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{{Short description|Extinct genus of endemic
{{good article}}
{{Automatic taxobox
| fossil_range = Late [[Eocene]] - early [[Oligocene]] {{fossil range|37|30}}
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}}
'''''Diplobune''''' ([[Ancient Greek]]: {{lang|grc|διπλοῦς}} (double) + {{lang|grc|βουνός}} (hill) meaning "double hill") is an extinct genus of [[Paleogene|Palaeogene]] [[artiodactyl]]s belonging to the
''Diplobune'' was an [[apomorphy and synapomorphy|evolutionarily derived]] medium to large-sized anoplotheriid with shared similarities to the [[sister taxon]] ''Anoplotherium''
Such unique traits along with hints of slow-walking locomotion
The evolutionary history of ''Diplobune'' is not complete, but it lived in western Europe back when it was an [[archipelago]] that was isolated from the rest of Eurasia, meaning that it lived in an environment with various other faunas that also evolved with strong levels of endemism. It, like ''Anoplotherium'', arose long after a shift towards drier but still subhumid conditions that led to abrasive plants and the extinctions of the large-sized [[Lophiodontidae]], becoming a regular component of late Eocene faunal communities. It survived through the [[Grande Coupure]] extinction event of western Europe in the earliest Oligocene but seemingly lost at least one species in the process. ''D. minor'' appeared in the early Oligocene as likely the last representative of the Anoplotheriidae, leaning towards specialization in forested, subhumid environments with freshwater bodies.
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=== Early History ===
[[File:Diplobune bavarica fossils.png|thumb|left|1877 illustrations of ''Diplobune bavarica'' fossil remains]]
In 1862, Swiss palaeontologist [[Ludwig Rütimeyer]] discussed his hypothesis that ''[[Anoplotherium]] secundarium'' was a [[transitional species]] to the genus ''[[Dichobune]]''. He noticed that the inner mounds of the [[molar (tooth)|molars]] of
However, the status of ''Diplobune'' as a subgenus of ''Dichobune'' did not last long. In 1870, German palaeontologist [[Oscar Fraas]] wrote about a mammal with numerous remains from the locality of [[Munich]], its molars being similar but not identical to ''A. commune'' in terms of typical species diagnoses. He noticed the bicuspid characteristic and assigned the fossil materials to ''Diplobune''. He also wrote that based on its dentition, ''Dichobune'' had no evolutionary relationship with the anoplotheriids, making ''Diplobune'' a distinct genus. Although Fraas was the sole author of his article, he credited his colleague [[Karl Alfred von Zittel]] for the name ''D. bavaricum'', which the specimens belonged to.<ref name="fraas">{{cite journal|last=von Fraas|first=Oscar Friedrich|year=1870|title=Diplobune bavaricum.|journal=Palaeontographica|volume=17|pages=177–184|url=https://www.biodiversitylibrary.org/item/44253#page/187/mode/1up}}</ref>
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=== Classification ===
[[File:Ruetimeyer Ludwig.jpg|right|thumb|Portrait of [[Ludwig Rütimeyer]], who originally erected the name ''Diplobune'' as a subgenus, which then was determined to be a distinct genus]]
''Diplobune'' belongs to the Anoplotheriidae, a [[Paleogene|Palaeogene]] artiodactyl family endemic to western Europe that lived from the middle Eocene to the early Oligocene (~44 to 30 Ma, possible earliest record at ~48 Ma). The type species of the genus is ''D. minor'', first described long after the genus name was first created. The exact evolutionary origins and dispersals of the anoplotheriids are uncertain, but they exclusively resided within the continent when it was an [[archipelago]] that was isolated by seaway barriers from other regions such as [[Balkanatolia]] and the rest of eastern Eurasia. The Anoplotheriidae's relations with other members of the Artiodactyla are not well-resolved, with some determining it to be either a [[tylopod]] (which includes [[camelid]]s and [[merycoidodont]]s of the
The Anoplotheriidae consists of two subfamilies, the [[Dacrytheriinae]] and [[Anoplotheriinae]], the latter of which is the younger subfamily that ''Diplobune'' belongs to. The Dacrytheriinae is the older subfamily of the two that first appeared in the middle Eocene (since the [[Mammal Paleogene zones|Mammal Palaeogene zones]] unit MP13, possibly up to MP10), although some authors consider them to be a separate family in the form of the Dacrytheriidae.<ref name="endemic">{{cite book|editor-last1=Prothero|editor-first1=Donald R.|editor-last2=Foss|editor-first2=Scott E.|last1=Erfurt|first1=Jörg|last2=Métais|first2=Grégoire|year=2007|title=The Evolution of Artiodactyls|publisher=Johns Hopkins University Press|chapter=Endemic European Paleogene Artiodactyls|pages=59–84}}</ref><ref>{{cite journal|last1=Orliac|first1=Maeva|last2=Gilissen|first2=Emmanuel|year=2012|title=Virtual endocranial cast of earliest Eocene Diacodexis (Artiodactyla, Mammalia) and morphological diversity of early artiodactyl brains|journal=Proceedings of the Royal Society B|volume=279|issue=1743|pages=3670–3677 |doi=10.1098/rspb.2012.1156|pmid=22764165 |pmc=3415922 }}</ref> Anoplotheriines made their first appearances by the late Eocene (MP15-MP16), or ~41-40 Ma, within western Europe with ''[[Duerotherium]]'' and ''[[Robiatherium]]''. By MP17a-MP17b, however, there is a notable gap in the fossil record of anoplotheriines overall as the former two genera seemingly made their last appearances by the previous MP level MP16.<ref name="duerotherium">{{cite journal|last1=Cuesta|first1=Miguel-Ángel|last2=Badiola|first2=Ainara|year=2009|title=Duerotherium sudrei gen. et sp. nov., a New Anoplotheriine Artiodactyl from the Middle Eocene of the Iberian Peninsula|journal=Journal of Vertebrate Paleontology|volume=29|number=1|pages=303–308|doi=10.1671/039.029.0110|jstor=20491092 |bibcode=2009JVPal..29..303C |s2cid=55546022 |url=https://www.jstor.org/stable/20491092}}</ref>
By MP18, ''Anoplotherium'' and ''Diplobune'' made their first appearances in western Europe, but their exact origins are unknown. The two genera were widespread throughout western Europe based on abundant fossil evidence spanning from Portugal, Spain, United Kingdom, France, Germany, and Switzerland for much of pre-Grande Coupure Europe (prior to MP21), meaning that they were typical elements of the late Eocene up until the earliest Oligocene. The earlier anoplotheriines are considered to be smaller species whereas the later anoplotheriines were larger. Not all species of ''Diplobune'' were medium to large-sized however, as at least ''D. minor'' is known for having small weight estimates.<ref>{{cite book|last1=Schmidt-Kittler|first1=Norbert|last2=Godinot|first2=Marc|last3=Franzen|first3=Jens L.|last4=Hooker|first4=Jeremy J.|year=1987|chapter=European reference levels and correlation tables|title=Münchner geowissenschaftliche Abhandlungen A10|publisher=Pfeil Verlag, München|pages=13–31|url=https://www.researchgate.net/publication/234056546}}</ref><ref name="duerotherium"/><ref name="iberian"/> ''Anoplotherium'' and ''Diplobune'' are considered the most [[apomorphy and synapomorphy|derived]] (or evolutionarily recent) anoplotheriids based on dental morphology and achieved gigantism amongst non-[[Whippomorpha|whippomorph]] artiodactyls, making them some of the largest non-whippomorph artiodactyls of the
Conducting studies focused on the phylogenetic relations within the Anoplotheriidae has proven difficult due to the general scarcity of fossil specimens of most genera.<ref name="duerotherium"/> The phylogenetic relations of the Anoplotheriidae as well as the [[Xiphodontidae]], [[Mixtotheriidae]], and [[Cainotheriidae]] have also been elusive due to the [[selenodont]] morphologies (or having crescent-shaped ridges) of the molars, which were convergent with
In an article published in 2019, Romain Weppe et al. conducted a phylogenetic analysis on the [[Cainotherioidea]] within the Artiodactyla based on mandibular and dental characteristics, specifically in terms of relationships with artiodactyls of the
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|2=''[[Plesiomeryx|Plesiomeryx huerzeleri]]''}}}}}}}}}}}}}}}}}}}}}}
In 2022, Weppe created a phylogenetic analysis in his academic [[thesis]] regarding
== Description ==
=== Skull ===
[[File:
Skull materials of ''Diplobune'' are well known for multiple species, including one of ''D. minor'' uncovered between 1972 and 1975 in the [[Quercy]] locality of Itardies and one of ''D. secundaria'' that was uncovered in [[Saint-Capraise-d'Eymet]] (France) in 2000
|first2=Jean-Jacques|year=2013|title=Un crâne de Diplobune secundaria Cuvier, 1822 de Saint-Capraise-d'Eymet (Dordogne)|language=french|journal=Symbioses|volume=29|pages=43–46|url=https://www.researchgate.net/publication/279186555}}</ref> ''Diplobune'' differs from other anoplotheriids by the mandible increasing in height on the back side, its high articulation (or connection) with the cranium, its transverse elongation without any obliqueness, and its [[coronoid process of the mandible|coronoid process]] (projection) being wide to moderately wide plus curved backwards.<ref name="endemic"/><ref name="iberian"/> Many cranial traits observed in ''Anoplotherium'' are also found in its close relative ''Diplobune'', such as the glenoid (or hollow) surface being high in relation to the [[base of skull]] unlike ''Dacrytherium'', a narrow [[occipital bone|occiput]] (back of the skull) that is enhanced just above the [[occipital condyles]], and two small [[occipital bun]]s for muscle attachment.<ref name="skulls">{{cite journal|last1=Pearson|first1=Helga Sharpe|year=1927|title=On the Skulls of Early Tertiary Suidae, together with an Account of the Otic Region in Some Other Primitive Artiodactyla|journal=Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character|volume=215|issue=421–430 |pages=440–445|doi=10.1098/rstb.1927.0009|doi-access=free}}</ref> The upper
The mandibles of ''Diplobune'' reveal that its body's height increases towards the rear area, and the [[angle of the mandible]] is prominent. The [[mandibular condyle]] has a high position while the mandible's coronoid process has a low position. These traits are more pronounced compared to most other Paleogene ungulates, although they are not as clearly pronounced in ''D. minor''.<ref name="interpretation"/><ref name="itardies"/>▼
In 1927, Helga Sharpe Pearson reviewed cranial features of ''Diplobune'' based on a ''D. bavarica'' skull from the Phosphorites of [[Escamps, Lot|Escamps]], France and a ''D.'' sp. skull from [[Ulm]], Germany (the latter skull is larger). The hind area of the [[basilar part of occipital bone]] (basioccipital area) is convex. The position of the [[condylar canal]] and muscle arrangements of the basioccipital area of ''Diplobune'' are different from ''Anoplotherium'' and ''Dacrytherium''. The postglenoid process is bulky and projects down compared to the two anoplotheriid genera. The two skulls are similar to those of ''Anoplotherium'' by the thickened neck of the [[eardrum]] that projects vertically downwards below the opening area of the [[ear canal]]. The [[stylomastoid foramen]] is small while the [[hyaloid fossa]] is large.<ref name="skulls"/>
▲Jean Sudre also described ''D. minor'' based on known cranial materials in 1982, pointing out that ''D. minor'' was the smallest-known species and was also known from a crushed skull from [[Calaf]], Spain with various skeletal remains associated with it. The skull from Itardies measures about {{cvt|20|cm}} long and features traits typical of anoplotheriines, such as an elongated snout with parallel lateral walls in the front area, the upper area of the [[premaxilla]] extending backwards, low orbits of the eyes, strong [[post-orbital constriction]], [[infraorbital foramen]] being located directly above the P<sup>4</sup>, low [[zygomatic arch]]es that take upward bladelike, curved forms at the rear, broad and flat glenoid surface, and strong nuchal crests. The retroarticular process of the [[temporal bone]], however, is less developed compared to that of the skull of ''D. bavarica'' that was described by Pearson in 1927. In ''D. minor'', the post-tympanic process, which limits the hind area of the ear canal, is more elongated compared to the other preceding species of ''Diplobune'' or any anoplotheriine. The occipital condyles are prominent and elongated but are less developed compared to ''A. commune''.<ref name="interpretation"/>
▲The mandibles of ''Diplobune'' reveal that its body's height increases towards the rear area, and the [[angle of the mandible]] is prominent. The [[mandibular condyle]], at the back of the mandible, has a high position while the mandible's coronoid process has a low position. These traits are more pronounced compared to most other
=== Endocast anatomy ===
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In terms of the [[bony labyrinth]] (outer wall of the bony ear), the [[cochlea]], a cavity involved in hearing, composes 50% of the total volume of the bony labyrinth. ''D. minor'' has a cochlea shape index (or aspect ratio) between 0.62 and 0.72, meaning that its cochlea is pointed instead of flattened in shape.<ref name="petrosal"/><ref>{{cite journal|last=Ekdale|first=Eric G.|editor-last=Soares|editor-first=Daphne|year=2013|title=Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals|journal=PLOS ONE|volume=8|issue=6|pages=e66624 |doi=10.1371/journal.pone.0066624 |pmid=23805251 |pmc=3689836 |bibcode=2013PLoSO...866624E |doi-access=free }}</ref> The length of the cochlea of ''D. minor'' based on multiple specimens vary, measuring from {{cvt|18.1|mm}} to {{cvt|19.7|mm}} (8% variation).<ref name="petrosal"/>
The ''D. minor'' specimen UM ITD 1083 has an [[interaural time difference|estimated interaural distance]] of {{cvt|96|mm}}, translating to a function interaural delay before arrival to the ear of 277
==== Brain ====
[[File:Diplobune cranial cast.jpg|thumb|Endocranial cast of ''Diplobune'', Stuttgart State Museum of Natural History]]
In 1928, palaeoneurologist [[Tilly Edinger]] wrote about multiple endocasts of ''D. bavarica'' from their skulls from the collection of the [[State Museum of Natural History Stuttgart]], one complete but most others partial.
In 1969, Colette Dechaseaux conducted an extensive study on known
Despite the
The widths of the cerebral hemispheres of ''Diplobune'' are further back compared to ''Anoplotherium''. The upper surface of the cerebral hemispheres of ''Diplobune'' is flatter, and the neocortex lowering forward from the approximate back third of its length so that the latter can connect with the base of the [[olfactory peduncle]]. In comparison, the same cerebral hemispheres surface of ''Anoplotherium'' is convex, and the neocortex to some extent maintains thickness. The
=== Dentition ===
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| footer = ''D. secundaria'' mandible from the [[Natural History Museum of Basel]] (left) and ''D. quercyi'' teeth from the palaeontological collection of the [[University of Tübingen]] (right)
}}
The [[dental formula]] of ''Diplobune'' and other anoplotheriids is {{DentalFormula|upper=3.1.4.3|lower=3.1.4.3}} for a total of 44 teeth, consistent with the primitive dental formula for early-middle
''Diplobune'' is very similar in dentition to the similarly derived ''Anoplotherium'' but differs primarily by the generally smaller sizes and its two
=== Vertebrae ===
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The [[scapula]] (or shoulder blade) is triangular, asymmetrical, and wide, its low scapular index value of 118 potentially implying both a broad [[thorax]] and support for [[lateral movement|lateralized movements]]. The [[glenoid fossa]] has a circular shape and is approximately perpendicular to the body of the scapula.<ref name="interpretation"/>
The low surface of the [[radius (bone)|radius]] of ''D. minor'' reveals two articular [[facet joint]]s for the [[lunate bone]] and [[scaphoid bone]], both of which are separated by a transverse ridge. The arrangements of the bones are similar to those of ''Anoplotherium'' (with less concave articular facets, however) and the [[Suidae]]. The [[ulna]], independent of the radius, has a compressed and stretched lower end, of which ''Anoplotherium'' differs from ''Diplobune'' by the same end being more quadrangular in outline. The [[carpal bone]] arrangements of ''Diplobune'' within the front limbs are the lunate bone, scaphoid bone, and [[triquetral bone]] in the first row (or bottom row) and the [[hamate bone]] (or uncinate bone), [[capitate bone]], and [[trapezoid bone]] in the second row.<ref name="leg"/><ref name="karl"/>
The shape of the lunate bone is similar to those of both ''Anoplotherium'' and the Merycoidodontidae of North America, its
In the 2nd row of the carpus, the trapezoid, capitate, and hamate correspond with [[metacarpal]] fingers II, III, and IV, respectively. The trapezoid has an initially flat and strongly concave facet that articulates with the scaphoid and a curved facet that articulates with the capitate. The external area of the trapezoid also has a small articular facet that corresponds to the [[trapezius]] surface muscles that indicate a remnant of a "first" finger that is absent by development. The upper face of the capitate is divided by a crest into the smaller portion with a facet for the lunate that articulates at a nearly vertical and straight outline and the larger portion which has a facet for the scaphoid that articulates in an inclined and slightly concave outline. The hamate, which corresponds with the 4th metacarpal, has a small facet for the third. The general arrangements of the carpus of ''Diplobune'' are the same as ''Anoplotherium''.<ref name="leg"/> However, the digit II of ''Diplobune'' compared to ''Anoplotherium'' is more mobile because of the more extensive articular surface of the former's trapezoid with the corresponding scaphoid.<ref name="thumb"/>
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Sudre also described hind limb remains attributed to ''D. minor''. The femur of ''D. minor'' is characterized by its [[lesser trochanter]] being close to the spheroidal [[femoral head]], the distance separating them being equivalent to 1/4 of the bone's length as opposed to 1/3 for ''A. commune'' and ''D. secundaria''. The morphology of the [[fibula]] is typical of those of early ungulates and has a facet on the proximal side for articulation with the [[tibia]]. The tibia shows strong backward inclination of the proximal articular surfaces, which indicates a flexed position of the knee. The tibial crest ridge reaches the mid-length area of the [[diaphysis]] of the tibia, similar to ''Anoplotherium''.<ref name="interpretation"/>
The [[calcaneum]] of ''Diplobune'' and other anoplotheriids is robust and short
The [[Astragalus (bone)|astragalus]] (or ankle bone) of ''D. minor'' is both wide and long but is shorter than that attributed tentatively to ''D. bavarica?'' by Schlosser in 1883. The two lips of the proximal trochlea are asymmetrical due to the greater height of the outer lip compared to the inner lip. The lips of the distal trochlea are symmetrical in comparison. The sustentacular facet is bordered in the center by a prominent wrinkle, also present in [[Suina]] and basal ruminants but absent in later ruminants. The planar shape of the sustentacular facet might suggests a morphology in between ruminants and suines for a type of lateral mobility of the calcaneus in the area.<ref name="interpretation"/>
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=== Size ===
[[File:Diplobune size comparison chart.png|thumb|Estimated size comparisons of ''D. minor'' and ''D. secundaria'' based on known fossil remains]]
The weight estimates of ''D. bavarica'' and ''D. quercyi'' have not been offered in any recent study on ''Diplobune'', while ''D. minor'' has been subjected to a few weight estimate studies. ''D. minor'' has long been suggested to have been the smallest species of its genus since at least 1982.<ref name="interpretation"/> This has been proven in 1995 when Jean-Noël Martinez and Sudre made weight estimates of
In 2014, Takehisa Tsubamoto reexamined the relationship between astragalus size and estimated body mass based on extensive studies of extant terrestrial mammals, reapplying the methods to
|s2cid=54686160 |doi-access=free}}</ref>
[[File:Body Mass Estimates European Paleogene Artiodactyls.jpg|thumb|center|Estimated body masses (kg) of
Maeva J. Orliac et al. suggested in 2017 that the mean body mass of ''D. minor'' based on five astragali from Itardies that belong to the species is {{cvt|19.9|kg}}. Based on a slightly deformed but complete cranium specimen UM ITD 43, which measures {{cvt|16.5|cm}}, the estimated body mass is {{cvt|18.9|kg}}. The mean of the two body mass estimates is {{cvt|19.4|kg}}.<ref name="petrosal"/> In 2022, Weppe determined based on a body mass formula that ''D. secundaria'', while not as massive as ''A. commune'' in weight, was a large herbivore that weighed approximately {{cvt|130|kg}}.<ref name="thesis"/>
Cyril Gagnaison and Jean-Jacques Leroux suggested that based on the ''D. secundaria'' skull from Saint-Capraise-d'Eymet, the size of the individual would have been approximately {{cvt|2|m}} in length and {{cvt|1.2|m}} in height up to the [[withers]] (or the ridge of the shoulder blade).<ref name="secundaria"/>
== Palaeobiology ==
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== Palaeoecology ==
{{further|Mammal
=== Early Pre-Grande Coupure Europe ===
[[File:Middle Eocene Paleogeography Tethys Dispersals.jpg|thumb|left|[[Palaeogeography]] of Europe and Asia during the middle Eocene with possible artiodactyl and perissodactyl dispersal routes.]]
For much of the Eocene, a hothouse climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the Perissodactyla, Artiodactyla, and [[Primates]] (or the suborder Euprimates) appeared already by the early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The [[omnivorous]] forms mostly either switched to folivorous diets or went extinct by the middle Eocene (47 - 37 Ma) along with the archaic "[[condylarths]]." By the late Eocene (approx. 37 - 33 Ma), most of the ungulate form dentitions shifted from bunodont cusps to cutting ridges (i.e. lophs) for folivorous diets.<ref name="evolution">{{cite journal|last1=Eronen|first1=Jussi T.|last2=Janis|first2=Christine M.|last3=Chamberlain|first3=Charles Page|last4=Mulch|first4=Andreas|year=2015|title=Mountain uplift explains differences in Palaeogene patterns of mammalian evolution and extinction between North America and Europe|journal=Proceedings of the Royal Society B|volume=282|number=1809|doi=10.1098/rspb.2015.0136|pmid=26041349 |pmc=4590438 }}</ref><ref name="chiroptera">{{cite journal|last=Maitre|first=Elodie|year=2014|title=Western European middle Eocene to early Oligocene Chiroptera: systematics, phylogeny and palaeoecology based on new material from the Quercy (France)|journal=Swiss Journal of Palaeontology|volume=133|issue=2 |pages=141–242|doi=10.1007/s13358-014-0069-3|s2cid=84066785 |doi-access=free}}</ref>
Land-based connections to the north of the developing Atlantic Ocean were interrupted around 53 Ma, meaning that North America and Greenland were no longer well-connected to western Europe. From the early Eocene up until the Grande Coupure extinction event (56 Ma - 33.9 Ma), the western Eurasian continent was separated into three landmasses, the former two of which were isolated by seaways: western Europe (an archipelago), Balkanatolia, and eastern Eurasia (Balkanatolia was in between the [[Paratethys Sea]] of the north and the [[Neotethys Ocean]] of the south).<ref name="balkanatolia"/> The [[Holarctic]] mammalian faunas of western Europe were therefore mostly isolated from other continents including Greenland, Africa, and eastern Eurasia, allowing for endemism to occur within western Europe.<ref name="chiroptera"/> The European mammals of the late Eocene (MP17 - MP20) were mostly descendants of endemic middle Eocene groups as a result.<ref name="equoids">{{cite journal|last1=Badiola|first1=Ainara|last2=Perales-Gogenola|first2=Leire|last3=Astibia|first3=Humberto|last4=Suberbiola|first4=Xabier Pereda|year=2022|title=A synthesis of Eocene equoids (Perissodactyla, Mammalia) from the Iberian Peninsula: new signs of endemism|journal=Historical Biology|volume=34|issue=8|pages=1623–1631|doi=10.1080/08912963.2022.2060098|s2cid=248164842 }}</ref>
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The appearances of derived anoplotheriines by MP18 occurred long after the extinction of the endemic European perissodactyl family [[Lophiodontidae]] in MP16, including the largest lophiodont ''[[Lophiodon]] lautricense'', which weighed over {{cvt|2000|kg}}. The extinction of the Lophiodontidae was part of a faunal turnover, which likely was the result of 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.<ref>{{cite journal|last1=Robinet|first1=Céline|last2=Remy|first2=Jean Albert|last3=Laurent|first3=Yves|last4=Danilo|first4=Laure|last5=Lihoreau|first5=Fabrice|year=2015|title=A new genus of Lophiodontidae (Perissodactyla, Mammalia) from the early Eocene of La Borie (Southern France) and the origin of the genus Lophiodon Cuvier, 1822|journal=Geobios|volume=48|issue=1|pages=25–38|doi=10.1016/j.geobios.2014.11.003|bibcode=2015Geobi..48...25R }}</ref><ref>{{cite journal|last1=Perales-Gogenola|first1=Leire|last2=Badiola|first2=Ainara|last3=Gómez-Olivencia|first3=Asier|last4=Pereda-Suberbiola|first4=Xabier|year=2022|title=A remarkable new paleotheriid (Mammalia) in the endemic Iberian Eocene perissodactyl fauna|journal=Journal of Vertebrate Paleontology|volume=42|issue=4|doi=10.1080/02724634.2023.2189447|bibcode=2022JVPal..42E9447P |s2cid=258663753 }}</ref> 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.<ref name="Evolution of European carnivorous mammal assemblages">{{cite journal|last1=Solé|first1=Floréal|last2=Fischer|first2=Valentin|last3=Le Verger|first3=Kévin|last4=Mennecart|first4=Bastien|last5=Speijer|first5=Robert P.|last6=Peigné|first6=Stéphane|last7=Smith|first7=Thierry|year=2022|title=Evolution of European carnivorous mammal assemblages through the Paleogene|journal=Biological Journal of the Linnean Society|volume=135|issue=4|pages=734–753|doi=10.1093/biolinnean/blac002}}</ref><ref name="ungulates">{{cite journal|last=Blondel|first=Cécile|year=2001|title=The Eocene-Oligocene ungulates from Western Europe and their environment|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=168|issue=1–2 |pages=125–139|doi=10.1016/S0031-0182(00)00252-2|bibcode=2001PPP...168..125B |url=http://doc.rero.ch/record/20314/files/PAL_E4294.pdf }}</ref> MP16 also marked the last appearances of most European [[crocodylomorphs]], of which the [[Alligatoroidea|aligatoroid]] ''[[Diplocynodon]]'' was the only survivor due to seemingly adapting to the general decline of tropical climates of the late Eocene.<ref>{{cite journal|last1=Martin|first1=Jeremy E.|last2=Pochat-Cottilloux|first2=Yohan |last3=Laurent|first3=Yves|last4=Perrier|first4=Vincent|last5=Robert|first5=Emmanuel|last6=Antoine|first6=Pierre-Olivier|year=2022|title=Anatomy and phylogeny of an exceptionally large sebecid (Crocodylomorpha) from the middle Eocene of southern France|journal=Journal of Vertebrate Paleontology|volume=42|issue=4|doi=10.1080/02724634.2023.2193828|bibcode=2022JVPal..42E3828M |s2cid=258361595 }}</ref><ref>{{cite journal|last=Martin|first=Jeremy E.|year=2015|title=A sebecosuchian in a middle Eocene karst with comments on the dorsal shield in Crocodylomorpha|journal=Acta Palaeontologica Polonica|volume=60|issue=3|pages=673–680|doi=10.4202/app.00072.2014|s2cid=54002673 |doi-access=free}}</ref><ref>{{cite journal|last=Antunes|first=Miguel Telles|year=2003|title=Lower Paleogene Crocodilians from Silveirinha, Portugal|journal=Palaeovenebrata|pages=1–26|volume=32|url=https://palaeovertebrata.com/articles/keyword/476}}</ref>
Unfortunately, the temporal ranges of two ''Diplobune'' species ''D. bavarica'' and ''D. quercyi'' are uncertain, as they are not currently recognized in the Mammal
=== Late Eocene ===
Line 258 ⟶ 256:
After a considerable gap in anoplotheriine fossils in MP17a and MP17b, the derived anoplotheriines ''Anoplotherium'' and ''Diplobune'' made their first known appearances in the MP18 unit.<ref name="duerotherium"/> They were exclusive to the western European archipelago, but their exact origins and dispersal routes are unknown. By then, ''Anoplotherium'' and ''Diplobune'' lived in Central Europe (then an island) and the Iberian Peninsula, only the former genus of which later dispersed into southern England by MP19 due to the apparent lack of ocean barriers.<ref name="iberian"/><ref name="bipedal"/>
''Diplobune'' coexisted with a wide diversity of artiodactyls in western Europe by MP18, ranging from the more widespread [[Dichobunidae]], [[Tapirulidae]], and [[Anthracotheriidae]] to many other endemic families consisting of the Xiphodontidae, [[Choeropotamidae]] (recently determined to be polyphyletic, however), [[Cebochoeridae]], [[Amphimerycidae]], and Cainotheriidae.<ref name="endemic"/><ref name="Revision of the Eocene artiodactyls"/><ref>{{cite journal|last1=Bai|first1=Bin|last2=Wang|first2=Yuan-Qing|last3=Theodor|first3=Jessica M.|last4=Meng|first4=Jin|year=2023|title=Small artiodactyls with tapir-like teeth from the middle Eocene of the Erlian Basin, Inner Mongolia, China|journal=Frontiers in Earth Science|volume=11|pages=1–20|doi=10.3389/feart.2023.1117911 |bibcode=2023FrEaS..1117911B |doi-access=free }}</ref><ref>{{cite journal|last1=Kostopoulos|first1=Dimitris S.|last2=Koufos|first2=George D.|last3=Christanis|first3=Kimon|year=2012|title=On some anthracotheriid (Artiodactyla, Mammalia) remains from northern Greece: comments on the palaeozoogeography and phylogeny of Elomeryx|journal=Swiss Journal of Palaeontology|volume=131|issue=2 |pages=303–315|doi=10.1007/s13358-012-0041-z|s2cid=195363034}}</ref> ''Diplobune'' also coexisted with palaeotheriids, including those endemic to the Iberian Peninsula until MP19 when they were replaced by typical palaeothere genera.<ref name="equoids"/> Late Eocene European groups of the clade [[Ferae]] represented predominantly the [[Hyaenodonta]] ([[Hyaenodontinae]], [[Hyainailourinae]], and [[Proviverrinae]]) but also contained [[Carnivoramorpha]] ([[Miacidae]]) and [[Carnivora]] (small-sized [[Amphicyonidae]]).<ref name="Evolution of European carnivorous mammal assemblages"/> Other mammal groups present in the late Eocene of western Europe represented the [[leptictida]]ns ([[Pseudorhyncocyonidae]]),<ref>{{cite journal|last=Hooker|first=Jerry J.|year=2013|title=Origin and evolution of the Pseudorhyncocyonidae, a European Paleogene family of insectivorous placental mammals|journal=Palaeontology|volume=56|issue=4|pages=807–835|doi=10.1111/pala.12018|bibcode=2013Palgy..56..807H |s2cid=84322086 |doi-access=free}}</ref> primates ([[Adapoidea]] and [[Omomyoidea]]),<ref>{{cite journal|last1=Marigó|first1=Judit|last2=Susanna|first2=Ivette|last3=Minwer-Barakat|first3=Raef|last4=Malapeira|first4=Joan Madurell|last5=Moyà-Solà|first5=Salvador|last6=Casanovas-Vilar|first6=Isaac|last7=Gimenez|first7=Jose Maria Robles|last8=Alba|first8=David M.|year=2014|title=The primate fossil record in the Iberian Peninsula|journal=Journal of Iberian Geology|volume=40|issue=1|pages=179–211|doi=10.5209/rev_JIGE.2014.v40.n1.44094|doi-access=free}}</ref> [[eulipotyphla]]ns ([[Nyctitheriidae]]),<ref>{{cite journal|last1=Manz|first1=Carly|last2=Bloch|first2=Jonathan Ivan|year=2014|title=Systematics and Phylogeny of Paleocene-Eocene Nyctitheriidae (Mammalia, Eulipotyphla?) with Description of a new Species from the Late Paleocene of the Clarks Fork Basin, Wyoming, USA|journal=Journal of Mammalian Evolution|volume=22|issue=3 |pages=307–342|doi=10.1007/s10914-014-9284-3|s2cid=254704409 }}</ref> [[chiroptera]]ns,<ref name="chiroptera"/> [[Herpetotheriidae|herpetotheriid]]s,<ref>{{cite journal|last1=Badiola|first1=Ainara|last2=Cuesta|first2=Miguel-Ángel|year=2006|title=Los marsupiales del yacimiento del Eoceno Superior de Zambrana (Álava, Región Vasco-Cantábrica)|journal=Estudios Geológicos|language=spanish|volume=62|issue=1|pages=349–358|doi=10.3989/egeol.0662130|doi-access=free}}</ref> [[apatotheria]]ns,<ref>{{cite journal|last=Sigé|first=Bernard|year=1997|title=Les mammiféres insectivoresdes nouvelles collections de Sossís et sites associes (Éocène supérieur, Espagne)|journal=Geobios|volume=30|issue=1|pages=91–113|doi=10.1016/S0016-6995(97)80260-4}}</ref> and endemic [[rodent]]s ([[Pseudosciuridae]], [[Theridomyidae]], and [[Gliridae]]).<ref>{{cite book|last=Dawson|first=Mary R.|year=2003|chapter=Paleogene rodents of Eurasia|title=Distribution and migration of tertiary mammals in Eurasia.|volume=10|pages=97–127}}</ref> The alligatoroid ''Diplocynodon'', present only in Europe since the upper Paleocene, coexisted with pre-Grande Coupure faunas as well, likely consuming insects, fish, frogs, and eggs due to prey partitioning previously with other crocodylomorphs that had since died out by the late Eocene.<ref>{{cite journal|last1=Hastings|first1=Alexander K.|last2=Hellmund|first2=Meinolf|year=2016|title=Evidence for prey preference partitioning in the middle Eocene high-diversity crocodylian assemblage of the Geiseltal-Fossillagerstätte, Germany utilizing skull shape analysis|journal=Geological Magazine|volume=154|issue=1|pages=1–28|doi=10.1017/S0016756815001041|s2cid=131651321 }}</ref><ref>{{cite journal|last1=Chroust|first1=Milan|last2=Mazuch|first2=Martin|last3=Luján|first3=Àngel Hernández|year=2019|title=New crocodilian material from the Eocene-Oligocene transition of the NW Bohemia (Czech Republic): an updated fossil record in Central Europe during the Grande Coupure|journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|volume=293|issue=1|pages=73–82|doi=10.1127/njgpa/2019/0832|s2cid=199104151 }}</ref> In addition to snakes, frogs, and [[Salamandridae|salamandrids]], rich assemblage of lizards are known in western Europe as well from MP16-MP20, representing the [[Iguanidae]], [[Lacertidae]], [[Gekkonidae]], [[Agamidae]], [[Scincidae]], [[Helodermatidae]], and [[Varanoidea]], most of which were able to thrive in the warm temperatures of western Europe.<ref name="reptiles">{{cite journal|last=Rage|first=Jean-Claude|year=2012|title=Amphibians and squamates in the Eocene of Europe: what do they tell us?|journal=Palaeobiodiversity and Palaeoenvironments|volume=92|issue=4 |pages=445–457|doi=10.1007/s12549-012-0087-3|s2cid=128651937 }}</ref>
The MP18 locality of La Débruge of France indicates that ''D. secundaria'' with a wide variety of mammals, namely the [[herpetotheriid]] ''[[Peratherium]]'', rodents (''[[Blainvillimys]]'', ''[[Theridomys]]'', ''[[Plesiarctomys]]'', ''[[Glamys]]''), hyaenodonts (''[[Hyaenodon]]'' and ''[[Pterodon (mammal)|Pterodon]]''), amphicyonid ''[[Cynodictis]]'', palaeotheres (''Plagiolophus'', ''[[Anchilophus]]'', ''Palaeotherium''), dichobunid Dichobune, choeropotamid ''[[Choeropotamus]]'', cebochoerids ''[[Cebochoerus]]'' and ''[[Acotherulum]]'', anoplotheriids ''Dacrytherium'' and ''Anoplotherium'', tapirulid ''[[Tapirulus]]'', xiphodonts ''[[Xiphodon]]'' and ''[[Dichodon (mammal)|Dichodon]]'', cainothere ''[[Oxacron]]'', amphimerycid ''[[Amphimeryx]]'', and anthracothere ''[[Elomeryx]]''. The MP19 locality of Escamps has similar faunas but also includes the herpetotheriid ''[[Amphiperatherium]]'', pseudorhyncocyonid ''[[Pseudorhyncocyon]]'', bats (''[[Hipposideros]]'', ''[[Vaylatsia]]'', ''[[Vespertiliavus]]'', ''[[Stehlinia]]''), primates (''[[Microchoerus]]'', ''[[Palaeolemur]]''), cainothere ''[[Paroxacron]]'', and xiphodont ''[[Haplomeryx]]''.<ref name="MP"/>
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=== Grande Coupure ===
[[File:Anthracotherium magnum.jpg|thumb|Restoration of ''[[Anthracotherium]] magnum'', an anthracothere genus that arrived in western by the Grande Coupure]]
The [[Grande Coupure]] event of western Europe is well-recognized in the palaeontological record as one of the largest extinction and faunal turnover events in the Cenozoic era.<ref>{{cite journal|last1=Sun|first1=Jimin|last2=Ni|first2=Xijun|last3=Bi|first3=Shundong|last4=Wu|first4=Wenyu|last5=Ye|first5=Jie|last6=Meng|first6=Jin|last7=Windley|first7=Brian F.|year=2014|title=Synchronous turnover of flora, fauna, and climate at the Eocene-Oligocene Boundary in Asia|journal=Scientific Reports|volume=4|number=7463|page=7463 |doi=10.1038/srep07463|pmid=25501388 |pmc=4264005 |bibcode=2014NatSR...4E7463S }}</ref> The event is coincident with [[climate forcing]] events of cooler and more seasonal climates, the result being a 60% extinction rate of western European mammalian lineages while Asian faunal immigrants replaced them.<ref name="hampshire">{{cite journal|last1=Hooker|first1=Jerry J.|last2=Collinson|first2=Margaret E.|last3=Sille|first3=Nicholas P.|year=2004|title=Eocene–Oligocene mammalian faunal turnover in the Hampshire Basin, UK: calibration to the global time scale and the major cooling event|journal=Journal of the Geological Society|volume=161|issue=2|pages=161–172|doi=10.1144/0016-764903-091|bibcode=2004JGSoc.161..161H |s2cid=140576090 |url=http://doc.rero.ch/record/13418/files/PAL_E228.pdf }}</ref><ref>{{cite journal|last1=Legendre|first1=Serge|last2=Mourer-Chauviré|first2=Cécile|last3=Hugueney|first3=Marguerite|last4=Maitre|first4=Elodie|last5=Sigé|first5=Bernard|last6=Escarguel|first6=Gilles|year=2006|title=Dynamique de la diversité des mammifères et des oiseaux paléogènes du Massif Central (Quercy et Limagnes, France)|journal=STRATA|language=french|series=1|volume=13|pages=275–282|url=https://www.researchgate.net/publication/232607296}}</ref><ref name="unearth">{{cite journal|last1=Escarguel|first1=Gilles|last2=Legendre|first2=Serge|last3=Sigé|first3=Bernard|year=2008|title=Unearthing deep-time biodiversity changes: The Palaeogene mammalian metacommunity of the Quercy and Limagne area (Massif Central, France)|journal=Comptes Rendus Geoscience|volume=340|issue=9–10|pages=602–614|doi=10.1016/j.crte.2007.11.005|bibcode=2008CRGeo.340..602E |url=https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.1016/j.crte.2007.11.005/ }}</ref> The Grande Coupure is often marked by palaeontologists as part of the Eocene-Oligocene boundary as a result at 33.9 Ma, although some estimate that the event began 33.6-33.4 Ma.<ref name="age">{{cite journal|last1=Costa|first1=Elisenda|last2=Garcés|first2=Miguel|last3=Sáez|first3=Alberto|last4=Cabrera|first4=Lluís|last5=López-Blanco|first5=Miguel|year=2011|title=The age of the "Grande Coupure" mammal turnover: New constraints from the Eocene–Oligocene record of the Eastern Ebro Basin (NE Spain)|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=301|issue=1–4|pages=97–107|doi=10.1016/j.palaeo.2011.01.005|bibcode=2011PPP...301...97C |hdl=2445/34510 |hdl-access=free}}</ref><ref>{{cite journal|last1=Hutchinson|first1=David K.|last2=Coxall|first2=Helen K.|last3=Lunt|first3=Daniel J.|last4=Steinthorsdottir|first4=Margret|last5=De Boer|first5=Agatha M.|last6=Baatsen|first6=Michiel L.J.|last7=Von der Heydt|first7=Anna S.|last8=Huber|first8=Matthew|last9=Kennedy-Asser|first9=Alan T.|last10=Kunzmann|first10=Lutz|last11=Ladant|first11=Jean-Baptiste|last12=Lear|first12=Caroline|last13=Moraweck|first13=Karolin|last14=Pearson|first14=Paul|last15=Piga|first15=Emanuela|last16=Pound|first16=Matthew J.|last17=Salzmann|first17=Ulrich|last18=Scher|first18=Howie D.|last19=Sijp|first19=Willem P.|last20=Śliwińska|first20=Kasia K|last21=Wilson|first21=Paul A.|last22=Zhang|first22=Zhongshi|year=2021|title=The Eocene-Oligocene transition: A review of marine and terrestrial proxy data, models and model-data comparisons|journal=Climate of the Past|volume=17|issue=1|pages=269–315|doi=10.5194/cp-17-269-2021|bibcode=2021CliPa..17..269H |s2cid=234099337 |doi-access=free }}</ref> The event correlates directly with or after the [[Eocene-Oligocene extinction event|Eocene-Oligocene transition]], an abrupt shift from a greenhouse world characterizing much of the Paleogene to a coolhouse/icehouse world of the early Oligocene onwards. The massive drop in temperatures stems from the first major expansion of the Antarctic [[ice sheets]] that caused drastic [[pCO2|pCO<sub>2</sub>]] decreases and an estimated drop of ~{{cvt|70|m}} in sea level.<ref>{{cite journal|last1=Toumoulin|first1=Agathe|last2=Tardif|first2=Delphine|last3=Donnadieu|first3=Yannick|last4=Licht|first4=Alexis|last5=Ladant|first5=Jean-Baptiste|last6=Kunzmann|first6=Lutz|last7=Dupont-Nivet|first7=Guillaume|year=2022|title=Evolution of continental temperature seasonality from the Eocene greenhouse to the Oligocene icehouse –a model–data comparison|journal=Climate of the Past|volume=18|issue=2|pages=341–362|doi=10.5194/cp-18-341-2022|bibcode=2022CliPa..18..341T |doi-access=free }}</ref>
The seaway dynamics separating western Europe from other landmasses to strong extents but allowing for some levels of dispersals prior to the Grande Coupure are complicated and contentious, but many palaeontologists agreed that glaciation and the resulting drops in sea level played major roles in the drying of the seaways previously acting as major barriers to eastern migrants from Balkanatolia and western Europe. The [[Turgai Strait]] is often proposed as the main European seaway barrier prior to the Grande Coupure, but some researchers challenged this perception recently, arguing that it completely receded already 37 Ma, long before the Eocene-Oligocene transition. Alexis Licht et al. suggested that the Grande Coupure could have possibly been synchronous with the Oi-1 glaciation (33.5 Ma), which records a decline in atmospheric [[carbon dioxide|CO<sub>2</sub>]], boosting the Antarctic glaciation that already started by the Eocene-Oligocene transition. The Oi-1 glaciation, similar to the first glaciation event, caused large drops in sea level and pushed the global climate towards a coolhouse/icehouse environment.<ref name="balkanatolia"/><ref>{{cite journal|last1=Boulila|first1=Slah|last2=Dupont-Nivet|first2=Guillaume|last3=Galbrun|first3=Bruno|last4=Bauer|first4=Hugues|last5=Châteauneuf|first5=Jean-Jacques|year=2021|title=Age and driving mechanisms of the Eocene–Oligocene transition from astronomical tuning of a lacustrine record (Rennes Basin, France)|journal=Climate of the Past|volume=17|issue=6|pages=2343–2360|doi=10.5194/cp-17-2343-2021|bibcode=2021CliPa..17.2343B |s2cid=244097729 |doi-access=free }}</ref> The extinctions of a majority of endemic artiodactyls have been attributed to competition with immigrant faunas, environmental changes from cooling climates, or some combination of the two.<ref name="age"/>
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