Editing Eocene (section)

== Fauna ==

During the Eocene, plants and marine faunas became quite modern. Many modern [[bird]] orders first appeared in the Eocene. The Eocene oceans were warm and teeming with [[fish]] and other sea life.

=== Vertebrates ===
<!--grossly over-represented for this article, we should probably split this whole chapter out as a separate article and have a brief summary and 'main' link here-->

==== Mammals ====

The oldest known [[fossil]]s of most of the modern mammal orders appear within a [[Uintan|brief period during the early Eocene]]. At the beginning of the Eocene, several new mammal groups arrived in North America. These modern mammals, like [[artiodactyl]]s, [[perissodactyls]], and [[primate]]s, had features like long, thin [[leg]]s, feet, and [[hand]]s capable of grasping, as well as differentiated [[teeth]] adapted for chewing. [[Insular dwarfism|Dwarf]] forms reigned. All the members of the new mammal orders were small, under 10&nbsp;kg; based on comparisons of tooth size, Eocene mammals were only 60% of the size of the primitive Palaeocene mammals that preceded them. They were also smaller than the mammals that followed them. It is assumed that the hot Eocene temperatures favored smaller animals that were better able to manage the heat.<ref>Abigail R. D’Ambrosia ''et al''. (2017) Repetitive mammalian dwarfing during ancient greenhouse warming events.Sci. Adv.3,e1601430.DOI:10.1126/sciadv.1601430</ref><ref>Katherina B. Searing ''et al''. (2023) Melting climates shrink North American small mammals. 120 (50) e2310855120 https://doi.org/10.1073/pnas.2310855120.</ref>

Rodents were widespread. East Asian rodent faunas declined in diversity when they shifted from ctenodactyloid-dominant to cricetid–dipodid-dominant after the MECO.<ref>{{Cite journal |last1=Li |first1=Qian |last2=Li |first2=Qi |last3=Xu |first3=Rancheng |last4=Wang |first4=Yuanqing |date=7 September 2022 |title=Rodent faunas, their paleogeographic pattern, and responses to climate changes from the early Eocene to the early Oligocene in Asia |journal=[[Frontiers in Ecology and Evolution]] |volume=10 |doi=10.3389/fevo.2022.955779 |doi-access=free |issn=2296-701X }}</ref>

Both groups of modern [[ungulate]]s (hoofed animals) became prevalent because of a major radiation between Europe and North America, along with carnivorous ungulates like ''[[Mesonyx]]''. Early forms of many other modern mammalian orders appeared, including [[horse]]s (most notably the ''[[Eohippus]]''), [[bat]]s, [[Proboscidea|proboscidians]] (elephants), primates, and [[rodent]]s.  Older primitive forms of mammals declined in variety and importance. Important Eocene land fauna fossil remains have been found in western North America, Europe, [[Patagonia]], [[Egypt]], and [[southeast Asia]]. Marine fauna are best known from [[South Asia]] and the [[southeast United States]].{{citation needed|date=February 2022}}

After the Paleocene–Eocene Thermal Maximum, members of the [[Equoidea]] arose in North America and Europe, giving rise to some of the earliest [[equid]]s such as ''[[Sifrhippus]]'' and basal European equoids such as the [[palaeothere]] ''[[Hyracotherium]]''.<ref>{{cite journal|last1=Secord|first1=Ross |last2=BLoch |first2=Jonathan I. |last3=Chester|first3=Stephen G. B.|last4=Boter|first4=Doug M.|last5=Wood|first5=Aaron R. |last6=Wing |first6=Scott L.|last7=Kraus|first7=Mary J.|last8=McInerney |first8=Francesca A. |last9=Krigbaum |first9=John |year=2012|title=Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum|journal=Nature |volume=335 |issue=6071 |pages=959–962 |doi=10.1126/science.1213859}}</ref><ref>{{cite journal |last1=Bronnert |first1=Constance|last2=Métais |first2=Grégoire |year=2023 |title=Early Eocene hippomorph perissodactyls (Mammalia) from the Paris Basin |journal=Geodiversitas |volume=45|number=9 |pages=277–326 |doi=10.5252/geodiversitas2023v45a9 |url=https://sciencepress.mnhn.fr/en/periodiques/geodiversitas/45/9}}</ref> Some of the later equoids were especially species-rich; ''[[Palaeotherium]]'', ranging from small to very large in size, is known from as many as 16 species.<ref>{{cite journal |last=Remy |first=Jean-Albert|year=1992 |title=Observations sur l'anatomie cranienne du genre Palaeotherium (Perissodactyla, Mammalia): mise en évidence d'un nouveau sous-genre, Franzenitherium |journal=Palaeovertebrata |volume=21 |number=3–4 |pages=103–224 |url=https://www.researchgate.net/publication/273459309}}</ref><ref>{{cite journal|last=Ruiz-Colmenares|first=Miguel Ángel Cuesta|year=1993 |title=Los Palaeotheriidae (Perissodactyla, Mammalia) del Eoceno de la Cuenca del Duero (Castilla y León, España)|journal=Estudios Geológicos |volume=49 |number=1–2 |pages=87–109|doi=10.3989/egeol.93491-2341 |doi-access=free}}</ref>

Established large-sized mammals of the Eocene include the ''[[Uintatherium]]'', ''[[Arsinoitherium]]'', and [[brontotheres]], in which the former two, unlike the latter, did not belong to ungulates but groups that became extinct shortly after their establishments.

Large terrestrial mammalian predators had already existed since the Paleocene, but new forms now arose  like ''[[Hyaenodon]]'' and ''[[Daphoenus]]'' (the earliest lineage of a once-successful predatory family known as [[bear dogs]]). [[Entelodonts]] meanwhile established themselves as some of the largest omnivores. The first [[nimravids]], including ''[[Dinictis]]'', established themselves as amongst the first [[feliforms]] to appear. Their groups became highly successful and continued to live past the Eocene.

''[[Basilosaurus]]'' is a well-known Eocene [[whale]], but whales as a group had become very diverse during the Eocene, which is when the major transitions from being terrestrial to fully aquatic in [[cetacea]]ns occurred. The first [[sirenia]]ns were evolving at this time, and would eventually evolve into the extant [[manatee]]s and [[dugong]]s.

<gallery class=center mode=nolines widths=160 heights=160>
File:Dinoceras mirabile Marsh MNHN.jpg|Cast of skull of ''[[Uintatherium anceps]]'', a dinoceratan
File:Andrewsarchus09DB.jpg|Reconstruction of ''[[Andrewsarchus]]'', an artiodactyl
File:Basilosaurus isis fossil, Nantes History Museum 03.jpg|''[[Basilosaurus]]'', a whale
File:Pakicetus Canada.jpg|''[[Pakicetus]]'', an amphibious cetacean
File:Moeritherium lyonsi (fossil mammal) (Eocene) (32167459460).jpg|''[[Moeritherium]]'', a basal proboscidean
File:Brontotherium skull IMG 4441.jpg|''[[Megacerops]]'', a brontotheriid
File:Hyracodon nebraskensis.jpg|''[[Hyracodon]]'', a perissodactyl
File:Leptictidium auderiense skeleton.JPG|''[[Leptictidium]]'', a small mammal, likely bipedal
File:Peratherium skull.jpg|''[[Peratherium]]'', a herpetotheriid
File:Hesperocyon skull Smithsonian.jpg|''[[Hesperocyon]]'', a canid
</gallery>

==== Birds ====

Eocene birds include some enigmatic groups with resemblances to modern forms, some of which continued from the Paleocene. Bird taxa of the Eocene include carnivorous [[psittaciform]]s, such as [[Messelasturidae]], [[Halcyornithidae]], large flightless forms such as ''[[Gastornis]]'' and ''[[Eleutherornis]]'',<ref>{{Cite journal |last1=Buffetaut |first1=Eric |last2=Angst |first2=Delphine |date=November 2014 |title=Stratigraphic distribution of large flightless birds in the Palaeogene of Europe and its palaeobiological and palaeogeographical implications |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825214001263 |journal=[[Earth-Science Reviews]] |volume=138 |pages=394–408 |doi=10.1016/j.earscirev.2014.07.001 |bibcode=2014ESRv..138..394B |access-date=20 July 2024 |via=Elsevier Science Direct}}</ref> long legged falcon ''[[Masillaraptor]]'', ancient [[galliformes|galliforms]] such as [[Gallinuloides]], [[Rail (bird)|putative rail relatives]] of the family [[Songzia|Songziidae]], [[Pelagornithidae|various pseudotooth birds]] such as ''[[Gigantornis]]'', the [[ibis]] relative ''[[Rhynchaeites]]'', primitive swifts of the genus ''[[Aegialornis]]'', and primitive penguins such as ''[[Archaeospheniscus]]'' and ''[[Inkayacu]]''.{{citation needed|date=February 2022}}

Many Eocene birds in [[Central Europe]] evolved tuberculate vertebrae as an adaptation against predation, with flightless birds facing low predation pressure during this time as a result.<ref>{{Cite journal |last1=Mayr |first1=Gerald |last2=Göhlich |first2=Ursula B. |last3=Roček |first3=Zbyněk |last4=Lemierre |first4=Alfred |last5=Winkler |first5=Viola |last6=Georgalis |first6=Georgios L. |date=22 November 2023 |title=Reinterpretation of tuberculate cervical vertebrae of Eocene birds as an exceptional anti-predator adaptation against the mammalian craniocervical killing bite |journal=[[Journal of Anatomy]] |volume=244 |issue=3 |pages=402–410 |doi=10.1111/joa.13980 |pmc=10862156 |pmid=37990985 }}</ref>

<gallery class=center mode=nolines widths=160 heights=160>
File:Primobucco mcgrewi USNM PAL 336284 img1.jpg|''[[Primobucco]]'', an early relative of the [[Coraciidae|roller]] 
File:Pseudocrypturus Smithsonian fossil.jpg|''[[Pseudocrypturus]]'', Early Eocene, Wyoming 
File:Diatrymaskeleton.JPG|''[[Gastornis]]'', a flightless bird
</gallery>

==== Fishes ====

Fishes, both [[Chondrichthyes]] such as sharks and rays, and [[Osteichthyes]] (bony fishes), are abundant in the [[London Clay]].

<gallery class=center mode=nolines widths=160 heights=160>
File:Carcharocles sokolowi teeth.png|Teeth of ''[[Otodus sokolovi]]'', an otodontid shark
File:Xiphodolamia.jpg|Teeth of ''[[Xiphodolamia]]''. a mackerel shark, [[London Clay]]
File:Heliobatis radians with two Knightia eocaena (3bce1f6e-f693-43d1-aa0f-67ba7fc50895).tif|''[[Heliobatis]]'' and ''[[Knightia]]''
File:FOS655.jpg|Eel, cf. ''[[Echelus]] branchialis'', collected by [[Louis Agassiz]]
File:FOS794.jpg|Vertebrae of a [[Lamniformes|lamniform]] shark, London Clay, [[Isle of Sheppey]]
</gallery>

==== Reptiles ====

Reptile fossils from this time, such as fossils of [[pythons]] and [[turtle]]s, are abundant.<ref>{{Cite journal |last1=Georgalis |first1=Georgios L. |last2=Abdel Gawad |first2=Mohamed K. |last3=Hassan |first3=Safiya M. |last4=El-Barkooky |first4=Ahmed N. |last5=Hamdan |first5=Mohamed A. |date=2020-05-22 |title=Oldest co-occurrence of Varanus and Python from Africa—first record of squamates from the early Miocene of Moghra Formation, Western Desert, Egypt |journal=[[PeerJ]] |volume=8 |pages=e9092 |doi=10.7717/peerj.9092 |pmc=7255343 |pmid=32509449 |doi-access=free }}</ref>

<gallery class=center mode=nolines widths=160 heights=160>
File:Turtle with crocodile bite marks, Eocene, Green River Formation, Kemmerer, Lincoln County, Wyoming, USA - Houston Museum of Natural Science - DSC02006.JPG|''[[Hummelichelys]]'' with crocodile bite marks
File:Borealosuchus wilsoni (15529256785).jpg|''[[Borealosuchus]]'', a crocodyliform
</gallery>

=== Molluscs ===

<gallery class=center mode=nolines widths=160 heights=160>
File:Cerithium giganteum, snails, Middle Eocene, Verona, Italy - Houston Museum of Natural Science - DSC01968.jpg|''[[Cerithium]]'' shells
</gallery>

=== Arthropods ===

Several rich fossil insect faunas are known from the Eocene, notably the [[Baltic amber]] found mainly along the south coast of the [[Baltic Sea]],<ref>{{cite journal |last1=Wolfe |first1=Alexander P. |last2=Tappert |first2=Ralf |last3=Muehlenbachs |first3=Karlis |last4=Boudreau |first4=Marc |last5=McKellar |first5=Ryan C. |last6=Basinger |first6=James F. |last7=Garrett |first7=Amber |date=1 July 2009 |title=A new proposal concerning the botanical origin of Baltic amber |journal=[[Proceedings of the Royal Society B]] |volume=276 |issue=1972 |pages=3403–3412 |doi=10.1098/rspb.2009.0806 |pmid=19570786 |pmc=2817186 }}</ref> amber from the [[Paris Basin]], France, the [[Fur Formation]], [[Denmark]], and the [[Bembridge Marls]] from the [[Isle of Wight]], England. Insects found in Eocene deposits mostly belong to genera that exist today, though their range has often shifted since the Eocene. For instance the [[Bibionidae|bibionid]] genus ''[[Plecia]]'' is common in fossil faunas from presently temperate areas, but only lives in the tropics and subtropics today.<ref>{{Cite journal |last=Buschman |first=Lawrent L. |date=1976 |title=Invasion of Florida by the "Lovebug" Plecia nearctica (Diptera: Bibionidae) |url=https://www.jstor.org/stable/3493971 |journal=The Florida Entomologist |volume=59 |issue=2 |pages=191–194 |doi=10.2307/3493971 |issn=0015-4040}}</ref> Platypleurin cicadas diversified during the Eocene.<ref>{{Cite journal |last1=Price |first1=Benjamin W. |last2=Marshall |first2=David C. |last3=Barker |first3=Nigel P. |last4=Simon |first4=Chris |last5=Villet |first5=Martin H. |date=29 March 2019 |title=Out of Africa? A dated molecular phylogeny of the cicada tribe Platypleurini Schmidt (Hemiptera: Cicadidae), with a focus on African genera and the genus Platypleura Amyot & Audinet-Serville |url=https://resjournals.onlinelibrary.wiley.com/doi/10.1111/syen.12360 |journal=[[Systematic Entomology]] |volume=44 |issue=4 |pages=842–861 |doi=10.1111/syen.12360 |bibcode=2019SysEn..44..842P |access-date=20 July 2024 |via=Wiley Online Library}}</ref> Ostracods flourished in the oceans.<ref>{{Cite journal |last1=Shahin |first1=Abdalla |last2=El Khawagah |first2=Samar |last3=Shahin |first3=Banan |date=May 2023 |title=Implication of middle Eocene to early Miocene ostracodes from the N. El Faras-1X Well, Qattara Depression, Egypt, for paleobathymetry and paleobiogeographic reconstruction |url=https://linkinghub.elsevier.com/retrieve/pii/S0377839823000439 |journal=Marine Micropaleontology |volume=181 |pages=102244 |doi=10.1016/j.marmicro.2023.102244 |access-date=20 July 2024 |via=Elsevier Science Direct}}</ref>

<gallery class=center mode=nolines widths=160 heights=160>
File:Harpactocarinus punctulatus, crab, Eocene, Rialo Formation, Monte Baldo Quarry, Verona, Italy - Houston Museum of Natural Science - DSC01954.JPG|''[[Harpactocarcinus]]'', a crab
File:Palaeoncoderes eocenicus L. PITON et N. THEOBALD 1937 Holotype.jpg|''[[Palaeoncoderes]]'', a [[beetle]]
</gallery>

=== Other phyla ===

<gallery class=center mode=nolines widths=160 heights=160>
File:Echinolampas ovalis M Eocene Civrac-en-Médoc France.JPG|''[[Echinolampas]]'', a [[sea urchin]]
</gallery>

=== Microbes ===

Calcareous nannoplankton were a prominent feature of Eocene marine ecosystems.<ref>{{Cite journal |last1=Arias-Villegas |first1=Viviana |last2=Bedoya Agudelo |first2=Erika L. |last3=Vallejo-Hincapié |first3=Felipe |last4=Aubry |first4=Marie-Pierre |last5=Pardo-Trujillo |first5=Andrés |date=August 2023 |title=Late Eocene to Early Miocene calcareous nannofossil biostratigraphy from the ANH-San Jacinto- 1 well: Stratigraphic implications for the Sinú-San Jacinto basin in the Caribbean region of Colombia |url=https://linkinghub.elsevier.com/retrieve/pii/S089598112300281X |journal=[[Journal of South American Earth Sciences]] |volume=128 |pages=104470 |doi=10.1016/j.jsames.2023.104470 |bibcode=2023JSAES.12804470A |access-date=20 July 2024 |via=Elsevier Science Direct}}</ref>