''Leptotheridium'' is an extinct genus of

Palaeogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

endemic to western Europe that lived from the Middle to Late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

. It was erected by the Swiss palaeontologist

Hans Georg Stehlin Hans Georg Stehlin (1870–1941) was a Swiss paleontologist and geologist. Stehlin specialized in vertebrate paleontology, particularly the study of Cenozoic mammals. He published numerous scientific papers on primates and ungulates. He was presid ...

in 1910 and contains the species ''L. lugeoni'' and ''L. traguloides''. Its phylogenetic position is unclear, with researchers determining that it belonged to either the

Anoplotheriidae Anoplotheriidae is an extinct family of artiodactyl ungulates. They were endemic to Europe during the Eocene and Oligocene epochs about 44—30 million years ago. Its name is derived from the ("unarmed") and θήριον ("beast"), translating ...

(specifically the subfamily

Dacrytheriinae Anoplotheriidae is an extinct family of artiodactyl ungulates. They were endemic to Europe during the Eocene and Oligocene epochs about 44—30 million years ago. Its name is derived from the ("unarmed") and θήριον ("beast"), translating ...

) or the

Xiphodontidae Xiphodontidae is an extinct family (biology), family of herbivorous even-toed ungulates (order (biology), order Artiodactyla), endemic to Europe during the Eocene 40.4—33.9 million years ago, existing for about 7.5 million years. ''P ...

due to its dental and postcranial anatomy. The small-sized artiodactyl genus is unique from its close relatives in that it seemingly lacks the first lower

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

s, weak

selenodont Selenodont teeth are the type of molars and premolars commonly found in ruminant herbivores. They are characterized by low crowns, and crescent-shaped cusps when viewed from above (crown view). The term comes from the Ancient Greek roots (, ' ...

y (crescent-like ridges) in its dentition, and has three-lobed canines. It is one of the earlier artiodactyl species to have appeared in the fossil record of Europe.

Taxonomy

In 1910, the Swiss palaeontologist

erected the genus ''Leptotheridium'', which he stated had a dental form similar to that of ''

Catodontherium ''Catodontherium'' is an extinct genus of Paleogene, Palaeogene artiodactyl belonging to the family Anoplotheriidae. It was endemic to Western Europe and had a temporal range exclusive to the middle Eocene, although its earliest appearance depe ...

''. The first species that he created was ''Leptotheridium Lugeoni'', designating it as the type species. The species was established based on a partial

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

with dentition from the Swiss locality of

Mormont ''Le Mormont'' is a hill in the Swiss canton of Vaud, rising to an elevation of 605 metres, with a Topographic prominence, prominence of about 115 metres. It is part of the Éclépens municipality between lakes Lake Neuchatel, Neuchatel and La ...

and was first designated to '' Rhagatherium valdense'' by

François Jules Pictet de la Rive François-Jules Pictet de la Rive (27 September 180915 March 1872) was a Switzerland, Swiss zoologist and palaeontologist. Biography He was born in Geneva. He graduated B. Sc. at Geneva in 1829, and pursued his studies for a short time at Paris, ...

and

Aloïs Humbert Aloïs Humbert (22 September 1829 – 13 May 1887) was a Swiss naturalist and paleontologist who specialized in the study of myriapods. He also described new vertebrates (fishes, reptiles, mammals), molluscs and flatworms. Biography Humbert was ...

in 1869. The second species that he named was ''L. traguloïdes'' based on a maxilla fragment from a locality in

Egerkingen Egerkingen is a Municipalities of Switzerland, municipality in the district of Gäu (district), Gäu in the Cantons of Switzerland, canton of Solothurn (canton), Solothurn in Switzerland. History Egerkingen is first mentioned in 1201 as ''in Egri ...

that was initially classified to '' Mixtotherium gresslyi'' by Ludwig Ruetimeyer in 1891.

Classification

Leptotheridium lugeoni mandible reconstruction

The taxonomic position of ''Leptotheridium'' had long been in dispute as palaeontologists had classified it either to the

, two

families that were endemic to western Europe during the

. In 1910, Stehlin suggested that ''Leptotheridium'' was close in affinity to ''

Dacrytherium ''Dacrytherium'' (Ancient Greek: (tear, teardrop) + (beast or wild animal) meaning "tear beast") is an extinct genus of Paleogene, Palaeogene artiodactyls belonging to the family Anoplotheriidae. It occurred from the Middle to Late Eocene of W ...

'' and ''

'', members of the anoplotheriid subfamily

. In 1917, the French palaeontologist

Charles Depéret Charles Jean Julien Depéret (25 June 1854 – 18 May 1929) was a French geologist and paleontologist. He was a member of the French Academy of Sciences, the Société géologique de France

placed ''Leptotheridium'' in the Dacrytheriidae (now an anoplotheriid subfamily). The systematic placement of ''Leptotheridium'' within the Dacrytheriinae (or Dacrytheriidae) had been followed by other palaeontologists like Jean Viret in 1961 and Jean Sudre in 1978. In 2000, the palaeontologists Jerry J. Hooker and Marc Weidmann reclassified ''Leptotheridium'' to the Xiphodontidae, rejecting its previous classification to the Dacrytheriinae due to differences in dental and postcranial anatomy as well as the lack of any preorbital fossa. He argued that its dentition was very to that of ''

Xiphodon ''Xiphodon'' is the type genus of the extinct Paleogene, Palaeogene artiodactyl family Xiphodontidae. It, like other xiphodonts, was endemic to Western Europe and lived from the Middle Eocene up to the earliest Oligocene. Fossils from Montmartre ...

'', thus further supporting the reclassification. In 2006, Miguel Angel Cuesta et al. chose to follow Hooker and Weidmann in the classification of ''Leptotherium'' to the Xiphodontidae instead of the Anoplotheriidae. In 2022, Weppe created a phylogenetic analysis in his academic

thesis A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: D ...

regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families. The phylogenetic tree, according to Weppe, is the first to conduct phylogenetic affinities of all anoplotheriid genera, although not all individual species were included. His research placed ''Leptotheridium'' into a clade with the dacrytheriines ''Catodontherium'' and ''Dacrytherium'', thus positioning it as a member of the Dacrytheriinae rather than the Xiphodontidae.

Description

''Leptotheridium'' is described as being a small-sized artiodactyl that lacks preorbital fossae and is diagnosed as having poorly developed

(crescent-like ridges) crests in its dentition, especially evident by the forms of the postprotocrista and postparaconule ridges on the upper

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

(M/m). It was smaller than ''Catodontherium'' and ''Dacrytherium'' in size and has overall bunoselenodont (

bunodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...

(rounded) and selenodont dentition). Unlike with other members of the Anoplotheriidae and Xiphodontidae known by dental sets, that of ''Leptotheridium'' is incomplete (meaning that it has fewer than 44 total teeth) because of the lack of a first lower

(P/p), or P₁. The canines (C/c) are incisiform (

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

-shaped (I/i)) but are divided into three deep lobes (trilobed). The premolars are not shaped like molars, with P⁴ being elongated and having an external conical point. P⁴ is slightly elongated with a slightly wide back area. P₂ is very similar to P₃ in shape but differs by its narrower shape. The upper molars are roughly quadrangular in shape and contain prominent paraconule cusps, which along with the

mesostyle Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

cusps are prominent like in ''Catodontherium'' but less spherical than in ''Dacrytherium''. There are

diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...

ta in between both the lower canine and P₂ and the P₂ and P₃ teeth; the canine still remains in contact with the incisors. ''Leptotheridium'' was additionally previously by an

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

previously assigned to it that was described as being very narrow and elongated with a narrow tibial groove and a straight bone axis. However, it was later reassigned to ''

Haplomeryx ''Haplomeryx'' is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the Middle Eocene up to the earliest Oligocene. ''Haplomeryx'' was first established as a genus ...

'' while some postcranial fossils that were assigned previously to ''Xiphodon'' were reclassified to ''Leptotheridium''. In terms of the reassigned astragalus, it is narrow plus elongated in form, its tibial groove appearing narrow but deep. The back calcaneal facet, occupying a significant portion of the astragalus' back face, is wide. The

calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel; : calcanei or calcanea) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is t ...

appears similar to that of ''Dacrytherium'' but differs by a more elongated back tuberosity.

Palaeoecology

Middle Eocene Paleogeography Tethys Dispersals

For much of the

, a hothouse climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the Perissodactyla, Artiodactyla, and

Primates Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers and simians ( monkeys and apes). Primates arose 74–63 ...

(or the suborder Euprimates) appeared already by the early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

forms mostly either switched to folivorous diets or went extinct by the Middle Eocene (47–37 million years ago) along with the archaic "

condylarths Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely considered to be a wast ...

". By the Late Eocene (approx. 37–33 mya), most of the ungulate form dentitions shifted from bunodont (or rounded) cusps to cutting ridges (i.e. lophs) for folivorous diets. Land connections between western Europe and North America were interrupted around 53 Ma. From the early Eocene up until the

Grande Coupure Grande means "large" or "great" in many of the Romance languages. It may also refer to: Places * Grande, Germany, a municipality in Germany * Grande Communications, a telecommunications firm based in Texas * Grande-Rivière (disambiguation) * Ar ...

extinction event (56–33.9 mya), western Eurasia was separated into three landmasses: western Europe (an archipelago),

Balkanatolia For some 10 million years until the end of the Eocene, Balkanatolia was an island continent or a series of islands, separate from Asia and also from Western Europe. The area now comprises approximately the modern Balkans and Anatolia. Fossil mammal ...

(in-between the

Paratethys Sea The Paratethys sea, Paratethys ocean, Paratethys realm or just Paratethys (meaning "beside Tethys"), was a large shallow inland sea that covered much of mainland Europe and parts of western Asia during the middle to late Cenozoic, from the lat ...

of the north and the

Neotethys Ocean The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasian ...

of the south), and eastern Eurasia. The

Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...

mammalian faunas of western Europe were therefore mostly isolated from other landmasses including Greenland, Africa, and eastern Eurasia, allowing for endemism to develop. Therefore, the European mammals of the Late Eocene (MP17–MP20 of the Mammal Palaeogene zones) were mostly descendants of endemic Middle Eocene groups. ''Leptotheridium'', or more specifically ''L. traguloides'', first appeared in the fossil record at the Swiss localities of Egerkingen-Huppersand (MP13? or MP14?) and Egerkingen α + β (MP14). By then, it would have coexisted with perissodactyls (

Palaeotheriidae Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia, from the mid-Eocene to the early Oligocene. They are classified in Equoidea, along with the livin ...

Lophiodontidae Lophiodontidae is a family of browsing, herbivorous, mammals in the Perissodactyla suborder Ancylopoda that show long, curved and cleft claws. They lived in Southern Europe during the Eocene epoch. Previously thought to be related to tapirs, it ...

, and Hyrachyidae), non-endemic artiodactyls (

Dichobunidae Dichobunidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia. The Dichobunidae include some of the earliest known artiodactyls, such as ''Diacodexis''. Description T ...

and Tapirulidae), endemic European artiodactyls (

Choeropotamidae Choeropotamidae, also known as Haplobunodontidae, are a family (biology), family of extinct mammal herbivores, belonging to the artiodactyls. They lived between the lower/middle Eocene and lower Oligocene (about 48 - 30 million years ago) and th ...

, Cebochoeridae, and Anoplotheriidae), and primates (

Adapidae Adapidae is a family of extinct primates that primarily radiated during the Eocene epoch between about 55 and 34 million years ago. Adapid systematics and evolutionary relationships are controversial, but there is fairly good evidence from the ...

). The Amphimerycidae and non-disputed members of the Xiphodontidae made their first appearances by the level MP14. The stratigraphic ranges of the early species of ''L. traguloides'' also overlapped with

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...

ns (

Herpetotheriidae Herpetotheriidae is an extinct family of metatherians, closely related to marsupials. Species of this family are generally reconstructed as terrestrial, and are considered morphologically similar to modern opossums. They are suggested to have b ...

cimolesta Cimolesta is an extinct order of non-placental eutherian mammals. Cimolestans had a wide variety of body shapes, dentition and lifestyles, though the majority of them were small to medium-sized general mammals that bore superficial resemblances t ...

ns (

Pantolestidae Pantolestidae is an extinct family of semi-aquatic, non-placental eutherian mammals. Forming the core of the equally extinct suborder Pantolesta, the pantolestids evolved as a series of increasingly otter-like forms, ranging from the Middle Pa ...

, Paroxyclaenidae), rodents ( Ischyromyidae, Theridomyoidea, Gliridae),

eulipotyphla Eulipotyphla (, from '' eu-'' + '' Lipotyphla'', meaning truly lacking blind gut; sometimes called true insectivores) is an order of mammals comprising the Erinaceidae ( hedgehogs and gymnures); Solenodontidae (solenodons); Talpidae ( mole ...

ns, bats,

apatotheria Apatemyidae is an extinct family of placental mammals that took part in the first placental evolutionary radiation together with other early mammals, such as the leptictids. Their relationships to other mammal groups are controversial; a 2010 st ...

ns,

carnivoraformes Carnivoramorpha ("carnivoran-like forms") is a clade of placental mammals of clade Pan-Carnivora from mirorder Ferae, that includes the modern order Carnivora and its extinct stem-relatives.Bryant, H.N., and M. Wolson (2004“Phylogenetic Nomenc ...

(

Miacidae Miacidae ("small points") is a former paraphyletic family of extinct primitive placental mammals that lived in North America, Europe and Asia during the Paleocene and Eocene epochs, about 65–33.9 million years ago.IRMNG (2018). Miacidae Cope, ...

), and hyaenodonts (

Hyainailourinae Hyainailourinae ("hyena-like Felidae, cats") is a Paraphyly, paraphyletic subfamily of Hyaenodonta, hyaenodonts from extinct paraphyletic family Hyainailouridae. They arose during the Bartonian, Middle Eocene in Africa, and persisted well into th ...

, Proviverrinae). Other MP13-MP14 sites have also yielded fossils of turtles and

crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ...

, and MP13 sites are stratigraphically the latest to have yielded remains of the bird clades Gastornithidae and

Palaeognathae Palaeognathae (; ) is an infraclass of birds, called paleognaths or palaeognaths, within the class Aves of the clade Archosauria. It is one of the two extant taxon, extant infraclasses of birds, the other being Neognathae, both of which form Neo ...

Based on the Egerkingen α + β locality, ''L. traguloides'' coexisted with the herpetotheriid ''

Amphiperatherium ''Amphiperatherium'' is an extinct genus of metatherian mammal, closely related to marsupials. It ranged from the Early Eocene to the Middle Miocene in Europe. It is the most recent metatherian known from the continent. Description Like modern ...

'', ischyromyids '' Ailuravus'' and '' Plesiarctomys'', pseudosciurid '' Treposciurus'',

omomyid Omomyidae is a group of early primates that radiated during the Eocene epoch between about (mya). Fossil omomyids are found in North America, Europe & Asia, making it one of two groups of Eocene primates with a geographic distribution spanning ...

Necrolemur ''Necrolemur'' is a small bodied omomyid with body mass estimations ranging from . ''Necrolemur''’s teeth feature broad basins and blunt cusps, suggesting their diet consisted of mostly Frugivore, soft fruit, though examination of microwear patt ...

'', adapid ''

Leptadapis ''Leptadapis'' is a genus of adapiform primate that lived in Europe during the middle Eocene. Fossils of the genus have been found in the Escanilla Formation of Spain and Egerkingen Egerkingen is a Municipalities of Switzerland, municipality i ...

'', proviverrine '' Proviverra'', palaeotheres (''

Propalaeotherium ''Propalaeotherium'' was an early genus of perissodactyl Endemism, endemic to Europe and Asia during the early Eocene. There are currently six recognised species within the genus, with ''P. isselanum'' as the type species (named by Georges Cuvier ...

'', '' Anchilophus'', '' Lophiotherium'', '' Plagiolophus'', ''

Palaeotherium ''Palaeotherium'' is an extinct genus of Equoidea, equoid that lived in Europe and possibly the Middle East from the Middle Eocene to the Early Oligocene. It is the type genus of the Palaeotheriidae, a group exclusive to the Paleogene, Palaeogen ...

''), hyrachyid '' Chasmotherium'', lophiodont ''

Lophiodon ''Lophiodon'' (from , 'crest' and 'tooth') is an extinct genus of mammal related to chalicotheres. It lived in Eocene Europe , and was previously thought to be closely related to ''Hyrachyus''. ''Lophiodon'' was named and described by Georges ...

'', dichobunids '' Hyperdichobune'' and '' Mouillacitherium'', choeropotamid '' Rhagatherium'', anoplotheriid ''Catodontherium'', amphimerycid ''Pseudamphimeryx'', cebochoerid '' Cebochoerus'', tapirulid '' Tapirulus'', mixtotheriid '' Mixtotherium'', and the xiphodonts '' Dichodon'' and ''Haplomeryx''. MP16 marks the first appearance of ''L. lugeoni'' and the last known appearance of ''L. traguloides'' based on occurrences at multiple localities such as Robiac and Lavergne. Within the French locality of Le Bretou, both species of ''Leptotheridium'' cooccurred with the herpetotheriids ''Amphiperatherium'' and ''

Peratherium ''Peratherium'' is a genus of metatherian mammals in the family Herpetotheriidae that lived in Europe and Africa from the Early Eocene to the Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (ge ...

'', pseudorhyncocyonid ''

Leptictidium ''Leptictidium'' is an extinct genus of small mammals that were likely bipedal. Comprising eight species, they resembled today's bilbies, bandicoots, and elephant shrews, and occupied a similar niche. They are especially interesting for their c ...

'', nyctitheres '' Cryptotopos'' and '' Saturninia'',

notharctid Notharctidae is an extinct family of adapiform primates found primarily in North America and Europe. Classification *Family Notharctidae **Subfamily Asiadapinae **Subfamily Cercamoniinae **Subfamily Notharctinae Notharctinae is an extinct ...

Anchomomys ''Anchomomys'' is a genus of adapiform primate that lived in Europe and Africa during the middle Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of ...

'', omomyids ''Necrolemur'' and '' Pseudoloris'', glirid '' Glamys'', pseudosciurid '' Sciuroides'', bats ('' Carcinipteryx'', ''

Hipposideros ''Hipposideros'' is one of the most diverse genera of bats, with more than 70 species. They are collectively called roundleaf bats after the shape of their nasal ornament. It is the type genus of the family Hipposideridae. It is divided into spe ...

'', '' Palaeophyllophora'', '' Vaylatsia'', '' Vespertiliavus''), proviverrine '' Allopterodon'', carnivoraforme '' Quercygale'', cebochoerids '' Acotherulum'' and ''Cebochoerus'', anoplotheriids (''Catodontherium'', ''Dacrytherium'' and ''Robiatherium''), xiphodonts (''Xiphodon'', ''Dichodon'', ''Haplomeryx''), dichobunids ''

Dichobune ''Dichobune'' is the type genus of the Dichobunoidea, an extinct paraphyletic superfamily consisting of some of the earliest artiodactyls known in the fossil record. It was a primitive artiodactyl genus that was endemic to western Europe and live ...

'' and ''Mouillacitherium'', lophiodont ''

'', and palaeotheres (''Anchilophus'', ''

Eurohippus ''Eurohippus'' is an extinct genus of equoid ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with t ...

'', '' Pachynolophus'', '' Metanchilophus'', '' Leptolophus'', ''Plagiolophus'', ''Palaeotherium''). After MP16,

faunal turnover The turnover-pulse hypothesis, formulated by paleontologist Elisabeth Vrba, suggests that major changes to the climate or ecosystem often result in a period of rapid extinction and high turnover of new species (a "pulse") across multiple different ...

occurred, marking the disappearances of the lophiodonts and European hyrachyids as well as the extinctions of all European crocodylomorphs except for the

alligatoroid Alligatoroidea is one of three superfamilies of crocodylians, the other two being Crocodyloidea and Gavialoidea. Alligatoroidea evolved in the Late Cretaceous period, and consists of the alligators and caimans, as well as extinct members more c ...

Diplocynodon ''Diplocynodon'' is an extinct genus of eusuchian, either an alligatoroid crocodilian or a stem-group crocodilian, that lived during the Paleocene to Middle Miocene in Europe. Some species may have reached lengths of , while others probably did ...

''. The causes of the faunal turnover have been attributed to a shift from humid and highly tropical environments to drier and more temperate forests with open areas and more abrasive vegetation. The surviving herbivorous faunas shifted their dentitions and dietary strategies accordingly to adapt to abrasive and seasonal vegetation. The environments were still subhumid and full of subtropical evergreen forests, however. The Palaeotheriidae was the sole remaining European perissodactyl group, and frugivorous-folivorous or purely folivorous artiodactyls became the dominant group in western Europe. The temporal range of ''Leptotheridium'' occurred up to MP17b, as evident by the appearances of ''L. aff. lugeoni'' in the French locality of Fons 4 (MP17a) and ''L. cf. lugeoni'' in another French locality of Perrière. In Perrière, its fossils were found with those of the

herpetotheriid Herpetotheriidae is an extinct family of metatherians, closely related to marsupials. Species of this family are generally reconstructed as terrestrial, and are considered morphologically similar to modern opossums. They are suggested to have bee ...

s ''

'' and ''

'', pseudorhyncocyonid '' Pseudorhyncocyon'',

apatemyid Apatemyidae is an extinct family of placental mammals that took part in the first placental evolutionary radiation together with other early mammals, such as the leptictids. Their relationships to other mammal groups are controversial; a 2010 st ...

Heterohyus ''Heterohyus'' is an extinct genus of apatemyid from the early to late Eocene. A small, tree-dwelling creature with elongated fore- and middle fingers, in these regards it somewhat resembled a modern-day aye-aye. Three skeletons have been found ...

'',

nyctitheriid Nyctitheriidae is a family of extinct eulipotyphlan insectivores known from the Paleocene and Eocene epochs of North America and Asia and persisting into the Oligocene of Europe. Several genera, including '' Nyctitherium'', '' Paradoxonycteris'', ...

'' Saturninia'', various bats, rodents (Gliridae, Theridomyidae),

s '' Pseudoloris'' and '' Microchoerus'', adapid ''Leptadapis'', hyaenodontid '' Hyenodon'', miacid '' Quercygale'', palaeotheres ('' Lophiotherium'', ''

'', and '' Plagiolophis''), dichobunid '' Mouillacitherium'', cebochoerid '' Acotherulum'', mixtothere ''Mixtotherium'', anoplotheriid ''Dacrytherium'', tapirulid '' Tapirulus'', xiphodonts '' Dichodon'' and ''

'', and the amphimerycid '' Pseudamphimeryx''.

Notes

References

{{Taxonbar, from=Q131808274 Prehistoric Artiodactyla genera Fossil taxa described in 1910 Paleogene mammals of Europe