Editing Gaviiformes (section)

===Fossil record===
[[File:Plongeon catmarin oisillon.jpg|thumb|right|[[Red-throated loon]] (''G. stellata''), the smallest living ''Gavia'' [[species]]. Some [[Miocene]] members of this [[genus]] were smaller still.]]
In prehistoric times, the loons had a more southerly distribution than today, and their fossils have been found in places such as [[California]], [[Florida]] and [[Italy]]. The conflicting molecular data regarding their relationships is not much resolved by the [[fossil]] record; though they seem to have originated at the end of the [[Late Cretaceous]] like their presumed relatives, modern loons are only known with certainty since the [[Eocene]]. By that time almost all modern bird orders are at least strongly suspected to have existed – if not known from unequivocally identified specimens – anyway.<ref name=m2009/>

The oldest known stem-gaviiform is ''[[Nasidytes]]'' from the [[Ypresian|Early Eocene]] aged [[London Clay]] of England, dating to around 55 million years ago.<ref>{{Cite journal |last1=Mayr |first1=Gerald |last2=Kitchener |first2=Andrew C |date=2022-07-14 |title=Oldest fossil loon documents a pronounced ecomorphological shift in the evolution of gaviiform birds |url=https://academic.oup.com/zoolinnean/advance-article/doi/10.1093/zoolinnean/zlac045/6643590 |journal=Zoological Journal of the Linnean Society |volume=196 |issue=4 |language=en |pages=1431–1450 |doi=10.1093/zoolinnean/zlac045 |issn=0024-4082}}</ref>

''[[Colymboides]]'' is widely known from early [[Priabonian]] – about 37 [[million years ago]] (Ma) in the [[Late Eocene]] – to [[Early Miocene]] (late [[Burdigalian]], less than 20 Ma) [[limnic]] and [[Ocean|marine]] rocks of western [[Eurasia]] north of the [[Alpide belt]], between the [[Atlantic]] and the former [[Turgai Sea]]. It is usually placed in the Gaviidae already, but usually<ref>Some (notably [[Robert W. Storer]]) have disagreed, usually because they separated ''[[Gaviella]]'' in the basalmost subfamily of the Gaviidae and considered ''Colymboides'' the ancestor of ''Gavia''. More recent authors generally disagree at least regarding the latter: [[#Storer|Storer (1956)]], [[#Olson|Olson (1985)]], [[#Mayr2009|Mayr (2009: pp. 75–76)]]</ref> in a [[subfamily]] [[Colymboidinae]], with the modern-type loons making up the '''Gaviinae'''. But the ''Colymboides'' material is generally quite distinct from modern loons, and may actually belong in a now-extinct family of primitive gaviiforms. Furthermore, the supposed genus could well be paraphyletic, so that for example ''Dyspetornis'' – which is now contained therein – might have to be separated again. A leg of an undescribed small diver was found in the [[Late Oligocene]] deposits at [[Enspel]] ([[Germany]]); it too may or may not belong to ''Colymboides''. Of the [[crown group|crown genus]] ''Gavia'', nearly ten prehistoric species have been named to date, and about as many undescribed ones await further study. The genus is known from the Early Miocene onwards, and the oldest members of them are rather small (some are smaller than the [[red-throated loon]]). Throughout the late [[Neogene]], the genus by and large follows [[Cope's Rule]].<ref name="Brodkorb1953">[[#Brodkorb1953|Brodkorb (1953), 1963: pp. 223–225]], [[#Olson|Olson (1985: pp. 212–213)]], [[#Mlikovsky|Mlíkovský (2002: pp. 63–64)]], [[#Mayr2009|Mayr (2009: pp. 75–76)]]</ref>

Some older fossils are sometimes assigned to the Gaviiformes. From the [[Late Cretaceous]], the genera ''[[Lonchodytes]]'' ([[Lance Formation]], Wyoming) and ''[[Neogaeornis]]'' ([[Quinriquina Formation]], [[Chile]]) have been described; both are usually allied with orders which are considered related to loons. In particular the latter is still sometimes explicitly proposed as a primitive loon as they both were initially, but other authors consider ''Neogaeornis'' a [[hesperornithiformes|hesperornithiform]]; note however that neither Gaviiformes nor Hesperornithiformes are known from the [[Southern Hemisphere]] or anywhere near it. ''Lonchodytes'' was more certainly quite close to loons, but probably closer still to some of the loons' relatives. ''[[Eupterornis]]'' from the [[Paleocene]] of [[Châlons-sur-Vesle]] ([[France]]) has some features reminiscent of loons, but others seem more similar to [[Charadriiformes]] such as gulls ([[Laridae]]). A piece of a [[carpometacarpus]] supposedly from [[Oligocene]] rocks near [[Lusk, Wyoming]] was described as ''[[Gaviella pusilla]]'', but this handbone also shows some similarities to the [[plotopterid]]s which were flightless [[wing-propelled diver]]s and if these are [[apomorph]]ic would make an unconvincing member of the Gaviidae (though it still could be a small-winged gaviiform in a yet-undescribed family "Gaviellidae"<ref>Not to be used without quotation marks, as it is not a valid [[taxon]].</ref>): while the carpometacarpus in ''Gavia'' is somewhat [[convergent evolution|convergent]] to that of wing-propelled divers, enabling the wings to be used as rudders for quick underwater turns, ''Colymboides'' still had an unspecialized [[plesiomorph]]ic hand. ''Parascaniornis'', sometimes allied to the loons by early authors, was eventually determined to be a [[junior synonym]] of the hesperornithiform ''[[Baptornis]]''. A supposed mid-[[Eocene]] diver fossil form [[Geiseltal]] ([[Germany]]) was erroneously assigned to ''Gavia''.<ref>[[#Brodkorb1963|Brodkorb (1963: pp. 220–223)]], [[#Olson|Olson (1985)]], [[#Mlikovsky|Mlíkovský (2002: pp. 64, 259–261)]], [[#Mayr2009|Mayr (2009: p. 20)]]</ref>