extend downwards into the berriasian of eastern europe ( i.  belbekensis 
 ianin , 1972 ) .
relationships between these nominal taxa remain unclear and the group is in need of careful taxonomic revision . here , we follow the generic assignment and diagnosis of lazo ( 2006 ) . 
order ostreida frussac , 1822superfamily ostreoidea rafinesque , 1815family gryphaeidae vialov , 1936subfamily exogyrinae vialov , 1936  exogyrinae ?
a single large , fragmentary mould of an indeterminate ammonite from the upper aptian of the puez marl member , with numerous small oyster specimens cemented onto the original outer shell surface of the dissolved cephalopod shell ( nhmw 2013/0292/0011 ) .  remarks .
most of the small specimens ( < 10  mm ) are hardly distinguishable from each other , since they are coated with a thin , encrusting layer of sediment .
the aragonitic ammonite shell has dissolved and most of the oyster specimens , formerly attached to the external shell surface , are now incorporated into the external mould of the cephalopod . as a result ,
the bivalves are mostly visible from the attachment surface only . however , in a few specimens that grew near the venter of the ammonite , the outside of the free ( right ) valve is exposed .
although a proper identification is impossible , three characters favour an assignment to the exogyrinae .
the free valves are strongly carinate and coiled dextrally , and the shell surface is more - or - less smooth .
moreover , the shells of exogyrinae typically consist of relatively dark calcite crystals ( nikolaus malchus , pers .
comm . , 2012 ) , as can be seen in a few broken specimens from puez .
the oysters cemented onto both lateral sides and the venter of the ammonite , which means that they either colonised the living cephalopod or settled on its empty , floating shell . in either case , they have to be considered allochthonous elements in the fauna . 
order pectinida j. gray , 1854suborder anomiidina j. gray , 1854superfamily dimyoidea p. fischer , 1886family dimyidae p. fischer , 1886genus atreta 
 tallon , 1862  type species .
ostrea blandina 
 d'orbigny , 1850 , by the subsequent designation of cox ( 1964 ) . 
order ostreida frussac , 1822 superfamily ostreoidea rafinesque , 1815 family gryphaeidae vialov , 1936 subfamily exogyrinae vialov , 1936   material .
a single large , fragmentary mould of an indeterminate ammonite from the upper aptian of the puez marl member , with numerous small oyster specimens cemented onto the original outer shell surface of the dissolved cephalopod shell ( nhmw 2013/0292/0011 ) .  
most of the small specimens ( < 10  mm ) are hardly distinguishable from each other , since they are coated with a thin , encrusting layer of sediment .
the aragonitic ammonite shell has dissolved and most of the oyster specimens , formerly attached to the external shell surface , are now incorporated into the external mould of the cephalopod . as a result ,
the bivalves are mostly visible from the attachment surface only . however , in a few specimens that grew near the venter of the ammonite , the outside of the free ( right ) valve is exposed .
although a proper identification is impossible , three characters favour an assignment to the exogyrinae . the free valves are strongly carinate and coiled dextrally , and the shell surface is more - or - less smooth .
moreover , the shells of exogyrinae typically consist of relatively dark calcite crystals ( nikolaus malchus , pers .
the oysters cemented onto both lateral sides and the venter of the ammonite , which means that they either colonised the living cephalopod or settled on its empty , floating shell . in either case , they have to be considered allochthonous elements in the fauna .  
order pectinida j. gray , 1854 suborder anomiidina j. gray , 1854 superfamily dimyoidea p. fischer , 1886 family dimyidae p. fischer , 1886 genus atreta 
 tallon , 1862   type species .
ostrea blandina 
 d'orbigny , 1850 , by the subsequent designation of cox ( 1964 ) .  
fourteen right valves , all preserved on external moulds of ammonites , with only attachment surface visible ( nhmw 2013/0292/00120025 ) .  measurements .
l ( max )  =  10  mm ; h ( max )  =  9.5  mm .  description . only attachment surface and external rim of right valves visible .
shell obliquely d - shaped in outline , with straight side forming dorsal margin ; posterior - ventral shell portion slightly extended .
external rim of shell markedly curved upwards ( in life position ) , resulting in shallow , bowl - like shape .
attachment surface basically smooth , with faint commarginal growth lines extending from umbo ; umbo positioned slightly below dorsal margin .
several specimens possess prominent pseudo - sculpture of ribs or reticulate pattern , caused by underlying ornament of ammonite shells that acted as substrate ( xenomorphism ) .  remarks .
unfortunately , only the attachment surfaces of right valves are visible , and the characteristic dimyid attachment scars of the anterior and posterior adductor muscles can not be observed . whether the left valves are still attached or not also remains unknown . however , the slightly oblique d - shape of the shells , the umbo , which is positioned significantly below the dorsal shell margin , and the upwardly curved shell rim permit a fairly confident assignment to atreta . in the absence of ornament details of the left valves , a specific attribution is impossible . material .
fourteen right valves , all preserved on external moulds of ammonites , with only attachment surface visible ( nhmw 2013/0292/00120025 ) .   measurements .
l ( max )  =  10  mm ; h ( max )  =  9.5  mm .   description . only attachment surface and external rim of right valves visible .
shell obliquely d - shaped in outline , with straight side forming dorsal margin ; posterior - ventral shell portion slightly extended .
external rim of shell markedly curved upwards ( in life position ) , resulting in shallow , bowl - like shape .
attachment surface basically smooth , with faint commarginal growth lines extending from umbo ; umbo positioned slightly below dorsal margin .
several specimens possess prominent pseudo - sculpture of ribs or reticulate pattern , caused by underlying ornament of ammonite shells that acted as substrate ( xenomorphism ) .   remarks .
unfortunately , only the attachment surfaces of right valves are visible , and the characteristic dimyid attachment scars of the anterior and posterior adductor muscles can not be observed . whether the left valves are still attached or not also remains unknown . however , the slightly oblique d - shape of the shells , the umbo , which is positioned significantly below the dorsal shell margin , and the upwardly curved shell rim permit a fairly confident assignment to atreta . in the absence of ornament details of the left valves , a specific attribution is impossible .
as can be seen in the photographs , the specimens themselves show no preferred orientation of their umbones , but they are usually attached to the lower half of the cephalopod shell , when in life position ( lukeneder , 2008 ) .
having presumably been attached to live ammonites , atreta thus was not part of the autochthonous deep - water fauna of the puez formation . 
suborder entoliidina hautmann , 2011superfamily entolioidea teppner , 1922family propeamussiidae abbott , 1954genus parvamussium 
 sacco , 1897  type species .
pecten ( pleuronectes ) duodecimlamellatus 
 bronn , 1831 , by original designation .  remarks .
parvamussium was proposed as a subgenus of amusium ( now assigned to the pectinidae ) by sacco ( 1897 , p. 48 ) , and distinguished from amusium s. str . by its smaller size and fewer , strong and unpaired internal costae , which do not extend to the shell margin .
sacco ( 1897 ) also noted a close relationship between parvamussium and propeamussium , but did not explicitly list similarities or differences . according to dijkstra and gofas ( 2004 , p. 37 ) ,  propeamussium differs from parvamussium by the reduction or absence of the byssal notch on the right valve , by the internal riblets commencing earlier in the ontogeny , and by the gape at the anterior and posterior margins. all jurassic to oligocene propeamussiids that have been studied thoroughly to date belong to parvamussium ( dhondt , 1971 , tamura , 1973 , sundberg , 1989 , waller , 2006 ) ; propeamussium did not evolve earlier than the miocene .
suborder entoliidina hautmann , 2011 superfamily entolioidea teppner , 1922 family propeamussiidae abbott , 1954 genus parvamussium 
 sacco , 1897   type species .
parvamussium was proposed as a subgenus of amusium ( now assigned to the pectinidae ) by sacco ( 1897 , p. 48 ) , and distinguished from amusium s. str . by its smaller size and fewer , strong and unpaired internal costae , which do not extend to the shell margin .
sacco ( 1897 ) also noted a close relationship between parvamussium and propeamussium , but did not explicitly list similarities or differences . according to dijkstra and gofas ( 2004 , p. 37 ) ,  propeamussium differs from parvamussium by the reduction or absence of the byssal notch on the right valve , by the internal riblets commencing earlier in the ontogeny , and by the gape at the anterior and posterior margins. all jurassic to oligocene propeamussiids that have been studied thoroughly to date belong to parvamussium ( dhondt , 1971 , tamura , 1973 , sundberg , 1989 , waller , 2006 ) ; propeamussium did not evolve earlier than the miocene .
the terminology used below is adopted from waller , 1986 , waller , 2006 . the term 
antimarginal refers to shell elements arranged perpendicular to successive shell margins ( waller , 1986 ) , whereas  radial denotes straight elements originating from the umbonal region , and meeting shell margins at variable angles during growth .
radial as well as antimarginal elements on the inside and outside of the shell are termed 
medium - sized ( l  <  30  mm ) parvamussium with up to 19 internal costae .
left valve ornamented with two alternating sets of radial costellae of different strength , crossed by less prominent commarginal lirae , resulting in regular reticulate pattern . 
the holotype is an articulated specimen with slightly detached and displaced valves ( fig .  7 ;
paratype 1 , a left valve , with internal mould and shell preserved ( fig . 
8a  c ; internal mould ; nhmw 2005z0245/0004 ( a  b ) ; shell ; nhmw 2005z0245/0027 ( c ) ) .
paratype 3 , a right valve , with internal mould and shell preserved ( fig . 
in addition , six left valves and two right valves have been examined ( nhmw 2013/0292/00290036 ) . 
holotype : l  =  26  mm ; h  =  23  mm ; paratype 1 : l  =  26  mm ; h  =  25  mm ; paratype 2 [ fragment ] : l  =  12  mm ; h  =  17.5  mm ; paratype 3 [ fragment ] : l  =  16  mm ; h  =  19  mm .  type locality .
puez limestone member , puez formation ; barremian ; the holotype is from the upper barremian of horizon p1 174 ( see fig .  2 ) . 
shell fragile , semi - translucent , slightly longer than high , markedly inaequilateral , with extended allometric growth in posterior - ventral direction ( fig . 
apical angle c. 120. auricles relatively small , more or less equal sized , with straight margins , meeting at almost right angles .
set of c. 25 well - developed resilial teeth visible on inside of posterior auricle in one specimen ( fig . 
medium - sized ( l  <  30  mm ) parvamussium with up to 19 internal costae .
left valve ornamented with two alternating sets of radial costellae of different strength , crossed by less prominent commarginal lirae , resulting in regular reticulate pattern .  
the holotype is an articulated specimen with slightly detached and displaced valves ( fig .  7 ;
paratype 1 , a left valve , with internal mould and shell preserved ( fig . 
8a  c ; internal mould ; nhmw 2005z0245/0004 ( a  b ) ; shell ; nhmw 2005z0245/0027 ( c ) ) .
paratype 3 , a right valve , with internal mould and shell preserved ( fig . 
in addition , six left valves and two right valves have been examined ( nhmw 2013/0292/00290036 ) .  
holotype : l  =  26  mm ; h  =  23  mm ; paratype 1 : l  =  26  mm ; h  =  25  mm ; paratype 2 [ fragment ] : l  =  12  mm ; h  =  17.5  mm ; paratype 3 [ fragment ] : l  =  16  mm ; h  =  19  mm .   type locality .
puez limestone member , puez formation ; barremian ; the holotype is from the upper barremian of horizon p1 174 ( see fig .  2 ) .  
referring to the name of the type locality , piz de puez .   description .
shell fragile , semi - translucent , slightly longer than high , markedly inaequilateral , with extended allometric growth in posterior - ventral direction ( fig . 
apical angle c. 120. auricles relatively small , more or less equal sized , with straight margins , meeting at almost right angles .
set of c. 25 well - developed resilial teeth visible on inside of posterior auricle in one specimen ( fig . 
shell interior ornamented with up to 19 distinctly antimarginal internal costae ; 8 costae present at the earliest visible growth stage ; additional costae becoming gradually inserted in interspaces with growth ( fig . 
external radial costellae and commarginal lirae of left valve visible as incisions also on inside of shell in central part of disc ( fig . 
8c ) . numerous minute , slightly undulating radial incisions along inner margin of left valve ( fig . 
8c ) . inside of marginal apron additionally strengthened with two or three low commarginal lirae ( fig . 
outside of left valve ornamented with up to more than 120 radial costellae and more than 100 commarginal lirae .
radial costellae at each growth stage consisting of two alternating sets ; primary costellae twice as high and wide as secondary costellae . with growth , secondary costellae
become more prominent , approaching primary costellae in height and strength . at this stage ,
insertion of secondary and tertiary costellae gradual ; not coincident in all parts of shell . in late growth stages , all radial costellae attain similar height and strength ( fig . 
radial and commarginal interspaces almost equally wide ( approximately twice as wide as costellae or lirae ) , causing very regular reticulate pattern . internal costae and pallial margin visible from outside of
left valve due to semi - translucent shell ; often dark reddish - brown in colour ( figs . 
7a and 8a ) . external surface of right valve and nature of byssal notch , if any , unknown .
ornament of regular commarginal lirae on exterior of right valve visible clearly also from inside in the form of narrow commarginal incisions ( fig . 
8f  g ) . remarks . compared to most extant and fossil species of parvamussium ,
pizpuezense n. sp . is of medium size , as are most mesozoic representatives of the genus .
9a  c ; musum d'histoire naturelle de la ville de genve ; bviii-44 - 30933 ) is probably the most closely related congener from the hauterivian to barremian of the montagne des voirons ( haute - savoie , rhne - alpes , southeast france ) .
thus , it corresponds well , both with regard to geological age and palaeogeography , with specimens from piz de puez .
however , p.  agassizi differs significantly from p.  pizpuezense n. sp . in the ornamentation of the left valve . the specimen figured by pictet and loriol ( 1858 ) on plate 9 , figure 2 , which is herein designated lectotype ( see fig . 
9b ) , is much smaller than the holotype of p.  pizpuezense n. sp .
it obviously is an internal mould with remnants of shell , providing , however , a relatively good impression of external morphology .
parvamussium agassizi is ornamented with approximately 50 radial costellae , which occur in two alternating sets of different strength , just as in p.  pizpuezense n. sp . , and even correspond in number to the appropriate growth stage in the latter .
however , in p.  agassizi the costellae are much broader than in p.  pizpuezense n. sp . , with narrow interspaces and sharp crests .
most significantly , however , the left valve of p.  agassizi lacks any commarginal ornamentation .
two species from the berriasian of the crimea peninsula ( ukraine ; arkadiev and bogdanova , 2012 ) that presumably belong to parvamussium were first described by retowski ( 1893 ) .
pecten ( amusium ) pawlovi 
 retowski , 1893 clearly differs from parvamussium pizpuezense n. sp . in its significantly higher number of internal costae ,
> 22 according to retowski ( 1893 ) and 3334 according to arkadiev and bogdanova ( 2012 ) .
pecten ( amusium ) sokolowi 
 retowski , 1893 is slightly smaller than parvamussium pizpuezense n. sp . and has almost straight radial internal costae , whereas they are distinctly antimarginal in the new species .
pecten ( amusium ) sokolowi has only up to 70 external radial costellae and much weaker commarginal lirae than p.  pizpuezense n. sp . as far as we are aware , no additional species of parvamussium have been described from tethyan cretaceous rocks in europe .
the turonian to maastrichtian boreal species parvamussium inversum ( nilsson , 1827 ) reaches only up to 8  mm in length and height , and is thus distinctly smaller than p.  pizpuezense n. sp . moreover , it lacks radial ornamentation on the left valve ( griepenkerl , 1889 , dhondt , 1971 ) .
johnson ( 1984 ) revised the jurassic propeamussiidae from europe and adjacent regions and recognised three species , which he assigned to the genus propeamussium ; however , that author did not discuss the relationships between propeamussium , parvamussium and allied genera . from his descriptions , however , it becomes clear that the jurassic species all retain at least a weak byssal notch in adulthood and thus belong to parvamussium according to the taxonomic concept applied herein .
this observation is supported by waller ( 2006 ) , although he regarded the early to middle jurassic representatives of the propeamussiidae as intermediate between the triassic genus filamussium 
 waller , 2006 and the late jurassic to recent parvamussium , based on differences in the ordering of calcite prisms .
since waller ( 2006 ) did not establish a separate genus for early to middle jurassic taxa , we herein continue to treat the respective species as representatives of parvamussium .
parvamussium pizpuezense n. sp . differs from the three jurassic species in being longer than high , in its inaequilateral shell and in its left valve that is more densely ornamented with more than 100 radial costellae and commarginal lirae .
additionally , the late pliensbachian to early bajocian ( see johnson , 1984 ) parvamussium laeviradiatum ( waagen , 1868 ) clearly differs from all other congeners in its dorsally extended , horn - like auricles in the right valve .
this species was placed in a separate genus , varientolium , by andreeva ( 1966 ) .
parvamussium laeviradiatum and the late pliensbachian to bathonian p.  pumilum ( lamarck , 1819 ) also differ from p.  pizpuezense n. sp . in having no more than 13 near - straight radial internal costae
; no additional internal costae are intercalated . the late jurassic ( late oxfordian to early tithonian ) parvamussium nonarium ( quenstedt , 1857 )
has slightly antimarginal internal costae and intercalary costae , but differs from p.  pizpuezense n. sp . in being much smaller , and in having much coarser reticulate ornamentation on the left valve .
an additional species not mentioned by johnson ( 1984 ) , pecten spendiarovi 
 abel , 1897 , from the kimmeridgian to tithonian klentnice beds of northeast austria ( schneider et  al . , 2013 ) , probably also belongs to parvamussium .
it is much more slender than p.  pizpuezense n. sp . and has radial external costellae on both valves , according to the drawings of abel ( 1897 ) ; the holotype of p.  spendiarovi could not be traced in vienna , and may be lost .
several mesozoic species of parvamussium from the circum - pacific area ( california , japan , indonesia , thailand ) were discussed in detail by sundberg ( 1989 ) and saengsrichan et  al .
these all are distinctly smaller than p.  pizpuezense n. sp . and differ in the number and arrangement of internal costae and external disc ornamentation .
extraordinarily large parvamussium species ( l  >  90  mm ) with 13 internal costae extending from umbo to approximately 70% of shell height .  material .
holotype , a large articulated specimen from the upper lower barremian of the puez limestone member at piz de puez ( nhmw 2013/0292/0037 ) .
paratype , a medium - sized left valve from the same unit at ra stua , north of cortina d'ampezzo , belluno province , veneto ( museo paleontologico 
l  =  92  mm ; h  =  87  mm ; paratype : l  =  c. 65  mm ; h  =  c. 63  mm [ paratype measurements based on photograph ] .  type locality . piz de puez , dolomites , south tyrol , italy and ra stua , north of cortina d'ampezzo , province of belluno , veneto , italy . 
shell exceptionally large ( l ( max )  =  92  mm ) , semi - translucent ; slightly longer than high ; anterior , ventral and posterior shell margins well rounded , forming a subcircular segment ; dorsal shell margin straight .
apical angle c. 115. auricles comparably large , almost perfectly trigonal ; posterior auricle significantly larger than anterior one .
posterior auricle ornamented with growth lines , becoming more prominent , almost plicate , just below the dorsal margin .
extraordinarily large parvamussium species ( l  >  90  mm ) with 13 internal costae extending from umbo to approximately 70% of shell height .   material .
holotype , a large articulated specimen from the upper lower barremian of the puez limestone member at piz de puez ( nhmw 2013/0292/0037 ) .
paratype , a medium - sized left valve from the same unit at ra stua , north of cortina d'ampezzo , belluno province , veneto ( museo paleontologico 
l  =  92  mm ; h  =  87  mm ; paratype : l  =  c. 65  mm ; h  =  c. 63  mm [ paratype measurements based on photograph ] .   type locality . piz de puez , dolomites , south tyrol , italy and ra stua , north of cortina d'ampezzo , province of belluno , veneto , italy .  
shell exceptionally large ( l ( max )  =  92  mm ) , semi - translucent ; slightly longer than high ; anterior , ventral and posterior shell margins well rounded , forming a subcircular segment ; dorsal shell margin straight .
apical angle c. 115. auricles comparably large , almost perfectly trigonal ; posterior auricle significantly larger than anterior one .
posterior auricle ornamented with growth lines , becoming more prominent , almost plicate , just below the dorsal margin .
shell interior ornamented with initially seven ( ? ) and finally up to 11 near - straight radial internal costae in adulthood .
new costae inserted across anterior and posterior parts of shell during ontogeny . outside of left valve ornamented with up to c. 120 slightly irregular , sinuous , radial costellae .
earlier growth stage ornamented with c. 60 costellae only ; additional set of costellae gradually but almost simultaneously emerging from shell surface at shell height of c. 55  mm . no commarginal lirae present ; growth lines irregular , faint .
posterior and central portions of dissolved apron removed during preparation . outside of right valve , including potential byssal notch ,
unknown .  remarks . the unique combination of the most conspicuous features of parvamussium mordsdrum n. sp . , i.e. its extraordinary size and the ornamentation of c. 120 costellae , clearly distinguish this species from all other jurassic and cretaceous species of the genus . 
a single disc fragment with remnants of shell from the barremian puez limestone member ( nhmw 2012/0292/0038 ) .  measurements .
shell exterior with nine , equally - spaced , narrow radial incisions obviously not corresponding to internal costae .
shell ornamented with numerous ( > 150 ) slightly sinuous radial lines of regularly spaced , minute pits .
since major portions of the shell , including the entire hinge region , are lacking , a comprehensive description and accurate identification are impossible .
certainly , the specimen belongs to a distinct , third species of pectinid affinities . 
obviously all three shells were originally of calcitic mineralogy , making a placement within the pteriomorphia very likely . due to the poor preservation , confident identifications are impossible . 
subclass , order , family and genus indet.bivalvia indet.fig .  12 .  material .
a single external mould of a left ( ? ) valve ( nhmw 2013/0292/0042 ) .  measurements . l  =  23  mm ; h  =  19  mm .  description .
shell subcircular in outline , with slight postero - dorsal slope and faintly indicated postero - ventral flexure ; almost flat .
it seems that this specimen is barely compressed , since the growth lines appear regular and undistorted .
obviously the specimen did not possess calcitic shell portions , since calcitic shells , even those of the fragile , translucent propeamussiidae , are perfectly preserved in the puez sediments , whereas aragonite is entirely dissolved .
the specimen is preserved inside the body chamber of a specimen of the ammonite phyllopachyceras ladinum .
remarks . the unique combination of the most conspicuous features of parvamussium mordsdrum n. sp . , i.e. its extraordinary size and the ornamentation of c. 120 costellae , clearly distinguish this species from all other jurassic and cretaceous species of the genus .  
a single disc fragment with remnants of shell from the barremian puez limestone member ( nhmw 2012/0292/0038 ) .   measurements .
shell exterior with nine , equally - spaced , narrow radial incisions obviously not corresponding to internal costae .
shell ornamented with numerous ( > 150 ) slightly sinuous radial lines of regularly spaced , minute pits .
since major portions of the shell , including the entire hinge region , are lacking , a comprehensive description and accurate identification are impossible .
certainly , the specimen belongs to a distinct , third species of pectinid affinities .  
obviously all three shells were originally of calcitic mineralogy , making a placement within the pteriomorphia very likely . due to the poor preservation , confident identifications are impossible .  
a single external mould of a left ( ? ) valve ( nhmw 2013/0292/0042 ) .   measurements .
l  =  23  mm ; h  =  19  mm .   description .
shell subcircular in outline , with slight postero - dorsal slope and faintly indicated postero - ventral flexure ; almost flat .
it seems that this specimen is barely compressed , since the growth lines appear regular and undistorted .
obviously the specimen did not possess calcitic shell portions , since calcitic shells , even those of the fragile , translucent propeamussiidae , are perfectly preserved in the puez sediments , whereas aragonite is entirely dissolved .
the specimen is preserved inside the body chamber of a specimen of the ammonite phyllopachyceras ladinum .
the type locality of the puez formation has been sampled intensely during the last 10 years . given that more than 1200 ammonite specimens have been collected over this period ( lukeneder and aspmair , 2006 , lukeneder , 2008 ) , the fact that fewer than 50 bivalves have been recovered seems surprising .
furthermore , only a part of the bivalve fauna from the puez formation comprises autochthonous elements .
even these individuals belong to several successive benthic communities of early to late late barremian age . however , as already outlined above , population densities of deep - water bivalves commonly are low and our relatively comprehensive collection from the puez formation provides a rare opportunity to study such a fauna .
the calcitic shells of atreta and the small oysters were cemented to the external surface of aragonitic ammonite shells that are now dissolved .
thus , we can not tell whether the bivalves settled on live or dead ammonites . for the oysters , which attached on both sides and on the venter of the ammonite shell
, it seems likely that they cemented to a live or at least floating cephalopod .
moreover , atreta and the oysters were filter feeders and needed a considerable amount of suspended organic matter to survive .
the near - total absence of filter - feeding organisms from the bottom community , however , suggests that bottom waters were nutrient depleted .
inoceramid palaeobiology remains poorly understood , but these bivalves were apparently distributed widely from inner shelf to abyssal depths , although it seems that they were probably most abundant close to continental landmasses and oceanic islands ( crampton , 1996 and references therein ) .
they were epifaunal to semi - infaunal suspension feeders that could occupy a wide range of substrate types .
obliquely elongate forms , such as inoceramus sp . from the puez formation , may have been semi - infaunal , whereas more circular taxa are likely to have been fully epifaunal recliners ( crampton , 1996 ) .
some species are likely to have been byssate , at least at early growth stages , although it is not known whether this was the case for the taxa described here .
many inoceramids were apparently tolerant of dysaerobic conditions ( e.g. , sageman , 1989 ) , which explains their presence in some strata lacking other shelly faunas . however , there is no evidence for dysaerobic conditions from those layers of the puez formation that have yielded bivalve fossils .
they have adapted to a carnivorous life style , preying on copepoda ( hicks and marshall , 1985 ) , foraminifera , and different kinds of eggs and larvae ( morton and thurston , 1989 ) .
this is reflected in a small , reduced stomach , and strongly modified gills that have lost their filtering capacity ( morton and thurston , 1989 , waller , 2006 , mikkelsen and bieler , 2008 ) .
most extant species in the propeamussiidae inhabit bathyal or abyssal zones ( knudsen , 1970 , mikkelsen and bieler , 2008 ) , and their carnivorous life style clearly represents an adaptation to such environments in which suspended nutrients are usually scarce .
apart from the propeamussiidae , only some poromyida , which thrive predominantly in similar habitats , have developed carnivorous feeding strategies ( e.g. , knudsen , 1979 , poutiers and bernard , 1995 ) .
related to their feeding habits , most propeamussiids , including parvamussium , are free - living recliners , capable of swimming ( waller , 2006 ) .
the shell of the propeamussiid right valve consists of an inner layer of crossed lamellar aragonite , a very thin middle layer of lathic or foliated calcite , and an outer layer of columnar prismatic calcite .
in contrast , the shell of the left valve is composed of only two layers , i.e. an inner layer of crossed - lamellar aragonite and an outer layer of foliated calcite ( waller , 2006 ) .
the internal costae in both valves consist of lathic calcite and are embedded in the aragonitic inner layer . a major part of the hinge elements is also composed of aragonite .
this complex microstructure pattern explains the unique preservation of some of the specimens described above . in most specimens ,
furthermore , the internal costae became detached from the remainder of the shell , and are now commonly transposed onto the internal mould , simply because of a better adhesion to the marly sediment than to the smooth interior of the calcitic shell ( fig . 
moreover , the external ornament of the shells can be traced from interior view mainly because of the lack of the aragonitic shell portions ( fig . 
the shape and arrangement of the internal costae varies from almost straight and radial as seen in parvamussium mordsdrum n. sp . , to distinctly antimarginal as in p.  pizpuezense n. sp . to date
however , new internal costae are formed at the anterior and posterior ends of the disc in species with straight internal costae , whereas they are usually inserted between existing costae in species with antimarginal costae .
moreover , the growth of radial vs antimarginal costae must have involved different modes of shell morphogenesis , as has been suggested for shell folds by crampton and gale ( 2009 and references therein ) .
the fossil record of the propeamussiidae starts in the middle to late triassic ( hautmann , 2001 , waller , 2006 ; a carboniferous first occurrence date was proposed by mikkelsen and bieler 2008 , but has not been supported by data ) and , despite the relative scarcity of well - preserved deep - water assemblages , is largely continuous through all stages to the present day .
the great majority of propeamussiids has been recorded from ( fossil ) bathyal environments ( e.g. , lffler , 1999 , dijkstra and gofas , 2004 , del ro et  al . , 2008 , dijkstra and maestrati , 2008 , dijkstra and maestrati , 2010 , harzhauser et  al . , 2011 ) , although the family exhibits a total depth range from the intertidal zone down to c. 5000  m ( waller , 2006 ) .
it has been proposed that the propeamussiidae thrived in shallow neritic environments until the early cenozoic and subsequently retreated to greater water depths ( damborenea , 2002 , del ro et  al . , 2008 ) .
evidence from the puez formation of the dolomites ( piz de puez and ra stua ) as well as from the montagne des voirons ( pictet and loriol , 1858 ) , however , suggests that several species of parvamussium already were adapted to life at greater water depths during the early cretaceous .
cenozoic records of propeamussiids from shallow waters should be regarded with caution , since they may have come from regions that are subject to vigorous coastal upwelling , as has been suggested for lower pliocene deposits at velern - antena and velern - carretera ( estepona region , southern spain ; aguirre et  al . , 2005 )
that have yielded abundant propeamussiids ( lozano francisco , 1997 , studencka et  al . , 2012 ) ; thus , these records may represent exceptions from the rule .
waller ( 2006 ) and mikkelsen and bieler ( 2008 ) noted general sizes of up to 120  mm , but did not cite any particular species or references .
huber ( 2010 ) indicated a maximum shell height of 90  mm , measured for the recent propeamussium dalli ( e.a .
regardless of precise upper limits , it is clear that parvamussium pizpuezense n. sp . is medium sized , whereas parvamussium mordsdrum n. sp . , reaching 92  mm in length , clearly ranges into the top size class for the family . obviously , evolutionary size increase in the sense of cope 's rule is not the driving force of gigantism in propeamussiids , since exceptionally large taxa occur throughout the evolutionary history of the group ( waller , 2006 ) .
more likely , specific environmental factors , which remain unknown , may have promoted evolution of large species . in total , a single individual of p.  mordsdrum n. sp . and 16 specimens of parvamussium pizpuezense n. sp . from the puez formation at piz de puez have been collected ( including those stored at naturmuseum sdtirol , bolzano , which were not examined in detail for the present study ) .
thus , propeamussiidae account for a major portion of the autochthonous benthic fauna of the puez formation .
coincidentally , no shallow - water taxa are recorded from the respective sediments , which may clearly indicate deposition at significant depths .
the large individual of p.  mordsdrum n. sp . provides indirect evidence of a rich meiofauna ( potentially including inoceramid larvae ) , which generally is the preferred prey of the glass scallops .
in addition to bivalves , the autochthonous fauna of the puez formation comprises benthic foraminifera , scleractinia ( cycloseris ? ) , serpulidae ( glomerula ? ) , ostracoda , brachiopoda ( pygope , triangope ) , ophiuroidea and echinoidea ( lukeneder and aspmair , 2006 , lukeneder , 2008 ) .
discoid solitary corals of the genus cycloseris ? settled exclusively on dead ammonite shells and achieved a maximum diameter of more than 40  mm ;
such corals are inferred to have lived for several years ( lukeneder , 2008 ; compare also hamel et  al . , 2010 ) .
similar conditions can be deduced from pygopid brachiopods , which are usually also inferred to have favoured low - energy , deep - water environments with low sedimentation rate ( kzmr , 1993 , lukeneder , 2002 ; compare also vrs , 2005 ) .
bivalvia from the lower cretaceous puez formation at the type locality , piz de puez ( dolomites , south tyrol , northern italy ) , occur in very low abundance .
given the amount of sedimentary rock screened over the past decade , however , the bivalves examined here , numbering fewer than 50 , are inferred to represent a reasonably comprehensive sample of the once - living fauna .
small oysters and atreta have been found attached to the outside of ammonite shells and are interpreted to be allochthonous elements .
however , the collection also provides insight into an autochthonous mesozoic deep - water bivalve community , which is dominated by glass scallops of the genus parvamussium .
the abundant parvamussium pizpuezense n. sp . and the rare , giant p.  mordsdrum n. sp . presumably were adapted to low - nutrient deep - water conditions , living as epifaunal - reclining carnivores and preying on various meiofauna .
scarce epifaunal , suspension - feeding inoceramidae probably indicate occasional recruitment of larvae into an environment with low levels of suspended organic matter .
the two new species of parvamussium from the dolomites and the contemporary p.  agassizi ( pictet and loriol ) from southern france clearly show that several members of this genus had adapted to deep - water environments as early as the early cretaceous , and thus occupied a similar ecological niche to their modern counterparts .
 a bivalve assemblage from the lower cretaceous puez formation at the type locality , piz de puez ( dolomites , south tyrol , northern italy ) is described . 
 given the large amount of sedimentary rock screened during the course of this study , the < 50 bivalves examined here , although occurring in very low abundance , are considered to represent a reasonably comprehensive sample . 
 the assemblage provides insight into an autochthonous , mesozoic , deep - water bivalve community , which was dominated by glass scallops . 
 two species are described as new , parvamussium pizpuezense n. sp . and the giant p.  mordsdrum n. sp . 
 presumably , they lived as epifaunal - reclining carnivores and preyed on various meiofauna , occupying a similar ecologic niche as their modern counterparts . 
 scarce epifaunal , suspension - feeding inoceramidae entered only by occasional recruitment of larvae into an environment that is inferred to have been characterised by low levels of suspended nutrients . 
Introduction
Geological setting
Material and methods
Systematic palaeontology
Discussion
Conclusions