Excavated in 1949, Grotta dei Moscerini, dated MIS 5 to early MIS 4, is one of two Italian Neandertal sites with a large assemblage of retouched shells (n = 171) from 21 layers. The other occurrence is from the broadly contemporaneous layer L of Grotta del Cavallo in southern Italy (n = 126). Eight other Mousterian sites in Italy and one in Greece also have shell tools but in a very small number. The shell tools are made on valves of the smooth clam Callista chione. The general idea that the valves of Callista chione were collected by Neandertals on the beach after the death of the mollusk is incomplete. At Moscerini 23.9% of the specimens were gathered directly from the sea floor as live animals by skin diving Neandertals. Archaeological data from sites in Italy, France and Spain confirm that shell fishing and fresh water fishing was a common activity of Neandertals, as indicated by anatomical studies recently published by E. Trinkaus. Lithic analysis provides data to show the relation between stone tools and shell tools. Several layers contain pumices derived from volcanic eruptions in the Ischia Island or the Campi Flegrei (prior to the Campanian Ignimbrite mega-eruption). Their rounded edges indicate that they were transported by sea currents to the beach at the base of the Moscerini sequence. Their presence in the occupation layers above the beach is discussed. The most plausible hypothesis is that they were collected by Neandertals. Incontrovertible evidence that Neandertals collected pumices is provided by a cave in Liguria. Use of pumices as abraders is well documented in the Upper Paleolithic. We prove that the exploitation of submerged aquatic resources and the collection of pumices common in the Upper Paleolithic were part of Neandertal behavior well before the arrival of modern humans in Western Europe.

Funding: National Science Foundation Grant 1118143, BCS Archaeology, to PV (PI) and SS (co-PI). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability: All relevant data are within the paper and its Supporting Information files. The lithics and shell materials from Grotta dei Moscerini are housed in two places: 1. Istituto Italiano di Paleontologia Umana Convitto Nazionale Regina Margherita, in the town of Anagni (Latium, Italy). 85 artifacts and 17 retouched shells are housed in the Pigorini Museum of prehistory and Ethnography in Rome. The pumices are housed in the Istituto Italiano di Paleontologia Umana in the town of Anagni.

Copyright: © 2020 Villa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

An ESR chronology from Moscerini was published in 1991 by [ 5 ] together with amino-acid chronology (AAR) measurements on molluscs. As the site was no longer accessible for additional sampling, small remains of sediments adhering to some sampled teeth provided U, Th and K content for the estimation of dose rate. Thus error ranges are not listed. Red deer teeth and one hippopotamus tooth from layers 39, 38, 35, 33, 26 and 25 were analyzed. Except for those from layers 35 and 25, two sub-samples were measured for each tooth. In the absence of in situ measurement of external dose rate, these ESR dates must be considered cautiously and cannot support any detailed interpretation of the chronology of the archaeological sequence. The lower part of the sequence might have accumulated during MIS 5, in agreement with [ 5 ] correlation of the basal sandy beach deposits (layer 44) with the Last Interglacial supported by AAR (amino acid geochronology). The upper part might date to the end of MIS 5 or beginning of MIS 4. Table 1 shows the dates obtained using the Linear Uptake (LU) results since the Early Uptake model yields what may be considered minimum ages [ 2 ].

Numbers to the left are meters below datum, numbers in smaller font are layers. Red shading indicates all layers with the retouched shells described in the present paper. Blue shading corresponds to layers of which the lithic industry was analyzed by us. The grey dots mark layers that contained one or more pumices. Based on Segre’s observations, layer 16, layers 35–36 and especially layer 44 contained pumices but we did not find these pumices in the material stored at Anagni. Drawing by Sylvain Soriano based on field drawings and information provided by Aldo Segre, courtesy of Aldo Segre.

Artifacts are present throughout the sequence from layer 41 up to layer 14 but they become rare upward to layer 1. Evidence of fire (charcoal and ashes, sometimes burnt bones) occur in almost all layers (layers 11, 14–16, 18–19, 22–26, 29–33, 35, 36, 38–41). Yellow and light grey pumices occur in several levels (grey dots in Fig 3 ).

Many layers are sandy with small angular clasts; two layers (41–40) consist of sandy-clay fill with rare pebbles (4 and 8 cm in diameter respectively). Four episodes of rock fall are documented in layer 3, layers 8–9, layers 27–28 and layer 38. Excavation photos in Stiner [2: 3.14; 3.19 A] show many fissures in the cave vault, probable cause of the rock falls present in the deposits. A wave-cut notch and several rows of lithodomes i.e. holes formed and inhabited by bivalves that live mainly in the area battered by waves (Lithophaga lithophaga, Linnaeus 1798) present on the north wall ( Fig 2B ) at approximately the level of layers 8–20 [2: p. 47] and are thought to mark the maximum level of the sea corresponding to MIS 5.5. At that time the cave was probably free of continental deposits, totally washed out by the high sea level. Lithodome scars were also noted by Segre on the large limestone blocks of layer 38, most likely fallen from the cave wall.

The top of the sequence is sealed by a 25 cm thick stalagmite horizontal layer (layer 2). The lowermost layer (layer 44) is a sandy deposit rich in marine molluscs. Strombus bubonius was not seen by [ 2 ] but was recorded in Segre’s field notes. Its lowest level also had many yellow and light grey pumices and some unretouched pebbles of 4–5 cm in diameter. It is interpreted as a sandy beach deposit and considered to date from the Last Interglacial. Layer 42 is described by Segre as a volcanic tuff. Layer 41 is the first archaeological layer with a stalagmitic lens at the base and few stone artifacts (N = 7).

The site is no longer accessible because it was buried in early 1970s under rocks and boulders blasted from the side of the hill during construction of the coastal highway (Via Flacca). Thus none of the scholars who first studied fauna or industries [ 2 – 4 ] were able to enter the site.

(A) Plan view of Grotta dei Moscerini. (B) Cross-sectional view of the cave with estimated extent of cultural deposits prior to the Holocene sea rise. The numbers correspond to layers in Fig 3 . Drawing by Sylvain Soriano based on field drawings by the late Aldo Segre.

A test pit was opened inside the cave approximately 15 meters away from the modern entrance ( Fig 2A ). It was excavated by arbitrary levels (labelled Interno 1 to Interno 4, from the top to the base). It is impossible to correlate the main section and the internal trench but according to [ 3 ] it is likely that these levels correspond with the latest layers from the main section. If we take into account the gentle dipping of layers toward the interior of the cave, the layers from the internal test pit might be even (partly) younger.

The cave is close to the modern shoreline and the base of the stratigraphic section is about 3 m asl [2: fig 3.14]. The almost 9 m thick sequence was drawn and described by A. Segre in 1949 and divided into geological layers numbered (top to bottom) from 1 to 44. The archaeological materials were recovered and labelled according to these layers. According to photos taken during the excavation [2: fig 3.19 D] dry sieving with a relatively small (5 or 10 mm) mesh was used suggesting that there are minor recovery biases.

It was discovered during a 1936–38 survey of coastal caves from Rome to Gaeta by A.C. Blanc, A. Segre and co-workers of the Italian Institute of Human Paleontology. It was excavated in August 1949 under the supervision of A.C. Blanc [ 2 ]. A 2 m. by 1.5 m. trench was established on the deposits behind the dripline of the cavity. Since the main excavated area is small (only 3 sq m. representing 5% of the total preserved site area of 56 sq m.) the assemblage sizes for individual layers are also small.

Moscerini is one of the largest coastal caves in the Latium, between Sperlonga and Gaeta and about 5 km from Grotta Sant’Agostino [ 1 ]. The site is located at the base of a limestone cliff on the south-eastern flank of a small coastal promontory ( Fig 1 ).

The petrological analysis of the Moscerini pumices providing information on their texture and glass composition are discussed in the section “Origin of the Moscerini cave pumices”. Their mineralogical composition indicates a provenience from the Campanian volcanoes. Analytical procedures are described in the S1 File . Similar methods were used for the major and trace-element composition analysis of a pumice from a Middle Paleolithic cave in northern Italy (Grotta di Santa Lucia), see section “Analysis of the Santa Lucia pumice” and specific details of techniques in the S1 File .

Variations of density of lithic artifacts per layer (in blue) at Moscerini cave in the main excavation compared to the number of retouched shells per layer (in orange). Lithic pieces with broad provenience (layers 1–5, N = 4; layers 12–17, N = 36) where not included here. The internal test pit (layers Int 1. to Int. 4) is excluded from the analysis since the size of its excavated surface is unknown.

The low density of lithic finds in almost all layers forced us to group layers into three sets for the study, as done by Kuhn [ 3 ]. Layer INT 1 was included because it is the youngest layer of the series [3: p. 61]. Criteria for grouping layers are exposed in the S2 File p.3, and S2 File , Fig 5A . Tables detailing the technological composition of the assemblage for each layer are also in S2 File ( Table 2A and 2B and Table 3A and 3B ). Technological differences (frequencies of cores and flake types) between assemblages from each later are minimal and no significant changes can be seen on these grounds. Thus we choose to indicate the general assemblage composition in Table 2 , and to seek the technological and techno-economical differences through the use of significant ratios, as in S2 File , Fig 5B–5H . In the main text lithic analysis is used primarily to explore the significance of recycling, reworking and use of patinated blanks in relation to shell tools (see”Relationship of stone and shell tools”).

The study of the lithic and shell assemblages is based on quantitative and qualitative analyses, including metrical, taphonomic, technological and typological attributes, as described in previous publications [7: S5 File ]. We coded all specimens in Excel files. Photographs were taken with a Nikon D 800. The description of the lithic industry (text, tables and figures) is provided in the S2 File .

Permits to study and take photos of the materials were obtained from the President of the Italian Institute of Human Paleontology (Fabio Parenti and more recently Stefano Grimaldi) and from the Soprintendenza of the Pigorini Museum (Prot. N. 2408, 25.02.03/15 and MBAC-S-MNPE Pigorini Cl. 23.03.02/3).

Layers 16 to 37 and layers Interno 1 to 4 yielded 49 pumices or pumice fragments. They are kept in the storage area of the Italian Institute of Human Paleontology in the town of Anagni (Latium). Level provenience was written on paper labels; we added an inventory number and bagged each in individual plastic Minigrips.

Two features help in distinguishing the two species: 1. the distal edge (fringe) of Callista chione is smooth but it is indented in Glycymeris ( Fig 4B and 4D ); 2. the different morphology of the hinge ( Fig 4E and 4F ). Fragments that lack these portions of the shell are difficult to identify. The external surface of valves in Glycymeris is marked by radial lines from the umbo to the distal edge; in Callista the radial lines are so thin that the surface appears smooth and shining. However on beached specimens or specimens that have been altered (encrusted, abraded) in the cave these differences are no longer easy to see. Thus the species identification on shell fragments that lack the hinge or an intact distal edge is uncertain and may require microscopic analysis. All retouched shells were analyzed under a microscope by Carlo Smriglio and their identification as Callista is sound.

We examined all shells of Callista and extracted the retouched pieces, adding several specimens to the bag containing retouched pieces selected by previous workers. All the unretouched pieces in the archaeological layers, that is excluding layer 44 and 43 which are the beach levels at the base of the sequence, are heavily fragmented. We did not count the unretouched pieces due to the difficulty of distinguishing Callista from Glycymeris on fragments without the hinge, as noted by Stiner who provides a total of 1230 unretouched and retouched Callista and Glycymeris fragments summed together [2: table 6.12]. However using the ratio of total hinge specimens of Callista (n = 182) versus Glycymeris (n = 85) provided by Stiner [2: table 6.13] we can say that about 68% of the 1230, i.e. about 836 specimens are Callista fragments. This is a plausible estimate of the total retouched and unretouched Callista chione specimens in the archaeological layers.

Retouched Callista chione are found in many levels of Moscerini, from 42 to 14, for a total of 171 specimens. This large assemblage, including unretouched fragments, is housed in the Italian Institute of Human Paleontology in the town of Anagni, with 17 retouched specimens kept in the Pigorini Museum of Prehistory and Ethnography in Rome.

Differently from our previous studies of a Middle Paleolithic (MP thereafter) industry from Latium [ 7 ], the sorting threshold was lowered to 10 mm instead of 15 mm to enlarge our sample. Flake fragments without platform, flakes <1 cm and chunks were excluded from analysis. All cores, core fragments, tools, tool fragments were selected regardless of size.

The bulk of the lithic assemblage from Grotta dei Moscerini (N = 1139, excluding artifacts without stratigraphic provenience, labelled Ripulitura scavo, Ripulitura esterna or Esterno) is housed at the Italian Institute of Human Paleontology in the town of Anagni (Latium) whereas a small sample (N = 85) is stored and partly exhibited in the Pigorini National Museum of Prehistory and Ethnography in Rome. Of the 85 artifacts at the Pigorini Museum only 35 could be fully analysed; the rest of the pieces were in showcases, hence not available for detailed analysis. All modified shells were studied whereas we selected only the lithic artifacts coming from layers containing modified shells ( Fig 3 ). Layers 15, 16 and 20 where retouched shells are missing were added for stratigraphic continuity of data. With the exception of Interno 1, the highest and youngest level in the interior test pit, lithics from the lower levels of the test pit were not studied due to lack of correlation with the main excavation area.

Shell tools occur mainly in layers where the density of lithic remains is low; this is generally interpreted to mean that the frequency of shell tools is a response to raw material shortage. According to [ 23 – 25 ] shell tools were a response to poor availability of lithic raw material. It is in layers 26 to 22 that there is the highest frequency of shell tools and stone tools are less abundant. In this phase II, stone tools are very retouched (Fig 5: C in S2 File ) and there is low evidence of tool reworking or recycling (Fig 5: G in S2 File ) a fact also normally interpreted as due to a shortage of raw material and opportunistic reuse of older stone tools. But local flint from beach deposits is present indicating that the location of the outcrops was known but they were not intensively exploited. The highest frequency of double patina and the highest frequency of non-local flint, suggests that Neandertals of phase 2 arrived with a set of tools from afar and that at Moscerini they collected lithic resources in a very opportunistic way and at very close range. They may have moved to Moscerini cave for specialized tasks linked to coastal resources. In the Upper Paleolithic shell fishing was done most often in winter [ 26 ]. It seems that limited activities and ephemeral seasonal occupations are the reasons for the abundance of shell tools. Simply put, the cave has a long stratigraphic sequence but the human occupations were of short duration.

The density of lithics varies throughout the stratigraphy but it determines successive phases with unequal occupation intensity of the cave, the highest being from layers 21 to 14. Due to the small sample of stone tools from each layer we merged adjacent levels in four phases (Fig 5 in S2 File ) to emphasize changes throughout the sequence. Phasing was done with respect to variations in the amount of lithic and shell tools in layers.

The density of lithic artifacts per cubic meter (n/m 3 ) that can be used as a proxy of the intensity of site occupation varies greatly throughout the stratigraphy ( Fig 5 ; Table 7 in S2 File ). In most of the layers density is low or very low, especially in the top of the sequence, from layer 13 upward. In more than half of the layers, the density is equal or lower to 20 pieces per m 3 . Compared to other European MP cave sites such as Geissenklösterle (16 to 109 lithic artifacts/m 3 in MP layers), Hohle Fels (33 to 703 artifacts/m 3 ) [ 21 ] or Orgnac 3 (48 to 1974 lithic artifacts/m 3 ) [ 22 ], densities at Moscerini are low, except in layers 18, 20, 21 and 37, suggesting that occupations of the cave were very discontinuous and/or low intensity. For sure only a small area of the cave has been excavated and the frontal part of the deposits had been eroded by the rising of the Holocene sea ( Fig 3B ) [2 p. 46]. Even so the amount of fallen blocks is not enough to suggest that the greater part of the deposits had been removed. The cubic density of the remains is very low for a cave and it does suggest discontinuous and low intensity occupations.

Fig 5 shows that shell tools are unevenly distributed throughout the stratigraphic sequence at Moscerini so one can wonder if their manufacture and use can be a response to changes in lithic techno-economy, including raw material procurement. Does the use of shell tools correspond to a decrease in stone tools production and/or increase in the intensity of stone tool use (increase of retouched tools, recycling)?

The frequency of retouched tools on cores, pebbles or chunks (19.3% of retouched tools; Table 5 in S2 File ) is high. It is the same in the Early MP industry from level d at Torre in Pietra (19.8%) [ 7 ] but it is less frequent at Sant’Agostino layer A1 (9.7%) and at Fossellone layer 23 alpha (3.2%). Like the use of patinated blanks, recycling is recorded all along the stratigraphic sequence [for recycling at Grotta del Cavallo see 15 ]. Kombewa flakes (flakes from flaked-flakes on ventral surface; 5.2% of flakes, retouched or not) are more frequent than in other MP of the area we studied (Fossellone layer 23 alpha: 2.3%; Sant’Agostino layer A1: 0.9%; Torre in Pietra level d: 1.4%). Recycling includes also the production of flakes on ventral face of retouched tools (Fig 4: C in S2 File ) or on dorsal face of flakes or retouched flakes (Nahr-Ibrahim flaking) (Fig 4: G in S2 File ) [ 19 – 20 ]. This type of recycling represents 3.0% of flakes, retouched or not, but exotic flint was three times more frequently recycled this way than local flint. The sieving mesh used in the excavation was too large to collect all the very small flakes from tool making but some large ones (N = 20) have been identified (Fig 4: E in S2 File ).

Frequency of retouched pieces at Moscerini in our sample is the highest we have observed in our previous studies of the MP from the Latium (Table 4 in S2 File ). Cores were as frequently retouched as flakes (44.4% of cores vs. 45.4% of flakes) suggesting that the selection of blanks to be retouched was not especially determined by the technological status of the blank. This can explain why flint pebbles, fragments of pebbles or chunks have been sometimes directly retouched or shaped bifacially to obtain scrapers (9.1% of retouched tools) (Figs 2C, G; 3I; 4A, in S2 File ). Due to reduction of retouched tools, the identification of the blank from 13 retouched tools was impossible and 21 flakes were so much retouched that the type of flake was unidentifiable. Reduction of retouched tools is sometimes evidenced by discrepancies between the final size of the tool and remaining flaking features of the blank itself. In two cases (Figs 2F and 4M in S2 File ) we have noticed a very large diameter of the impact point on the platform (~7mm) whereas these retouched tools are less than 20 mm wide. As Hertzian cone fracture developed at the margin of the contact point of the hard hammer [ 17 – 18 ] the diameter of the impact point reflects the size of the hammer. Thus we can conclude that the size of these two blanks before retouch was at least three to four times larger.

Raw material procurement includes pieces with double patina. They are patinated or altered blanks with unpatinated retouch (N = 24) or debitage from patinated/altered cores (N = 3) (Fig 2: D and Fig 3: D in S2 File ). Both local (N = 24) and non-local flint (N = 3) were collected in this condition. Collection and use of older, patinated blanks is now commonly described in MP industries [ 11 – 16 ]. The use of blanks with double patina is not a marginal phenomenon at Moscerini as they represent 6.5% of the retouched tools although a higher frequency was observed in the industry from Fossellone layer 23 alpha [15.5% of retouched tools on blanks with double patina) [ 9 ].

Raw materials are more diversified at Moscerini than in other lithic industries from Latium we have previously studied [ 7 – 9 ]. As in most if not all MP sites from the Latium [ 3 ] the main local raw material is small flint pebbles that have been almost exclusively collected in secondary position in beach deposits or fluvial stream or terraces (Figs 1: 3–4, 6–8 in S2 File ). The higher roundness of the flint pebbles at Moscerini than at Sedia del Diavolo/Monte delle Gioie [ 8 ] points to an origin in beach deposits (active or fossil) rather than fluvial deposits or riverbed [ 10 ]. In agreement with such a provenience, 89.0% of cortical surfaces on local flint are rolled or abraded (Table 1 in S2 File ). Chert, (silicified) limestone and quartzite are much less frequent but they were collected on the same type of outcrop. A non-local origin is hypothesized for at least three types of flint: a grey-blue chalcedony-like flint (Fig 1: 1 in S2 File ), a light brown to dark brown semi-translucent flint (Fig 1: 2, 5 in S2 File ) and a grey to black, translucent or semi-translucent flint. Sources of these types of flint are still unknown. Within these non-local raw materials, pieces with abraded or rolled cortex are rare (3.2%) so most of the procurement was made on primary or sub-primary outcrops. This is a major difference with local flint from beach deposits. For a detailed discussion on non-local raw material see S2 File , pp. 3–4.

The shell tool assemblage

Shell tools are made exclusively on Callista chione (Linnaeus 1758) a smooth clam of the Veneridae family, which lives on the coasts of the whole Mediterranean Sea and on the coasts of the eastern Atlantic from the British Isles to Morocco [24, 27]. The marine mollusk is edible and is now commercially exploited in Portugal, Spain, France, Italy and Greece [28]. It inhabits soft sandy sea floors in coastal waters ranging from -1 to -180 m, it can reach up to 10 cm in length and it burrows close to the sediment-water interface. The shell syphons reach up to the surface of the sediment so the animal is able to feed, excrete and reproduce. Thus the shell presence under the sand can be perceived.

Implements made on Callista chione are known from 11 Mousterian sites of which 10 are in Italy and 1 in southern Greece in Kalamakia Cave [23–24]; see below the section « Shell tools in time and space »). However most sites seem to have very small numbers of retouched Callista chione and the implements have not been reported in detail. Until now the best known was Grotta del Cavallo with 126 retouched shells from layer L, analyzed in detail by [24–25].

The Mousterian stratigraphic sequence of Grotta del Cavallo, approximately 4 m thick, dates between MIS 5.5 (129 to 116 ka) [29] at the base (layer N, a Tyrrhenian beach gravel) and 45.5 ± 1.0 ka at the top (layer Fa, a volcanic ash layer; [30]. Layer G in the middle of the sequence is another ash layer dated to 108.7 ± 0.9 ka [30]. Thus layer L below G must date between MIS5.5 and MIS 5.2, and is broadly contemporaneous to the early part of the Moscerini sequence.

Retouched Callista chione are found in many levels of Moscerini, from 42 to 14, for a total of 171 specimens (Table 3). Most retouched specimens (n = 128/171) come from levels 21 to 26 representing a deposit of about 1 m thick, rich in charcoal and stalagmite lenses, based on observation by Segre 1949 reported in [2].

Callista chione is edible but at Moscerini it seems to have been used mostly to make scrapers. Other kinds of mollusks living in shallow waters (Cardium, Glycimeris) occur at Moscerini in small quantities but the most common are the Mediterranean mussels (Mytilus galloprovincialis) which occur in colonies under water (maximum depth -4-5 m) but adhering to rocks and therefore easier to collect in large quantities (NISP = 1537) [2]. None of these shells were retouched or modified in any way; they were most probably collected for food only [2].

Taphonomic characteristics are described as in [31]. Parts of valve (Fig 6A and 6B) morphometric features and temporal relations between retouch and breaks are coded as in [24]. The Moscerini shell tools were, until now, known only from a study by Silvana Vitagliano [4] who inventoried about 100 retouched pieces. The 17 pieces drawn in her publication are those now kept in the Pigorini Museum.

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larger image TIFF original image Download: Fig 6. (A, B) Modern left valve of Callista chione: (A) external (dorsal) surface; (B) internal (ventral) surface. Glossary of valve parts as in [24]. (C) no. PV7, fragment of a right valve with umbo and hinge, retouch on external face affected by dissolution. This is a beached specimen. (D) no. 3, left valve, retouched fragment of distal fringe. Two slightly abraded serpulid calcareous tubes are encrusted on the internal face. Serpulid worms generally attach themselves to the outer valve; the presence of remnants of the worm protective tube indicates that the bivalve died at sea and the shell was later beached. (E) FIB (Focused Ion Beam) image of a well preserved serpulid tube, on Moscerini no. 185 layer 24, a specimen gathered from the sea floor; (F) FIB image of an abraded serpulid tube, on Moscerini no. 153 layer 21, beached specimen. Both images courtesy of Carlo Smriglio and Andrea di Giulio. The photographs were taken at the LIME (Interdepartmental Laboratory of Electron Microscopy) of Roma Tre University with a Dualbeam FIB/SEM-Helios Nanolab (FEI Company, Eindhoven, The Netherlands). Scale bar of C and D = 1 cm. https://doi.org/10.1371/journal.pone.0226690.g006

Procurement of shells According to [24] the valves of Callista chione at Grotta del Cavallo were collected by Neandertals after the death of the mollusk on the nearby beach. During storms shells can be thrown on the beach by waves. Clues used were the presence of abrasion, perforations caused by marine organisms, dissolution and encrustations by barnacles and other aquatic animals on the ventral surface of the shell. However the criteria used to identify beached specimens are not present on all specimens so we were not sure that all shells were routinely collected from the beach as opposed to gathering from the sea floor. One of us, Carlo Smriglio who is a specialist of Mediterranean modern and fossil shells, examined under a microscope all the Moscerini specimens in the Italian Institute of Human Paleontology. Beached specimens can be distinguished from specimens that were collected as live animals in the sea, using a number of criteria: (a) degree of opacity or shine of the outer valve; (b) state of preservation of the internal and external surfaces; (c) presence or absence of encrusting marine organisms; (d) traces of abrasion or rounding of the hinge (Figs 6–8). Our data base indicates that 23.9% of the specimens (40 of 167 that could be determined) were gathered from the sea floor (Table 4). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 7. Specimens of Callista chione some gathered from the sea floor (A, B, D) and some washed up on the beach (C, E). (A) No.74, unretouched umbo. The unabraded and shiny surface indicates that the bivalve was gathered from the sea floor. (B) No. 16, left valve, the break to the right is posterior to the retouch but the retouched edge is complete; note the shiny dorsal surface. Pits are post-depositional, not borings due to marine organisms because they are present also in retouched areas; (C) No. 33, the retouched edge is broken on the left side, the internal and external surfaces have an opaque, chalky appearance with dissolution indicating that the shell was washed up and collected on the beach. (D) no. 14, mesial part of a right valve covered with postdepositional concretions and a retouched edge broken on the right side but the break is prior to retouch; the unabraded and shiny dorsal surface shows that the shell was gathered from the sea floor. (E) No. 24, left valve with an intact portion of the fringe to the right, the left side is broken but the fracture is prior to the retouch; the eroded band following the growth lines and the opaque external surface indicate a beached specimen. Scale bar = 1 cm. https://doi.org/10.1371/journal.pone.0226690.g007 PPT PowerPoint slide

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larger image TIFF original image Download: Fig 8. General morphology of retouched shell tools, Figs C-L are from the Pigorini Museum. (A) No. 13, almost complete small shell preserving the umbo and the hinge. The retouched edge is on the dorsal face, a rare occurrence. (B) No.73, almost complete shell preserving the umbo and the hinge; burnt after retouch. (C) No. 106182, the retouched edge is complete. (D) No. 106190 with three complete retouched edges. (E) No. 106192 the edge is complete. (F) No. 106183 the retouched edge is complete, burnt after retouch. (G, H, I, K) Nos. 106189, 106184, 106185, 106185 the retouched edge is complete. (J, L) Nos. 106188, 106195 the breaks at the base do not affect the retouch. Scale bar = 1 cm. https://doi.org/10.1371/journal.pone.0226690.g008 PPT PowerPoint slide

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larger image TIFF original image Download: Table 4. Grotta dei Moscerini, procurement of retouched shells (undetermined cases excluded). https://doi.org/10.1371/journal.pone.0226690.t004 In modern times the clam is fished by dredging, that is, using small boats towing dredges over the sea bottom. Dredges consist of a small (45 to 70 cm) semicircular iron bar with an attached net bag or metallic grid and three or six metal rods that scoop the sandy bottom [32]. It is also collected by hand by scuba divers working in shallow coastal waters (<10 m) along the Adriatic coast of Croatia [33]. In the northern part of the Adriatic Sea there are sand banks where Callista can be collected at < 0.5–1 m depth [34].