The record of Deinotheriidae from the Miocene of the Swiss Jura Mountains (Jura Canton, Switzerland)

The Miocene sands of the Swiss Jura Mountains, long exploited in quarries for the construction industry, have yielded abundant fossil remains of large mammals. Among Deinotheriidae (Proboscidea), two species, Prodeinotherium bavaricum and Deinotherium giganteum, had previously been identified in the Delémont valley, but never described. A third species, Deinotherium levius, from the locality of Charmoille in Ajoie, is reported herein for the first time in Switzerland. These occurrences are dated from the late early to the early late Miocene, correlating to the European Mammal biozones MN4 to MN9. The study is completed by a discussion on the palaeobiogeography of dinotheres at European scale.


Introduction
The order of Proboscidea currently regroups large mammals whose common characteristic is the possession of a trunk and tusks. Within the Afrotherians superorder, it has for sister group the Sirenia order (dugongs and manatees). Its extant representatives belong to the Elephantidae family with only three species of elephants living in Africa or Asia (Loxodonta africana, Loxodonta cyclotis and Elephas maximus). However, this order is much more diversified in the fossil record.
The Proboscideans have an African origin with the basal genus Erytherium, found in the early late Paleocene of Morocco (Gheerbrant 2009), as well as other primitive forms with small sizes belonging to the genera Numidotherium and Barytherium. These primitive forms were only found in the late 2 early Eocene and the late Eocene and early Oligocene, respectively, of Africa (Tassy 1990). The gomphotheres (Gomphotheriidae) and the dinotheres (Deinotheriidae) are the firsts proboscideans found outside of Africa in the fossil record. Their occurrence in Europe is linked to the Proboscidean Datum Event (sensu Tassy 1990) of the late early Miocene (ca. 19.5-17.5 Ma;Göhlich 1999). This biogeographic event resulted from the counter clockwise rotation of Africa and Arabia plates leading to a collision with the Anatolian plate and the formation a landbridge connecting Africa and Eurasia at the end of the early Miocene (Rögel 1999a, b). This geographic change allowed remarkable terrestrial mammal exchanges including the gomphotheres and the dinotheres (e.g. Göhlich 1999, Sen 2013. Within the phylogeny of Proboscideans (Fig. 1), dinotheres are included in a clade of mega herbivores together with other Elephantiformes (Phiomia, Mammut americanum, Gomphotherium and Elephantidae) of which they are the sister group (Hutchinson et al. 2011). The differentiation between dinotheres and other mega proboscideans (Elephantiformes) could have occurred as soon as the end of the Eocene. However, phylogenetic relationships within the Deinotheriidae family remain uncertain to this day. The Jura Canton lies at the palaeogeographic junction between the Cenozoic tectonic and sedimentary provinces of the Upper Rhine Graben and the North Alpine Foreland Basin (Sissingh 2006). The regional fluvio-lacustrine sediments of the Miocene Bois de Raube Formation (OSM; Obere Süsswassermolasse = Upper freshwater molasses), were deposited both in Delémont Basin (near Delémont) and in Ajoie area (near Porrentruy). After Kälin (1997), this formation is subdivided in three members differing by a markedly different heavy mineral spectrum and pebble content: a basal Montchaibeux Member (''RoteMergel und Dinotheriensande des Mont Chaibeux'' of Liniger 1925), a middle conglomeratic Bois de Raube Member (''Vogesenschotter des Bois de Raube'' of Liniger 1925) in Delémont Basin, and an upper Ajoie Member (''Hipparionsande von Charmoille'' of Liniger 1925). The formation covers the biochronological interval MN4 to MN9 (Kälin 1997, Choffat & Becker 2017, Prieto et al. 2017) and includes three historical localities that yielding dinothere remains (Greppin 1867(Greppin , 1870Stehlin 1914;Schäfer 1961;Kälin 1993

Material
The studied material of Dinotheriidae, coming exclusively from in the Swiss Jura Canton, includes: (1) the famous reconstituted mandible of Prodeinotherium bavaricum from the Montchaibeux locality (Bachmann 1975). A copy of this mandible is housed in the collections of the Jurassica Museum whereas the original specimen is housed in the collections Natural History Museum of Bern; (2) a copy of the lower molar of Deinotherium giganteum from the Bois de Raube locality (Greppin 1867(Greppin , 1870, housed in the Jurassica Museum and whose the original seems to be housed in the  (4) the specimens of Deinotheriidae from Charmoille (Stehlin 1914, Schäfer 1961, Kälin 1993, 1997, Choffat & Becker 2017 which consists in some fragments of tusks from the Jurassica Museum collection and more complete dental specimens housed in the Museum of Natural History of Basel.

Terminology and measurements
The dental terminology for Deinotheriidae mainly follows that of Aiglstorfer et al. (2014) and Pickford & Pourabrishami (2013) (Fig. 3), and is illustrated in this paper for a better understanding of the characters descriptions and discussions. The measurements written in the tables or in the text are given in millimetres (precision at 0.1 mm), those in brackets are estimated.

Description
The P4 is damaged anteriorly and moderately worn. It is nearly quadratic in occlusal view, just slightly wider than long. The ectoloph is complete bearing an ectoflexus weakly developed, and distinct The anterior and posterior cingula are strong and continuous, although the anterior one is thinner in its middle part. The lingual cingulum is less pronounced but closes the lingual medifossette. The labial side of the tooth lacks any cingulum, but it is characterised by a deep ectoflexus.
The mandible NMBE-5031977, restored from 5 fragments, is incomplete. The ramus is low and slightly inclined forward, the mandibular angle forms a right dihedron, the base of the corpus is straight, and the posterior margin of the symphysis is located below the front of the p4. The i2 are The m3 is morphogically similar to the m2. However, the hypolophid is slightly reduced in width compared to the metalophid and the posterior cingulid is more pronounced but strongly reduced in width, giving a longer and trapezoidal outline in occlusal view.

Comparisons
The referred dental remains are typically from the Deinotheriidae family with mainly bilophodont jugal teeth associated to a sublophodont (well-developed ectoloph and uncomplete metaloph) P4 and a trilophodont m1, as well as i2 oriented downwards and backwards (Huttunen 2002a).
14 The specimens differentiate from Deinotherium proavum and D. giganteum species by considerably smaller dimensions (Gräf 1957, Vergiev & Markov 2010, Pickford & Pourabrishami 2013, Aiglstorfer et al. 2014, Țibuleac 2018. Deinotherium levius presents also bigger dimensions, but the differences are less significant (Gräf 1957, Pickford & Pourabrishami 2013. However, the strong development of the convolute and the near absence of postprotocrista and posthypocrista on the M2 clearly exclude an attribution at the Deinotherium genus (Harris 1973, Huttunen 2002b, Poulakakis et al. 2005, Duranthon et al. 2007, Aiglstorfer et al. 2014. Likewise the moderately developed curve of the i2 can be distinguished from the more pronounced one of D. giganteum and the subvertical one of D. levius (Gräf 1957).
Although, in Prodeinotherium, the entostyle is usually lacking on P3-4 and the metaloph usually complete on P4, these particular characters, present on the referred P4 NMB-Mch.4, can be attributed to generic variability (e.g. Harris 1973, Ginsburg & Chevrier 2001, Aiglstorfer et al. 2014. Also by its dimensions the almost absence of an ectolflexus and the quadratic outline in occlusal view, this specimen shows strong similarities with Prodeinotherium species, particularly of P. bavaricum (Ginsburg & Chevrier 2001, Duranthon et al. 2007, Pickford & Pourabrishami 2013. Based on the morphology of the P4 (nearly absence of ectolflexus and the quadratic outline), the M2 (developed convolute) and the lower cheek teeth (m1 with transverse lophids roughly straight and of equal width), as well as the modest curve of the i2, the specimens can be referred to the genus Prodeinotherium (Gräf 1957, Harris 1973, Huttunen 2002a, Huttunen & Göhlich 2002, Duranthon and al. 2007). Additioanly, after Ginsburg & Chevrier (2001) and Pickford & Pourabrishami (2013), the specimens cannot referred to the species P. cuvieri due to their larger dimensions, but rather to P.
bavaricum of which size ismuch closer (e.g. Gräf 1957, Kovachev & Nikolov 2006, Huttunen & Göhlich 2002. Genre Deinotherium Kaup, 1829 European species: Deinotherium giganteum Kaup, 1829, D. proavum (Eichwald, 1835)    The m2 is bilophodont and nearly rectangular (slightly longer than wide). The anterior cingulid is unobservable whereas the posterior one is low and strong but narrower than the hypolophid. The median valley is opened on both sides, without labial and lingual cingulids. Each conid has a slightly developed and anteriorly extending cristid, except the praehypocristid which extends anterolingually and reaches the bottom of the median valley.

Comparisons
The specimens from Charmoille show the typical features of Deinotheriidae: lower tusks oriented downward, P4 bearing an ectoloph, trilophodont D4 and m1, and a bilophodont pattern for the remainder of the cheek teeth (Huttunen 2002a). They differ from Prodeinotherium by being larger, by a trapezoidal outline and a more distinct ectoflexus in P4, as well as a narrower tritolophid compared to other lophids in m1 (Gräf 1957, Ginsburg & Chevrier 2001, Duranthon et al. 2007).
Among the Deinotherium species, they display more affinities with D. levius by the size (slightly smaller than those of D. giganteum, Pickford & Pourabrishami 2013), by a subcomplete metaloph without a notch separating it from the metacone and the presence of a strong entostyle on P4, by a protolophid and metalophid of equal lengths in p4 (rectangular outline vs trapezoidal outline in D. giganteum), and by a short posterior cingulid on m2 (Gräf 1957, Duranthon et al. 2007). This attribution also seems to be supported by the i2 NMB-Cm478 that displays a sub-straight tusk tip, characteristic of D. levius according to Gräf (1957).

Material referred
Complete m2

Comparisons
The m2 displays a bilophodont pattern with a well-developed posterior cingulid which are typical of the Deinotheriidae family (Huttunen 2020a). This m2 can be differentiated from m2s of Prodeinotherium by their sizes that are on average up to more than 30% larger than those of P. cuvieri and about 20% larger than those of P. bavaricum (e.g. Gräf 1957, Ginsburg & Chevrier 2001, Huttunen & Göhlich 2002, Pickford & Pourabrishami 2013. In addition, the praehypocristid is remarkably more developed than in P. bavaricum (as is the posterior cingulid too), then the tooth can be undoutbly referred to the genus Deinotherium (e.g. Huttunen 2002a, b, Huttunen & Göhlich 2002, Duranthon and al. 2007, Țibuleac 2018.

20
A specific identifiction within the genus Deinotherium remains very difficult based on morphological characters whereas only evolutionary trends seem to be observable along time (e.g. Gräf 1957, Ginsburg & Chevrier 2001, Duranthon et al. 2007, Pickford & Pourabrishami 2013. However , Pickford & Pourabrishami (2013) suggest specific attributions by highlighting, contrary to Gräf (1957), discontinuous size ranges from one species to another. Based on these observations, m2s of D.
proavum are always larger than 90 mm and can exceed than 100 mm, what unambiguously excludes our specimen from Bois de Raube whose length is 82.6 mm ( Tab. 5

Discussion
Fossil record of Deinotheriidae in the Jura The age of the dinotheres discovered in the Swiss Jura Mountains is based on the regional litho-and biostratigraphy established by Kälin (1993Kälin ( , 1997 and Prieto et al. (2017) and fits the biostratigraphic range of the species at European scale. The records correlate to MN4-6(-7) for P. bavaricum in Montchaibeux, to MN6-7/8 for D. giganteum in Bois de Raube and to MN9 for D. levius in Charmoille.
The latter record indicates the first report of D. levius in Switzerland and matches the latest occurrences of this species in Europe (Fig. 8).
21 Figure 8. Stratigraphic extend of five species of European Deinotheriidae (P. cuvieri, P. bavaricum, D. levius, D. giganteum and D. proavum). The dashed lines represent enlarged occurrences for each species, supported by the fossil record of the appendix 1. The correlations with the European fauna of reference are according to Berger (2011) and the ones with the regional lithostratigraphy to Kälin (1993Kälin ( , 1997 and Prieto et al. (2017).

Biogeographic distribution of European Deinotheriidae
The dinotheres known since the late Oligocene in Africa arrived later in Eurasia, following the mid-Burdigalian Proboscidean Datum Event (ca. 19.5-17.5 Ma). This event is related to the terrestrial corridor, called the Gomphotherium Landbridge, allowing a faunal exchange between Eurasia and the Arabian Plate of which the proboscideans were the palaeontological index-fossils (Tassy 1990, Göhlich 1999, Rögel 1999a, b, Koufos et al. 2003. Although the first, short-lasting migration corridors evolved already during the Aquitanian or perhaps earlier in Asia (e.g. Tassy 1990, Antoine et al. 2003, the main wave of migration of the Gomphotherium Landbridge started during the mid-Burdigalian in Europe, with the arrivals of the earliest gomphotheres, deinotheres and mammutids at the end of MN3 (Tassy 1990, Koufos et al. 2003. Among the early occurrences of European dinotheres in MN3-4, Prodeinotherium cuvieri is endemic to the west of Europe (France and Spain) while P. bavaricum presents a more balanced distribution all over Europe (Fig. 9). This period corresponds to the Teeth of Deinotheriidae show a remarkable increase of their dimensions throughout their evolution (Pickford & Pourabrishami 2013) which reflects an evolution toward larger size for the whole family (Aiglstorfer et al. 2014, Codrea & Margin 2009). According to Agustí & Antón (2002), the Prodeinotherium were 2 meters tall at the shoulder, while Deinotherium might have reached 4 meters. Some species of Deinotheriidae presented body mass far greater than those of extant elephants. For comparison, the highest record of an African elephant weight is of 6.64 tonnes (Larramendi 2016), whereas the average is in general includes between 4 and 5 tonnes. The most ancestral dinotheres, Chilgatherium harrisi, weighted already 1.5 tonnes (Sanders et al. 2004 The body size and mass of mammals is linked to a large number of physiologic and ecologic traits (Blueweiss et al. 1978, Brown et al. 2004). The lifestyle, the living environment and thedistribution of the species are parameters particularly linked to the size (for a synthesis see McNab 1990 andEisenberg 1990). Having a large body size and mass brings consequently non negligible advantages for the survival of a population, such as a lower mortality rate, a more stable population dynamic and a better resistance to sickness and limiting environment factors (Langer 2003, Erb et al. 2001).
Among large mammals, the mega herbivores are more immunised against the predation thanks to their huge size and mass, providing also a protection to the youngest because of their generally gregarious behaviour (Hummel & Clauss 2008). This advantage might have been particularly important during the Miocene that also sees a significant size augmentation of some predators (e.g., Hyainailouros sulzeri, Amphicyon giganteus, Machairodus giganteus; Agustí & Antón 2002). Due to the opening of environments during the Neogene (e.g. Suc et al. 1999, Favre et al. 2007, Costeur et al. 2007, Costeur & Legendre 2008, the folivore herbivores, such as the dinotheres, also had to browse more distances from an arboreal patch to another to find food. Large mammals present a potential of geographic distribution and of displacement more important on long distances (e.g. Brown 1995, Gaston 2003, the displacements ask indeed less energy per distance unit for large animals (Owen- Smith 1988 According to the Bergmann law (Bergmann 1847, Blackburn & Hawkins 2004, although this rule suffers from numerous exceptions (Meiri & Dayan 2003), a large body mass also allows a limitation of the heat loss and presents a significant advantage in a colder climate. All these advantages linked to large size and mass could have supported the natural selection of larger dinotheres and in turn could explain the regular augmentation of size of this family during the Neogene.
The structure of the check teeth of dinotheres, although lophodonts like extant elephants, is more specifically bilophodont and in fact closer to tapirs. The latter are essentially folivores and spend up to 90% of their active time to feed on fruits, leaves, barks and flowers (Huttunen 2002a, Sanders 2018, Naranjo 2009). Likewise, dinotheres seem specialised in a regime consisting of dicotyledons leaves and are generally linked to open forest environments (Konidaris et al. 2017, Čkonjević & Radović 2012, Aiglstorfer and al. 2014).
In the more derived representatives of Deinotherium, the occiput is slightly inclined backwards and the occipital condyles elevated, characterizing a higher head posture The appendicular skeleton also presents a modification of the graviportal structure initially known in Prodeinotherium leading to a more agile anatomic type with notably a greater amplitude of movements for the anterior limbs