Rivista Italiana di Paleontologia e Stratigrafia volume I u I numero 3 tavola 1 pagrne J,/ r-Jòu Dicembre 1995

BIOMECHANICAL FRAGMENTATION IN SHELL-BEDS FROM THE LATE OF THE LOMBARDIAN BASIN (NORTHERN ITALY). PRELIMINARY REPORT

ANDREA TINTORI

Key-zaords: Triassic, Biofragmentation, , Durophagy, Pa- possible origin for the shell fragments found in the leoenvironment. shell-bed in the Zogno2 vertebrate locality, of the upper-

Riassunto. Frammenti di conchiglie sono molto diffusi nelle most (Zorzino Limestone) (Tintori, coquine presenti sia al tetto del Calcare di Zorzino che nelle sopra- I993b). In addition, several shell-beds in the younger stanti unità bacinali Norico-Retiche, benchè depostesi in a ambienti upper Argiliite di Riva di Solto (Riva di Solto Shale, bassa energia. IJaspetto spigoloso dei frammenti, in associazione alla ARS2 of ef al., 1,994) show complete individuals presenza di evidenti tracce di predazione del tutto simili a quelle do- Jadoul vute ai moderni pesci, fa ritenere che la bioframmentazione ad opera or single valves together s/ith sharp shell fragments of dei numerosi pesci durofagi fosse molto imponante già nel Triassico the same kind of those from th.e Zogno2 shell-bed. The Superiore. few complete fishes that have been found in the upper Riva di Solto Shale belong to durophagous species (Tin- Abstract. Shell-beds rich in shell fragments are very common 1983 pers.obs.). in the Lombardia basinal facies in the Late Triassic. Biofragmentation tori, and Scattered remains, which are by durophagous fishes, which were very common, must be regarded quite common in the shell-beds themselves, have also as the main taphonomic process on the basis of the shape of frag- been identified as belonging to durophagous species. ments and the presence of predatory traces, such as semicircular Ejecta and coprolites found, togerher with com- notches on the fragment edges or punctures on whole valves. Scatte- plete and well articuiated vertebrate specimens, above red patches of shell-fragments are also common and are considered as ejecta andlor coprolites from durophagous fishes. Funhermore, shell and below the shell-bed in Zogno2, contain similar shell material fragmented by living [ìsh (Pogonias crornis and Diplodus sar- fragments (Fig. 3). grs among others) is comparable in shape with the Triassic material presented here. The shell-beds here described were deposited in a low energy environment, which precludes waves or currents mechanical P.za Brembma damages. Paralepi"dotus ornatus, the most common Triassic duropha- gous , pycnodonts, other semionotids and the placodont reptile I Parina Psephoderrna alpinum, are the most important shell-predators in the Val Taleggio Late Triassic. Modiolus, Laternula and Protocardia were the more commonly preyed mol1uscs.

Introduction.

The Late Triassic of Lombardy yields severai fossi- liferous levels, the most important of which are those rich in nicely preserved vertebrates (Fig. 1). During the initial stage of a new research program f4. intended to compare the dentition and the diet of mo- dern durophagous teleosts with those of Late Triassic neopterygians found in those sites, I observed fragmen- ted lamellibranch shells, together with rare whole valves, from the gut content of the white bream Diplodus sargus Map of the Bergamo area. Asterisks mark the cited fossil (Fig. 2) Such biomechanical fragmentation provides a sltes.

- Dipanimento di Scienze della Terra, Università degli Studi, Via Mangiagalli 34,L2A83 Milano. 372 A. Tintori

F;o ) Donax shell material from the gut of a recent Diplodus sar- Ejecta made of fragmented ModioLus-lìke shells. Zorzino gzs. Note the presence of rare whole valves. Scale-bar: 10 Limestone, , Late Triassic, 82 locality near Brembil- mm. la (Bergamo-Italy). Scale-bar: 1O mm.

Biological shell fragmentation. assemblages, it may be difficult to establish if fragments were generated by sediment compaction crushing whole The importance oI biomechanical fragmentation valves or during collection and preparation of the sam- of shells has been reported for recent environments (Tre- ple, or if fragments were originally present in the rock. win & \flelsh, 1976; Boucot 1981.; Vermeij, 1993; Cadée, , Only a careful survey in the field and time-consuming 1,994; Cate & Evans, 1994) but has received less empha- preparation will allow identification of in-piace' crus- sis in paleoenvironmental studies. Several authors deal hed shells versus isolate fragments. Furthermore, frag- with evidence of fossil-shell predation (see for instance ments produced by predators, could be reworked in a Boucot, 1981, 1990; Robba 6c Ostinelli, 1925), but high energy environment or weakened by bioerosion, so usually only for paleobiological purposes. Furthermore, that the original fragment characters wrll disappear (Tre- in most cases they refer to repaired shells of molluscs win & Velsh, 1976; Cadée,1994). Thus, rapid burial is (repaired shell) were which could survive the attack or required ro'freeze' in a sheil-bed the original structure left almost complete even if predation was successful. of shelly material (see for instance Trewin 6c 'ù7e1sh, (1968), (1972) and Robba Carter Boyd & Newell & 1972) so that reliable identification of the origin of sheil Ostinelli (1975) recorded shells showing sequences of fragments would be possible. Following Kidwell (1991) holes, possibly from teeth of fish, which are represented classification of shell-beds, our coquinas are confidently in the assemblage only by isolated teeth or otoliths. assigned rc single event-concentration type, thus caused Zangerl and Richardson (1963, pp. 135-138, pl. 44, fig. by a rapid and simple process, mostly consisting in tur- D) figured ejecta (gastric residue pellet) similar in shape bidity currents or storm concentrations. These coquinas and size to those from the Zorzino Limestone and recor- are much harder than the surrounding shaly or marly ded large amounts of shell fragments. Though they layers and can be easily collected in large slabs. "have no record of possibie predators on molluscs", in my opinion their ejecta can be confidently ascribed to Material and methods. fishes, as the much more common eiecta made of fish remains. Late Triassic shell-beds from L.ombardy, though However, in general, only identifiable fossils are tightly cemented, offer the opportunity of sound obser- described in palaeoenvironmental studies. Fragmented vations if well prepared. Zogno2 shell-bed shows a thin material is generally not described. Dealing with fossil marly film covering the lower surface, which is the Trizs sic biofragmentation 373

more interesting because conrains the largest fragments. The possibility that a graded-bed is produced by in-pla- Slabs which remained exposed for at least a couple of ce bioturbation (Cadée, 1.976; Trewin & Welsh, 1976) is years show a natural preparation because atmospherical here not considered because, generally the sea bottom agents leave shell-fragments in good evidence. In this was anoxic as the preservarion of hundreds of totally case, it is sufficient to remove the remaining shale in articulate fishes and other organisms undoubtedly indi between the fragments. Freshly collected slabs un- cate (Tintori , L992). derwent a repeated trearmenr with hot (boiling) dilute Shell material found in ejecta and coprolites, from hydrogen peroxide for few minures followed by drying this and other similar localities (Fig. 2), shows the same in a stove. After each cycle the softed matrix was remo- shape and size of that from the shell-bed. It must be ved by thin needles. pointed out that ejecra and coprolites have been preser- The Riva di Solto Shale shell-beds must be mecha- ved only because of anoxic bottom conditions and lack nicaliy prepared. Shell material is very thin and fragile of reworking. and the shaly matrix, soaked with ethyl alcohol, can be easily removed by needles from both the lower and up- per surfaces. The Riva di Solto Shale shell-beds. Careful investigations of prepared surfaces allow to Shell-beds are also common in the units overlying discriminate whole valve crushed in place by sediment the Zorzino Limestone, namely the Riva di Solto Shale compaction (Fig. 5; Pl. 1, fig. A), from original isolated and the Calcare di ht (Zu Limestone), reaching 2-3"/o of fragments. So far only qualitative analysis has been carri- the whole thickness in some members (Boccaletti, 1983; ed on, mainly in the search of predatory traces. Jadoul et al., 1994). They are currently interpreted as storm layers (Boccaletti, 1983; Masetti et al., 1989). De- positional environment had to be rather quiet, apart for The Late Triassic shell-beds. storm-waves, judging from shales and marls surrounding shell-beds (|adoul et al., 1994). Higher environmental The Zogno2 shell-bed. energy is also represented by thick oolithic or bioclastic The thin shell-bed at the Zogno2 locality lies at beds that show totaily different characters (Boccaletti, the top of level 10, a 30 cm thick fossiliferous unit (Tin- 1983; Lakew, 1990) and are common in the upper part tori, 1993b), just below the barren, unlaminated bed 9. of the sequence. In this preliminary reporr, only a few The shell-bed has an irregular thickness, varying be- coquinas from the upper Riva di Solto Shale (ARS2 of tween two and three centimeters and usually splits in Jadoul et aI.,1994) have been investigated. two sub-units. The lowermost sub-unit yields the largest The dominant bivalves in these latter coquinas are fragments and the rare whole valves. Almost all the frag- small endobiontic pelecypods such as Protocardia, Nucu- ments are from Modiolus shells (Pl. 1, fig. B), mostiy of lana, Laternula. Bissate epifauna was srill presenr, small size. In addition, very rare Isognomon and 'Macro- though very rare in most cases. Again scattered remains dus' are present. All shell fragments show sharp edges of vertebrates are relatively common and most can be and corners and, in a few cases, small semicircular ascribed to durophagous organisms (Brembodus, Sargo- notches are visible along the otherwise straight edges don, and Psepboderma) for which teeth (Pl. 1, fig. C, D). These notches can be confidently con- have been found and identified by the author. The pre- sidered as predatory traces as similar ones have been de- servation of vertebrate isolated elements can be related tected on shell fragments found in the gut of Diplodus to absent, or very short, sediment reworking. The up- sargus (Fig.4). Minute remains of bone, teeth and scales per surface of these storm-layers, consists in a pavement are scattered among shell material. of whole valves or articulated specimens, while sharp In thin secrion, bioclasts appear densely packed, shell fragments are very common in the lower part of with some intraclast and scarce micritic matrix. A size each layer (Pl. 1, fig. A). Shell convexity is mainly gradation is present, so that a deposition by a turbidity upward directed. Rare subcircolar holes are present on current may be assumed. Turbidites have been already upper complete specimens (Fig. 5A), as well as notches recorded in the Zorzino Limestone basins and in areas along the sheli edge (Fig. 5B). These boreholes can con, more proximal than the fossiliferous sires they are much fidently identified as tooth marks, though it cannot be more common (fadoul, 1936). The paleotopography of checked whether the inner side was chipped, which the area (iadoul et al., 7992) and lack of an erosional usually is the case for tooth punctures in shells preyed base of the shell-bed, implies that the original slope was by Diplodus sargus (Fig. 4). This morphology, for im- not steep and the source area was nearby. Furthermore, pact-holes, is probably independent from the mecha- slope instability is proved by slumped laminated beds in nism causing it. Pether (1995) ascribes similar holes on the same vertebrate level at Zogno2 (Tintori, 1993b). Holocene Tellina shells to the new ichnogenus -Beli Pl. 1 A. Tintori Tr ia s s i c b i ofr a gm en tati o n 375

Fio 4 Selected Donax shell material from the gut of a recenr Diplodus sargus, showing different kind of tooth-marks. a, exterior and b, interior view of same punctured whole valve; full arrow, exterior, and open arrow, interior view of tooth-notches along the valve edge or a fracture line. Note the flared inner edge of tooth traces. Scale bar: 1O mm. chnus, rnterpreting them as due to stomatopod crusta- Boreholes by gastropods and cephalopods show a ceans. Actually, those Tellina specimens have been de- more regular shape and have a more restricted strati- scribed after a mining process which involves separarion graphic range: the first are known only since late Early of coarse sediments by energetic sieving. Furrhermore, for gastropods and Pliocene for octopus ce- there is no notice of similar behaviour by living sroma- phalopod (Sohl, 1969; Robba Ec Ostinelli, 1925; Boucot, topod (Pether, 1995). Shells vzith mechanical impact- 1990). A single find of possible naticid gasrropod bore- hole, showing one-side flaring, can be found in high holes from the Carnian Cassian Formation of Northern energy environment such as beaches made of coarse Italy is recorded, but it is usually considered as an isola- sand and small pebbles (pers.obs.). Thus, depositional ted experiment (Fùrsich k Wendt, 1977). environment is very important in interpreting the origin Diagenetic features, such as pseudo-borings by of similar boreholes: higher is the environmenr energy, pressure-dissolution (Lescinsky & Benninger, 7994) can lower is the confidence on rheir orisin. also be excluded for our Norian samples, because of the

PLATE 1

Fig. A - Lower surface of a shell-bed from Riva di Solto Shale - Member 2, Berbenno (Bergamo, Italy). Fragments and isolated complete valves (mainly showing downward directed concavity) are irregularly rrrixed. Scale-bar: 10 mm. Fig. B-D - Lower surface of the Zogno2 shell-bed (Zorzino Limestone, Zogno, Bergamo, Italy), showing the largest fragments due to size-grada- tion. Arrows point to tooth-marks. Scale-bars: 10 mm. 376 A. Tintori bored shells were covered only by the shaly matrix. separated by shaly or marly layers which often yield Furthermore, the subcircular shape of the holes do not scattered bivalves, commonly articulated, but rarely in fit for the flat shell fragments making the coquina bed. life position. Dominance of infaunal bivalves does not preclude predation from fishes, especialiy from those with pre- hensii chisel-like anterior teeth (Brembodus, ). The vertebrate durophagous fauna. In fact, the recent Diplodus sargus can exciusively prey Durophagous vertebrate fauna of the Zorzi.no on infauna (see the Donax remains of Fig. 2 which Limestone include the most common marine reptile made the only gut content of a couple of specimens). species, the placodont Psephoderma alpinwm (Pinna & The matrix of these shell-beds is fine-grained, indicating Nosotti, 1989; Renesto & Tintori, 1995), and at least a quiet environment, well below normal wave base whe- eight out of the 40-50 fish species, the pycnodonts re mechanical shell breakage is unlikely. Storm-beds are Brembodws, Gibbodon and Eornesodon (Tintori, 1981), I-egnonotus and an undescribed Macrosemiidae (Tintori & Renesto, 1983) and the semionotíds Sargod,on tomicus, noricurn and Paralepidotus ornatus (Tintori, 1983; in press). The presence of teeth of these species in the shell-beds of the Riva di Solto Shale and the Zu Limestone, is evidence of their survival until the end of the Triassic. Each of these organisms has a peculiar fee- ding activity, that can be inferred from the type of den- tition and body shape and size. Pycnodonts, for instan- ce, possibly fed on encrusting organisms, which were detached by their nibbling anterior teeth and then crus- hed by the molariforms, as well as on freeliving shelled benthos. Gut content of a few pycnodonts (Lehman, 1966; Viohl, i990) proved they predated on echinoids, corals and bivalves. At Norian time pycnodonts were small and relatively uncommon. Therefore, prey species would include only small organisms. Similarly, the ma- crosemiid lzgnonotus was only a few centimetres long and its teeth were not very powerful. On the other hand, both Psepboderma and Sargodon were large, rea- ching respectively 2m and 1m in length, but they were also rare. Paralepidotus ornatus was, by far, the most common fish feeding on shelled molluscs. So far, about one hundred specimens ol Paralepidotus ornatus have been prepared, ranging from seven up to 50 cm in stand- ard length (Tintori, in press). Crushing teeth are borne by the vomers and the dermopalatines as well as by the dentalosplenial and the coronoid in the lower jaw. When Paralepidotus reach,ed a standard length oÎ 25-30 cm its teeth became hemisphericals, which are weii adapted to crush shelled mollusc (Tintori, 1,992).In ad- dition there are some indications of schooling, since rare mass mortality events affected several specimens of Paralepidotus ornAtLts, mainly of similar size (Tintori, 1993a). Thus, it is probable that Paralepidotus is the main shell fragment producer in these Norian basins and most of the shell-bearing ejecta can be confidently

A and B, Protocardia whole valve from the upper surface ascribed to it. Crustaceans too could prey on molluscst of a Argillìte di Riva di Solto (Member 2) shell-bed from however only a few undescribed, very large specimens Berbenno (Bergamo, Italy), Norian, Late Triassic. Vhite seem to be adapted to this trophic niche (see also Pinna, arrow, possible tooth mark; black arrow, whole valve 1974; Garassino Teruzzi, 1993), so impor- showing in place fragmentation due to sediment compacta- & that their tion. Scale bar: 10 mm. tance had to be limited i

Tr ias s i c b i ofragmen tati o n 377

Discussion. ving rise to many marine durophagous species. The pre- sence of numerous durophagous predators suggests the The feeding activity of modern durophagous fish possibiiity of high rates of biomechanical shell fragmen- such as Pogonias crornis (the Black drum, see Cate & tation. Evans, 1994) or Diplodus sargus (the white bream, Bini, Possibly, shell fragmenrs now found 1970), suggests that biomechanical fragmenrarion by Tri- in the Zo- gno2 shell-bed remained close ro the mollusc (mainly assic durophagous may have been an important source Modiolws and Isognomon) banks were Paralepidotus fed. of shell fragments. Late Triassic shell-beds are often rich Accumulation of large amounts of these in shell fragments, ejecta and coprolites conrain similar bioclasts along the upper part of the basin flanks, led to local instabili- shell fragments. This cannor be considered as a 'frozen ty and, perhaps during a storm, to turbidity currents or behavior', caregory 1 of reliabiliry sensu Boucor (1,990), to mass flows (see also et al., 1992) that ran along thus a direct prove for fishes eating shell, especially if Jadoul .want the gentie slope for a rather short distance in the same we to ascribe these traces to a single fish species. way as other coarse-grained shallow sediments (fadoul, Actually, shell fragments have never been recorded in 1986). The iive attached bivalves were nor removed by the coelomatic cavity of our Triassic fishes. This may be storm waves (Fig. 6A). The result was thar shell due to the fact that most hard material is often rejected only fragments were redeposited in a thin layer along the after being crushed in the mouth (Cave, 1,978; Buxton & iower pan of the basin flank, in anoxic waters. This Clarke, 1991). In addition, hear.y scale covering of mosr storm event could also mix the oxic and anoxic waters, of the Norian fishes precludes observations of the inte- leading to a temporary oxigenation of the bottom. The rior. FIowever, I feel confident in assigning these shell barren, nonlaminared level 9, which overlies the shell- fragments to reliability cafegory 2A ('close association bed, may represent the record of this oxic or disaerobic of a behavioral nature, bur nor actually in position', stage, when a few benthic organisms could colonize the Boucot 1990), considering them to be remains of bivalve usually anoxic bottom, predation by fishes and reptiles. In the Late Triassic, The round, flat ejecta and, more rarely, cylindrical neopterygians undergo their first important radiation gi- coprolites made of shell fragments which are present in the laminated beds yielding vertebrares above and below the sheli-bed, can be explained as fish moving a few hundreds of meters from their feeding environmenr and egesting or defecating, in this case, above the anoxic part of the basin. Though this behaviour is uncommon, de- mersal fishes having usually a rarher restricted living area (Boucot, 1981), it has been proved in modern fis- hes, whose gut-content is very rarely made of exotic shell material (Cave, 1978; Cate & Evans, 1994). Sharpness of the fragments in the shell-bed, ejecta and coprolites, comparable with that from iiving fishes gut content (Cate & Evans, 1994; pers.obs.), impiies that H they were neither submitted to a high energy environ- {)v_\/ l\l ,{ll " U ll rt tD " " "oU * - ment, such as beaches or tidal channels, /-.Ns c? where bioclasts are abraded and rounded, oo o \ I 0 o A ^ nor to long post-mortem ex- posure that leads to encrustation or boring by algae and other organisms (Cadée, 1968). Thus, it is assumed that Blll I the fish mouthed and crushed live molluscs, and nor vv\y previously fragmented shells, during their search for ---É# food on the bottom. #:Z--,- q *,-s'-- s:-"="i-4:-_-": Also, monotypy of preys is characteristic of bot- tom-feeding fishes, which prefer to predate mainly on a single locally abundant species, changing only under un- Fig. 6 - The origin of shell-beds. A) Zogno2: storm-waves rewor- favourable (Dugas, ked loose fragments, mainly from fish-predation, leaving condition t986). Bivalves living byssate live specimens in place. A turbidite current rran- around the anoxic part of the basins were mainly byssa- sporred the fragments down to the anoxic pan of the ba- te and pooriy differentiated, with local dominance of a sin. Only fragmented shells are present. B) Riva di Solto single or few species. For instance, in the same srrari- Shale (tr{ember 2): storm-waves winnowed fine-grained se- diment, concentrating shells in place. Live, dead and frag- graphic position of the Zogno2 shell-bed, in a adjacent mented shells are represented. area of Val Taleggio (Gaetani & Tintori, 1.979), there is a 378 A. Tintori

similar one made of whole valves of Modiolus, Isogno- REFERENCES rnon, Geroillia and'Macrodus', more or less in the same proportions. Presence of fragments of a single species in the Zogno2 shell-bed can be related either to the presen- Bini G. (1,97A) - Atlante dei pesci delle coste italiane. Osteitti, ce of monotypic banks in the source area or to selective v. 4,763 pp., Mondo Sommerso Ed., Roma. Boccaletti M. (1983) - Geologia delle alte Valli Taleggio e Ima- feeding on Modiolus. \Whole valves of Modiolus and Iso- gna e microfacies del Calcare di Zu. Unpub. Thesis, gnomon, are common in the vertebrate levels, together Unip. Milano,203 pp., Milano. with other benthic invertebrates (pers. obs.). FIowever, Boucot A.J. (1981) - Principles of Benthic Marine Paleoecolo- Modiolus has a shell and a more elongate shape thinner gy. V. of 463 pp., Academic Press, New York. than Isognomon. These characters may explain the small Boucot A. J. (1990) - Evolutionary Paleobiology of Behavior mouthed Paralepidotus preference in handling Modiolus and Coevolution. V. of 725 pp., Elsevier, Amsterdam. rather than Isognomon. Boyd D. \7. E< Newell N.D. (1972) - Taphonomy and diagene- In the Riva di Solto Shale most of the shell-beds sis of a fossil assemblage from 'lflyoming. can be interpreted as in place storm reworking of a li- Journ. PaLeont., v. 46, pp. 1-15, Lawrence. ving community of endobiotic molluscs in a muddy Buxton C.D. EÈ Clarke J.R. (1991) - The biology of the white bottom. In this case, live, naturally dead and preyed Musselcracker Sparodon durbanensis (Pisces: Sparidae) on the Eastern Cape Coast, South Africa. J. Afr. Mar. shells were concentrated as the storm waves reworked J. Sc., v. 10, pp.285-296, Cape Town. the superficial sediments, moving away most of the mud Cadée G.C. (1968) Moliuscan biocoenoses and thanatocoe- (Fig. 68). Later in sequence, shailower bottoms on the noses in the Ria de Arosa, Galicia, Span. Zool. Wrhan- (Boccaletti, 1983; Jadoui et a1., 1994) provrded higher del., v. 95, pp. l-121, Leiden. eîergy environments, so that biomechanical fragmenta- Cadée G.C. (1976) - Sediment reworking by Arenicola mari tion characters were canceled by physical and other bio- na oî rida,l flats in the Dutch \fadden Sea. Neth. J. Sea logical events. Res., v. 10, pp.44A-460, Amsterdam. Cadée G.C. (1994) - Eider, Shelduck and other predators, the '!?adden main producers of shell fragments in the Sea: Conclusions. Paleoecological Implication. PaLaeontology, v. 37, pp. 181.-2A2, London. It is highly probable, reliability category 2A of Carter R.M. (1968) - On the biology and palaeontology of Boucot (1990), that shell fragments making the Zogno2 some predators of bivalved mollusca. Palaeogeog. PaLaoe- sheli-bed were produced by feeding activity of bottom cLim. Palaeoec., v. 4, pp. 29-65, Amsterdam. dwelling fish (mostly Paralepidotu) in a shallow, quiet Cate A.S. & Evans l. (1994) - Taphonomic Significance o{ the environment along the basin margins. Similar origin can Biomechanical Fragmentation of Live Molluscan Shell be proposed for at least part of the fragments of the Material by a Bottom-feeding Físh (Pogonias cromi) in Texas Coastal Bays. Palaios, v. 9, pp. 254-274, Lawrence. other described shell-beds from the Riva di Solto Shale Cave R.N. (1978) - Predator-prey relationships involving the member 2, though in a different environment and with American oysrer, Crassostrea oirginica (Gmelin), and different depositional mechanism. the black dr:um, Pogonias cromis (Linnaeus), in Missisipi The possibility that sheil-fragments in other Me- Sound. Unpubl. Thesis, Soutbeastern Louisiana Unio., 43 sozoic and post-Mesozoic single-event shell-beds are bio- pP. mechanical in origin rather than produced by mechani- Dugas C.N. (1986) - Food habits of black drrm, Pogonias cro- cal fragmentation must be considered. Presence of scat- mis, in southeast Louisiana with emphasis on their pre- the American oyster, Crassostrea airginica. tered fish remains in shell-beds, can be considered as dation of Louis. Dep. V/ild. Fish. Contrib. Mar. Res. Lab. Tècb. Bull., particularly important in order of this identification sin- v. 40, pp. 32-38, Grand Terre Island. ce they are not usually preserved in high-energy envi- Fùrsich F.T. & \lendt J. 0977) - Biostratinomy and Palaeoe- ronments. cology of the Cassian Formation (Triassic) of the Sout- hern Alps. Palaeogeog. Palaoeclim. Palaeoec., v. 22, pp. 257-323, Amsterdam. Gaetani M. & Tintori L. (1,979) - The Upper Triassic in Cen- tral Lombardy. R. Assereto and G. Pisa Field Symposium Field Guide-Book, pp. 27-31, Mrlano. Achnouledgemmts, Garassino A. & Teruzzt G. (1993) - A new decapod crusta- Thanks are due to A. Cate (Houston) and G.C. Cadée (Den cean assemblage from the Upper Triassic of Lombardy Burg) for critical reading of the manuscript, as well for improving the (N. Italy). Paleont. Lomb., n.s., v. 1, pp. 1-27,Mtlano. language and providing me unavailable literature. E. Robba and C. F. (1986) - Stratigrafia e paleogeografia del Norico nel- Corselli spent time in discussing with me about molluscs. Drawing Jadoul by S. Renesto, photographies by G. Chiodi and the author, le Prealpi Bergamasche occidentali. Rit. It. Paleont. preparation o{ Triassic material by L. Manarolla. Strat.,v.91 (1985), n.4, pp. 479-51,2, Milano. Tr ia s s ic bi ofra gm en tation 379

Jadoul F., Berra F. & Frisia S. (1992) - Stratigraphic and paleo- Tintori A. (1981) - Two new Pycnodonts (Pisces, Actinopte- geographic evolution of a carbonate platform in an ex- rygii) from the Upper Triassic of Iombardy 0.{. ft"iy). tensional tectonic regime: the example of the Dolomia Ria. It. Paleont. Strat., v. 86, n. 4, pp.795-824, Milano. Principale in lombardy (Italy). Riv. It. Paleont. Strat., v. Tintori A. (1983) - Hypsisomatic Semionotidae (Pisces, Acti- 98, n. 1, pp.29-44, Milano. nopterygii) from the Upper Triassic of Lombardy Jadoul F., Masetti D., Cirilli S., Berra F., Claps M. Ec Frisia S. (N.kaly) Ria. It. Paleont. Strat., v.88, n. 3, pp. 417-442, (1994) - Norian-Rhaetian stratigraphy and paleogeo- Milano. graphical evolution of the Lombardy Basin (Bergamasc Tintori L. (1992) - Fish taphonomy and tiassic anoxic ba- Alps). Excursion 81 - 15th IAS Regional Meeting, sins from the Alps: a case history. Rio. It. Paleont. Ischia, Italy. Strat., v.97 (1991), t 3-4, pp. 393-408, Milano. Kidwell S.M. (1991) - The Stratigraphy of Sheli Concentra- Tintori A. (1993a) - Attritional aersus mass morraliry in No- tion. In Allison P.A. Ec Briggs D.E.G. (Eds) - Tapho- rian (Late Triassic) marine vertebrates from Northern nomy: Releasing the Data Locked in the Fossil Record, Italy. First European Palaeontological Congress: Orga- pp. 217-290, Plenum Press, New York. nism palaeoenvironment interactions. Abstracts, p. 125, Lakew T. (1990) - Microfacies and Cyclic Sedirnentation of Lyon. the Upper Triassic (Rhaetian) Calcare di Zu (Southern Tintori A. (1993b) - The Zogno2 locality. Mesozoic Fishes: \ r f\rps).^t rdctesl v. tz' pp. L6/-ztt. Eflangen. Systematics and Paleoecology. Field Guide Book., p. 39, Lehman JP. (1966) - . In Piveteau J. - Traité de Eichstàtt. Paléontologie, IV-3, pp. 1.-242,Masson Ed., Paris. Tintori A. (in press) - Paralepidotus ornatus (Agassiz, 1833- Lescinsky H.L. €t Benninger L. (1994) - Pseudo-borings and 43): a semionotid from the Norian (Late Triassic) of Predator Traces: Artifacts of Pressure-dissolution in Fos- Europe. In Arraria G. & Viohl G. (Eds.) - Mesozoic siliferous ShaJ,es. Palaios, v. 9, pp. 599-604, Lawrence. Fishes: Systematics and Paleoecology. Proceedings of tbe Masetti D., Stefani M. Er Burchell M. (1989) - Asymmetric First Intern. Meeting, Eichstàtt, 1993. cycles in the Rhaetic facies of the Southern Alps: Tintori A EE Renesto S. (1983) - The Macrosemiidae (Pisces, Platform-basin interactions governed by eustatic and cli- Actinopterygii) from the Upper Triassic of I-ombardy matic oscillations. Rlz. It. Paleont. Strat., v.94, n. 3, pp. (N. Italy). Riv. It. Paleont. Strat., v. 89, n. 2, pp. 2A9- 401-424, Milano. 222,Ml,ano. Pether J. 0995) - Belicbnus new ichnogenus, a ballistic trace Trewin N.H. E V'eish \L (1972) - Transpon, breakage and on mollusc shells from the Holocene of the Benguela sortirg of the bivalve Mactra corallina on Aberdeen be- Region, South Africa. J. Paleont., v. 69, pp. l7L-181, ach, Scotland. Palaeogeog. Palaeoclim. Palaeoecol., v. 12, Lawrence. pp. 19 3-2A4, Amsterdam. Pinna G. 0974\ - I crostacei della fauna triassica di Cene in Trewin N.H. Ec Velsh \L (1976) - Formation and composi- Val Seriana (Bergamo). Mern. Soc. It. Sc. Nat., v.21., pp. tion of a graded estuarine shell bed. Palaeogeog. Palaeo- 1-33, Milano. clim. Palaeoecol., v. 19, pp. 219-23Q, Amsterdam. Pinna G. & Nosotti S. (1989) - Anatomia, morfologia funzio- Vermey G.J. (1993) - A Natural History of Shells. Y. of 207 nale e paleoecologia del Rettile Placodonte Psephoderma pp., Princeton lJniv. Press, Princeton. alpinum Meyer, 1858. Mern. Soc. It. Sc. Nat., v. 5, pp. Viohl G. (1990) - Piscivorous fishes of the Solnhofen Litho- 17-50, Milano. graphic Limestone. In Boucot A.J. - Evolutionary Paleo- Renesto S. & Tintori A. (1995) - Functional morphology and biology of Behavior and Coevolution, pp. 2874A3, EI- the ecology of the Late Triassic placodont Psephoderma sevier, Amsterdam. alpinum Meyer. Riv. It. Paleont. Strat., v. 101, n. 1, pp. Zangerl R. & Richardson E.S. (1963) - The paleoecological 37-48, Milano. history of two Pennsylvanian Black Shales. Fieldiana Robba E. & Ostinelli F. (1975) - Studi paleoecologici sul Plio- Geol. Mem., v. 4, pp. l-239 , Chtcago. cene ligure. I. Testimonianze dr predazione sui Mollu- schi pliocenici di Albenga. Rio. It. Paleont. Strat., v. 81, n. 3, pp. 309-372, Milano. Sohl N.F. (1969) - The Fossil Record o{ Shell Boring by Sra:ls. Am. Zool., v. 9, pp.725-734, Lawrence. Receipd Marcb 23, 1995; accepted September 30, 1995