Trapped in a roman well: amphibians and reptiles from Tenuta Zuccarello near Marcon, Venice, Italy

ABSTRACT The Roman well US 100, located in the Tenuta Zuccarello near Venice, has yielded a large number of different animals remains, dated back to 2000 ± 40 years BP. Amphibians and reptiles are represented by at least 11 taxa: two caudates (Lissotriton gr. L. vulgaris, Triturus gr. T. cristatus), three anurans (Bombina sp., Bufo bufo, Rana dalmatina vel R. latastei), one turtle (Emys orbicularis), at least two lizards (Anguis gr. A. fragilis, Lacerta gr. L. viridis), and three snakes (Natrix natrix, cf. Coronella sp., Hierophis viridiflavus). Based on this assemblage, an ecotonal environment with water bodies, open and humid areas, as well as dry and sunny areas, is here suggested for the surroundings of the well when the sediments deposited. Most of the identified taxa were found in other Venetian sites since the Pleistocene, suggesting a certain continuity in the amphibians and reptiles population in Veneto during the Quaternary. The only taxon that is absent from the Venetian Lagoon today is Bombina. Its presence in a 2000-years-old archaeological site proves that the disappearance of suitable environments for the genus is a recent phenomenon near the Lagoon. This may support future reintroduction projects in suitable areas, following a conservation palaeobiology perspective.


Introduction
Fossil remains found inside fillings of geomorphological structures such as stream gullies or karstic fissures are very frequent (e.g. Freudenthal et al. 1976;Sala et al. 1994;Bonfiglio et al. 1997;Delfino and Bailon 2000;Abbazzi et al. 2004;Fraser and Wells 2006;Arzarello et al. 2007;Delfino and Atzori 2013;Rook et al. 2015;Rage 2016;Villa et al. 2016Villa et al. , 2018. These natural structures can act either as traps in which living animals fall and then die or as gatherers of sediments and remains washed away from the nearby area. From the Holocene onwards, artificial structures built by modern humans have flanked the natural ones in originating a similar system of fossil or subfossil accumulation. One of such artificial structure is the well. Being basically vertical cavities in the ground, wells are structurally similar to natural fissures and may equally accumulate sediments inside. These sediments might include plant remains, invertebrate and vertebrate remains, as well as tools used by the people living around the well (e.g. Arobba et al. 2013). Of course, the accumulation might originate from direct filling by people, who may actively throw remains and tools inside the well. However, falls of animals in the well or washing of remains inside it are also possible. This paper is based on remains coming from a similar accumulation originated in a Roman well discovered in July 2000 during an excavation campaign directed by the Soprintendenza Archeologica per il Veneto -Museo Archeologico Nazionale di Altino. The well, located in the Tenuta Zuccarello near Marcon (province of Venice, Italy; Figure 1), was named US 100. It was part of a wide agricultural area located between the Zero and Dese Rivers, including cultivated fields and other agricultural structures such as small drainage canals. The well has an average diameter of 80 cm and was filled by clayey-silty and clayey-sandy sediments. Two different filling sequences were recognised, but they are considered approximately coeval. A rather large number of faunal remains were found in the well, representing both invertebrates (molluscs) and vertebrates (amphibians, reptiles, birds, and small mammals). A preliminary list of the taxa recovered in the well is given by Bon et al. (2010), but a very brief account is also reported here.
Molluscs include mainly terrestrial species, but some freshwater taxa and even few marine elements are also present. As far as bird remains are concerned, nearly complete skeletons of two individuals of Athene noctua and of a Sturnus vulgaris were found, together with other unidentifiable remains. Most of the remains found in the well consist of bones of small mammals (insectivores and rodents; see Bon et al. 2010, for a complete list of the 13 species identified). These indicate a humid and somewhat forested landscape, without a strong manmade influence. Domestic animals are represented by three bones only (all pertaining to medium-or large-sized mammals; Bon et al. 2010), suggesting that the well never acted extensively as a dump. Fragments of pottery artefacts are rare in the fillings rich with faunal remains.
The faunal remains are very well preserved and have been radiocarbon dated at 2000 ± 40 years BP (Bon et al. 2010). Bon et al. (2010) considered the assemblage to be originated because of the well acting as a trap, based on the good preservation of the remains, the absence of signs of transport, digestion and predatory activities, and the dominance of wild species. However, the alternative possibility of remains of animals that died in the nearby and were later washed into the well should also be taken into account, considering that some kind of superficial water body was most likely in direct contact with the well (as suggested by the presence of some of the freshwater molluscs; Bon et al. 2010). This second explanation might better agree with the fact that some vertebrate taxa are represented only by few remains and not by a number of skeletal elements congruent with complete, or roughly complete, individuals as one would expect in case of animals falling into the well and then being subject to little or no disturbance.
In this paper we focus on the analysis of the amphibians and reptiles, in order to better characterize the herpetofauna recorded in the two fillings (Figure 2-4). This is part of a wider study on the late Quaternary herpetofaunas from Veneto (Delfino et al. 2008) aimed at the understanding of the evolution of the modern amphibians and reptiles communities in the region.

Materials and methods
We studied 8315 remains of amphibians and reptiles coming from US 100 at Tenuta Zuccarello. The identifications are based on diagnostic features found in the literature as well as on direct comparisons with disarticulated skeletons stored in the Massimo Delfino Herpetological Collection (MDHC), housed in the Department of Earth Sciences of the University of Torino. The anatomical terminology follows Ratnikov and Litvinchuk (2007) for caudates, Sanchiz (1998) and Bailon (1999) for anurans, Młynarski (1976) and Hervet (2000) for chelonians, Barahona and Barbardillo (1997) and Klembara et al. (2010) for lizards and Szyndlar (1984) for snakes. The most significant specimens were photographed with a Leica M205 microscope equipped with the Leica application suite V 3.3.0 in the University of Torino. The remains are stored in the collections of the Natural History Museum of Venezia (MSNVE).
Abbreviationscl, minimum centrum length; CL, maximum centrum length; pr-po = miminum distance between anterior margin of prezygapophyses and posterior margin of postzygapophyses; PR-PO = maximum distance between anterior margin of prezygapophyses and posterior margin of postzygapophyses.

Description
Trunk vertebrae are small and opisthocoelous (cl: 1.1 mm; CL: 2 mm; pr-po: 1.4 mm; PR-PO: 2.2 mm), with a well-developed neck, well-developed anterior ventral crests, moderately or well-developed posterior ventral and zygapophyseal crests and large subcentral foramina (sometimes replaced by a various number of smaller foramina). The anterior surface of the condyle is flat and roughly vertical or inclined in antero-ventral direction. The high neural arch shows a very high neurapophysis with a horizontal dorsal margin and a roughly vertical or anteriorly sloping anterior margin, running from the anterior fourth of the arch to its posterior margin. In dorsal view, the anterior margin of the arch is straight and is located near the anterior margin of the prezygapophyses or by their anterior third, whereas the posterior one is placed slightly anteriorly to the posterior margin of the postzygapophyses and shows a large and deep notch in the middle. Laminae are flat or slightly concave in anterior view. The humerus is 4.6 mm long. It has a thin shaft and a crista ventralis strongly inclined in anterior view compared to the proximal end of the bone.
The femur is 4.8 mm long and has a moderately thin shaft. The area between the caput femoris and the trochanter is moderately elongated and the distal margin of the bone is only slightly convex. Description MSNVE-23361 is a small opisthocoelous trunk vertebra (centrum length: 1.7 mm; distance between anterior margin of prezygapophyses and posterior margin of postzygapophyses: 2 mm), with a weakly developed neck, moderately developed ventral and zygapophyseal crests and large subcentral foramina. The anterior surface of the condyle is flat and vertical in lateral view. No clearly developed neurapophysis is present on the moderately high neural arch: only a hint of it is visible in the middle of its dorsal surface. The anterior margin of the arch is concave and its bottom is located by the anterior third of the prezygapophyses, whereas the posterior one is wavy, presents a small notch in the middle and extends slightly beyond the posterior margin of the postzygapophyses. Laminae are slightly convex in anterior view.  (MSNVE-23361) in anterior (f), dorsal (g), right lateral (h), ventral (i) and posterior (j) views. Bombina sp.: left ilium (MSNVE-23362/10) in lateral (k) and medial (l) views. Bufo bufo: right ilium (MSNVE-23363/24) in lateral (m) and medial (n) views. Rana dalmatina vel R. latastei: right ilium (MSNVE-23364/39) in lateral (o) and medial (p) views. Anura indet.: sacral vertebra fused with the urostyle (MSNVE-23365/15) in dorsal (q) and ventral (r) views. avc, anterior ventral crest; cd, crista dorsalis; l, lamina; nc, neck; ne, neurapophysis; pa, pars ascendens; pd, pars descendens; pzc, prezygapophyseal crest; sd, sacral diapophysis; sf, subcentral foramen; sv, sacral vertebra; ts, tuber superior; u, urostyle.

Identification
The opisthocoelous centrum, the presence of subcentral foramina, the moderately or well-developed ventral and zygapophyseal crests and the notch on the posterior margin of the neural arch are diagnostic features of the trunk vertebrae of salamandrids (Ratnikov and Litvinchuk 2007). The different morphologies of MSNVE-23360/1 and 2 and MSNVE-23361 clearly suggest the presence of two different taxa. The almostlacking neurapophysis, the concave anterior margin of the neural arch, the small posterior medial notch and the convex laminae allow the attribution of the latter to the genus Triturus (Ratnikov and Litvinchuk 2007) (Ratnikov and Litvinchuk 2007). Moreover, its very small size can suggest that it belonged to a juvenile. The other vertebrae can be assigned to Lissotriton because of very high neurapophysis, horizontal dorsal margin of the latter, straight anterior margin of the neural arch, well-developed posterior medial notch and flat or slightly concave laminae (Ratnikov and Litvinchuk 2007). Trunk vertebrae of Ichthyosaura and Ommatotriton are morphologically similar to those of Lissotriton, but MSNVE-23360/1 and 2 cannot be referred to those genera since the anterior margin of their neural arch is not located posteriorly to the anterior third of the  c, costal; d, diapophysis; h, hypapophysis; hk, hemal keel; mg, Meckel's groove; ns, neural spine; p, pygal; pa, parapophysis; pap, parapophyseal process; pp, posterior projection; prp, prezygapophyseal process; sp, suprapygal; z, zygosphene. prezygapophyses and the anterior margin of their neurapophysis can be vertical (Ratnikov and Litvinchuk 2007); moreover, the largest vertebrae herein described are much smaller than the maximum size reached by trunk vertebrae of those two genera: CL: 3.1 mm and PR-PO: 3.6 mm for Ichthyosaura and CL: 4.4 mm and PR-PO: 5.0 mm for Ommatotriton (Ratnikov and Litvinchuk 2007). The maximum size of the vertebrae from Tenuta Zuccarello is also smaller than that of L. montandoni (CL: 3.4 mm and PR-PO: 3.8 mm) and comparable with that of L. vulgaris (CL: 2.5 mm and PR-PO: 2.9 mm) as reported by Ratnikov and Litvinchuk (2007), but since trunk vertebrae of such species are strongly similar, we simply referred MSNVE-23360/1 and 2 to the species complex Lissotriton gr. L. vulgaris. We include at least L. vulgaris and L. italicus in this complex, but the comparative osteology of Lissotriton species in general is poorly known and therefore other species cannot be excluded a priori. MSNVE-23360/3 and 4 have been assigned to the same species complex because of the small size and the thin shaft, but also because of the strongly inclined crista ventralis of the humerus, the elongated area between caput femoris and trochanter and the slightly convex distal margin of the femur (Holman 1998

Description
Parasphenoids are cross-shaped. Pars medialis and partes laterales have a wide end and the former is almost twice as  large and roughly twice as long as the latter. A large, triangular processus posterior is present posteriorly. No prominent ridges are present on the ventral surface. Atlases are opisthocoelous. Their anterior cotyles are dorsoventrally inclined and separated medially by a moderately wide spatium interglenoidale. Both ventral surface of the centrum and dorsal surface of the neural arch are smooth, without ventral keel and carina neuralis.
Trunk vertebrae are opisthocoelous and have a dorsoventrally compressed centrum. Transverse processes are cylindrical and placed posteriorly to the prezygapophyses. The neural arch is moderately long and shows a pseudozygosphene on the anterior margin. There is no developed carina neuralis, but a small posterior point is present in the middle of the posterior margin of the dorsal surface of the arch. MSNVE-23362/16 differs from this morphology in having both an anterior and a posterior condyle, no posterior point and strongly dorso-ventrally compressed transverse processes. Moreover, its left process is bifurcated.
Sacral vertebrae have both an anterior and a posterior condyle. The dorsal surface of their neural arch shows a pseudo-zygosphene anteriorly and no carina neuralis. The sacral diapophyses are well developed antero-posteriorly.
Urostyles have an anterior cotyle and two small transverse apophyses near the anterior end. In MSNVE-23362/5, the left apophysis is moderately large by its base and has a pointed end curving in postero-lateral direction, whereas the right one is truncated and does not curve posteriorly. There is no crista dorsalis.
Humeri are moderately thin and have a straight diaphysis in ventral view. The eminentia capitata is spherical and shifted laterally. The crista ventralis is well developed, but there is no crista paraventralis. The crista lateralis is moderately developed, whereas the crista medialis varies from moderately developed to well developed. The fossa cubitalis ventralis is not developed and the olecranon scar is well marked.
There is no crista dorsalis on the thin shaft of the ilia (Figures 2K-L, 4(A,B)) and only a very small hint of tuber superior is visible on the dorsal surface of their body. The pars descendens is not developed, whereas the pars ascendens is moderately developed.
Femurs are thin. In dorsal view, their distal epiphysis is slightly larger than the proximal one. A low crista femoris is present on the medial surface, near the proximal epiphysis.
Tibiofibulae are small, thin and straight. Their epiphyses are strongly larger than the diaphysis.

Description
The well-ossified sphenetmoids are roughly as long as they are large. They have a very short anterior process and moderately developed lateral processes, which are little individualized in ventral view. The incisura semielliptica is large. In anterior view, a moderately developed sella amplificans is visible in each antrum olfactorium of MSNVE-23363/1, but its roof is not indented. Parasphenoids are cross-shaped, with partes laterales almost as long as the pars medialis. The end of the former is pointed, whereas that of the latter is more rounded. A small and triangular processus posterior is present. A ridge runs on the ventral surface of partes laterales, starting from an osseous swelling located at their meeting point. In MSNVE-23363/7, the ridges and the swelling are very well developed and another ridge runs anteriorly from the middle of the latter to the base of pars medialis.
The large prootics are almost completely fused with the exoccipitals. They have a large and robust prootic process and an occipital condyle that is subrectangular-shaped in posterior view. The ridges on the dorsal surface are very well developed and thick.
Pterygoids do not show an alary dilatation. The long ramus maxillaris is strongly curved medially. The other two rami (posterior and interior) are shorter than the former and are almost equally long. The width of the three branches is roughly the same. The middle part of the tympanic border is gutter-shaped in ventral view.
Squamosals show a moderately developed lamina along the transverse branch, whose lateral surface is not ornamented. Both anterior and posterior portion of the transverse branch are short.
Atlases are large and robust and have a posterior dorsoventrally compressed condyle and a short neural arch. The neural canal has an ogival section. Except for MSNVE-23363/ 35, the atlases show a moderately developed osseous expansion under each postzygapophysis.
Trunk vertebrae are large, robust and procoelous. They have a large centrum, short lateral walls, a short neural arch and laterally-, antero-laterally-or postero-laterally-directed transverse processes located posteriorly to the prezygapophyses.
Sacral vertebrae are procoelous and have two well-separated, circular condyles posteriorly. Sacral diapophyses are moderately expanded antero-posteriorly and do not show a fossa by their base. A well-developed carina neuralis is present on the dorsal surface of the neural arch.
The clavicle is large, moderately robust and straight. Coracoids are robust and their ends are similar in width. Scapulae are robust and longer than they are large. On the margo anterior, only a very small hint of crista anterior is present near the pars acromialis. The cavitas glenoidalis is well visible in ventral view. There is no supraglenoidal fossa.
Suprascapulae are large and L-shaped. Their margins are regular and the two branches of the L create an angle of 90°. The anterior margin is folded in ventral direction.
Radioulnae are robust. The two portions of the distal epiphysis are almost equally large and slightly compressed in distal view. Only in MSNVE-23363/21, the radial portion is subcircular and larger than the ulnar one.
Ilia ( Figure 2M-N) have no crista dorsalis. A dorsally rounded tuber superior is present. There are neither a lamina calamita on the shaft nor a preacetabular fossa on the body. The pars ascendens is short, whereas the pars descendens is well developed.
Femurs are robust and show a well-developed crista femoris, which splits proximally forming a triangular structure.
Tibiofibulae are robust and stocky. The two portions of the proximal epiphysis are roughly subelliptical and roughly parallel, whereas those of the distal one are roughly subcircular. On both epiphyses, the lateral portion is larger than the medial one. MSNVE-23363/31 shows a roughly cylindrical osseous proliferation developed in medio-distal direction on the medial side of the diaphysis.

Description
Premaxillae bear teeth and show two well-developed posterior processes by the lateral and medial sides of the pars dentalis, whose posterior margin is therefore concave in dorsal view.
Maxillae are large-sized and elongated. They bear teeth and are devoid of ornamentation on the lateral surface. There is no processus palatinus. In lateral view, the frontal process is rectangular or subrectangular and the lamina anterior is low.
The paired frontoparietals are straight and rectangular in dorsal view. The dorsal surface is flat and smooth, except for two very low ridges starting from the parietal eminence (canthus postero-lateralis): the medial ridge, running anteriorly and forked in its anterior half, and the very low developed occipital ridge, running postero-medially. The parietal eminence is shifted laterally, by the beginning of the welldeveloped processus lateralis. A shallow occipital canal is present laterally to the eminence. On the ventral surface, the incrassatio frontoparietalis is double, with a circular posterior portion. One of the frontoparietals, MSNVE-23364/7, is fused with a prootic/exoccipital complex. In such specimen, the complex is completely fused. The prootic process tends to narrow distally and the occipital condyle is roughly subelliptical in posterior view.
The well-ossified sphenetmoids are slightly longer than they are large. Anterior and lateral processes are moderately developed and the latter are moderately to well individualized in ventral view. The incisura semielliptica is moderately deep. No sella amplificans is visible in anterior view. In ventral view, the posterior portion of the bone does not shrink.
Parasphenoids are slender. They have an anteriorly pointed pars medialis, which is twice as long as the lobeshaped partes laterales. The width of the three partes is similar. A moderately small and triangular-shaped processus posterior is present, whereas there are no ridges on the ventral surface.
Prootics fused with exoccipitals are morphologically similar to those of MSNVE-23364/7, except for MSNVE-23364/57 in which the fusion is not complete.
Squamosals are T-shaped. They do not develop a lamina along the transverse branch and their lateral surface is smooth. Anterior and posterior portions of the transverse branch are equally long, except for MSNVE-23364/23 (the largest one) in which the posterior part is shorter. The distal end of the descending branch is distinctly lobed. A moderately developed internal ridge runs along the medial surface of the descending branch.
Pterygoids do not show expansions on the margo maxillaris. Their ramus interior is strongly shorter than the ramus posterior.
Angulars are large and moderately slender, with a welldeveloped, vertical processus coronoideus.
Atlases Urostyles have two circular anterior condyles and a high crista dorsalis. The neural arch is narrow or moderately narrow in anterior view and there are no transverse processes.
Coracoids have a moderately thin body and a pars epicoracoidalis which is strongly larger than the pars glenoidalis.
MSNVE-23364/50 is a thin, straight and elongated clavicle. Scapulae are longer than they are large and have no crista anterior. The pars acromialis hides partially the cavitas glenoidalis in ventral view, but does not participate in the articulation with the humerus. A low-to well-developed internal ridge is visible on the dorsal surface of the pars glenoidalis and of the body of the bone. One of the scapulae, MSNVE-23364/49, is fused with a thin and straight clavicle.
Humeri are moderately thin and straight in ventral view. They do not have a crista paraventralis, whereas the crista ventralis is well developed. The spherical eminentia capitata is aligned with the diaphysis. Cristae medialis and lateralis go from not developed (MSNVE-23364/29-31 and 51; MSNVE-23376/20 and 21) to low developed (MSNVE-23364/32, 33 and 52) and well developed (MSNVE-23364/34 and 35;MSNVE-23376/19); in the latter case, the crista medialis runs up to the middle of the diaphysis and slightly bends in dorsal direction. A deep fossa cubitalis ventralis is present and the olecranon scar is narrow and elongated. MSNVE-23364/ 31 shows a ventrally developed and rounded spur located proximally to the medial epicondyle.
Radioulnae are slender. The radial portion of their distal epiphysis is subcircular in distal view, whereas the ulnar one is slightly compressed. A distally developed, subcylindrical osseous proliferation can be seen on the ventro-lateral surface of the radial portion of the distal epiphysis of MSNVE-23364/38. Ilia ( Figure. 2O-P, 4G-H) have a high crista dorsalis, not distinctly bending in medial direction. The tuber superior is present, but it is not strongly individualized and does not exceed the height of the crista. Both partes ascendens and descendens are well developed and neither interiliac tubercle nor groove are present. The angle between tuber and pars ascendens is slightly greater than 90°.
Femurs are long and thin and do not have a crista femoris.
Tibiofibulae are slender. The portions of the proximal epiphysis are roughly subelliptical and roughly parallel, whereas those of the distal one are roughly subcircular. On both epiphyses, the lateral portion is slightly larger than the medial one. MSNVE-23364/46 and 47 show a stocky osseous swelling near the distal and the proximal epiphyses respectively.
Anura indet. MSNVE-23365/7 is broken by the middle of the diaphysis and shows an anomalous development of the bone tissue by the breakage.

Identification
Anurans remains have been identified using diagnostic features reported by Bailon (1999). Ilia are particularly informative and allow the distinction of three different taxa. The ones with a high and vertical (that is, not bending) crista dorsalis, a not strongly individualized tuber superior and an angle of more than 90°between tuber and pars ascendens can be referred to the genus Rana and in particular to R. dalmatina because of the crista being higher than the tuber. However, Bailon does not consider in his key Rana latastei, which is also currently present in the area of Tenuta Zuccarello (Sillero et al. 2014). Given that clear osteological features distinguishing R. dalmatina from R. latastei are currently unknown, we here decided to assign all ilia showing the Rana morphology to R. dalmatina vel R. latastei. Ilia devoid of crista dorsalis can be further distinguished based on the morphology of the tuber superior and of the posterior portion of the body: a well-developed tuber and a short pars ascendens are features of the genus Bufo, whereas poorly developed tuber and pars descendens identify Bombina. The absence of lamina calamita and preacetabular fossa on the ilia of Bufo rules out Bufo calamita and Bufo viridis, whereas the dorsally rounded tuber superior allows their assignment to B. bufo. The other skeletal elements have been attributed to one of the three taxa following the key of Bailon (1999); elements that could be identified only at the generic level of Rana and Bufo have been tentatively referred to the previously recognized species. A number of fragmented or uninformative elements are referred only to indeterminate anurans. MSNVE-23365/15 could resemble a sacral vertebra of a juvenile of Pelobates fuscus because of the fused urostyle and the cotyle (Bailon 1999), but it is different from a similarsized specimen stored in the collection of the University of Torino (MDHC 181) in the well-differentiated prezygapophyses, the absence of a contact between diapophyses and urostyle and the rod-like shape of the latter. Diapophyses are morphologically similar to those of Bombina, in which the fusion between the sacral vertebra and the urostyle is possible (Madej 1965). However, sacral vertebrae of Bombina have an anterior condyle (Bailon 1999) and so we decided not to assign MSNVE-23365/15 to this taxon, identifying it only as an indeterminate anuran. Nevertheless, it could represent a pathological condition of Bombina. It has to be noted that other pathological specimens have been found both among the material attributed to Bombina and among the one assigned to the other taxa (e.g. MSNVE-23362/16, MSNVE-23363/31, MSNVE-23364/38 and MSNVE-23365/7). Among the humeri of B. bufo and R. dalmatina vel R. latastei, MSNVE-23363/18, 19, 32 and 33 (9 humeri), MSNVE-23364/34 and 35 (18 humeri) and MSNVE-23376/19 (2 humeri) belonged to male individuals, whereas MSNVE-23363/17 and 20 (6 humeri), MSNVE-23375/4 and 5 (2 humeri), MSNVE-23364/29-33, 51 and 52 (88 humeri) and MSNVE-23376/20 and 21 (4 humeri) belonged to females (Bailon 1999  Description MSNVE-23373/1 is a partial fragmented carapace including nuchal, neurals 1-6, suprapygal 2, pygal, right costals 1-8, right peripherals 1-10, left costals 2-5 and 7-8, left peripherals 1, 3-5 and 7-10. Due to its irregular shape, the small bone located anteriorly to the suprapygal 2 ( Figure 3A) is tentatively considered an accessory element and not the suprapygal 1. The dorsal surface is smooth, with moderately shallow grooves for the horny shields. Although broken, the carapace is rather flat.
No change in declivity occurs at the contact between suprapygal 2 and the pygal. The grooves marking the contact between pleurals and marginals are located strongly laterally in respect to the sutures between costals and peripherals. The nuchal is hexagonal and larger than it is long. The postero-lateral margins are slightly longer than the anterolateral ones and the posterior margin is short. On its dorsal surface, are clearly evident the grooves marking the contacts between cervical and the first marginals, cervical and the first vertebral, the first marginals and the first vertebral, the first vertebral and the first pleurals.
Neurals are hexagonal and slightly larger than they are long, except for the first one, which is subrectangular and longer than it is large. Both anterior and posterior margins of neural 1 are convex, whereas its lateral margins are only slightly rounded. The other neurals have a slightly concave anterior margin and a slightly convex posterior one; their antero-lateral margins are very short. Neurals 1, 3 and 5 show the grooves between vertebrals on the dorsal surface (between vertebral 1 and 2, 2 and 3 and 3 and 4 respectively). All the grooves are located in the posterior half of the plates.
Suprapygal 2 ( Figure 3A) has 6 sides and is roughly trapezoidal in shape. Its width is distinctly smaller than that of vertebral 5. There are no grooves on its dorsal surface.
The pygal ( Figure 3A) is slightly trapezoidal and larger than it is long. The grooves between left and right marginals 12 and between them and vertebral 5 can be seen on its dorsal surface. A shallow notch is present on the posterior margin of the plate, between the marginals.
All costals show a short postero-medial side at their proximal end: in costal 1-7 this side is very short, whereas in costal 8 it is longer than the antero-medial one ( Figure 3A). The first costal is the longest one. The groove marking the contact between vertebrals and pleurals passes through the dorsal surface of all costals; costals 1, 3, 5 and 7 also show the contact between consecutive vertebrals, whereas on 2, 4 and 6 there are the grooves between consecutive pleurals. The contact between vertebral 1 and pleural 1 passes through the middle of the suture between nuchal and costal 1, whereas the contact between vertebral 4 and 5 is located almost by the suture between costal 7 and 8. The free portion of the ribs is well developed and inserts in the peripherals.
Peripherals 4-7 show ventrally the surface for the ligamentous contact with the plastron. The lateral border of the fourth, fifth and sixth ones is folded in ventral direction, whereas the eighth, ninth and tenth ones are horizontally raised in their lateral portion. Width and length are similar in peripherals 8-10, whereas peripherals 1 and 2 are very slightly larger than they are long and peripherals 3-7 are longer than they are large.
The cervical horny element was very narrow and shorter than the first third of the nuchal. Its posterior margin was straight, without indentation for the first vertebral.
Vertebrals 1-4 were hexagonal and larger than they were long; their lateral margins were wavy. Vertebral 1 covered also a very small part of peripheral 1, but not the lateral extremities of the nuchal. Vertebral 5 was heptagonal, roughly trapezoidal and larger than it was long; it covered the anterior half of the pygal.
All pleurals but the fourth one were larger than vertebrals. The first one was the largest, whereas the fourth one was the smallest. Width and length were similar in pleural 1 and 4, whereas pleural 2 and 3 were larger than they were long. The grooves between consecutive pleurals do not continue in those between consecutive marginals.
Marginals were distinctly longer than they were large. Grooves between them are never located by the sutures between peripherals. Right and left marginals 12 were separated.
The femur is slender, elongated and strongly curved. The head of the bone is moderately large, whereas tuberositas internus and trochanter are similar in size.
Identification According to Hervet (2000), all the morphological characters of MSNVE-23373/1 listed above identify the carapace of E. orbicularis, even though the contact between vertebral 4 and 5 located on costal 7 near the suture with costal 8 is a feature of Mauremys leprosa. Since this is the only relevant exception, we referred MSNVE-23373/1 to the former species, together with the other chelonian remains.  /1-2).

Description
The small, unpaired premaxilla has a large and arrow-shaped nasal process. It bears five conical, monocuspid teeth, provided with a slightly posteriorly curved and non-striated tip.
Maxillae are small and bear large, conical, monocuspid teeth, strongly curving posteriorly at the tip. Teeth are well spaced from each other and do not show striae. Their number goes from 4 to 7.
MSNVE-23368/12 is a small, paired frontal with a moderately ornamented dorsal surface and a well-developed crista cranii frontalis. In dorsal view, it is triangular and anteroposteriorly elongated. A well-developed posterolateral process is visible by the postero-lateral corner of the bone. In lateral view, the articulation surface with the prefrontal covers two thirds of the length of the bone and no ventral process of the crista cranii is recognizable.
The small, unpaired parietals show a moderately developed ornamentation on the dorsal surface and a large parietal foramen in the middle of the parietal table (although partially obliterated in MSNVE-23368/6). A small and smooth area levis is present between the dorsal ornamentation and the posterior margin of the bone, whose center is marked by a deep parietal notch. A long and slender supratemporal process runs postero-ventrally from each postero-lateral corner of the bone. In ventral view, one can see the very small fossa parietalis, strongly smaller than the parietal notch.
The quadrate and the coronoid are small-sized. Dentaries ( Figure 4I-J) are small and distinctly curved dorsally in the posterior portion. They bear teeth similar to those of the maxillae, whose number goes from 4 to 9. In lateral view, the dorsal crest covers less than a half of the length of the teeth. The intramandibular septum ends by the last tooth position or slightly anteriorly. No surangular spine can be seen on the posterior margin of the bone and the posterior end of the angular process is located strongly anteriorly to that of the coronoid process.
Compound bones are small and have a short and quadrangular retroarticular process.
Osteoderms are very small and very thin. They are suboval in shape and have no ridges on the external surface.

Description
Premaxillae have a leaf-shaped posterodorsal process and show 9 to 11 tooth positions. The maximum width of their shelf reaches 3.8 mm.
Maxillae are very large and present 16 to 20 tooth positions. Their maxillary shelf reaches a maximum length of 11.5 mm. The anterior projection of the dorsal process and the lappet on the anterior process are well developed (except for the lappet of MSNVE-23366/2 and 4, which is poorly developed). The posterior process shows a clear step near its end.
Jugals are large and are provided with a well-developed quadratojugal process. There is no medial process on the palatal shelf. In lateral view, the exposed portion of the anterior part is very small.
The unfused frontals reach 13 mm in length. They are not constricted in the medial region and show a strongly interdigitated posterior margin. In dorsal view, the articulation surface with the dorsal process of the maxilla is very small.
The postorbital is large and not fused with the postfrontal. The anteromedial process is present and well developed.
Pterygoids are very large, reaching 16 mm in length. They present a strong pterygoid recess and a large number of pterygoid teeth on the ventral surface.
In medial view, quadrates have a rounded anterior outline. Their anterior platform is flat and they reach a maximum length of 6 mm.
Bones composing the otooccipital regions are very large. The sphenoid shows an undepressed ventral surface and strongly laterally expanded basipterygoid processes. Its ventrolateral crests form the anterior wall of the sphenoccipital tubercles. Prootics have a very well developed alar process and a very distinct posterior process. The paroccipital process of the otooccipital is very long. The anterolateral margins of the supraoccipital are distinctly convergent and the processus ascendens is largely ossified.
Dentaries ( Figure 3G-H) have a large and medially opened Meckel's groove. They are very large, with a dental shelf reaching 14 mm in length. The posterior projections are almost equal in size. Number of tooth positions goes from 21 to 27.
Articulars are large and straight in medial view. They are fused with surangulars.
The teeth on maxillae and dentaries are pleurodont, cylindrical and mono-, bi-or tricuspid. In the premaxillae, only mono-and bicuspid morphologies are present.
Vertebrae are large and antero-posteriorly elongated. Their centrum is circular in posterior view, with a well-developed keel on the ventral surface (only in the cloacal ones the keel is less developed). The maximum centrum length of presacral vertebrae is 4.8 mm. Caudal vertebrae ( Figure 4K-N

Description
Remains assigned to indeterminate lacertids are morphologically similar to those referred to Lacerta gr. L. viridis, but much smaller. The maximum length of the shelf of the maxillae is 6 mm and they bear 13 to 17 tooth positions. Pterygoids reach a maximum length of 9 mm and have no pterygoid teeth. The maximum length of the quadrate is 3.4 mm. As for the dentaries, the maximum length is 7 mm and the number of tooth positions goes from 16 to 23. In MSNVE-23367/5, the ventral projection is longer than the dorsal one. Otooccipital regions are not completely fused. Alar and posterior processes of the prootics, paroccipital processes of the otooccipitals and the processus ascendens of the supraoccipital are less developed than the same structures in remains referred to Lacerta gr. L. viridis. Maximum centrum length of presacral vertebrae is 2.3 mm. Autotomy plane is absent in caudal vertebra MSNVE-23367/ 10 and present in MSNVE-23367/12. Both MSNVE-23367/14 and 15 are represented by two fused cloacal vertebrae each. Interclavicles are small and cross-shaped.

Identification
The presence of a small-sized species of anguid is testified by the small vertebrae with a dorso-ventrally compressed centrum (Delfino et al. 2011). Anguid remains can be referred to Anguis gr. A. fragilis (including A. cephallonica, A. colchica, A. fragilis, A. graeca and A. veronensis;Gvoždík et al. 2013) because of: large, conical, monocuspid and strongly posteriorly curved teeth without striae on the tip; strongly reduced fossa parietalis; dorsal crest covering less than a half of teeth on the dentary; end of the intramandibular septum located by or nearly to the last tooth position; posterior portion of dentaries dorsally curved; no surangular spine; short retroarticular process; elongation of vertebrae; parallel margins in the posterior half of the centrum; small size, thinness and rounded shape of the osteoderms; absence of ridges on the latter (Holman 1998;Delfino 2002;Delfino et al. 2011;Klembara et al. 2014). Maxillae and dentaries bearing pleurodont, cylindrical, mono-, bi-or tricuspid teeth are, on the other hand, a feature of the family Lacertidae (Bailon 1991;Delfino 2002;Delfino et al. 2011). Following Barahona and Barbardillo (1997), the largest remains can be assigned to Lacerta gr. L. viridis, a species complex comprising middlesized European lacertids of the genus Lacerta. Assignment of the remains to Timon lepidus, the largest lacertid currently living in Europe, is prevented by frontals not constricted, stepped posterior process of the maxillae, flat anterior platform of the quadrates, strong pterygoid recess and sphenoids with an undepressed ventral surface (Barahona and Barbardillo 1997). Smaller remains of lacertids, whose identification is notoriously tricky (Villa et al. 2017), have been attributed only to indeterminate members of the family. They could represent another smaller species, but also juveniles of Lacerta gr. L. viridis. The length of the posterior projections of MSNVE-23367/5 seems to confirm the second hypothesys (Barahona and Barbardillo 1997). Serpentes Linnaeus, 1758Colubridae Oppel, 1811'Natricines' sensu Szyndlar, 1991bNatrix Laurenti, 1768 Natrix natrix (Linnaeus, 1758) ( Figure 3K-O) Referred material -I filling: 67 trunk vertebrae (MSNVE-23369/1-2).

Description
Trunk vertebrae have an elongated vertebral centrum, a sigmoid-shaped and obtuse hypapophysis and a neural spine whose antero-dorsal corner is moderately to well developed anteriorly. The distal end of the prezygapophyseal processes is obtuse and the parapophyseal processes are obtuse and moderately thin. In posterior view, the neural arch is vaulted.

Description
Trunk vertebrae have an elongated centrum (centrum length is 3 mm in both specimens) and are provided with a moderately low neural spine. The anterior margin of the zygosphene shows a very little developed median convexity. Instead of a developed hypapophysis, they have a weakly defined hemal keel, which broadens posteriorly. Prezygapophyseal processes are very short and stocky and the proximal portion of the prezygapophyses is thick. Parapophyses are longer than diapophyses. In posterior view, the neural arch is depressed. in this specimen, a thick supraangular crest is present ventrally to the articulation surface with the quadrate and the retroarticular process is short and straight.
Trunk vertebrae ( Figure 3U-Y) are provided with an elongated centrum (CL: 6 mm) and with a neural spine, which is longer than it is high. A well-developed hemal keel is present on the ventral surface of their centrum; its posterior portion is flat and larger than the anterior one. The anterior margin of the zygosphene is almost straight, but in some small specimen (MSNVE-23371/4: 35 vertebrae) it can present a very little developed median convexity. Prezygapophyseal processes are long and the neural arch is vaulted in posterior view.
Description MSNVE-23372/5 is a trunk vertebra provided with an anomalous hemal keel. It is well developed, but splits into two flanked portions by its posterior end. The vertebra has an elongated centrum, a little developed neural spine, a straight anterior margin of the zygosphene with a small V-shaped notch in the middle, long prezygapophyseal processes and a vaulted neural arch in posterior view. Identification Trunk vertebrae can be referred to the operative taxa 'natricines' or 'colubrines' based on the presence or absence of the hypapophysis, whereas the presence of a neural spine and the elongated centrum rule out Scolecophidia and Boidae respectively (Szyndlar 1984(Szyndlar , 1991a(Szyndlar , 1991b. In addition, trunk vertebrae provided with hypapophysis are not referable to Viperidae because of the sigmoid shape of the latter, the vaulted neural arch, the anteriorly developed antero-dorsal corner of the neural spine and the obtuse prezygapophyseal processes (Szyndlar 1984). Among 'natricines', obtuse ends of both hypapophysis and parapophyseal processes are features of Natrix natrix (Szyndlar 1984(Szyndlar , 1991b. Vertebrae devoid of hypapophysis can be further separated into two different morphologies: on the one hand, there are vertebrae with a weakly developed and not flat hemal keel and on the other hand vertebrae whose keel is well developed and flat. The former morphology, together with the small size (CL < 5 mm), the short prezygapophyseal process, the poorly developed neural spine and the depressed neural arch, is distinctive of the genus Coronella (Szyndlar 1984(Szyndlar , 1991a. Szyndlar (1984Szyndlar ( , 1991a reports the robustness of the proximal portion of the prezygapophyses and parapophyses longer than diapophyses as diagnostic features of Coronella austriaca, but these informations were based on few comparative material and the same author (Szyndlar 1991a) notes that vertebrae of this species are strongly similar to those of Coronella girondica. Even though only C. austriaca is currently reported in the Laguna Veneta (Sillero et al. 2014), localities where both species occur are present not so far from there in the Po Plain and therefore we decided not to rule out C. girondica based on biogeography. MSNVE-23370/1 and 2 are thus identified only at a generic level. On the other hand, vertebrae with a flattened and posteriorly wider hemal keel, an almost straight anterior margin of the zygosphene, long prezygapophyseal processes, an elongated neural spine and a centrum exceeding 5 mm in length can be referred to Hierophis viridiflavus (Szyndlar 1984(Szyndlar , 1991a. According to Szunyoghy (1932) and Szyndlar (1984Szyndlar ( , 1987, a well-developed supraangular crest is found only in compound bones of H. viridiflavus among European 'colubrines'. The Pliocene species Coluber robertmentensi also showed this feature (Szyndlar 1984), but it was later synonymized with H. viridiflavus (Szyndlar 1991a). A pathological trunk vertebra and a number of other skeletal elements are attributed to indeterminate snakes.

Discussion
At least 11 different taxa have been identified based on the amphibians and reptiles remains coming from the Roman well of Tenuta Zuccarello. These taxa are two caudates (Lissotriton gr. L. vulgaris, Triturus gr. T. cristatus), three anurans (Bombina sp., Bufo bufo, Rana dalmatina vel R. latastei), one turtle (Emys orbicularis), two lizards (Anguis gr. A. fragilis, Lacerta gr. L. viridis), and three snakes (Natrix natrix, cf. Coronella sp. and Hierophis viridiflavus). The presence of a third lizard species, representing a smallsized lacertid, cannot be clearly established, given that small lacertid remains identified only at family level might equally pertain to young green lizards. All 11 taxa are recorded in the I filling, which by far has yielded the highest amount of remains, whereas only six of them (the three anurans, the two lizards and H. viridiflavus) are present in the II filling. Nevertheless, this might just be due to the distinctly lower amount of remains found in the latter filling, rather than to a real absence of the other taxa at the moment of the deposition. In both fillings, the assemblage is dominated by agile frogs (Rana dalmatina vel R. latastei). These frogs are usually found in forested environments and in the surrounding meadows (Speybroeck et al. 2016). An ecotonal area with both partially open and humid areas and drier and sunnier areas is suggested for the surroundings of the well by the presence of Anguis, Lacerta and Hierophis (Speybroeck et al. 2016). In any case, the large amounts of amphibians remains, as well as the recovery of E. orbicularis and N. natrix, are evidence for the presence of water bodies. At least some of the latter could have been ephemeral, as testified by the remains of Bombina (Speybroeck et al. 2016).
According to the data reported by Delfino et al. (2008) and Villa et al. (2018), most of the taxa that compose the herpetofaunistic assemblage of Tenuta Zuccarello have a long fossil history in the Quaternary of Veneto. Lissotriton gr. L. vulgaris is known from the Early Pleistocene of Monte La Mesa. Bombina was also found in the same site, as well as in the nearby Early Pleistocene locality of Rivoli Veronese. Anguis gr. A. fragilis is reported from the Early Pleistocene of Rivoli Veronese and the earliest Middle Pleistocene of Grotta della Fata Nana. Coronella is known in the fossil assemblage of Rivoli Veronese and in Brecce di Montorio (Late Pleistocene). Remains of B. bufo, Lacerta gr. L. viridis, N. natrix and H. viridiflavus were recovered from a number of Venetian sites, spanning from the beginning of the Pleistocene to the Holocene. Agile frogs attributable either to R. dalmatina or R. latastei are currently known with certainty only from the herein studied site, but representatives of the genus Rana that are not identified at the species level are known in Veneto since the Early Pleistocene and therefore the presence of these frogs in the region in earlier times is possible. Of the 11 taxa, Triturus gr. T. cristatus is the only one that has never been recovered in any other site in Veneto, whereas E. orbicularis was found only in a single other Holocene locality, Lova di Campagna Lupia.
If compared with the amphibians and reptiles currently living near the Venetian Lagoon (see Sindaco et al. 2006;Bonato et al. 2007;and Sillero et al. 2014), the assemblage of the Tenuta Zuccarello well clearly lacks various taxa, notably anurans of the Bufotes viridis complex and the genus Pelophylax as well as wall lizards of the genus Podarcis. It is not easy to explain the absence of common taxa such as these ones in terms of environmental features of the area in the past, taking also into account the wide range of habitats that they inhabits today. Moreover, it has to be noted that at least some of these taxa has been found in nearby sites of similar age (e.g. green frogs in Lova di Campagna Lupia and Oderzo; Delfino et al. 2008). Their absence from Tenuta Zuccarello is therefore puzzling. Of course, as far as small lacertid lizards like Podarcis are concerned, they might be represented, though unrecognised, among the small lacertid remains identified only at family level. On the other hand, almost all of the taxa found in the Roman well are still represented near the Lagoon. The only exception is Bombina, which currently lives in most of the Veneto region (Bombina variegata; Bonato et al. 2007;Sillero et al. 2014), but not near the Lagoon. The other two fossil occurrences of the genus in Veneto, both Early Pleistocene in age, are located in the Verona province (Delfino et al. 2008;Villa et al. 2018), that is within the current range of B. variegata. Tenuta Zuccarello represents therefore the first occurrence of Bombina outside its current range.
In addition to giving new information on the past distributional dynamics of this anuran, this occurrence has important implications for conservation sciences also. As a matter of fact, conservation biologists have recently started to use data coming from palaeontological and archaeozoological studies in their works. This even led to the definition of a new science, the conservation palaeobiology, which uses palaeontological/archaeozoological data about past communities of organisms to reconstruct a purported 'undisturbed' (or 'slightly disturbed') condition on which to base studies of human impacts on modern communities (see e.g. Dietl and Flessa 2011;Conservation Paleobiology Workshop 2012;Wood et al. 2012). Nakamura et al. (2009Nakamura et al. ( , 2013 gave some examples of the application of this approach to amphibians and reptiles. In the case of Tenuta Zuccarello, the presence of Bombina proves that the distribution of the genus extended towards the Venetian Lagoon in the recent past. This suggests that the disappearance of suitable environments for the genus is a rather recent phenomenon and may support future reintroduction projects in suitable areas. Furthermore, it shows that the Roman settlement in Veneto was not the main cause of the local disappearance of this anuran, given that it was still able to live in the agricultural landscape revealed by the excavation activities that also discovered the well at Tenuta Zuccarello (Bon et al. 2010). However, a complete evaluation of the impact that the Romans had on Bombina, as well as the causes of its disappearance from the Lagoon, are still hindered by the absence of remains coming from both older and younger sites in the area.

Conclusions
The Roman well discovered in the Tenuta Zuccarello, named US 100 by its discoverers, has yielded more than 8000 remains of amphibians and reptiles. These remains represent a herpetofaunistic assemblage composed by at least 11 different taxa, including two caudates, three anurans, one turtle, two lizards and three snakes. The assemblage suggests an ecotonal environment with water bodies, open and humid areas, as well as dry and sunny areas. All the taxa are still present in the Veneto region, and most of them were found in other Venetian sites since the beginning of the Pleistocene. This might be an evidence of a certain continuity in the amphibians and reptiles population of the region during the Quaternary.
Nevertheless, Bombina is here found for the first time outside of its current range in Veneto, supporting a recent contraction of its distribution and a recent withdrawal from the area surrounding the Venetian Lagoon. It is still not clear whether the Roman settlement had a distinct impact on its presence in the area, but Tenuta Zuccarello provides evidence to reject the hypothesis that its disappearance might have been directly caused by the changes made by the Romans to the environment of the Lagoon. Further findings in other sites in the area are needed in order to get more information on this issue.