This is the accepted version of the article:
Morales, Jorge; Abella, Juan; Sanisidro, Oscar; [et al.]. «Ammitocyon kainos
gen. et sp. nov., a chimerical amphicyonid (Mammalia, Carnivora) from the late
Miocene carnivore traps of Cerro de los Batallones (Madrid, Spain)». Journal of
Systematic Palaeontology, (May 2021). DOI 10.1080/14772019.2021.1910868


This version is available at https://ddd.uab.cat/record/241083

under the terms of the            license
               Ammitocyon kainos gen. et sp. nov., a chimerical amphicyonid

             (Mammalia, Carnivora) from the late Miocene carnivore traps of

                             Cerro de los Batallones (Madrid, Spain)



                Jorge Moralesa, Juan Abellab,c,*, Oscar Sanisidrod and Alberto Valencianoe



  a
           Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, C/José

           Gutiérrez Abascal, 2, 28006 Madrid, Spain; bInstitut Català de Paleontologia Miquel

             Crusafont, Edifici Institut de Ciència i Tecnologia Ambientals - Institut Català de

           Paleontologia (ICTA-ICP), Campus de la UAB, Carrer de les Columnes s/n, 08193,

           Cerdanyola del Vallès, 08193, Barcelona; cInstituto Nacional de Biodiversidad, Pje,

              Rumipamba N. 341 y Av. de los Shyris (Parque La Carolina), Quito, Ecuador;
  d
           Departamento de Ciencias de la Vida, GloCEE Global Change Ecology and Evolution

           Research Group, Universidad de Alcalá, Plaza de San Diego s/n, Alcalá de Henares,

               28801 Madrid, Spain; eDepartamento de Ciencias de la Tierra and Instituto

                Universitario de Investigación en Ciencias Ambientales de Aragón (IUCA),

                            Universidad de Zaragoza, 50009 Zaragoza, Spain



                           (Received 18 January 2021; accepted 11 March 2021)




In the present paper, we describe the cranio-dental remains of three individuals of an

Amphicyonidae previously determined as Thaumastocyon sp. from the late Miocene (c.

9 Ma) pseudokarstic site of Batallones-3. Dentognathic differences in relation to other

Thaumastocyoninae enable a new taxon, Ammitocyon kainos gen. et sp. nov., to be


	
  	
  
defined; it is both the most recent and the most complete member of this subfamily

known in the fossil record. The results of our phylogenetic analysis demonstrate that

this new form reached the maximum degree of specialization within

Thaumastocyoninae, a group that includes the most hypercarnivorous Amphicyonidae

species of the Miocene. The masticatory apparatus of A. kainos is extremely derived,

with the loss of the mesial premolars (P3 / P2 and p1–p3) and the third molars (M3 /

m3). The robustness of the chin and muzzle is in contrast with the slender and highly

sectorial postcanine dentition (p4 / m2 and P4 / M2), features that are consistent with

the values provided by the analysis of the bending resistance of the mandible performed

for these specimens. All the anatomical features combined, both cranial and postcranial,

reveal the complexity of the body plan of A. kainos. This species combines derived

hypercarnivorous dentition with one of the most robust postcranial skeletons recorded

for all large caniform carnivorans, outlining an enigmatic taxon that presents unique

ecological adaptations.



Keywords: Carnivora; Amphicyonidae; hypercarnivory; late Miocene; Iberian

Peninsula



https://zoobank.org/urn:lsid:zoobank.org:pub:



*
      Corresponding author. Email: juan.abella@icp.cat



Introduction




	
  	
  
Amphicyonidae constituted one of the most important groups of caniform carnivorans

for many of the Cenozoic European and North American faunas; from approximately 40

Ma until 9 Ma, when they disappear simultaneously from both continents (Hunt 1998;

Werdelin & Simpson 2009). Tomiya & Tseng (2016), recently proposed a North

American origin for this family, based on the significant cladogenesis experienced by

the family on this continent during the Eocene. Unlike the Amphicyonidae associations

of North America, the Eocene fossil record in Europe displays a lower level of diversity

(Springhorn 1997). However, during the Oligocene and especially the Miocene, the

European Amphicyonidae became highly diverse, presenting a wide range of both sizes

and dental adaptations. Three subfamilies are commonly recognized in Europe during

this period: Amphicyoninae Trouessart (1885), Haplocyoninae De Bonis (1996) and

Thaumastocyoninae Hürzeler (1940). Interestingly, all three groups reached a

hypercarnivorous adaptive peak at some points in their fossil records, albeit through

disparate modifications of their dentition (Hunt 1998). The first one of these groups to

develop a derived sectorial morphology was Haplocyoninae, which have been closely

related to the North American Temnocyoninae Hunt (1998) (Ginsburg 1999; Hunt

2011). Both Haplocyoninae and Temnocyoninae show a profound modification of their

dentitions, as observed in Haplocyonoides mordax Hürzeler (1940) and Haplocyonoides

suevicus Peigné & Heizmann (2003), which represent the last members of

Haplocyoninae in Western Europe. In these species, both molars are derived, lacking

lingual cuspids. The lower carnassial only comprises a paraconid, a protoconid and a

hypoconid, all of which are aligned and buccolingually compressed. Similarly, the m2

is restricted to the protoconid and the hypoconid. However, neither of these two molars

shows a pronounced mesiodistal elongation characteristic of the more hypercarnivorous

forms. Additionally, there is no elongation of the P4, which is still short and robust with



	
  	
  
a very strong and lingually projected protocone. The upper molars retain an unequivocal

lingual development, albeit with a narrow protocone. The buccal cusps of the M1 are

low and separated from the protocone by a deep depression for the occlusion of the m1

hypoconid. Furthermore, similar to what occurs in Temnocyonine, the premolars are

robust, showing no reduction in size or number. Hence, both these subfamilies

developed a mixed dental pattern combining both shearing and crushing functions in a

manner unique to the Carnivora (Hunt 1998, 2011). A particular case involves

Daphoenictis tedfordi Hunt (1974), which displays a precocious hypercarnivore

dentition rather different from other amphicyonids. The lower premolars are long, sharp

and possess a well-developed distal and mesial accessory cusp, analogous to the

premolars of the extant Lycaon pictus. Nonetheless, the lower and upper molar dentition

is more conservative, as in Haplocyoninae, albeit more sectorial (Emry & Hunt 1985;

Boardman & Hunt 2015). The last Haplocyoninae are recorded in the lower Miocene

(MN 2/3), coinciding with the appearance of the first Thaumastocyoninae such as

Ysengrinia Ginsburg, 1966, Crassidia Heizmann & Kordikova, 2000 or Peignecyon

Morales, Fejfar, Heizmann, Wagner, Valenciano & Abella, 2019, forms which are still

morphologically closer to the early Miocene Amphicyoninae (Morales et al. 2019).

Amphicyoninae and Thaumastocyoninae survived into the late Miocene, but with a

notable and gradual decline in diversity. Some of these latest representatives coexisted

on the Iberian Peninsula, sharing an advanced hypercarnivorous dentition (Peigné et al.

2008; Morales et al. 2017, 2019). Among them is Magericyon Peigné, Salesa, Antón &

Morales, 2008, a hypercarnivorous Amphicyoninae that appears sparsely in the fossil

record during the Vallesian (Ginsburg et al. 1981; Peignè et al. 2008). The adaptations

of Magericyon towards hypercarnivory differ from those of Haplocyoninae, not only in

the reduction of the premolars but also in the transformation of the entire dentition



	
  	
  
towards a hypercarnivorous model. This clearly indicates an Amphicyoninae origin in

contraposition with Haplocyoninae hypercarnivorism derived from the more

plesiomorphic taxa. Although this Amphicyoninae displays a rather derived

morphology, however, there is a qualitative jump towards hypercarnivorous adaptation

in the late Miocene Thaumastocyoninae species, such as Thaumastocyon dirus

Ginsburg, Morales & Soria, 1981 and Agnotherium antiquum Kaup, 1833, in which

extreme modifications have been found (Morlo et al. 2020). Indeed, Ammitocyon kainos

from the late Miocene of Batallones-3, Spain, a description and systematic study of

which is provided by the present paper, proves that these hypercarnivorous dental

adaptations were even further exacerbated in this terminal form, while also constituting

the first evidence that the process also involved relevant modifications of the postcranial

skeleton.



Geological setting



Batallones-3 (Fig. 1) is one of the nine palaeontological sites of the continental pseudo-

karst complex developed during the late Miocene (c. 9 Ma) at Cerro de los Batallones,

Madrid basin, Spain (Calvo et al. 2013). As in Batallones-1 (the first of the sites found

in the area) its faunal composition is completely skewed towards an overwhelming

predominance of carnivore remains, which has been explained as resulting from its role

as a natural trap prior to its final sedimentary infilling (Antón & Morales 2000; Abella

et al. 2011; Calvo et al. 2013; Domingo et al. 2011, 2012, 2013, 2016, 2018; Martín-

Perea et al. 2020). The deposits of these sites have been dated based upon their faunistic

composition as pertaining to the late Miocene (Late Vallesian, MN 10). Study of the

rodents revealed the existence of minor differences in the age of the deposits, indicating



	
  	
  
that Batallones-3 appears to constitute the most recent deposit of the series, and

Batallones-10 the oldest, but within the time span of the local subzones J2 / J3 (López-

Antoñanzas et al. 2010, 2014; Medina-Chavarrías et al. 2019). To date, 62 species of

vertebrates have been catalogued, 47 of which are mammals (Morales 2017). Studies of

the fauna of the mammal carnivorans can be consulted in Abella et al. (2012, 2013,

2015); Antón et al. (2004a, b, 2020); Fabre et al. (2015); Monescillo et al. (2014);

Peigné et al. (2005, 2008); Salesa et al. (2005, 2006, 2010, 2012, 2019); Siliceo et al.

(2014, 2015, 2017, 2019); Valenciano et al. (2015, 2020); for herbivorous mammals in

Domingo et al. (2019); Pickford (2015); Ríos & Morales (2019); Ríos et al. (2017);

Sánchez et al. (2009, 2011); and for other vertebrates in Vila et al. (2018); Morales

(2017); Pérez & Murelaga (2013); Pérez-García & Vlachos (2014).



Material and methods



Nomenclature and measurements

Dental nomenclature follows Morales et al. (2019). Anatomical descriptions are based

on Schaller (2007). Measurements (Tables 1, 2) were made using Mitutoyo Absolute

digital calliper to the nearest 0.1 mm. Measurements of the cranium and mandible

follow those of Siliceo (2015).



Abbreviations

BAT-1, Batallones-1 locality; BAT-3, Batallones-3 locality.



Institutional abbreviations




	
  	
  
CM, Carnegie Museum of Natural History, Pittsburgh, USA; MGUV, Museu de

Geologia de la Universitat de València, Burjassot, Spain; MNHL, Musée des

Confluences, Lyon, France; MNHN, Muséum national d’Historie naturelle, Paris,

France; MNCN, Museo Nacional de Ciencias Naturales, Madrid, Spain; NHMMZ,

Naturhistorisches Museum Mainz/Landessammlung für Naturkunde Rheinland-Pfalz,

Mainz, Germany; NHMW, Naturhistorisches Museum Wien, Vienna, Austria; NMP,

National Museum, Prague, Czech Republic (inv. no. NM-Pv); SMNS, Staatliches

Museum für Naturkunde Stuttgart, Stuttgart, Germany; UCB, Université Claude

Bernard Lyon 1, Lyon, France; YPM, Yale Peabody Museum, New Haven, USA.



Studied material

The fossil remains of Ammitocyon kainos gen. et sp. nov. from Batallones-3 are stored

in the collections of the Department of Paleobiología of the MNCN, and include: the

holotype both hemimandibles of the same individual BAT-3’09.1239 and BAT-

3'08.604; the paratypes BAT-3'10.1689, skull and BAT-3’11.453 complete mandible

probably belonging to the same individual, BAT-3'09.1124, isolated left m2.

           For comparison, we have studied the following Amphicyonidae taxa:

Magericyon anceps Peigné et al., 2008 from Batallones-1 and 3; Ysengrinia gerandiana

(Viret, 1929a) and Cynelos lemanensis (Pomel, 1846) from Saint Gérand le Puy

(France), early Miocene (MN 2) housed in UCB and MNHN; Peignecyon felinoides

Morales, Fejfar, Heizmann, Wagner, Valenciano & Abella, 2019 from Tuchořice

(Czech Republic), early Miocene (MN 3), whose holotype (NM-Pv 11600) is stored in

the collections of NMP, and the rest of the dentition are available as casts in the

collections of NMP and MNCN; Thaumastocyon dirus Ginsburg, Morales & Soria,

1981 from Los Valles de Fuentidueña (Spain), late Miocene (MN 9) housed in MNCN;



	
  	
  
Magericyon anceps Peigné, Salesa, Antón & Morales, 2008 from BAT-1 by cranium,

mandibles and postcranial remains (Peigné et al. 2018; Siliceo 2015) housed at MNCN;

the holotype of Agnotherium antiquum by a cast housed at NHMW, as well as the new

mandible of the same taxon described by Morlo et al. (2020) and housed at NHMMZ;

Tomocyon grivensis Viret, 1929b from La Grive Saint Alban (France), middle Miocene

(MN 7/8) housed in UCB and MNHL; Ysengrinia valentiana Belinchón & Morales,

1989 from Buñol (Spain), early Miocene (MN 4) housed in MGUV; Thaumastocyon

bourgeoisi Stehlin & Helbing, 1925 from Pont-Levoy (France), middle Miocene (MN

5) by casts housed in the MNHN; Daphoenodon superbus (Peterson, 1907) from Agate

Fossil beds National Monument (USA) and Ysengrinia americana (Wortman, 1901)

from the Harrison Formation (USA), early Miocene (late Arikarean) by casts housed in

MNCN; Pseudocyonopsis landesquei (Helbing, 1928) from the Oligocene of Europe

and Crassidia intermedia Heizmann & Kordikova, 2000 from the early Miocene of

Europe by their original publications (von Meyer 1849; Helbing 1928; Kuss

1965; Springhorn 1997; Heizmann & Kordikova 2000; Peigné & Heizmann 2003).



Cladistic analysis

In order to analyse the phylogenetic position of the new form of Amphicyonidae from

Batallones-3, we performed a cladistic analysis that included hyper- and

hypocarnivorous amphicyonid taxa, such as the Oligocene Pseudocyonopsis landesquei,

the early Miocene Daphoenodon superbus, Cynelos lemanensis, Ysengrinia americana,

Ysengrinia gerandiana, Ysengrinia valentiana, Crassidia intermedia and Peignecyon

felinoides, the middle Miocene Thaumastocyon bourgeois and Tomocyon grivensis, and

the late Miocene Thaumastocyon dirus and Agnotherium antiquum. We expanded the

phylogeny of Morales et al. (2019), including the taxa Thaumastocyon dirus from



	
  	
  
Valles de Fuentidueña and Agnotherium antiquum from Eppelsheim, updated according

to a recently described mandible (Morlo et al. 2020). We excluded from the analysis

several taxa related to the Thaumastocyoninae, such as Ysengrinia tolosana (Noulet,

1876), and Ysengrinia depereti (Mayet, 1908), because they represent poorly sampled

species. The cladistic analysis includes 13 taxa and 54 equally weighted and unordered

cranial, mandibular and dental characters (see Supplemental file 1). Some of these were

used by Viranta (1996), Peigné et al. (2008) and Morales et al. (2019). The complete

list of characters, the character-taxon matrix and the synapomorphy list per node are

available in Supplemental files 1, 2 and 3 respectively. We selected P. landesquei as the

outgroup. The analysis was performed with PAUP*4.0b10 (Swofford 2002).



Body mass estimation

To estimate the body mass of Ammitocyon kainos gen. et sp. nov. we followed the

methodology employed by Figueirido et al. (2011). We used the following formula in

this study (for the femur):



            Log10 (BM) = −1.742 (±0.310) + 2.659 (±0.249) Log10 (Fdml)



Fdml being the medio-lateral diameter of the femoral diaphysis at the mid-shaft. This

measurement is one of the most suitable in this specific case, due to the extremely

derived postcranial adaptations of the species.



Mandible biomechanics

In order to reconstruct the mechanical adaptations of this new genus and species we

followed the methodology performed by Hunt (2011) in the also hypercarnivorous



	
  	
  
Temnocyoninae (Amphicyonidae). We employed the methodology of Therrien (2005)

whereby the carnivoran mandible was modelled as a solid beam, used to represent

relative differences in biomechanical properties along the mandible, thus indicating its

resistance to forces applied during feeding and prey capture. Zx/Zy values are a

measure of relative bending strength on the sagittal and transverse planes of the

mandibular corpus considered by Therrien (2005) as mandibular force profiles.

Therefore, these Zx and Zy ratios estimate the relative differences between parasagittal

and transverse loadings along one single mandible with the advantage that these

patterns can then be compared among carnivoran species. Comparison of Z/L ratios for

different taxa reveals variations in the magnitude of applied force at different locations

along the mandible, while the ratio Zx/Zy reflects the relative mandibular force (or

overall mandibular shape). Furthermore, since Zx/Zy is proportional to the ratio of the

dorsoventral and mediolateral diameters of the mandibular corpus, a ratio < 1.00

indicates an adaptation toward bucco-lingual loads (wider than the deep mandibular

corpus). These forces are interpreted as an adaptation to stresses induced while biting

prey, either due to struggling motions or to other transverse or torsional stresses

produced by hard objects (Therrien 2005). We included the living species Canis lupus

(grey wolf), Crocuta crocuta (spotted hyena) and Panthera leo (African lion) together

with the indices from Hunt (2011) and the measurements of the lower jaw of M. anceps

from BAT-1 (Table 3). This enabled all these amphicyonids to be compared and further

evaluated to establish whether the adaptations to supposedly similar food sources were

similar among these groups.



Systematic palaeontology




	
  	
  
                           Order Carnivora Bowdich, 1881

                          Suborder Caniformia Kretzoi, 1943

                       Family Amphicyonidae Trouessart, 1885

                    Subfamily Thaumastocyoninae Hürzeler, 1940

                             Genus Ammitocyon gen. nov.




Diagnosis. Thaumastocyoninae with sectorial dentition, dental formula 3/3, 1/1, 2/1,

2/2, mandible presenting a long diastema between canine and p4, p4–m2 with strong

bucco-lingual compression, p4 of moderate size with small mesial cuspid and large

distal cuspid, m1 with short and low paraconid, absent metaconid, talonid short and

narrow, occupied by a strong hypoconid, the entoconid reduced to a weak buccal

cingulum; m2 relatively elongated, with a similar arrangement of the cuspids

(paraconid, protoconid and hypoconid) to that of the m1. Upper canine robust with

bucco-lingual compression, P4 elongated with a large parastyle (inferred) and lingual

root for the protocone well developed and placed transversely to the mesial-distal molar

axis. Furthermore, the M1 and M2 are reduced, displaying a triangular occlusal shape.

Postcranial robust, especially the bones of the zygopodial and autopodial segments.

Towards the distal parts of the limb the articulations become gradually less mobile,

some of these ankylosed or even completely immobile. All phalanxes short, ungual

phalanxes short with a rounded outline, and with a short and thickened claw.



Differential diagnosis. Ammitocyon differs from the rest of the genera included in

Thaumastocyoninae (Crassidia, Peignecyon, Thaumastocyon, Tomocyon and

Agnotherium) in the following autopomorphies: a very high position of the masseteric

fossa in the mandibular ascending ramus; development of a wide flattened surface in the



	
  	
  
premasseteric area; a horizontal mandibular ramus with the concave margo alveolaris in

its central part; a lower postcanine dental row which is not rectilinear but rather

arranged in a sigmoidal manner, the consequence of the imbrication of the distal part of

the p4 with the buccal base of the paraconid of the m1, and the change in orientation of

the m2, which turns in relation to the mesial-distal axis of the mandible, in such a way

that its trigonid is displaced lingually and the talonid is shifted buccally. The m2 is

elongated with a very well-developed paraconid, displaced towards a mesio-lingual

position, the metaconid is missing and the entoconid is very reduced.



Derivation of name. The epithet ‘Ammit’ refers to the name of a demoness and

goddess in ancient Egyptian religion who was part crocodile, lion and hippopotamus,

traits that are reminiscent of the proposed new genus, and ‘cyon’ from the Greek term

for dog.



Age. Late Miocene (MN10).



                               Ammitocyon kainos sp. nov.

                                         (Figs 2–4)



2017 Thaumastocyon sp. Morales, Abella & Valenciano: 340, Figures 7–8.

2019 Thaumastocyon sp. Morales et al.: 399.

2020 Thaumastocyon sp. Morlo et al.: 4.



Holotype. BAT-3’09.1239 and BAT-3’08.604, mandible with both rami.




	
  	
  
Paratypes. BAT-3'10.1689, skull and BAT-3’11.453 complete mandible, probably

belonging to the same individual. BAT-3'09.1124, isolated left m2.



Type locality. Batallones-3, Madrid, Spain.



Derivation of name. Kainos from the Greek term for ‘of a new kind’.



Diagnosis. As for the genus.



Age. Late Vallesian, MN10, local zone J.



Description

Skull. The sample consists of a single skull from the senile specimen BAT-3'10.1689

(Fig. 2). It is relatively robust, and although it is severely corroded, especially in its

dorsal region, many of its structures can be still described in detail. Compared to

Magericyon anceps (Peigné et al. 2008) the premaxilla is robust and possesses a battery

of bucco-lingually enlarged incisors (Supplemental file 4). The nasal bone is thick and

is rostrally protruded, forming a huge snout, with a wide nasal aperture. In dorsal view,

the snout is somewhat isolated from the rest of the skull by a deep notch on the outline

just rostral to the P4, which is laterally expanded. Most of the frontal and maxillary

bones are completely corroded, and many of the structures cannot therefore be

described. This is the case of the infraorbital foramen, in which only a deep depression

at the level of the mesial-most part of the P4 can be observed. The rostrum has an ‘8’-

shaped general outline in ventral view, with an enlarged rostral-most region, a narrower

area at the level of the P1 and the diastema and a wide and rounded caudal region



	
  	
  
between the P4 and the M2. The palate is caudally expanded, exceeding the level of the

last molars, a feature shared with Ysengrinia americana and some Temnocyoninae

(Hunt 2002, 2011). In addition, the postorbital processes both of the frontal and of the

jugal are well developed. This configuration results in a relatively large eye socket,

much more enclosed than in other closely related large-sized arctoid carnivorans. The

postorbital constriction is well marked, completely delimiting the frontal and the

parietal bones. In lateral view, the zygomatic arch is relatively thin and straight, only

curving ventrally towards the last portion of the squamosal bone. In dorsal view, the

rostral-most part of the jugal is enlarged, forming a flat surface throughout the ventral

part of the eye socket. The postglenoid process is located higher than the mastoid

process. The basicranium is wide and expanded at the level of the mastoid processes.

The posterior opening of the alisphenoid canal and the foramen ovale are close to each

other; as in other similar forms such as Magericyon (see Peigné et al. 2008) they are

located medial to the preglenoid process. The postglenoid foramen is large and is

located just caudal to the relatively thin and ventrally projected caudal wall of the

postglenoid process. The auditory region is anteroposteriorly short and is delimited by

the postglenoid and the mastoid process, forming a dorsally projected, oblique and

narrow auditory notch (Supplemental file 5). The bulla is thick and somehow inflated.

Meatal tube long and dorsally projected, with a longitudinal groove. The mastoid

process is robust and prominent; it is laterally inflated and rugose. On its dorsal side a

very smooth concave structure can be observed. The paraoccipital process is robust and

projected caudo-ventrally, surpassing the ventral edge of the mastoid process

(Supplemental file 5). The sagittal crest is well developed and convex, arising from the

postorbital constriction towards the nuchal crests. These are developed in height, but

due to severe corrosion of this portion of the skull, their lateral expansions cannot be



	
  	
  
evaluated. The parietal region is quite convex and is located in a relatively distal and

ventral position, in relation to the frontal region.



Upper dentition. The only preserved upper dentition belongs to the previously

described skull BAT- 3'10.1689 (Fig. 2, B- B’). As occurs with the lower dentition of

this specimen, it is well worn and some of the morphological features have been blurred

(Fig. 2, F and G). The incisor battery is extremely wide (Fig. 2, B-B’), each one well

separated from the other, similar to what can be observed in derived barbourofelids (e.g.

Tseng et al. 2010; Robles et al. 2013). The I3 is clearly larger than the I2 (no I1 is

recovered, but the size of the alveolus would appear to indicate that is clearly smaller

than the I2). Their most remarkable feature is their strong bucco-lingual width, much

more developed than that of any of the compared carnivorans (Table 1). As with the rest

of the dentition, they exhibit a high degree of wear. The canines are robust, with a wide

base and a moderate height. They display two vertical wear facets, one distal and

another in mesio-lingual position. The buccal wall is clearly convex and the lingual wall

is somewhat flattened. In the mesial-most part of the diastema a small residual P1 is

present; it has no homologue tooth in the lower dentition and its function is therefore

unclear. Both carnassials are extremely worn, the right one almost down to its roots,

while the left one still shows the buccal wall (Fig. 2). Most likely the protocone was still

quite well developed, judging by the size of its root; it is located in a relatively distal

position, possibly due to the strong development of the parastyle. In the left row, both

the P4 and the M1 show a strong oblique wear facet, reaching the base of the protocone.

The M1 would seem to have been relatively small, presenting a marked triangular

outline; in the buccal wall a moderate cingulum is present. The right row has conserved

an eroded M2. The only visible feature appears to involve its relatively small size and



	
  	
  
its triangular outline. No alveoli are observed for the M3, but the caudal part of the

maxillary bone is rather poorly preserved.



Mandible (Fig. 3). The sample consists of two complete adult mandibles: BAT-

3’09.1239 and BAT-3'08.604 (holotype) and BAT-3’11.453, with a highly worn

dentition, which probably belongs to the same individual as the BAT-3’10.1689 skull.

The mandible is robust and long, with a strong symphysis; it is relatively dorso-

ventrally slender between the canine and the p4, and bucco-lingually very thick under

both m1 and m2. The margo interalveolaris is sharp and in lingual view it displays a

concave profile, common in species with reduced premolars, and presents a long

diastema between the lower canine and the enlarged p4. There is only one well-

developed mental foramen, located below the postcanine diastema. In lateral view, the

ventral border of the mandibular body shows several points of inflexion, as it is convex

at the symphysis and under the m2; it is concave at the level of the diastema and the p4.

The distal-most region of the mandibular corpus, including the angular process, is

shifted towards the lingual side of the mandible, forming a marked convex structure in

ventral view. Consequently, the angular process is short and rounded, with a blunt distal

edge. The articular process is robust, and short along the latero-medial axis. The

articular facet for the skull is large and occupies practically the entire medial region.

The coronoid process is moderately developed in height but antero-posteriorly quite

large. It is orientated dorsally and has a verticalized posterior border, with a rather flat

dorsal tip. The masseteric fossa is located in an unusual position, starting at the level of

the dentition, contrary to what can be observed in almost all of the carnivorans, where it

is expanded ventrally. It is completely enclosed in its ventral region by a relatively deep

rim that separates the fossa itself from a flat region situated in a position analogous to



	
  	
  
the premasseteric fossa of some Ursoidea. The masseter muscle insertion area is

relegated to the most caudal corner of the ventral edge of the angular process. There is a

flat part between the masseteric fossa and the insertion of the digastric; it is very large

in one of the specimens, although it is not lingually expanded as can be seen in bears.



Lower dentition (Fig. 4). No incisors are preserved, but the right ramus preserves the

alveoli, the i3 is mesio-distally enlarged and is placed mesially to the smaller i2 and i1

alveoli. The canine has a robust root, with a high and relatively slender crown; a well-

developed mesio-lingual cristid, and another distal one that it is badly worn. The mesial

premolars (p1–p3) are missing, and as a result the diastema between the canine and the

p4 is long. The p4 is relatively large compared to the m1. It has a blunt mesial accessory

cuspid, slightly rotated lingually. The main cuspid is projected distally, showing a

marked and deep wear surface in its buccal wall that is large and was likely moderately

bucco-lingually compressed. The distal cuspid is relatively enlarged, and also exhibits a

strong wear facet on its buccal wall. Both the distal cuspid of the p4 and the mesial wall

of the paraconid of the m1 are imbricated, slightly tilting the m1lingually.

           The m1 is a rather simple tooth, with a mesio-distally aligned paraconid,

protoconid and hypoconid. The paraconid of the m1 possesses a large and well-

developed cingulum at the base of its lingual wall, while the buccal one is completely

smooth. There is quite a notable difference in height between the paraconid and

protoconid, which is taller. However, they share a large vertical wear facet on the buccal

wall. The mesial crisitid of the paraconid is displaced slightly towards a more lingual

position; it is subdivided and well isolated. The distal cristid of the protoconid is visibly

sharp as a consequence of a bucco-distal vertical wear facet. A slight inflexion in this

cristid marks the place for the metaconid, which, however, is completely reduced. The



	
  	
  
talonid is short and narrow, and buccally well separated from the trigonid by the

previously described wear facet. It is formed by a huge hypoconid with an oblique wear

facet, slightly tilted lingually, which practically occupies the whole cuspid. It also has a

lingual basal cristid, almost a cingulid, which runs from the posterior short cristid of the

hypoconid towards its lingual base. Its basal cingulid is quite small, both on its lingual

and buccal walls.

           The m2 is elongated, with the same cuspid alignment as the m1, and is missing

the metaconid. The paraconid is large and lingually placed, somewhat imbricated with

the hypoconid of the m1. The protoconid is rounded and pyramidal and the talonid is

severely worn. It functions as the distal-most occlusal region since this species lacks an

m3.



Postcranial skeleton (Fig. 5; Supplemental file 6). A description of the postcranial

bones and the functional anatomy of this new genus and species will be provided in a

subsequent manuscript. However, due to the extreme adaptations found in the skeleton

of A. kainos, a preliminary characterization of the recovered bones has been performed

in order to establish the palaeobiology of this species as a whole.

           The scapula is robust and almost square in overall shape. It has a large

subscapularis fossa and a scapular spine, the latter occupying the whole length of the

scapula. The acromiom is dorsally developed but does not surpass the glenoid cavity.

The humerus is robust, with a long wide deltoid tuberosity and a large lateral

supracondylar crest. It has no entepicondylar foramen. Its distal epiphysis is wide. The

radius and ulna are robust and short, with large muscular attachments along its

diaphysis. The manus is robust and short, especially towards the distal segments.

Relatively short and robust carpals, short and robust metapodials with flattened distal



	
  	
  
epiphysis and extremely robust phalanxes, especially the distal ones, which present an

almost rounded section. Articulation between the trapezium and Mc I rounded in section

but completely flat. Pelvis robust, although too fragmented to describe. Femur

fragmented, although it possesses sufficient complete parts to describe it as robust and

relatively short. Distal epiphysis wide and robust. Tibia robust and with wide proximal

epiphysis; with a short diaphysis. Distal epiphysis with a triangular section and with

relatively oblique, deep and reinforced articulation sulci for the astragalus. Pes wide and

short, especially towards the distal segments as in the manus. Tarsals robust and with

few contact facets. Calcaneus short with solid articulation facets for the astragalus and a

concave distal one for the cuboid. Astragalus with almost no distal neck and almost

rounded and convex articular facet for the navicular. No articulation facet between the

cuboid and navicular. Short and robust metatarsals with a flattened distal epiphysis.

Extremely robust phalanxes, especially the distal ones, which are almost rounded.



Discussion



Ammitocyon kainos gen. et sp. nov. has all the necessary morphological traits for

consideration as the most derived thaumastocyonine (sensu Morales et al. 2019). It

differs from all the other members of the subfamily (Crassidia, Ysengrinia, Peignecyon,

Tomocyon, Thaumastocyon and Agnotherium); consequently, a new genus and species

have been erected. Comparisons with these Thaumatocyoninae are necessarily limited

to dentition and mandible, since there is currently no cranial material that can be clearly

attributed to any of the species of the group.

           The known mandibles of the Thaumastocyoninae species (Stehlin & Helbing

1925; Viret 1927; Heizmann & Kordikova 2000; Morales et al. 2019; Morlo et al.



	
  	
  
2020) show the typical morphology of the Amphicyonidae, in which the depth of the

masseteric fossa surpasses the basal level of the postcanine row, to a greater or lesser

extent approaching the mandibular border (margo dorsalis) and clearly differ from the

distinctive morphology of A. kainos in which the lower edge of the masseteric fossa

does not exceed the depth of the margo alveolaris. The unique development of a wide

flattened surface in a premasseteric position in the mandible of A. kainos is difficult to

interpret. In any case, it does not seem to be a homologous structure in the other

mandibles attributed to the Thaumastocyoninae species. Another autapomorphy also

present in the mandible of A. kainos involves the development of a broad inflection or

concavity in the margo dorsalis, which extends from the genial tuberosity to the mesial

base of the ascending ramus. The sigmoidal arrangement of the postcanine row in the

margo alveolaris of the mandible of A. kainos is also unique among the

Thaumastocyoninae, in part as a consequence of the broad overlap between the distal

part of the p4 and the lingual base of the paraconid of the m1, but also because of the

rotated arrangement of the m2, whose paraconid contacts the disto-lingual base of the

talonid of the m1. In Agnotherium antiquum from Charmoille (Morlo et al. 2020) the p4

smoothly overlaps the buccal base of the m1 paraconid, but both teeth still maintain a

linear arrangement in the margo alveolaris. The m2 of A. kainos differs from the other

species of the group in the greater size and height of the paraconid, which is buccally

located towards a position analogous to that of the m1 paraconid. The loss of the

metaconid and the narrowing of the lingual area of the talonid endow the m2 of A.

kainos with the appearance of a small-sized lower carnassial.

           Some other characters of A. kainos reach a more specialized level than those of

other species of the group; as is the reduction of p1–p2, which is present not only in

Thaumastocyoninae, but also in another Amphicyonida; however, in A. kainos it



	
  	
  
presents an extreme degree, with the disappearance of all the lower premolars between

the canine and the p4. The main cuspid of the p4 of A. kainos is distally projected; a

morphology that is already manifested in Peignecyon felinoides and all more recent

species. The reduction of the postcanine dentition is one of the typical characteristics of

the Thaumastocyoninae. It is possible that A. kainos lacks the lower third molar, since in

the existing mandibles no alveolus is distinguished for this tooth. However, the state of

preservation of the skull does not unequivocally indicate the absence of the M3,

although it is likely due to the extreme reduction of the M2. In the lower dentition, the

m2 is greatly reduced in Thaumastocyoninae, and in Agnotherium antiquum from

Eppelsheim the reduction is very advanced (Morlo et al. 2020), as in Thaumastocyon

burgeoisi and Th. dirus (Stehlin & Helbing 1925; Ginsburg et al. 1981). However, in A.

kainos the morphological pattern of m2 differs from the rest of the species in the group,

as has already been mentioned. The morphology of the upper dentition of A. kainos is

only preserved in the one single skull discovered; which presents a high degree of wear,

characteristic of an elderly individual, as well as evidence of corrosion. However, the

P4 has a large parastyle, and an elongated cutting blade formed by the paracone and

metastyle; furthermore, both cusps are supported by two merged hypsodont roots.

Furthermore, both the M1 and the M2 are greatly reduced compared to the P4,

exhibiting a triangular outline similar to that of the M1 of Thaumastoyon species. This

combination of such derived features has no known equivalent in the remaining

Thaumastocyoninae; in Crassidia intermedia, Ysengrinia gerandiana and Peignecyon

felinoides the morphological pattern is still close to that of other Amphicyoninae,

although an incipient hypercarnivorous tendency can be inferred. Unfortunately, in the

most recent species of the subfamily, the only known upper dentition consists of

isolated teeth, a fact that hinders comparison, and in some cases casts doubt upon their



	
  	
  
association with a given species; as is the case of Tomocyon grivensis from the La

Grive-St-Alban karst site (Viret 1927), which possesses a very sectorial P4 and m1, but

little reduction in the grinding molars (m2 and M1); this constitutes a mixture of hyper-

and hypocarnivorous traits (Kuss 1962; Morales et al. 2019). The description of the new

Eppelsheim mandible attributed by Morlo et al. (2020) to Agnotherium antiquum, with

an m2 still encrypted in the alveolus presenting a strong reduction in size with respect to

m1, rejects the proposal by Kuss (1962) to include Tomocyon grivensis in Agnotherium.

However, this fact does not dispel the doubts regarding the peculiar character of

Tomocyon, a species comprising isolated dentition, from different diachronic karst

fillings, in which at least three large-sized Amphicyonidae species were present (Mein

& Ginsburg 2002).

           The differences between Ammitocyon kainos and all the other genera included in

the Thaumastocyoninae justify the erection of a new genus and species from the

Batallones-3 fossils.



Phylogenetic relationships



The phylogenetic relationships of the Thaumastocyoninae have recently been discussed

by Morales et al. (2019) in relation to the description of Peignecyon felinoides (from the

early Miocene site of Tuchořice, Czech Republic). This species is crucial with regard to

understanding the beginning of the Thaumastocyoninae clade because of the abundant

material, including upper and lower dentition. The new phylogenetic analysis is based

on that published by Morales et al. (2019), with the addition of new characters and three

taxa, Agnotherium antiquum —including the new mandible described by Morlo et al.,

(2020) —, Thausmastocyon dirus (Ginsburg et al., 1981) and Ammitocyon kainos. gen.



	
  	
  
et sp. nov. — the former two species were considered as one single taxonomic unit in

the previous analysis under the name of Thaumastocyon spp. —. The

Thaumastocyoninae clade (node B) can be recognized since the early Miocene with

Crassidia intermedia, Ysengrinia gerandiana and Peignecyon felinoides (Figs 6, 7). In

this clade, the reduction of second molars (m2 / M2) begins to be detected, a trend that

will be accentuated in successive dichotomies in the direction of a more

hypercarnivorous adaptation (including the modification of the carnassials: m1/P4).

This morphological trend was almost fully achieved at the beginning of the middle

Miocene with Thaumastocyon bourgeoisi from the locality of Pont Levoy, France

(Stehlin & Helbing 1925), in which the reduction of the m2 in relation to m1 reaches its

maximum, and the m1 reveals the morphology of the more derived forms of the group

such as Agnotherium antiquus or Ammitocyon kainos. The M1 of Th. bourgeoisi shows

the morphology that will characterize the most recent hypercarnivorous species, with a

strong reduction of the lingual area, which is limited to a vestigial lingual cingulum.

The species Thaumastocyon dirus Ginsburg et al. (1981) from the early late Miocene

(MN9) of Spain preserves the M1 morphology of Th. bourgeoisi, although it is even

more specialized, a fact that can be seen especially in the greater relative development

of the buccal cusps (paracone and metacone) and the definitive loss of the lingual

cingulum. Thaumastocyon species appear as a sister group to Ammitocyon, and this

relationship is strongly supported, despite the scarcity of data on Th. dirus. Further

difficulties arise with Agnotherium antiquum, originally only represented by an m1

presenting a high degree of wear, to which Morlo et al. (2020) added new data from a

sub-adult mandible from the same locality. However, its phylogenetic position is not

well resolved due to the absence of the upper dentition. Another taxon posing a similar

difficulty is Ysengrinia valentiana, a species represented by two molars (M1 and m2)



	
  	
  
(Belinchón & Morales 1989). These molars are morphologically transitional between

those of Peignecyon felinoides and Th. bourgeoisi, but the absence of information on

the morphology of the carnassials prevents a more accurate systematic position.

Tomocyon grivensis possesses a mixture of primitive and derived characters, and is

placed in the cladogram in a position that represents this duality; the sectorial

carnassials bring it closer to Thaumastocyon and Ammitocyon, but the retention of large

molars (M2 and m2) anchors it to the more primitive species of the group. It likely

plays an important role, or at least contributes to the unresolved topology of the more

derived species of the clade.

           Finally, the polyphyly detected in Ysengrinia is once again evidenced in this

cladistic proposal, as previously discussed by Morales et al. (2019). The species

Ysengrinia valentiana cannot be considered within this genus, being closer to

Peignecyon or Thaumastocyon than to the type species Ysengrinia gerandiana.

Similarly, Ysengrinia americana (see Hunt 2002; Morales et al. 2019) should be

excluded from Ysengrinia. This species presents a dental morphotype displaying a

lower degree of hypercarnivorism, clearly independent from both Thaumastocyoninae

and Haplocyoninae. Morphotypes close to Ysengrinia americana have been recorded in

Asia by Qiu et al. (1986), who determined a maxilla and an m1–m2 from Shanwang,

China as Thaumastocyoninae gen. et sp. nov.; it was subsequently redetermined as

Ysengrinia sp. by Qiu & Qiu (2013); Ysengrinia sp. has also been recorded in the

Bihoku group, Hiroshima (Japan) on the basis of an M1 morphologically close to

Ysengrinia americana (Kohno, 1997). Nonetheless, it is difficult to relate them to each

other, although their exclusion from Thaumastocyoninae would seem to be clear. The

basal position of Ysengrinia americana which constitutes a tricotomy with the

Thaumastocyoniae and the clade Cynelos-Daphoenodon could be interpreted as a



	
  	
  
persistence of an ancestral hypercarnivore dentition during the Miocene in North

America and Asia. The other two branches of the trichotomy show divergent dental

morphologies, one towards extreme hypercarnivorism (Thaumastocyoninae) and the

other less hypercarnivorous in which the postcarnassial teeth show an increase in size

(Amphicyoninae). The latter species will give rise to to the major Amphicyoninae

cladogenesis during the Miocene (Kuss 1965; Viranta 1996; Hunt 1998; Ginsburg 1999;

Peigné et al. 2008; Werdelin & Peigné 2010).



Palaeobiology approach



Ammitocyon kainos gen. et sp. nov. represents the most complete Thaumastocyoninae

known in the fossil record. Following the methodologies used by Figueirido et al.

(2011), who employ measurements of the postcranial skeleton, we estimated at 231 kg

the body size of the available specimen of Ammitocyon kainos. This value is within the

range of the estimation of body size obtained for this same specimen in Domingo et al.

(2016), rendering this species one of the top three largest carnivoran species of the

whole BAT-3 carnivoran guild, comparable to the sabre-tooth felid of a lion-sized

Machairodus aphanistus (Kaup, 1832), and the brown bear-sized ursid Indarctos

arctoides (Depéret, 1895). Ammitocyon was larger than Magericyon anceps and

presented a different morphological adaptation despite the hypercarnivorous adaptation

of both species. A significant contribution with regard to understanding the habitat and

palaeobiology of these large predators was provided by means of analysis of the carbon

stable isotopes in tooth enamel from carnivorous and herbivorous species from BAT-1

and BAT-3 (Domingo et al. 2016, 2017). In relation to Ammitocyon, we can extract

some relevant conclusions from these studies: (1) there are no major differences in the



	
  	
  
surrounding areas of the Batallones sites, dominated by C3 plants, woodland habitat

with patches of wooded grassland; these conditions were similar in the Los Valles de

Fuentidueña site (locality type of Thaumastocyon dirus), which is slightly older than the

Batallones localities; (2) the data suggest that the principal available food resource for

the large predators was the equid Hipparion, and that the interspecific competition was

therefore very high, particularly in BAT-3, with its higher number of large sympatric

carnivores; (3) Magericyon anceps is the only species from BAT-3 to show significant

differences with regard to prey, possibly hunting in a more open habitat. This highlights

the divergence between the two BAT-3 amphicyonids.

           The masticatory apparatus of A. kainos is unique among those known in

amphicyonids, lacking a clear correspondence with other mammalian hypercarnivores.

Many traits of this genus can be found in other hypercarnivorous species, but they are

not mutually associated. The new genus presents an unequivocal tendency towards the

dental simplification and the postcanine functional dentition comprising only p4–m2

(lower) and P4–M2 (upper). The carnassial function comprises a p4–m1 that occludes

with an elongated P4 by extending the parastyle and metastyle. But a functional

‘secondary carnassial pair’ is formed by the m1 talonid and the m2, both of which

occlude with the M1–M2 buccal wall. Postcarnassial (P4/m1) dentition in

hypercarnivores mammals is reduced, becoming almost totally lost in Feliformia (felids,

hyaenids and some viverrids), or strongly reduced in some Caniformia (e.g. Mustelidae)

(Ewer 1973). A distant analogy was detected in Ammitocyon with the molar dentition of

some creodont hyaenodonts but the phylogenetic distance and the great diversity and

complexity of this group prevented us from interpreting this singular parallelism. The

mental region is robust, presenting large curved canines, elongated bucco-lingually and

with broad roots relative to the height of the crown. Additionally, the loss of the



	
  	
  
premolars in the mandible is not accompanied by a shortening of the margo

interalveolaris. This combination of robust incisors and canines with sectorial and

slender postcanine dentition could be considered as a feature common to the

Thaumastocyoninae, although in Crassidia and Thaumastocyon it is not as derived as in

Ammitocyon. Indeed, the postcanine dentition in Ammitocyon reaches a very advanced

degree of sectorialization. The masticatory muscles and functional anatomy of the

cranio-mandibular articulation also displays certain singularities. Noteworthy among

these are the narrowing of the insertion of the M. masseter in the mandible, and

especially the almost complete reduction of the attachment area for the M. masseter

pars zygomaticomandibularis posterior in the mandible (following the nomenclature of

Brassard et al. 2020). The latter muscle constitutes the main grinding component of the

jaw movements in several carnivorans (Davis 1964). Therefore, the loss of this muscle

insertion area, together with the large development of the temporalis and digastricus

muscles could be an anatomical response, favouring slicing vs. the chewing, a fact that

allies well with the general morphology of the teeth. Conversely, the bio-mechanical

analysis performed in the present paper supports the hypothesis that the mandible of A.

kainos was much more resistant to medio-lateral movements than to dorso-ventral ones,

the region just mesial to the p4 constituting the least resistant part of the mandible, and

the symphysis being the only part capable of resisting both dorsoventral and lateral

movements (Fig. 8; Table 3). The values obtained in both Zx and Zy show large

differences in relation to those of the canids and amphicyonids measured in both

Therrien (2005) and Hunt (2011). Indeed, these values occupy an empty morphospace

in relation to this carnivoran sample; conferring to the mandible both much more

resistance to medio-lateral bending but less dorso-ventral resistance than any of the

compared extant and extinct carnivorans (Therrien 2005; Hunt 2011). This has several



	
  	
  
important consequences in the biomechanics of the mandible with regard to the forces at

play during hunting and feeding in Ammitocyon kainos.

           In the first place, the muzzle possesses greater bucco-lingual and dorso-ventral

resistance than the other species (Fig. 8). This could be related to the large incisors and

wide canines, which act as a throat or muzzle clamp and which would help to hold and

tear any outer layer of skin in the prey. This represents a completely different hunting

model than that of the canine shear bite of the large machairodontines (Antón et al.

2011). Furthermore, the low level of resistance to dorso-ventral bending of the

mandibular corpus in the postcanine means that it was likely unable to feed on hard

matter. This is consistent with the dental adaptations of this area of the jaw, in which the

P4 and m1 act as a shearing surface and the M1 and m2 as an independent second

cutting area. Finally, the large bucco-lingual resistance to bending along the whole

mandibular ramus was probably related to the ability to tear off pieces of flesh while

biting and moving the head from side to side with violent movements, similar to those

performed by pinnipeds (Ewer 1973; Hocking et al. 2013, 2017).

           The robustness of the postcranial skeleton of A. kainos can exceed that of bears

in many cases (Ewer 1973). Indeed, it has several features in common with the skeleton

of the extinct saber-toothed metatherian Thylacosmilus atrox Riggs, 1934, with its

relatively short limbs and short (and spreading) metapodials (Ercoli et al. 2012; Janis et

al. 2020). Some of the bones possess strengthened articulations that prevent lateral

movements between bones, especially in the hind limb. These limitations are not only

found at the ligament level; limiting bone structures can also be observed, such as

developed crests and contact facets, especially among the zygopodium and autopodium;

some of which are similar to those observed in cursorial mammals (Barone 1999, 2000;

Bertram 2016; Bohmer at al. 2020). The manus and pes are robust and short, with



	
  	
  
cramped metapodials that would have also limited lateral movements; some of these

even lack any flexing capacity (e.g. digit I in the manus). Finally, the sturdy phalanxes

are one of the most surprising features, since they are so short that they could not be

assembled into a digitigrade position, since the resulting surface was too small to

support this animal’s large body mass (Bertram 2016). However, when reconstructed as

a plantigrade there are also several discrepancies in the anatomy that cannot be

addressed until more detailed comparisons of its postcranial skeleton are made.



Conclusions



Ammitocyon kainos gen. et sp. nov. represents both the most recent and the most

complete member of the subfamily Thaumastocyoninae. It extends its temporal record

until the late Vallesian (c. 9.1 Ma), and contributes to updating our understanding of the

thaumastocyonine lineage. The results of our phylogenetic analysis prove that this new

form reached the maximum specialization within the Thaumastocyoninae, a group that

includes the most hypercarnivorous Amphicyonidae species of the Miocene.

Ammitocyon kainos (Fig. 9) can be interpreted as a chimerical carnivoran combining

one of the more hypercarnivorous dentitions from the suborder Caniformia, a large body

size and of one of the most robust postcranial skeletons of the group.

           At present, the general skeletal adaptations and body size of A. kainos might

suggest that this species acted as an occasional stalking hunter of large prey, or even a

kleptoparasite of other more active large carnivore hunters. The powerful bite of the

muzzle and some of its postcranial adaptations (for example, strong forearms and sturdy

hind limbs) would have helped both behaviours. However, there is a need for further




	
  	
  
anatomical studies of the complete skeleton in order to fully reconstruct a more detailed

model of its ecomorphology.



Acknowledgements



We are grateful to the following curators and collection managers for providing access

to the comparative material in their care: S. Fraile (MNCN), D. Berthet and F.

Vigouroux (MNHL), C. Argot (MNHN), U. Göhlich (NHMW), O. Fejfar and J.

Wagner (NMP), and P. Mein (UCB). We also wish to thank Dr. Robert M. Hunt Jr.

(University of Nebraska State Museum) for providing casts of Ysengrinia americana

and Daphonoedon superbus, and M. Morlo (Senckenberg Research Institute) for his

interesting contributions and providing access to the mandible of Agnotherium

antiquum. We are also indebted to D. Hontecillas (MNCN) for kindly sharing updated

pictures of Tomocyon grivensis from La Grive Saint Alban (France) housed in MNHL.

We would like to thank E. Cantero for his excellent preparation of some of the fossil

remains. The present study was supported by the Spanish Ministerio de Economía y

Competitividad (Research Projects PGC2018-094122-B100 and CGL2016-76431-P)

(AEI/ FEDER, UE), the Research Groups CSIC 64 1538 and CAM-UCM 910607, the

Generalitat de Catalunya (CERCA Programme, and Beatriu de Pinós contract 2017 BP

00223 from AGAUR to JA), and Gobierno de Aragón (E33_17R). Additionally, our

research received funding from the SYNTHESYS Project http://www.synthesys.info/,

which is financed by European Community Research Infrastructure Action under the

FP7 ‘Capacities’ Program under the grant agreement (SYNTHESYS; CZ-TAF-3329)

with JA. The ‘Juan de la Cierva Formación’ program (FJC2018-036669-I), from the

Spanish Ministry of Science, Innovation, and Universities also funded AV. We thank



	
  	
  
     Cormac De Brun for the thorough language review. The editor Z. Johanson, and the

     reviewers Dr. Morlo and ‘anonymous reviewer 2’ are also acknowledged for their

     valuable comments, which helped to improve the final version of the manuscript.



     Supplemental material



     Supplemental material for this article can be accessed at:



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Wortman, J. L. 1901. A new American species of Amphicyon. American Journal of Science,

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     Figure captions



     Figure 1. A, map of the Iberian Peninsula showing the location of Madrid and

     Valdemoro. B, location of Batallones-3 sites, west of Valdemoro.



     Figure 2. Ammitocyon kainos gen. et sp. nov. from Batallones-3, Spain. A, B, C, D, E,

     F, G, BAT-3'10.1689, skull (paratype). A, dorsal view; B, ventral view (stereo pair); C,

     lateral view; D, caudal view; E, rostral view; F, right P4–M2 in occlusal view; G, left

     P4–M1 in occlusal view.



     Figure 3. Ammitocyon kainos gen. et sp. nov. from Batallones-3, Spain. A, B, J, BAT-

     3’11.453, mandible (paratype). A, buccal view; B, occlusal view; J, rostral view; C,E, G

     BAT-3’09.1239, right hemimandible (holotype). C, buccal view; E, occlusal view; G,

     lingual view; D, F, H, BAT-3'08.604 left hemimandible (holotype). D, buccal view; F,

     occlusal view; H, lingual view; I, BAT-3’09.1239 and BAT-3'08.604, rostral

     composition view of the two hemimandibles.



     Figure 4. Ammitocyon kainos gen. et sp. nov. from Batallones-3, Spain. A, C, E, BAT-

     3’09.1239, postcanine right lower dentition (holotype). A, lingual view; C, occlusal



     	
  	
  
view; E, buccal view; B, D, F, BAT-3'09.1124, isolated left m2 (paratype). B, buccal

view; D, occlusal view; F, lingual view (stereo images).



Figure 5. Skeletal reconstruction of Ammitocyon kainos gen. et sp. nov. from

Batallones-3, Spain. Photographs used for recovered fossils of A. kainos from BAT-3;

idealized skeleton in 3D images reconstructed for the rest of the skeleton.

Measurements of scapula and long bones in Supplemental file 6.



Figure 6. Phylogenetic relationship of Ammitocyon kainos gen. et sp. nov. (majority

rule tree), within some selected Amphicyonidae. Pseudocyonopsis landesquei is the

outgroup. Searches were performed by means of the Branch and Bound and a bootstrap

analysis through 1,000 replicates. Eight trees are obtained (length 102 steps, consistency

index (CI) = 0.6373, homoplasy index (HI) = 0.3627, retention index (RI) = 0.6891).

Clade support was calculated using bootstrap analysis with 1,000 replicates, and Bremer

support values. The numbers below nodes are Bremer indices, and the numbers above

nodes are Bootstrap support percent-ages (only shown ≥ 50)



Figure 7. Biochronology and hypothesis of phylogenetic relationships of the species of

Thaumastocyoninae and selected Amphicyoninae based on the obtained tree (Fig. 6).

Chronological data after Cohen et al. (2013). Temporal range of the species based on

Hunt (1998); Ginsburg (1999); Peigné & Heizmann (2003); Morales et al. (2019).

Specimens figured: Daphoenodon superbus Peterson (1910) CM 1589 cast of the

holotype Skull from Agate Fossil Beds National Monument, USA. Ysengrinia

americana (Wortman, 1901) YPM 10061 cast of the holotype palate, original from

Harrison Formatio, USA (see Hunt, 2002). Crassidia intermedia (von Meyer, 1849)



	
  	
  
SMNS 4568 right M1 figured by Heizmann & Kordikova (2000) from Ulm, Germany

(mirrored). Ysengrinia gerandiana (Viret 1929a) MNHN-SG 393 reconstructed left and

right M1 from Saint Gérand le Puy, France. Peignecyon felinoides Morales et al.

(2019) TU 73916 right M1 from Tuchořice, the Czech Republic (mirrored). Ysengrinia

valentiana Belinchon & Morales (1989) PaN 319 left M1 from Buñol, Spain.

Thaumastocyon bourgeoisi Sthelin & Helbing (1925) Pont Levoy 705 left M1from

Pont Levoy, France Thaumastocyon dirus Ginsburg et al. (1991) LVF-6 right M1 from

Los Valles de Fuentidueña, Spain (mirrored). Ammitocyon kainos BAT-3'10.1689

reconstructed skull post canine dentition P4–M2, (P4–M1 left side, M2 right side) from

Batallones-3, Spain. Tomocyon grivensis Viret (1929b) LGR-1121 left M1 from La

Grive Saint Alban, France.



Figure 8. Mandibular force profiles of Ammitocyon kainos, Panthera leo, Crocuta

crocuta and Canis lupus. Values are presented for canine, p3–p4, p4–m1, m1–m2 and

post-m2 interdental gaps (when possible). Darker line represents values for each species

and grey lines the values of the other species used for comparison.



Figure 9. Ammitocyon kainos gen. et sp. nov. from Batallones-3, Spain. A, skull and

cervical vertebrae. (Idealized). B, reconstructed life appearance of the head and neck

(drawing by Oscar Sanisidro).




Table captions




	
  	
  
Table 1. Measurements (in mm) of the dentition of Ammitocyon kainos gen. et sp. nov.

from Batallones-3, Spain. Abbreviations: L, length; H, height; W, width.



Table 2. Measurements of cranium and mandible of Ammitocyon kainos gen. et sp. nov.

from Batallones-3, Spain. Abbreviations: lbC, basal length of the skull, from the

rostral part of the premaxilla to the rostral edge of the foramen magnum; lMM,

maximum mandibular length, from the central point of the mandibular condyle to the

most rostral end; Hc, height of the mandibular body at the level of the canine; Hm,

maximum mandibular height; lc, length of the mandibular body from the condyle to the

mesial border of the canine; Hp4m1, height of the mandibular body at the level of the

interdental space between p4 and m1; lp4m1, length of the mandibular body from the

central point of the condyle to the interdental space between p4 and m1.



Table 3. Mandibular force profiles of Panthera leo, Crocuta crocuta, Canis lupus,

Borocyon robustum, Delotrochanter oryktes, Temnocyon macrogenys, Magericyon

anceps and Ammitocyon kainos. Log Zx/L represents dorsoventral force resistance; Log

Zy/L represents labiolingual force resistance; Zx/Zy represents relative values for force

resistance. Values for P. leo, C. crocuta, Ca. lupus, B. robustum, D. oryktes, T.

macrogenys from Therrien (2005) and Hunt (2011). Values for M. anceps and A. kainos

measured for this work.




Supplemental file captions




	
  	
  
Supplemental file 1. Complete list of 54 equally weighted and unordered cranial,

mandibular, and dental characters used in the cladistic analysis.



Supplemental file 2. Character-taxon matrix (13 taxa and 54 characters) in nexus

format used in the cladistic analysis.



Supplemental file 3. Synapomorphies for selected nodes (see Figure 6), as indicated by

character numbers followed by character states within parentheses. Italics denote

ambiguous synapomorphies.



Supplemental file 4. A. Stereophotograhs of the skull of Ammitocyon kainos (BAT-

3'10.1689, skull paratype) in dorsal view. B. Stereophotograhs of the skull of

Magericyon anceps (BAT-3'13.2000) in dorsal view.



Supplemental file 5. Basicranium of Ammitocyon kainos (BAT-3'10.1689, skull

paratype) in ventral view. Abbreviations: gf: glenoid fossa; fo: foramen ovale; pf:

postglenoid foramen; ab: auditory bulla; sf: stylomastoid foramen; pp: paraoccipital

process; oc: occipital condyles; plf: posterior lacerate foramen; mp: mastoid process.



Supplemental file 6. Measurements (in mm) of the scapula, stylopod and zeugopod

bones of Ammitocyon kainos from Batallones-3, found associated to the skull BAT-

3’10.1689.

A= proximal-distal maximum length; B= cranial-caudal proximal epiphysis width;

C=medial-lateral proximal epiphysis width; D=cranial-caudal mid-diaphysis width;




	
  	
  
E=medial-lateral mid-diaphysis width; F= cranial-caudal distal epiphysis width;

G=medial-lateral distal epiphysis width.

In the scapula, measurements of B and C were taken at the glenoid cavity, and G of the

maximum width of the medial border. In the ulna measurements B and C were taken at

the olecranon above the trochlear notch.




	
  	
  
     Specimen         LC     WC     HC       LP4     WP4    LM1    WM1    LM2    WM2

BAT-3'10 1689 left    26.0   16.0   43.0     35.3    18.9   16.9   20.8
BAT-3'10 1689 right   27.5   16.0   40.0     36.9    18.5   16.6   20.1   12.6   14.5



     Specimen         Lc     Wc     Hc       Lp4     Wp4    Lm1    Wm1    Lm2    Wm2

BAT-3'11 453 right    30.0   16.0   36.5
  BAT-3'09 1239       24.0                   20.15   9.2    29.7   13.2   18.0   9.4
  BAT-3'08 604        24.0   16.0   42.0     20.2    8.5    28.6   12.3   15.4   7.9
  BAT-3'09 1124                                                           15.2   8.9
                                      	
  
                                                        BAT-3'11 453   BAT-3'11 453
Specimen   BAT-3'10 1689 BAT-3'08 604   BAT-3'09 1239
                                                           Left           Right

   lbC        379.59
  lMM                                           233.7       252.2          253.7
    lc                                         223.55       243.8         251.85
    Hc                       55.07              50.03        47.7           53.1
 Hp4m1                       53.85              51.23       55,63          47.42
 lp4m1                                         137.06      142.15          149.2
   Hm                       128.06             125.26
                                           	
  
                                 Log Zx/L
                         post m3     post m2   m1-m2    p4-m1    p3-p4   Canine
     Panthera leo                               -0.29    -0.47   -0.64    -0.38
    Crocuta cocuta                              -0.23    -0.45   -0.67    -0.61
     Canis lupus          -0.47       -0.55     -0.64    -0.77   -0.97    -0.92
  Borocyon robustum       -0.07       -0.21     -0.31    -0.54   -0.67    -0.55
Delotrochanter oryktes    -0.28       -0.34     -0.49    -0.73   -0.85    -0.55
Temnocyon macrogenys      -0.19       -0.26     -0.46    -0.65    -0.8    -0.58
  Magericyon anceps                   -0.92     -1.00    -1.27   -1.40    -0.60
  Ammitocyon kainos                   -0.99     -1.17    -1.13   -1.38    -0.78

                                 Log Zy/L
                         post m3     post m2   m1-m2    p4-m1    p3-p4   Canine
     Panthera leo                               -0.64    -0.80   -0.93    -0.48
    Crocuta cocuta                              -0.76    -0.83   -0.96    -0.69
     Canis lupus          -0.98       -1.05     -1.07    -1.09   -1.26    -0.88
  Borocyon robustum       -0.59       -0.67     -0.71    -0.93   -1.02    -0.63
Delotrochanter oryktes    -0.94       -0.94     -1.00    -1.16   -1.34    -0.71
Temnocyon macrogenys      -0.83       -0.89     -1.05    -1.07    -1.3    -0.69
  Magericyon anceps                   -0.41     -0.51    -0.79   -0.92    -0.52
  Ammitocyon kainos                   -0.32     -0.47    -0.58   -0.76    -0.22

                                 Zx/Zy
                         post m3    post m2    m1-m2    p4-m1    p3-p4   Canine
     Panthera leo                               2.28     2.11     1.94    1.25
    Crocuta cocuta                              3.43     2.37     1.93    1.20
     Canis lupus          3.23        3.10      2.67     2.12     1.94    0.90
  Borocyon robustum       3.33        2.88      2.56     2.41     2.23     1.2
Delotrochanter oryktes    4.51        4.01      3.24     2.67     3.13    1.46
Temnocyon macrogenys      4.35        4.05      3.73     2.66     3.23     1.3
  Magericyon anceps                   0.31      0.33     0.33     0.33    0.83
  Ammitocyon kainos                   0.21      0.20     0.28     0.24    0.27