Editing Penguin (section)

===Evolution===
[[File:CSIRO ScienceImage 11266 Penguin tracks.jpg|thumb|Penguin tracks in the sand on [[Bruny Island]], [[Tasmania]]]]
Although the [[evolution]]ary and [[biogeography|biogeographic]] history of Sphenisciformes is well-researched, many prehistoric forms are not [[Taxonomy#Alpha and beta taxonomy|fully described]]. <!-- Although penguin bones of any one species vary in size and few good specimens are known. Commenting this out as I have no idea how to properly integrate it into the text --> Some seminal articles about the evolutionary history of penguins have been published since 2005.<ref name="Ksepka"/><ref name="Baker"/><ref name="B&G">{{Cite journal | doi = 10.1111/j.1096-0031.2005.00065.x| title = A phylogeny of extant penguins (Aves: Sphenisciformes) combining morphology and mitochondrial sequences| journal = Cladistics| volume = 21| issue = 3| pages = 209–239| year = 2005| last1 = Bertelli | first1 = S. | last2 = Giannini | first2 = N. P. | s2cid = 85071808}}</ref><ref name="Slack">{{cite journal| doi = 10.1093/molbev/msj124| last1 = Slack| first1 = Kerryn E.| last2 = Jones| first2 = Craig M.| last3 = Ando| first3 = Tatsuro| last4 = Harrison| first4 = G.L. "Abby"| last5 = Fordyce| first5 = R. Ewan| last6 = Arnason| first6 = Ulfur| last7 = Penny| first7 = David| year = 2006| title = Early Penguin Fossils, plus Mitochondrial Genomes, Calibrate Avian Evolution| journal = [[Molecular Biology and Evolution]]| volume = 23| issue = #6| pages = 1144–1155| pmid = 16533822| citeseerx = 10.1.1.113.4549}} [http://mbe.oxfordjournals.org/cgi/content/full/msj124/DC1 Supplementary Material] {{Webarchive|url=https://web.archive.org/web/20091216110914/http://mbe.oxfordjournals.org/cgi/content/full/msj124/DC1 |date=December 16, 2009 }}</ref>{{overcite|date=October 2024}}<!-- This entire paragraph should probably be rewritten and updated -->

The [[Basal (phylogenetics)|basal]] penguins lived around the time of the [[Cretaceous–Paleogene extinction event]] in the general area of southern New Zealand and [[Byrd Land]], Antarctica.<ref name="Ksepka"/> Due to [[plate tectonics]], these areas were at that time less than {{convert|1500|km|mi}} apart rather than {{convert|4000|km|mi}}. The [[most recent common ancestor]] of penguins and [[Procellariiformes]] can be roughly dated to the [[Campanian]]–[[Maastrichtian]] boundary, around 70–68 mya.<ref name="Baker"/><ref name="Slack"/><ref>The exact divergence dates according to [[#Baker|Baker]] ''et al.'' (2006) mentioned in this section are not as precisely resolved, due to uncertainties of the [[molecular clock]] used.</ref>

====Basal fossils====
The oldest known [[fossil]] penguin species is ''[[Waimanu]] manneringi'', which lived 62 [[mya (unit)|mya]] in New Zealand.<ref name="Slack"/> While they were not as well-adapted to aquatic life as modern penguins, ''Waimanu'' were flightless, with short wings adapted for deep diving.<ref name="Slack"/> They swam on the surface using mainly their feet, but the wings were – as opposed to most other diving birds (both living and extinct) – already adapting to underwater locomotion.<ref>{{Cite journal | doi = 10.1073/pnas.1304838110| title = High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins| journal = Proceedings of the National Academy of Sciences| volume = 110| issue = #23| pages = 9380–9384| year = 2013| last1 = Elliott | first1 = K. H.| last2 = Ricklefs | first2 = R. E.| last3 = Gaston | first3 = A. J.| last4 = Hatch | first4 = S. A.| last5 = Speakman | first5 = J. R.| last6 = Davoren | first6 = G. K. | pmid=23690614 | pmc=3677478| bibcode = 2013PNAS..110.9380E| doi-access = free}}</ref>

''[[Perudyptes]]'' from northern Peru was dated to 42 mya. An unnamed fossil from [[Argentina]] proves that, by the [[Bartonian]] (Middle Eocene), some 39–38 mya,<ref>''Contra'' [[#Baker|Baker]] ''et al.'' (2006).</ref> primitive penguins had spread to [[South America]] and were in the process of expanding into [[Atlantic]] waters.<ref name="Clarke"/><!-- This entire paragraph needs to be rewritten, but I'm not sure how to -->

====Palaeeudyptines====
During the Late Eocene and the Early [[Oligocene]] (40–30 mya), some lineages of gigantic penguins existed. [[Nordenskjoeld's giant penguin]] was the tallest, growing nearly {{convert|1.80|m|ft|abbr=off|sp=us}} tall. The [[New Zealand giant penguin]] was probably the heaviest, weighing {{Convert|80|kg|lb}} or more. Both were found on New Zealand, the former also in the Antarctic farther eastwards.

Traditionally, most extinct species of penguins, giant or small, had been placed in the [[paraphyletic]] [[subfamily]] called [[Palaeeudyptinae]]. More recently, with new taxa being discovered and placed in the [[phylogeny]] if possible, it is becoming accepted that there were at least two major extinct lineages. One or two closely related ones occurred in [[Patagonia]], and at least one other—which is or includes the paleeudyptines as recognized today – occurred on most [[Antarctic]] and [[Subantarctic]] coasts.

Size plasticity was significant at this initial stage of [[Adaptive radiation|radiation]]: on [[Seymour Island]], Antarctica, for example, around 10 known species of penguins ranging in size from medium to large apparently coexisted some 35 mya during the [[Priabonian]] (Late Eocene).<ref name="Jadwiszczak"/> It is not known whether the palaeeudyptines constitute a [[monophyletic]] lineage, or whether gigantism was evolved independently in a restricted Palaeeudyptinae and the Anthropornithinae – whether they were considered valid, or whether there was a wide size range present in the Palaeeudyptinae as delimited (i.e., including ''[[Anthropornis nordenskjoeldi]]'').<ref name="Ksepka"/> The oldest well-described giant penguin, the {{convert|5|ft|m|adj=on}}-tall ''[[Icadyptes salasi]]'', existed as far north as northern [[Peru]] about 36 mya.

Gigantic penguins had disappeared by the end of the [[Paleogene]], around 25 mya. Their decline and disappearance coincided with the spread of the [[Squalodontidae]] and other primitive, fish-eating [[toothed whale]]s, which competed with them for food and were ultimately more successful.<ref name="Baker"/> A new lineage, the [[Paraptenodytes]], which includes smaller and stout-legged forms, had already arisen in southernmost South America by that time. The early [[Neogene]] saw the emergence of another morphotype in the same area, the similarly sized but more gracile [[Palaeospheniscinae]], as well as the radiation that gave rise to the current [[biodiversity]] of penguins.

====Origin and systematics of modern penguins====
Modern penguins constitute two undisputed [[clade]]s and another two more basal genera with more ambiguous relationships.<ref name="B&G"/> To help resolve the evolution of this [[Order (biology)|order]], 19 high-coverage genomes that, together with two previously published genomes, encompass all extant penguin species have been sequenced.<ref>{{Cite journal |last1=Pan |first1=Hailin |last2=Cole |first2=Theresa L. |last3=Bi |first3=Xupeng |last4=Fang |first4=Miaoquan |last5=Zhou |first5=Chengran |last6=Yang |first6=Zhengtao |last7=Ksepka |first7=Daniel T. |last8=Hart |first8=Tom |last9=Bouzat |first9=Juan L. |last10=Argilla |first10=Lisa S. |author-link10=Lisa Argilla |last11=Bertelsen |first11=Mads F. |date=September 1, 2019 |title=High-coverage genomes to elucidate the evolution of penguins |url= |journal=GigaScience |language=en |volume=8 |issue=9 |doi=10.1093/gigascience/giz117 |pmc=6904868 |pmid=31531675}}</ref> The origin of the Spheniscinae lies probably in the latest Paleogene and, geographically, it must have been much the same as the general area in which the order evolved: the oceans between the Australia-New Zealand region and the Antarctic.<ref name="Baker"/> Presumably diverging from other penguins around 40 mya,<ref name="Baker"/> it seems that the Spheniscinae were for quite some time limited to their ancestral area, as the well-researched deposits of the [[Antarctic Peninsula]] and [[Patagonia]] have not yielded Paleogene fossils of the subfamily. Also, the earliest spheniscine lineages are those with the most southern distribution.

The genus ''[[Aptenodytes]]'' appears to be the basalmost divergence among living penguins.<ref name="Ksepka">{{cite journal |doi=10.1111/j.1096-0031.2006.00116.x |last1=Ksepka |first1=D. T. |last2=Bertelli |first2=S. |last3=Giannini |first3=N. P. |title=The phylogeny of the living and fossil Sphenisciformes (penguins) |journal=Cladistics |volume=22 |year=2006 |pages=412–441 |issue=#5 |s2cid=85673628 |doi-access=free }}</ref><ref name=CB08>{{cite book |title=Systematics and Taxonomy of Australian Birds|vauthors=Christidis L, Boles WE |year=2008 |publisher=CSIRO Publishing |location=Canberra |isbn=978-0-643-06511-6 |page=97}}</ref> They have bright yellow-orange neck, breast, and bill patches; incubate by placing their eggs on their feet, and when they hatch the chicks are almost naked. This genus has a distribution centred on the Antarctic coasts and barely extends to some Subantarctic islands today.

''[[Pygoscelis]]'' contains species with a fairly simple black-and-white head pattern; their distribution is intermediate, centred on Antarctic coasts but extending somewhat northwards from there. In external [[morphology (biology)|morphology]], these apparently still resemble the common ancestor of the Spheniscinae, as ''Aptenodytes''{{'}} [[autapomorph]]ies are, in most cases, fairly pronounced [[Adaptation (biology)|adaptations]] related to that genus' extreme [[habitat]] conditions. As the former genus, ''Pygoscelis'' seems to have diverged during the Bartonian,<ref>
It is likely that, during the Bartonian, there was a near-synchronous but [[allopatric]] split between the ancestors of ''Aptenodytes'', ''Pygoscelis'', and the common ancestor of all remaining genera ([[#Baker|Baker]]).</ref> but the range expansion and radiation that led to the present-day diversity probably did not occur until much later; around the [[Burdigalian]] stage of the Early [[Miocene]], roughly 20–15 mya.<ref name="Baker"/>

The [[Genus|genera]] ''[[Spheniscus]]'' and ''[[Eudyptula]]'' contain species with a mostly Subantarctic distribution centred on [[South America]]; some, however, range quite far northwards. They all lack [[carotenoid]] colouration and the former genus has a conspicuous banded head pattern; they are unique among living penguins by nesting in burrows. This group probably radiated eastwards with the [[Antarctic Circumpolar Current]] out of the ancestral range of modern penguins throughout the [[Chattian]] (Late Oligocene), starting approximately 28 mya.<ref name="Baker"/> While the two genera separated during this time, the present-day diversity is the result of a [[Pliocene]] radiation, taking place some 4–2 mya.<ref name="Baker"/>

The ''Megadyptes''–''Eudyptes'' clade occurs at similar [[latitude]]s (though not as far north as the [[Galápagos penguin]]), has its highest diversity in the New Zealand region, and represents a westward dispersal. They are characterized by hairy yellow ornamental head feathers; their bills are at least partly red. These two genera diverged apparently in the Middle Miocene ([[Langhian]], roughly 15–14 mya), although the living species of ''Eudyptes'' are the product of a later radiation, stretching from about the late [[Tortonian]] (Late Miocene, 8 mya) to the end of the Pliocene.<ref name="Baker"/>

====Geography====
The geographical and temporal pattern of spheniscine evolution corresponds closely to two episodes of [[global cooling]] documented in the [[Paleoclimatology|paleoclimatic record]].<ref name="Baker" /> The emergence of the Subantarctic lineage at the end of the Bartonian corresponds with the onset of the slow period of cooling that eventually led to the [[Quaternary glaciation|ice ages]] some 35 million years later. With habitat on the Antarctic coasts declining, by the Priabonian more hospitable conditions for most penguins existed in the Subantarctic regions rather than in Antarctica itself.<ref name="Baker, A., Pereira, SL, Haddrath, OP, Edge, KA 2006">{{cite journal |author=Baker, A., Pereira, SL, Haddrath, OP, Edge, KA |title=Multiple gene evidence for expansion of extant penguins out of Antarctica due to global cooling |journal=Proceedings of the Royal Society B: Biological Sciences |volume=273 |year=2006 |doi=10.1098/rspb.2005.3260 |issue=#1582 |pages=11–7 |pmid=16519228 |pmc=1560011}}</ref> Notably, the cold Antarctic Circumpolar Current also started as a continuous circumpolar flow only around 30 mya, on the one hand forcing the Antarctic cooling, and on the other facilitating the eastward expansion of ''[[Spheniscus]]'' to South America and eventually beyond.<ref name="Baker" /> Despite this, there is no fossil evidence to support the idea of crown radiation from the Antarctic continent in the Paleogene, although DNA study favors such a radiation.<ref name="Baker, A., Pereira, SL, Haddrath, OP, Edge, KA 2006"/>

Later, an interspersed period of slight warming was ended by the [[Middle Miocene Climate Transition]], a sharp drop in global average temperature from 14 to 12 mya, and similar abrupt cooling events followed at 8 mya and 4 mya; by the end of the Tortonian, the [[Antarctic ice sheet]] was already much like today in volume and extent. The emergence of most of today's Subantarctic penguin species almost certainly was caused by this sequence of Neogene climate shifts.

====Relationship to other bird orders====
Penguin ancestry beyond ''[[Waimanu]]'' remains unknown and not well-resolved by molecular or morphological analyses. The latter tend to be confounded by the strong adaptive [[Autapomorphy|autapomorphies]] of the Sphenisciformes; a sometimes perceived fairly close relationship between penguins and [[grebe]]s is almost certainly an error based on both groups' strong diving adaptations, which are [[homoplasies]]. On the other hand, different [[DNA sequence]] datasets do not agree in detail with each other either.

[[File:Spheniscus humboldti -swimming -aquarium-8a.jpg|thumb|Humboldt penguins in an aquarium. The penguin is an accomplished swimmer, having [[Flipper (anatomy)|flippers]] instead of wings.]]
What seems clear is that penguins belong to a clade of [[Neoaves]] (living birds except for [[paleognath]]s and [[fowl]]) that comprises what is sometimes called "[[Aequornithes|higher waterbirds]]" to distinguish them from the more ancient [[waterfowl]]. This group contains such birds as [[stork]]s, [[Rallidae|rails]], and the [[seabird]]s, with the possible exception of the [[Charadriiformes]].<ref>{{Cite journal|doi=10.1554/04-235 |url=http://biology-web.nmsu.edu/houde/Parallel_radiations.pdf |pmid=15612298 |title=Parallel Radiations in the Primary Clades of Birds |journal=Evolution |volume=58 |issue=11 |pages=2558–73 |year=2004 |last1=Fain |first1=M. G. |last2=Houde |first2=P. |bibcode=2004Evolu..58.2558F |s2cid=1296408 |url-status=dead |archive-url=https://web.archive.org/web/20130407204436/http://biology-web.nmsu.edu/houde/Parallel_radiations.pdf |archive-date=April 7, 2013 }}</ref>

Inside this group, penguin relationships are far less clear. Depending on the analysis and dataset, a close relationship to [[Ciconiiformes]]<ref name="Slack"/> or to [[Procellariiformes]]<ref name="Baker"/> has been suggested. Some think the penguin-like [[Plotopteridae|plotopterids]] (usually considered relatives of [[cormorant]]s and [[anhinga]]s) may actually be a sister group of the penguins and those penguins may have ultimately shared a common ancestor with the [[Pelecaniformes]] and consequently would have to be included in that order, or that the plotopterids were not as close to other pelecaniforms as generally assumed, which would necessitate splitting the traditional Pelecaniformes into three.<ref>{{Cite journal| doi = 10.1111/j.1439-0469.2004.00291.x|url=http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/plotopteridae.pdf| title = Tertiary plotopterids (Aves, Plotopteridae) and a novel hypothesis on the phylogenetic relationships of penguins (Spheniscidae)| journal = Journal of Zoological Systematics and Evolutionary Research| volume = 43| pages = 61–71| year = 2005| last1 = Mayr| first1 = G.| access-date = July 8, 2006| archive-url=https://web.archive.org/web/20061013085236/http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/plotopteridae.pdf| archive-date = October 13, 2006| url-status = live}}</ref>

A 2014 analysis of whole genomes of 48 representative bird species has concluded that penguins are the [[sister group]] of Procellariiformes,<ref name = "Jarvis2014">{{Cite journal| doi = 10.1126/science.1253451| pmid = 25504713|url=https://pgl.soe.ucsc.edu/jarvis14.pdf| title = Whole-genome analyses resolve early branches in the tree of life of modern birds| journal = Science| volume = 346| issue = #6215| pages = 1320–1331| date = 2014| last1 = Jarvis| first1 = E. D.| author1-link = Erich Jarvis| last2 = Mirarab| first2 = S.| last3 = Aberer| first3 = A. J.| last4 = Li| first4 = B.| last5 = Houde| first5 = P.| last6 = Li| first6 = C.| last7 = Ho| first7 = S. Y. W.| last8 = Faircloth| first8 = B. C.| last9 = Nabholz| first9 = B.| last10 = Howard| first10 = J. T.| last11 = Suh| first11 = A.| last12 = Weber| first12 = C. C.| last13 = Da Fonseca| first13 = R. R.| last14 = Li| first14 = J.| last15 = Zhang| first15 = F.| last16 = Li| first16 = H.| last17 = Zhou| first17 = L.| last18 = Narula| first18 = N.| last19 = Liu| first19 = L.| last20 = Ganapathy| first20 = G.| last21 = Boussau| first21 = B.| last22 = Bayzid| first22 = M. S.| last23 = Zavidovych| first23 = V.| last24 = Subramanian| first24 = S.| last25 = Gabaldon| first25 = T.| last26 = Capella-Gutierrez| first26 = S.| last27 = Huerta-Cepas| first27 = J.| last28 = Rekepalli| first28 = B.| last29 = Munch| first29 = K.| last30 = Schierup| first30 = M.| display-authors = 29| pmc = 4405904| bibcode = 2014Sci...346.1320J| hdl = 10072/67425| access-date = August 28, 2015| archive-url=https://web.archive.org/web/20150224020622/http://pgl.soe.ucsc.edu/jarvis14.pdf| archive-date = February 24, 2015| url-status = dead}}</ref> from which they diverged about 60 million years ago (95% CI, 56.8–62.7).<ref name = "LiC2014">{{Cite journal | doi = 10.1186/2047-217X-3-27| title = Two Antarctic penguin genomes reveal insights into their evolutionary history and molecular changes related to the Antarctic environment| journal = GigaScience| volume = 3| issue = #1| pages = 27| date = December 12, 2014| last1 = Li | first1 = C. | last2 = Zhang | first2 = Y. | last3 = Li | first3 = J. | last4 = Kong | first4 = L. | last5 = Hu | first5 = H. | last6 = Pan | first6 = H. | last7 = Xu | first7 = L. | last8 = Deng | first8 = Y. | last9 = Li | first9 = Q. | last10 = Jin | first10 = L. | last11 = Yu | first11 = H. | last12 = Chen | first12 = Y. | last13 = Liu | first13 = B. | last14 = Yang | first14 = L. | last15 = Liu | first15 = S. | last16 = Zhang | first16 = Y. | last17 = Lang | first17 = Y. | last18 = Xia | first18 = J. | last19 = He | first19 = W. | last20 = Shi | first20 = Q. | last21 = Subramanian | first21 = S. | last22 = Millar | first22 = C. D. | last23 = Meader | first23 = S. | last24 = Rands | first24 = C. M. | last25 = Fujita | first25 = M. K. | last26 = Greenwold | first26 = M. J. | last27 = Castoe | first27 = T. A. | last28 = Pollock | first28 = D. D. | last29 = Gu | first29 = W. | last30 = Nam | first30 = K. | display-authors = 29 | pmid=25671092 | pmc=4322438| doi-access = free}}</ref>

The distantly related [[Puffin]]s, which live in the North Pacific and North Atlantic, developed similar characteristics to survive in the Arctic and sub-Arctic environments. Like the penguins, puffins have a white chest, black back and short stubby wings providing excellent swimming ability in icy water. But, unlike penguins, puffins can fly, as flightless birds would not survive alongside land-based predators such as polar bears and foxes; there are no such predators in the Antarctic. Their similarities indicate that similar environments, although at great distances, can result in similar evolutionary developments, i.e. [[convergent evolution]].<ref>{{Cite book |title=Introduction to Marine Biology |last=Karleskint |first=George |publisher=Cengage Publishing |year=2012 |isbn=978-1285402222 |pages=30 |url=https://books.google.com/books?id=9fEKAAAAQBAJ |access-date=August 15, 2018 |archive-date=July 21, 2020 |archive-url=https://web.archive.org/web/20200721052701/https://books.google.com/books?id=9fEKAAAAQBAJ |url-status=live }}</ref>