Anura Fischer 1813

Anura indet. Material. Hambach 6C: four premaxillae (IPB-HaH 2268/2270, IPB-HaH 2299); 51 fragments of maxilla (IPB-HaH 2233/2265, IPB-HaH 2282/2298, IPB-HaH 2300); 17 trunk vertebrae (IPB-HaH 2089/2097, IPB-HaH 2144/2145, IPB-HaH 2157/ 2158, IPB-HaH 2181/2183, IPB-HaH 2192); seven sacral vertebrae (IPB-HaH 2087, IPB-HaH 2206/ 2208, IPB-HaH 2217/2218, IPB-HaH 2225); 12 urostyles (IPB-HaH 2088, IPB-HaH 2197/2198, IPB-HaH 2201/2205, IPB-HaH 2216, IPB-HaH 2226/2227, IPB-HaH 2306); three coracoids (IPB-HaH 2313/2314, IPB-HaH 2378); nine humeri (IPB-HaH 2063, IPB-HaH 2303/2304, IPB-HaH 2311/ 2312, IPB-HaH 2317/2318, IPB-HaH 2331); five radioulnae (IPB-HaH 2301/2302, IPB-HaH 2309, IPB-HaH 2330, IPB-HaH 2335); two ilia (IPB-HaH 2319/2320); one ischium (IPB-HaH 2322); one femur (IPB-HaH 2326); 14 tibiofibulae (IPB-HaH 2054, IPB-HaH 2062, IPB-HaH 2064/2068, IPB-HaH 2305, IPB-HaH 2310, IPB-HaH 2327, IPB-HaH 2332/2334, IPB-HaH 2400); four indeterminate elements (IPB-HaH 2308, IPB-HaH 2315, IPB-HaH 2328, IPB-HaH 2398). Hambach 11: 29 maxillae (IPB-HaR 2044/2070, IPB-HaR 2177/ 2178); one angular (IPB-HaR 2114); two atlases (IPB-HaR 2025, IPB-HaR 2035); five trunk vertebrae (IPB-HaR 2024; IPB-HaR 2027/2029; IPB-HaR 2037); two sacral vertebrae (IPB-HaR 2026, IPB-HaR 2036); three urostyles (IPB-HaR 2038/ 2040); two coracoids (IPB-HaR 2125/2126); two scapulae (IPB-HaR 2072/2073); 10 humeri (IPB-HaR 2089/2095, IPB-HaR 2108/2109, IPB-HaR 2153); 16 radioulnae (IPB-HaR 2074/2079, IPB-HaR 2107, IPB-HaR 2123/2124, IPB-HaR 2128, IPB-HaR 2155/2157, IPB-HaR 2180/2182); four ilia (IPB-HaR 2085/2086, IPB-HaR 2104/2105); one ischium (IPB-HaR 2106); three femurs (IPB-HaR 2133/2134, IPB-HaR 2141); 25 tibiofibulae (IPB-HaR 2080/2082, IPB-HaR 2118/2122, IPB-HaR 2135/2140, IPB-HaR 2158/2168); one indeterminate element (IPB-HaR 2169). Hambach 11C: three maxillae (IPB-HaR 2422/2424); one ornamented bone fragment (IPB-HaR 2430); four tibiofibulae (IPB-HaR 2410/2413); one indeterminate element (IPB-HaR 2409). DISCUSSION The Middle Miocene and Late Pliocene Amphibians from Hambach Compared Deposition of the two fossiliferous levels in Hambach, stratum 6C (with site Hambach 6C) and stratum 11 (with sites Hambach 11 and 11C), is separated by about a dozen Myr and happened in very different global climatic contexts (the MCO vs a period of climate deterioration preceding the onset of Quaternary glacial cycles). This is clearly reflected in the faunal composition, with a far higher diversity in the Middle Miocene association compared to the Late Pliocene one and the presence of several taxa linked with subtropical conditions in the former (e.g., among amphibians and reptiles: cryptobranchids, Chelydropsis, Diplocynodon Pomel, 1847, cobras). Based on our observations and identifications (Table 1), the amphibian component of the Hambach faunas matches with this pattern, all in all. The Middle Miocene fossil assemblage from Hambach 6C includes at least six different urodeles and six anurans. The Hambach 11 and 11C combined assemblage, on the other hand, listed only half the number of urodeles, even though the total of recognized anurans amounts to the same value. The remains attributed to the indeterminate cryptobranchid and to Chelotriton stand as evidence of the already-mentioned “tropical” elements present during the Middle Miocene. In agreement with crocodylians (Mörs et al., 2000; Mörs, 2002) and cobras (Čerňanský et al., 2017), but in contrast with what happens with Chelydropsis turtles (which possibly persisted in the Upper Pliocene deposits; Mörs, 2002), the two urodeles are absent in younger sites at Hambach, hinting towards a likely extirpation between MN 5 and MN 16a. Other urodeles sharing the same pattern of a Miocene presence and Pliocene absence in Hambach include Euronecturus grogu and Triturus sp. It is interesting to note that the proteid E. grogu, of which Hambach 6C is the only occurrence known worldwide at the moment, seems to be replaced by Mioproteus, a member of a different “modern” lineage of Eurasian proteids (Macaluso et al., 2022b). The ranid frogs Pelophylax sp. and Rana sp. are also recognized in Hambach 6C only, but the presence of ranids in the Upper Pliocene as well is attested by few remains from Hambach 11. At least one of these remains, the ilium IPB-HaR 2087, may even display green frog features, and thus the absence of either one or the two ranids from the younger assemblage may be artifactual. Remarks. Numerous fossil elements can be assigned to anurans, but are either too poorly preserved or not taxonomically significant enough for a more refined identification. Reptiles While studying the amphibian material, we chanced upon a few remains of reptiles that were accidentally not included in Čerňanský et al.’s (2017) work. Most of these are fragments of poorly diagnostic bones, but at least two specimens are worth mentioning and figuring. IPB-HaH 2340 (Figure 23 A-B), from Hambach 6C, is probably a fragment of the posterodorsal process of a right jugal. The ornamentation recalls Chamaeleo andrusovi Čerňanský, 2010, even though the topotypic jugals of this species show two rows of protuberances instead of just one as in the case of the specimen from Hambach. It is here attributed to Chamaeleo aff. andrusovi, similar to the squamosal fragment described by Čerňanský et al. (2017) from the same site. IPB-HaR 2171 (Figure 23 C-D), from Hambach 11, can be associated to the same taxon as the nasal assigned by Čerňanský et al. (2017) to Pseudopus cf. pannonicus (Kormos, 1911), because they share a similar dermal sculpturing. Nevertheless, there are also amphibians clearly persisting in Hambach in both Middle Miocene and Late Pliocene times. These include at least two urodeles, Palaeoproteus cf. miocenicus and Lissotriton sp., and two anurans, Latonia sp. and Hyla sp. As mentioned, ranids can also be added to this list, even though detailed identification of the Pliocene remains at specific rank is prevented. Among frogs, palaeobatrachids and pelobatids show the reverse situation, with Late Pliocene remains that can be identified at species (P. eurydices) or, possibly, genus (cf. Eopelobates sp. and? Eopelobates sp.) ranks respectively, whereas only the general presence of the families can be reported for the Middle Miocene (even in a tentative way in the case of palaeobatrachids). On the opposed side, the toad Bufo gr. bufo is the only anuran whose presence is certified just for the Late Pliocene in Hambach. Therefore, considering the uncertainty surrounding the possible persistence of some taxa from the Middle Miocene, the composition of the Late Pliocene Hambach 11 and 11C amphibian assemblage is certainly impoverished compared to the older one from Hambach 6C, apparently mainly as far as the urodele component is concerned, but it appears to exhibit an overall similarity and continuity. This differs from other tetrapod groups, which are sporadically represented by the same or related taxa in both Miocene and Pliocene levels (e.g., some petauristid rodents and possibly the already-mentioned Chelydropsis turtles; Mörs et al., 2000; Mörs, 2002; Van Laere and Mörs, 2023). In terms of abundance, the highest numbers of remains identified per taxon in the Miocene assemblage are those referred to Chelotriton sp. (57 remains) and Latonia sp. (37 remains). These are, therefore, the taxa dominating the oldest Hambach oryctocenosis. Latonia persisted as dominant also in the Pliocene with 22 remains (18 from Hambach 11 and six from Hambach 11C), following P. eurydices represented by 27 remains (23 and four from Hambach 11 and 11C, respectively). As already mentioned, Chelotriton is not present in the Pliocene 11 and 11C sites, in agreement with a general European trend of extinction of this newt. The only Pliocene remains referred to this genus come in fact from the Upper Pliocene of southern France (Bailon, 1989; Macaluso et al., 2022a). The most-represented urodele in the Upper Pliocene of Hambach is Mioproteus cf. wezei, represented by 15 remains (nine and six, respectively, from Hambach 11 and 11C). Other taxa from both the Miocene and Pliocene assemblages are only represented by very few, less than 10 remains each (except for Triturus sp., with 12). Thus, these represent only very minor components of the fossil associations. Palaeobiogeographical Significance of the Hambach Amphibian Assemblages The amphibian fossil record from Hambach already proved to host unexpected surprises with the discovery of Euronecturus grogu, an enigmatic proteid (see Macaluso et al., 2022b) that is only known from its type locality of Hambach 6C at the moment. The extended study of the whole amphibian record revealed that this is not the only noteworthy taxon preserved in the site, and that significant findings were hidden in both the Miocene and Pliocene assemblages. Cryptobranchids are in general poorly represented in the fossil record, even though a particular concentration of Neogene cryptobranchid-bearing sites is found in central Europe, and more specifically in Southern Germany (Böhme et al., 2012). Still, they are almost unknown from the European early Middle Miocene, even though their presence in Lower, upper Middle and Upper Miocene sites (Westphal, 1958, 1970; Böttcher, 1987; Miklas, 2002; Böhme, 2003; Kvaček et al., 2004; Tempfer, 2004; Böhme et al., 2012; Vasilyan et al., 2013; Sach, 2016; Georgalis et al., 2019b; Szentesi et al., 2020) suggests their continuous persistence in the continent. As a matter of fact, Hambach 6C is currently the only known occurrence of a cryptobranchid from the early Middle Miocene time frame in Europe, and even adds to a limited Eurasian Langhian record that further includes only few localities in Kazakhstan (Chkhikvadze, 1982; Böhme et al., 2012). Cryptobranchids later declined in Europe during the Pliocene, with their last occurrence at Willershausen, in central Germany (Westphal, 1967; Böhme et al., 2012). Th