Introduction

The Amphicyonidae were an important component of carnivoran assemblages in North America and Eurasia during much of the Cenozoic era (Middle/Late Eocene to Late Miocene; Viranta 1996; Hunt 1998; Ginsburg 1999; Jiangzuo et al. 2021). In Africa, the oldest known records of amphicyonids date back to the Early Miocene, and they persisted there until the end of the Late Miocene, constituting the latest known records of this group (Werdelin and Peigné 2010). Recent work argued for a North American origin of the family (Tomiya and Tseng 2016). This hypothesis is supported by the more complete and diverse Paleogene record of amphicyonids in North America than in Western Europe and Asia. Since the Late Eocene, two successive and endemic groups of amphicyonids have been recognized in North America (Hunt 2011): the Eocene/Oligocene Daphoeninae Hough, 1948, and the Oligocene/Early Miocene Temnocyoninae Hunt, 1998. Although some authors have noted dental similarities between Eurasian Haplocyoninae Bonis, 1966 and the North American Temnocyoninae Hunt, 1998, these two groups are generally considered distinct (Bonis 1973; Jiangzuo et al. 2021; Hunt 1998, 2009, 2011; Peigné and Heizmann 2003). During the Eocene, Cynodictis Bravard and Pomel, 1850 was the only amphicyonid recorded in European faunas, represented by several species (Teilhard de Chardin 1915). However, more derived forms, which are interpreted as true Amphicyoninae, such as Pseudocyonopsis Kuss, 1965 and Cynelos Jourdan, 1862, have been present in Europe since the Early Oligocene (Ginsburg 1965, 1966; Springhorn 1977; Solé et al. 2021).

The Amphicyoninae underwent a significant radiation during the Miocene, with a general increase in size and diversification into a wide range of dental adaptations. These ranged from hypocarnivorous species that converged with bears, such as the Pseudarctini Schlosser, 1899, to hypercarnivorous species with felid-type dentition, such as the Thaumastocyoninae Hürzeler, 1940 (Peigné and Heizmann 2003; Morlo et al. 2019; Morales et al. 2019). Regardless of the taxonomic rank, the Thaumastocyoninae and the Amphicyoninae diverged early on, as evidenced by their separation from the beginning of the Early Miocene. Thaumastocyonines, a group of limited diversity, are extremely rare and appear sporadically in the fossil record, forming an anagenetic lineage (Morales et al. 2021a). Between the hypo- and hypercarnivorous amphicyonids, the mesocarnivorous type was always present in most carnivore assemblages until its extinction in the Late Miocene. These mesocarnivorous species were historically classified within the genus Amphicyon, with rare exceptions. The resurrection of the genus Cynelos Jourdan, 1862, proposed by Kuss (1965), was a remarkable achievement in our understanding of the systematics of the Amphicyonidae. This involved the separation of a group of species from the Early Miocene (Aquitanian/Burdigalian) of Europe characterized by their small-to-medium size, and their distinct dentition from that of the type species of Amphicyon, Amphicyon major Lartet, 1836. Most of the materials reviewed by Kuss (1965) came from classic European sites, such as Ulm, Hastlach and Wintershof-West (Germany), and Saint Gérand (France). Some of these were grouped into two species: Cynelos lemanensis (Pomel, 1846) and Cynelos rugosidens (Dehm, 1950). Within C. lemanensis, Kuss (1965) included the subspecies C. lemanensis lemanensis (Pomel, 1846) and C. lemanensis helbingi (Dehm, 1950), synonymizing Amphicyon acutidens Dehm, 1950 with the former. In the context of C. rugosidens, he accepted C. rugosidens rugosidens (Schlosser 1899) and C. rugosidens schlosseri (Dehm, 1950). Amphicyon dietrichi Dehm, 1950, also from the Wintershof-West site, was considered by Kuss (1965) to be a junior synonym of Pseudocyon bohemicus Schlosser, 1899 (now Paludocyon bohemicus) and was also included in the genus Cynelos (Peigné et al., 2008). Subsequent authors have largely accepted this proposal with few changes, although they have retained the species rank of Cynelos helbingi (e.g., Ginsburg 2002; Peigné and Heizmann 2003; Peigné et al. 2008).

Later authors significantly expanded the temporal range of Cynelos, including species from the Paleogene of Quercy, France (Ginsburg 1965, 1966), as well as extending its geographical range with species from Africa, Asia and North America (Savage 1965; Schmidt-Kittler 1987; Tedford and Frailey 1976; Hunt 1998; Hunt and Stepleton 2015; Hunt and Yatkota 2020; Jiangzuo et al. 2018). Consequently, Cynelos has become a “taxonomic catch-all”, in which the type species of the genus (C. lemanensis) has frequently been forgotten in a framework of excessive variability. Recently, Morales et al. (2021b) proposed the exclusion of two species of Cynelos– C. schlosseri from Wintershof-West and C. bohemicus from Tuchorice (Czech Republic)– defining two new genera: Dehmicyon, with A. schlosseri Dehm, 1950 as the type species; and Paludocyon, with P. bohemicus (Schlosser, 1899) as the type species. The dentition of these two genera notably diverges from that of Cynelos. Dehmicyon schlosseri shows affinities with the Pseudarctini, while Paludocyon maintains a more hypercarnivorous teeth.

This study provides a detailed description of one of the amphicyonine species from the early Middle Miocene site of els Casots (Catalonia, Spain), which is compared with related species belonging to the genera Paludocyon and Cynelos from Europe and North America. Based on this, we describe a new species of Paludocyon from els Casots and further provide a comprehensive review of European and North American Paludocyon and Cynelos species.

Age and geological background of els Casots

The els Casots fossil site is located at the southern margin of the Vallès-Penedès Basin (NE Iberian Peninsula)—an elongated half-graben parallel to the Catalan Coastal Ranges that formed during the late Oligocene and is mostly infilled by Miocene continental sediments ranging from about 20 to 7 Ma (Casanovas-Vilar et al. 2016, 2022a). The site was discovered in 1989 and initially excavated between 1989 and 1994. After many years of inactivity, systematic excavations resumed in 2018 and have continued ever since. More than 5,000 macrovertebrate fossil remains have been recovered from various fossiliferous levels (Moyà-Solà and Rius Font 1993; Casanovas-Vilar et al. 2011, 2022b; authors’ unpublished data). A revision of the existing collections yielded a significantly expanded faunal list comprising up to 80 vertebrate species (authors’ unpublished data), including fishes, amphibians, reptiles, birds, and mammals (Pickford and Moyà-Solà 1994, 1995 Duranthon et al. 1995; Alba et al. 2014; Díaz-Aráez et al. 2017; Jovells-Vaqué et al. 2017; Valenciano et al. 2020; Casanovas-Vilar et al. 2022a, 2022b). Macromammal remains are often found in association, and even partial skeletons have been found for various taxa, thus indicating that most of the fauna represents a parautochthonous assemblage (Casanovas-Vilar et al. 2022b). The amphicyonid material described herein was recovered from level Bc in 1991 while digging two trenches (trench 1 and 2) to study the stratigraphy of the site. Level Bc is a ~ 40 cm-thick level of yellowish ochre siltstones interpreted as shallow lacustrine facies. It is one of the uppermost levels of the excavation, located just 30 cm below the top of the site series (Casanovas-Vilar et al. 2022b: fig. 5).

The age of els Casots is well constrained thanks to a combination of bio- and magnetostratigraphic data (Casanovas-Vilar et al. 2022b). The rodent fauna indicates a correlation with Aragonian subzone Cb (16.15–15.94 Ma; boundaries after Van der Meulen et al. 2012), corresponding to the beginning of MN5 (earliest Middle Miocene). The geological cores sampled at the site down to the basement (36 m) record a long reverse magnetic polarity interval that, owing to biostratigraphic constraints, can only correspond to chron C5Br (15.974–15.160 Ma; boundaries after Ogg 2020). These data combined indicate an estimated age of ~ 15.9 Ma for the site, which is somewhat younger than previous estimates based on biostratigraphy, which correlated els Casots to the latest Early Miocene (MN4; e.g., Agustí and Llenas 1993; Agustí et al. 2001; Casanovas-Vilar et al. 2011, 2016; Jovells-Vaqué et al. 2017).

The presence of charophytes, helophytic plants, ostracods, fishes, and various tetrapods that are semiaquatic or tightly linked to water (amphibians, crocodilians, and tragulids) denotes a shallow freshwater lacustrine-palustrine environment, in accordance with sedimentological evidence (Casanovas-Vilar et al. 2022b; Sanjuan et al. 2023). Megathermic taxa, such as crocodilians or pythonid snakes, indicate warm conditions associated with the Miocene Climatic Optimum. Large mammals are congruent with the presence of forested habitats near the wetlands, whereas small mammals may suggest that more open woodlands occurred far from these humid areas (Casanovas-Vilar et al. 2022b). This paleoenvironmental interpretation agrees with slightly younger palynological data from the same area (Bessedik and Cabrera 1985; Jiménez-Moreno and Suc 2007; Rull et al. 2024).

Materials and methods

Studied and comparative material

Fossil remains of Paludocyon moyasolai sp. nov. are housed in the Institut Català de Paleontologia Miquel Crusafont (ICP; Sabadell, Spain): IPS10156, partial cranium with right C1–P4 and left P1–P3 and M3 and isolated M1 and M2; IPS11438, left m2.

The comparative sample includes the original fossils of Cynelos piveteaui Ginsburg, 1966 from Quercy, housed in the MNHN; Cynelos lemanensis (Pomel, 1846) from Saint Gérand-le-Puy, housed in the MNHN and the FSL; and Paludocyon bohemicus (Schlosser, 1899) from Tuchořice, housed in the NMP. Other species were included in the comparative sample based on the published literature and photographs of the original material: Pseudocyonopsis landesquei (Helbing, 1928) from La Milloque (France) and Gamersheim (Germany); Daphoenodon superbus Peterson, 1907 from the Agate Fossils Bed National Monument (USA), further including a cast of the holotype; Absonodaphoenus caroniavorus (White, 1942) comb. nov. from Thomas Farm (USA); Cynelos rugosidens Schlosser, 1899 from Haslach (Germany) and Saint-Gérand-le-Puy (France); Cynelos stenos Hunt and Yatkola, 2020 from Runningwater Quarry, Nebraska (USA); Cynelos idoneus (Matthew, 1924) from Sheep Creek Fm., Nebraska (USA); Cynelos malasi Hunt and Stepleton, 2015 from the Sespe Formation, Orange County, California (USA); and Paludocyon dietrichi (Dehm, 1950) comb. nov., Paludocyon helbingi (Dehm, 1950) comb. nov., and Paludocyon acutidens (Dehm, 1950) comb. nov. from Wintershof-West (Germany).

Dental nomenclature follows Morales et al. (2019). Dental measurements of crown length and width, as well as metastyle-parastyle length, were taken with a digital caliper to the nearest 0.1 mm. The measurements for various tooth loci (P4, M1, M2, m1 and m2) were compared to a selected sample of small and middle-sized amphicyonid species from genera Paludocyon and Cynelos, based on data taken from the literature (Schlosser 1899; Dehm 1950; Ginsburg 1965, 1977, 2002; Kuss 1965; Heizmann 1973; Peigné and Heizmann 2003; Hunt and Stepleton 2015; Morales et al. 2021b).

Cladistic analysis

We performed a maximum parsimony cladistic analysis to infer the phylogenetic relationships of the new species described in this paper. Characters (Online Resource 1) were treated as unordered and equally weighted. Some characters are modified from those proposed in previous works (Viranta 1996; Peigné et al. 2008; Morales et al. 2019; Jiangzuo et al. 2021). The matrix (Online Resource 2) comprises 43 dental characters (35 binary and 8 multistate) and 15 amphicyonid species from various genera, with an emphasis on Cynelos and Paludocyon. Pseudocyonopsis landesquei (Helbing, 1928) is the outgroup. The analysis was performed with PAUP*4.0b10 (Swofford 2002) using the branch-and-bound algorithm. Clade support was assessed with non-parametric bootstrapping (10,000 replicates) and Bremer decay indices.

Measurement abbreviations: L, maximum mesiodistal length; W, maximum buccolingual width; L P4, metastyle-parastyle length.

Cladistic abbreviations: CI, consistency index; HI, homoplasy index; RI, retention index.

Institutional abbreviations: AMNH, American Museum of Natural History, New York, USA; CM, Carnegie Museum of Natural History, Pittsburgh, USA; FMNH, Field Museum of Natural History, Chicago, USA; FSL, Faculté des Sciences de la Terre, Université Claude Bernard Lyon 1, France; ICP, Institut Català de Paleontologia Miquel Crusafont, Sabadell, Barcelona, Spain; IPS, acronym of the ICP collections (formerly Institut de Paleontologia de Sabadell); MNCN, Museo Nacional de Ciencias Naturales-CSIC, Madrid, Spain; MNHN, Muséum national d’Historie naturelle, Paris, France; MCZ, Museum of Comparative Zoology, Harvard University, USA. NMB, Naturhistorisches Museum Basel, Switzerland; NMP, National Museum, Prague, Czech Republic; OCPC, Orange County Paleontological Collection, Department of Geological Sciences, California State University, USA; SMNS, Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany; SNSB-BSPG, Staatliche Naturwissenschaftliche Sammlungen Bayerns, Munich, Germany. UNSM, Vertebrate Paleontology, University of Nebraska State Museum, Lincoln, USA.

Systematic Paleontology

Order Carnivora Bowdich, 1821

Family Amphicyonidae Trouessart, 1885

Subfamily Amphicyoninae Trouessart, 1885

Tribe Amphicyonini Trouessart, 1885

Diagnosis: Amphicyoninae with a tendency towards premolar reduction, presence of diastemata, robust carnassial teeth, m1 with unreduced talonid and metaconid always present, enlarged M1 and m2, M2 very broad buccolingually, M3 and m3 small but variably reduced.

Genus Paludocyon Morales et al., 2021b

Type species: Paludocyon bohemicus (Schlosser, 1899).

Type locality: Tuchořice (Czech Republic, Early Miocene).

Other included species: Paludocyon helbingi (Dehm, 1950) comb. nov., Paludocyon acutidens (Dehm, 1950) comb. nov., Paludocyon dietrichi (Dehm, 1950) comb. nov., and Paludocyon moyasolai sp. nov.

Age range: Early to Middle Miocene (MN3–MN5).

Diagnosis: See Morales et al. (2021b).

Differential diagnosis: Paludocyon differs from Pseudocyon Lartet, 1851 in the more robust m1 and m2, the broader m1 talonid with a better-developed hypoconid that occupies almost the entire talonid area, and less reduced p4 and m2 compared with the m1. It differs from Cynelos Jourdan, 1862 (C. lemanensis type species) in the lesser development of the m2 and m3 compared to the m1, and in the marked reduction of the lower premolars. It also differs in the m1 talonid broader than the trigonid, with a higher and larger hypoconid, and a reduced entoconid. The P4 of Paludocyon has an elongated paracone mesial crista, whereas in Cynelos it is short and more vertical. The M1 paracone of Paludocyon is higher and somewhat larger than the metacone, contrary to Cynelos, which both cusps are lower and have a similar size. Additionally, the lingual platform of the M1 is smaller than in Cynelos. The metacone of the M2 is smaller than the paracone; in Cynelos, however, both are similar in size. The differences compared to Amphicyon Lartet, 1836 (Amphicyon major Blainville, 1841 type species; see Ginsburg 1961; Peigné 2012) are significant. Apart from its lesser size, Paludocyon differs from Amphicyon by the relatively greater size of the premolars and the smaller diastemata. The upper molars are less robust than those of Amphicyon and show a minor buccal cusp development. The P4 of Paludocyon maintained a strong protocone while in Amphicyon is comparatively much reduced. The lower molars differ from those of Amphicyon in that they have less robust trigonids and higher talonid cuspids. The m1 talonid in Paludocyon is broader than the trigonid, opposite to the m1 morphology of Amphicyon. The m3 is relatively smaller than in Amphicyon. Paludocyon differs significantly from Heizmannocyon Ginsburg, 1999 in more slender upper molars (M1–M2) with a lesser reduced lingual platform. The lower dentition of Paludocyon shows a minor reduction of the premolars, having a larger p4 than Heizmannocyon and a smaller diastemata. Paludocyon has a more graceful m1, while Heizmannocyon has a robust m1 with a large development of the protoconid and metaconid, and with the talonid being somewhat narrower than the trigonid and dominated by a hypertrophied hypoconid.

Remarks: Before the inclusion of Pseudocyon bohemicus Schlosser, 1899 into Paludocyon (see Morales et al. 2021b), this species had been included in Amphicyon Lartet, 1839, Heizmannocyon Ginsburg, 1999, and Cynelos Jourdan, 1862. It had also been occasionally regarded as a junior synonym of Amphicyon steinheimensis Fraas, 1885 (Kuss 1965; Heizmann 1973; Viranta 1996). Ginsburg (1999) proposed that A. bohemicus, together with A. steinheimensis, would form a distinct lineage within Amphicyon, and erected the subgenus Heizmannocyon, with Amphicyon (Heizmannocyon) steinheimensis as the type species.

Paludocyon moyasolai sp. nov.

(Fig. 1)

Fig. 1
Fig. 1
Full size image

Paludocyon moyasolai sp. nov. from els Casots. a–f. Cranium, IPS10156, holotype: a. lateral left view; b. ventral part; c. left P4–M3 (stereo pair) in occlusal view; d. right P2 in lingual view and the left P3–M2 in buccal view; e. isolated right M1 in occlusal view; f. isolated right M2 in occlusal view. g–i. Left m2, IPS11438, paratype, stereo pairs in occlusal (g), buccal (h), and lingual (i) views. All specimens are depicted to the same scale except scale bars in a equal 10 cm, scale bar in b-i equal 5 cm

LSID urn:lsid:zoobank.org:act:6D44F1CB-3799-49D8-B97E-C6F71FA8B7C8.

Holotype: IPS10156, cranium with associated M1–M2 of the same individual.

Paratype: Left m2 (IPS11438).

Type locality: els Casots, Catalonia, Spain.

Age and distribution: Aragonian subzone Cb (MN5), earliest Middle Miocene (~ 15.9 Ma), only known from the type locality.

Etymology: Species epithet dedicated to Salvador Moyà-Solà, in recognition of his wonderful contribution to the development of European paleomastology (see review in Alba 2025).

Diagnosis: Medium-sized species of Paludocyon; P4 with reduced protocone; robust M1 with lingual platform reduced; M2 buccolingually broader than M1, with metacone smaller than paracone; M3 large and with well-defined trigone cuspids; m2 with a robust trigonid, protoconid and metaconid almost of the same height, protoconid with a weak basal buccal widening, short talonid of similar width as the trigonid, and large hypoconid occupying the buccal area of the talonid basin.

Differential diagnosis: Paludocyon moyasolai sp. nov. differs from other Paludocyon species in the buccolingually wider M2 greater than in M1, and by the larger and more molarized M3. Additionally, it differs from P. dietrichi in the more robust m2 and the buccolingually narrower M1.

Description

IPS10156 (Fig. 1a) is a strongly distorted cranium. The rostral part is poorly preserved, and only the right canine remains. The caudal portion of the cranium is also poorly preserved, so that its morphology cannot be adequately assessed. The two postcanine tooth series (Table 1) are preserved except for the left P2 (Fig. 1b–d). However, the right M1 and M2 are detached from the maxilla (Fig. 1e–f). The premolars increase in size from P1 to P3. They are separated from the canine and one another by a small diastemata. The P1 is uniradiculate, ovoid and unicuspidated. The P2 is a graceful premolar, mesiodistally elongated. The P3 is also elongated with a broader distal area. The P4 is robust, with a reduced protocone mesially placed that barely protrudes lingually. The paracone is strongly developed, particularly in width, whereas the metastyle is short and narrow. The buccal wall has a rectilinear profile with a well-developed cingulum. The M1 is a robust molar, with a subquadrangular occlusal shape that is lingually narrower than buccally. The paracone is high and somewhat larger than the metacone, and both cusps are basally separated by a middle depression. There is a moderately developed buccal cingulum. The protocone is low and slightly displaced mesially. The trigon basin is very wide. The lingual platform is reduced. A moderate lingual cingulum surrounds the protocone. The M2 has a subrectangular occlusal shape. It is mesiodistally shorter than the M1 but broader buccolingually. The paracone is slightly larger and higher than the metacone, and as in the M1 both cusps are separated by a small basal depression. The M2 protocone is centrally located and the trigon basin is well developed. A small paraconule and a distinct and strong subdivided metaconule are observable in the right M2. There is a lingual cingulum and a mesiolingualy well-developed platform. The M3 is also relatively large. The two buccal cusps are separated by a strong ectoflexus, with the paracone being much larger than the metacone, which is displaced lingually. The protocone is placed in a central position and is surrounded by a strong lingual cingulum.

Table 1 Measurements (in mm) of the dentition of Paludocyon moyasolai sp. nov. from els Casots. Abbreviations: L: mesiodistal length; W: buccolingual width
Full size table

Based on its size and morphology, the isolated left m2 (IPS11438) also belongs to the new species (Fig. 1g–i). It occludes perfectly with the upper molars and probably belongs to the same individual. The molar has a rectangular occlusal shape, being longer than wide. The trigonid is robust and moderately high, with the protoconid and metaconid almost equal in height, although the protoconid is somewhat larger. The protoconid displays a weak buccal basal widening. The paraconid is very small and barely distinguishable from the mesial cristids of the protoconid and metaconid. These cristids merge with one another, enclosing the deep, small trigonid basin mesiolingually. The talonid is shorter, almost as wide as the trigonid, with a large hypoconid that occupies the buccal half of the talonid basin. Its distal cristid bears a barely distinct hypoconulid and surrounds the entire distal part of the crown, joining the entocristid, which reaches the base of the metaconid. The basal cingulid is very weak.

Comparisons

Paludocyon moyasolai sp. nov. is characterized by the significant development of the M2 relative to the M1. This character distinguishes the Amphicyoninae from the rest of the Amphicyonidae subfamilies, including the Haplocyoninae Bonis, 1966, Daphoeninae Hough, 1948, Temnocyoninae Hunt, 1998, and Thaumastocyoninae Hürzeler, 1940. However, some more specialized Haplocyoninae genera, such as Gobicyon Colbert, 1939, can exhibit M2s that are comparable in size to the M1s (Jiangzuo et al. 2021). Much of the Amphicyoninae with large M2 from the Late Oligocene and Early Miocene of Europe display a strong development of crushing molars, alongside other characteristics such as reduced premolars, the presence of diastemata, and strengthened carnassial teeth (P4 and m1). Some of these forms of small/medium size (Fig. 2), which had generally been classified in the genus Amphicyon Lartet, 1836, were included by Kuss (1965) in Cynelos Jourdan, 1862, with the type species being Cynelos lemanensis (Pomel, 1846) from Saint Gérand. The use of Cynelos as a basal Amphicyoninae soon extended to other species from the late Oligocene and the Early Miocene in Europe (Ginsburg 1965, 1966; Springhorn 1977), Africa (Savage 1965; Schmidt-Kittler 1987), North America (Hunt 1972, 1998; Hunt and Stepleton 2015; Hunt and Yatkola 2020) and Asia (Jiangzuo et al. 2018). This widespread diversity of species has recently been addressed by Morales et al. (2021b), who proposed to establish two new genera: Dehmicyon Morales et al., 2021b and Paludocyon Morales et al. 2021b for Cynelos schlosseri (Dehm, 1950) and Cynelos bohemicus (Schlosser 1899), respectively.

Fig. 2
Fig. 2
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Bivariate plots of buccolingual width (W) and mesiodistal length (L) for upper and lower teeth of Paludocyon moyasolai sp. nov. from els Casots and selected small and medium-sized amphicyonines from Europe and North America: a. P4; b. M1; c. M2; d. m1; e. m2. Data obtained from Dehm (1950), Ginsburg (1965, 1977, 2002), Heizmann (1973), Hunt and Stepleton (2015), Kuss (1965), Morales et al. (2021b), Peigné and Heizmann (2003) and Schlosser (1899). Cynelos lemanensis from Ulm (Peigné and Heizmann 2003) is represented by the mean, maximum and minimum ranges of each dimension. Specimen 12293 corresponds to the holotype of Paludocyon helbingi comb. nov. (Dehm, 1950)

The new species from els Casots, P. moyasolai sp. nov., and P. bohemicus, have P4–M2 of similar size, although they differ in their proportions, particularly in the M2 (Fig. 3a–d). Both species share a strongly developed M2 compared to the M1, which is a derived character that separates them from C. piveteaui Ginsburg 1965–a species from the Oligocene of Quercy, France, which has a relatively smaller M2 (Fig. 3e–f). The M1 of both Paludocyon species have a short buccolingual width and a very robust buccal cusp. The paracone is larger and higher than the metacone, and the protocone is situated mesiolingually, surrounded by a moderately developed lingual cingulum. The M2 has a subrectangular occlusal shape with the buccal cusps unequal. The paracone is larger and higher than the metacone. The m2 is morphologically similar in both species, with a reduced paraconid, a short talonid with a moderate size, a low hypoconid, and a weak entocristid fused to the hypoconulid. Nevertheless, P. moyasolai sp. nov. can be distinguished from P. bohemicus by its shorter P4 with a reduced protocone, and a smaller protocone on the M1, as well as a more reduced lingual platform and a more developed mesiodistal lingual cingulum. The paracone and metacone of both M1 and M2 are basally separated. The M2 is buccolingually wider than the M1, and the M3 is larger with well-defined trigon cuspids.

Fig. 3
Fig. 3
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Comparison of the upper dentition of selected Amphicyoninae: a–b. Paludocyon moyasolai sp. nov. from els Casots, Spain, right P4–M3 (ICP10156, holotype), in occlusal (a) and buccal (b) views; c–d. Paludocyon bohemicus (Schlosser, 1899) from Tuchořice (Czech Republic), composite P4–M2 including mirrored left P4 (NM-Pv 11678), right M1 (NM-Pv11685) and mirrored left M2 (NM-Pv 11690), in occlusal (c) and buccal (d) views; e–f. Cynelos piveteaui Ginsburg, 1965 from Quercy (France), right P4–M2 (MNHN-F-9270), in occlusal (e) and buccal (f) views; g–i. Cynelos lemanensis (Pomel, 1846) from Saint-Gérand-le-Puy (France): g. left M1–M3 (FSL 213824) mirrored in occlusal view; h. left P4 (FSL 65655) mirrored in occlusal view; i. left M1–M3 (FSL 213824) mirrored in buccal view; j–k. Cynelos stenos Hunt and Yatkola, 2020 from Runningwater Quarry, Nebraska (USA), left P4–M3 (UNSM 44723) mirrored, in occlusal (j) and buccal (k) views; l–m. Cynelos idoneus (Matthew, 1924) from Sheep Creek beds (USA), right P4–M2 (AMNH M 18912), in occlusal (l) and buccal (m) views. Specimens are shown at a similar size (i.e., they are not to the same scale) to facilitate comparison of morphological differences. Abbreviations: bc, buccal cingulum; lc, lingual cingulum; lp, lingual platform; me, metacone; ms, metastyle; pa, paracone; ps, parastyle; pr, protocone; tb, trigon basin

Although the upper molars of P. moyasolai sp. nov. show significant wear, it can accurately be inferred that the paracone of the M1 is taller than the metacone. This character differentiates the species from C. lemanensis. Other differences are related to the advanced hypocarnivorous specialization of C. lemanensis, whose upper molars (M1–M2) are similar in size and morphology (Fig. 3g–i). The occlusal surface of these molars is enlarged by the development of their lingual platform. This contrasts with P. moyasolai sp. nov., whose M1 is shorter buccolingually, resulting in a significantly smaller lingual platform. The mesiodistal length of the M2 in P. moyasolai sp. nov. is shorter than in C. lemanensis. Nevertheless, P. moyasolai sp. nov. shares with C. lemanensis the large and molarized M3, and the basal separation of the paracone and metacone in the M1 and M2. The m2 of P. moyasolai sp. nov. differs from that of C. lemanensis in having a shorter talonid, and a less developed hypoconid. Cynelos rugosidens Schlosser, 1899, from Haslach, Germany, is closely related to C. lemanensis. Both species have the apomorphic crushing molars and a subquadrangular M1 shape with an enlarged lingual area. The M2 is also enlarged and is close in size and morphology to the M1. However, C. rugosidens has a simpler and smaller M3 that differs from the molariform morphology of C. lemanensis. Additionally, the M2 of C. rugosidens is less enlarged than that of C. lemanensis. On the other hand, C. acutidens, C. helbingi and C. dietrichi differ from C. lemanensis and C. rugosidens in the morphology of the upper molars (M1–M2), which have a subrectangular occlusal shape, a shortened buccolingual diameter, and a higher buccal wall, with the paracone being more developed than the metacone. Similarly, the lingual platform of M1 is reduced, a feature also shared with P. moyasolai sp. nov. and P. bohemicus. Consequently, we propose transferring these species to the genus Paludocyon, as P. helbingi (Dehm 1950) comb. nov., P. acutidens (Dehm 1950) comb. nov., and P. dietrichi (Dehm 1950) comb. nov.

Three species closely related to Cynelos and Paludocyon have been described in the North American fossil record. Cynelos malasi Hunt and Stepleton (2015) is represented by a skull fragment containing the left and right P4–M2, and the alveoli of the other teeth. Paludocyon moyasolai sp. nov. differs from C. malasi in having greater robustness, size, and height of the buccal cusps of the M1–M2, a weaker lingual platform and lingual cingulum, and probably a greater size of M3 relative to M2. However, P. moyasolai sp. nov. and C. malasi share the reduction in the buccolingual width of the M1, and the mesiolingual position of the protocone. In the M2, they share the subrectangular occlusal shape related to the short length of the buccal wall. In light of the current taxonomic modifications, these considerations align with Hunt and Stepleton (2015), who pointed out that C. malasi could represent a transitional stage between C. lemanensis and C. helbingi (herein Paludocyon helbingi comb. nov.). Nevertheless, due to the more derived condition of the characters shared with P. moyasolai sp. nov. and P. bohemicus, the North American species is more closely related to Paludocyon than to Cynelos. Cynelos idoneus (Matthew, 1924) from the Middle Miocene of Sheep Creek beds (Fig. 3j–k), is also closer to P. moyasolai sp. nov. Both species share M1–M2 with robust buccal cuspids, with the paracone being larger and higher than the metacone. However, they diverge in that the lingual cingulum is reduced in C. idoneus, and the M2 is less developed in terms of size and proportions, being much larger in P. moyasolai sp. nov. than in C. idoneus. Additionally, the M3 of C. idoneus is very reduced, almost vestigial, in contrast to the M3 size of P. moyasolai sp. nov. The third North American species, Cynelos stenos Hunt and Yatkola, 2020, from the Early Miocene of the Runningwater Formation is known by a complete skull and mandible (Fig. 3l–m). Unfortunately, the molar teeth of C. stenos are highly worn, which prevents comparison of features such as the relative height of the buccal cusps of the upper molars (M1–M2). This is an important character that is useful to distinguish Paludocyon from Cynelos. Paludocyon moyasolai sp. nov. differs from C. stenos in terms of the M1–M2 morphology: both molars in the North American species have the same occlusal shape due to the elongated buccal wall, which maintains the large buccolingual diameter. Consequently, the lingual platform is well developed and the protocone is placed far from the large lingual cingulum. Furthermore, the metacone is enlarged as a result of the elongation of the buccal wall in these molars, reaching the size of the paracone. The M3 of C. stenos is also large, and similar in size to that of P. moyasolai sp. nov., but this species has a subrectangular occlusal shape while C. stenos has an oval shape with the metacone displaced lingually. The m2 (Fig. 4) is the only lower tooth comparable between these species. It is significantly more robust in C. stenos than in P. moyasolai sp. nov., with a larger talonid. These features distinguish C. stenos from P. moyasolai sp. nov., positioning C. stenos closer to C. lemanensis. In summary, P. moyasolai sp. nov. diverges from P. bohemicus in some characteristics but is morphologically far from the European C. lemanensis and C. rugosidens. Further data on the lower dentition of P. moyasolai sp. nov. could clarify its systematic status within Paludocyon.

Fig. 4
Fig. 4
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Comparison of the left m2 in occlusal view of selected Amphicyoninae. a. Paludocyon moyasolai sp. nov. (IPS11438) from els Casots, Spain; b. Paludocyon bohemicus (Schlosser, 1899) (TU 739157, mirrored) from Tuchořice (Czech Republic); c. Cynelos lemanensis (Pomel, 1846) (MNHN.F. SG 490) from Saint-Gérand-le-Puy (France); d. Cynelos stenos Hunt and Yatkola, 2020 (UNSM 44723) from Runningwater Quarry, Nebraska (USA). Scale bar equal 1 cm

Discussion

Phylogenetic relationships

Understanding the Early Miocene radiation of amphicyonines inevitably requires a taxonomic revision of Cynelos. This is because Cynelos includes species with a long temporal range (Late Oligocene to Middle Miocene), a wide biogeographic distribution (Eurasia, Africa and North America), and a broad range of morphological variation (from small to large-sized and from hypo- to mesocarnivorous species). Due to the scarcity of available material for most of the considered species, the revision and phylogenetic analysis are restricted to dental characters. The obtained cladogram (Fig. 5) reveals a clade solidly supported (node A) that includes all Cynelos and Paludocyon species (Online Resource 3). Pseudocyonopsis landesquei (used as an outgroup) and Daphoenodon superbus, as primitive North American Amphicyonidae, along with Dehmicyon schlosseri (Dehm, 1950) from the Early–Middle Miocene of Europe and Absonodaphoenus caroniavorus comb. nov. from Thomas Farm (see Olsen 1958; White 1947; Tedford and Frailey 1976), are excluded from this clade. Tedford and Frailey (1976) already noted that De. schlosseri and Ab. caroniavorus are closely related to each other. They exhibit dental morphologies that differ from the other species analyzed here. Our cladogram supports this hypothesis, as these two species are recovered as sister taxa. However, their morphological differences are consistent with a generic distinction. Absonodaphoenus caroniavorus can be distinguished from De. schlosseri by the reduction of the parastyle and metastyle in the M1, as well as the lingual cingulum. The mesial and distal walls also exhibit a pronounced flexure, which is a consequence of the disproportionate length of the buccal and lingual walls. The paraconule and metaconule of the M1 and M2 are significantly reduced and fused with the protocone, forming a semicircular crista. The M3 appears to have been larger than in De. schlosseri, although for this species, only the alveolus is preserved. The lower dentition of Ab. caroniavorus exhibits more robust molars (m1 and m2), with shorter talonids compared to the tribe Pseudarctini. Morales et al. (2021b) related Dehmicyon to the Pseudarctini tribe (Ictiocyon and Pseudarctos), characterized by hypocarnivorous dental adaptations. Absonodaphoenus caroniavorus appears to have evolved a more advanced form of hypocarnivorous dentition than De. schlosseri, although both species retain numerous plesiomorphic characters.

Fig. 5
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Chronologically-calibrated most parsimonious cladogram showing the phylogenetic relationship of Paludocyon moyasolai sp. nov. relative to other selected amphicyonids. The analysis found a single most parsimonious tree with 100 steps, CI = 0.4800, HI = 0.5200, and RI = 0.6463. Bremer indices and bootstrap support percentages (only when ≥ 50) are reported below and above nodes, respectively. Chronological data after International Commission on Stratigraphy (2024; updated after Cohen et al. 2013). Black thick lines represent the age range of the type localities, and the dashed line corresponds to the known chronostratigraphic range of each species

The basal-most species of clade A is C. piveteaui, which is morphologically close to D. superbus and De. schlosseri, but displays some synapomorphies with the remaining species, such as an enlarged M2. Its classification in Cynelos is questionable but is provisionally retained here pending an in-depth review within a broader context. The next clade B is the best supported. It includes C. lemanensis and C. rugosidens from the Early Miocene of Europe, together with the remaining Cynelos and Paludocyon species. However, it is noteworthy that the more derived status of C. rugosidens is not particularly well supported. Both species share apomorphic crushing molars, and subquadrangular M1 with an enlarged lingual platform. They also have an enlarged M2 that is close in size and shape to the M1. The only difference is that the size of the M2–M3 is relatively smaller in C. rugosidens. Both species exhibit advanced hypocarnivorous specialization that is convergent with that of the Pseudarctini, but the morphological patterns differ. In C. lemanensis and C. rugosidens, the upper molars (M1–M2) have an enlarged occlusal surface, which increases the size of the teeth mesiodistally. In the Pseudarctini, in contrast, the occlusal surface increases due to the buccolingually widening of the trigon basin. Node C includes the North American species of Cynelos (C. stenos, C. idoneus, and C. malasi) and P. moyasolai sp. nov., as well as the other Paludocyon species, and is less supported than the previous node. This is not surprising considering that the complete dentition is only known in the Paludocyon species and C. stenos, while the lower dentition is unknown in C. malasi and C. idoneus. The North American species C. stenos, C. idoneus, and C. malasi appear in the cladogram as taxa successively branching, and despite their closer position, they display a heterogeneous distribution of some diagnostic characters. Cynelos stenos shares important features with C. lemanensis, including an enlarged lingual platform in the M1, similarly-sized paracone and metacone in the M1 and M2, and a complex M3. However, the upper dentition and the m2 of C. stenos are more robust than those of the European species. Unfortunately, the molars of C. stenos are heavily worn, which prevents the comparison of some features, such as the relative height of the buccal cusps in the upper molars (M1 and M2). Conversely, C. idoneus shows a robust M1 and M2 with the paracone larger and higher than the metacone. Furthermore, the M1 differs from that of C. stenos in the reduced lingual platform and in the weak lingual cingulum (the latter is restricted to the distolingual crown portion, while the protocone occupies the mesiodistal area). Moreover, in C. idoneus, the M2 is reduced compared with the M1, and the M3 alveolus indicates that this tooth was small. Cynelos malasi displays the same overall morphology of the M1 and M2 as C. idoneus, and both share a small M3. However, the height of the buccal cusps in C. malasi is low, as occurs in C. lemanensis, differing from the other species included in the clade C (unknown in C. stenos). The heterogeneous distribution of characters in these species explains its topology in the cladogram but does not permit a satisfactory taxonomic classification. This group also includes P. moyasolai sp. nov., which is the species closest to the Paludocyon clade (Node D). Its inclusion in Paludocyon is justified because it shares the most significant characteristics that define the genus. The Paludocyon clade (Node D) comprises the type species of the genus (P. bohemicus), as well as three species originally described by Dehm (1950) from the Early Miocene of Wintershof-West, now classified as P. helbingi comb. nov., P. acutidens comb. nov. and P. dietrichi comb. nov. Despite the peculiar morphology of the M2 of P. acutidens, the cladogram shows a close relationship between P. acutidens and P. helbingi, with a reduced M2 with a subquadrangular occlusal shape. These four species differ significantly from C. lemanensis and C. rugosidens in terms of the morphology of the M1 and M2. The M1 of Paludocyon has a subrectangular occlusal shape, a shortened buccolingual diameter, and a higher buccal wall. The paracone is more developed than the metacone. Similarly, the lingual platform of the M1 is greatly reduced. The lower dentition of Paludocyon is larger and more robust than that of C. lemanensis, but the variability of the lower dentition in P. helbingi shows an ample overlap with the size range of C. lemanensis (Fig. 2).

In summary, our phylogenetic results support the paraphyletic nature of Cynelos. The Cynelos species from Europe (C. rugosidens and C. lemanensis) are distantly related to the Paludocyon clade, which justifies their classification as distinct genera. Paludocyon moyasolai sp. nov. appears as the sister group of Paludocyon species, and it shares the most significant characters that define the genus. However, the three North American species have a doubtful taxonomic classification. Cynelos idoneus and C. malasi lack the most distinctive Cynelos features: an enlarged lingual platform of the M1, a large M2 compared to the M1, and a molarized M3. Cynelos stenos shares the general morphology of molars with C. lemanensis, but it has a more robust molar dentition, which distinguishes it from the European species. Despite the differences between these North American species and Cynelos, we provisionally retain their current taxonomic status while awaiting an in-depth revision of the Early Miocene North American Amphicyoninae.

Paleobiogeographic implications

Amphicyonines underwent a rapid radiation in the Early Miocene, spreading across Eurasia, Africa and North America. Some amphicyonid taxa have been recorded from both regions suggesting that large-scale dispersal events occurred, as it is also the case of the Ursidae, during the Oligocene-Miocene boundary at ~ 22 to 23 Ma (Hunt 2002, 2003, Hunt et al. 2018). The close relationships between certain European and North American Cynelos species pointed out by Hunt (1998, 2004) implies that they must have spread through Asia, even if they have yet to be recorded there—as the record of amphicyonines from the Early Miocene of Asia is very scarce (Wang et al. 2013). Early amphicyonines were also present in Africa during the Early Miocene, as represented by the endemic genus Hecubides Savage, 1965, which displays differences from Cynelos (Morales et al. 2016).

Our phylogenetic analysis shows that Cynelos is a paraphyletic genus, and that the relationships between the European and North American Cynelos species must be reconsidered according to this interpretation. The North American species C. malasi is dated at the latest Arikareean, ~ 19.2 Ma (Hunt and Stepleton 2015). This species appears in our phylogenetic analysis closer to Paludocyon than to Cynelos and with more primitive characteristics than the European Paludocyon species. The temporal divergence between C. malasi and P. helbingi (the oldest European species of Paludocyon) is dated at least before MN2, which is close to the beginning of the Miocene and coincident in age with the appearance of the first Amphicyoninae and Ursidae in the North American faunas previously indicated by Hunt et al. (2018). Consequently, the potential predecessors of C. malasi probably date back to the Late Oligocene or Early Miocene and spread through Asia to North America. This supposes the existence of an Amphicyoninae vacuum of ~ 4 Myr in the North American record, so that the only amphicyonids represented during this gap are the last Temnocyoninae and the Daphoeninae Daphoenodon (Hunt, 1998) (Hunt 2003, 2011). The other two North American species attributed to Cynelos, C. idoneus and C. stenos, have a different problem. Cynelos idoneus is recorded from the Sheep Creek Fm. dated to ~ 16.5 Ma (Woodburne 2006). The species is only known by upper dentition that is morphologically close to that of P. bohemicus and P. helbingi. The third species, C. stenos, was also related to C. helbingi (now P. helbingi) by Hunt and Yatkola (2020). However, those authors pointed out important differences between these two species, such as the large development of the distal lingual platform in the M1–M2 of C. stenos, which is not present in the European species. This character approaches the North American species to C. lemanensis, although in C. stenos the general robustness of the molar dentition is an important differential character relative to the European species, which only shows an incipient tendency to increase the crushing surface of the molars. The divergence between C. stenos and C. lemanensis goes back to the beginning of the Miocene, and as in the case of C. malasi, implies the existence of an important temporal gap without record of potential predecessors. The fact that these three North American species show close phylogenetic relationships to each other might suggest a differential evolutionary history from that of the European Cynelos and Paludocyon species. The dispersal of these species from Europe seems unlikely. Without current evidence, a dispersal from Asia, or an in situ evolution from the endemic Miocene Daphoeninae (Hunt 1977, 2001) seem to be more plausible alternatives.

Conclusions

Paludocyon moyasolai sp. nov. from els Casots is characterized by the large buccolingual width of the M2, which is larger than the M1, but with a moderate mesiodistal length, shorter than the M1. The M3 is also large and displays a molarized morphology. These features enable the distinction of P. moyasolai sp. nov. from other Paludocyon species. Paludocyon moyasolai sp. nov. has the M1 paracone taller than the metacone, and both cusps form a tall and robust buccal wall, which is a character shared with other Paludocyon species but distinguishes it from C. lemanensis and C. rugosidens. The only known lower molar of P. moyasolai sp. nov. (m2) is also closer to P. bohemicus. Additional data on the lower dentition would help to refine its systematic status within Paludocyon, albeit our cladistic results indicate a basal position within the Paludocyon clade. Additionally, we also provide the reconstructed life appearance of the head and neck (Fig. 6). The phylogenetic analysis supports a distant relationship between the Cynelos species from Europe (C. rugosidens and C. lemanensis) and the Paludocyon clade, justifying their classification as distinct genera. The North American species attributed to Cynelos have a complex systematic position. They appear in the phylogenetic analysis close to each other. Cynelos idoneus and C. malasi lack the most characteristic features of Cynelos: the enlarged lingual platform of the M1, the large M2 compared to the M1, and the molarized M3. Cynelos idoneus has a high buccal wall in the M1 and M2 similar to that of Paludocyon species. The opposite case is that of C. malasi, whose M1–M2 buccal walls are very low, and similar to those of C. lemanensis. In turn, C. stenos retained a M1 with an enlarged lingual platform, close to C. lemanensis and C. rugosidens but differing from these two species in the robust pattern of the molar dentition. This would hypothetically suggest that the North American Cynelos species evolved independently from the European genera.

Fig. 6
Fig. 6
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Paludocyon moyasolai sp. nov from els Casots, Spain. Reconstructed life appearance of the head and neck (illustration by Jesús Gamarra)