Trogons — a gaggle of colourful, medium-sized birds that stay in tropical and subtropical forests around the globe — are recognizable by an odd function: a foot by which the second toe is completely reversed. A newly described trogon species from the Early Eocene of Denmark, one of many earliest members of the group, lacked a completely reversed second toe.
The holotype of Daniatrogon kochi from the Early Eocene Fur Formation in Denmark. Scale bar – 10 mm. Picture credit score: Gerald Mayr, doi: 10.1080/14772019.2026.2727037.
Daniatrogon kochi lived in what’s now Denmark in the course of the Early Eocene epoch, roughly 55 million years in the past.
Essentially the most putting trait of the brand new species is its ft. In trendy trogons, the second toe factors backward and, along with the large toe, opposes the opposite two forward-facing toes, an association often called heterodactyl.
In Daniatrogon kochi, the claw of the second toe factors the identical means as these of the opposite entrance toes, although the toe could have been rotated barely inward.
Each different fossil trogon recognized from articulated skeletons has a completely reversed second toe.
As a result of the heterodactyl foot seems solely in trogons, it should have advanced alongside the lineage resulting in them, and Daniatrogon kochi affords a uncommon glimpse of the stage earlier than that occurred.
“Trogons are a gaggle of birds, which is in the present day present in tropical and subtropical areas of Africa, Asia and the Americas,” Dr. Gerald Mayr from the Senckenberg Analysis Institute and Pure Historical past Museum Frankfurt wrote in his paper.
“These colourful and predominantly insectivorous or frugivorous birds are properly characterised by their heterodactyl foot, by which the second toe is completely reversed and, along with the hallux, opposes the 2 different fore toes.”
“Disregarding a probable inaccurate identification of a heterodactyl foot in an Early Cretaceous enantiornithine and a likewise but to be corroborated document from an Early Oligocene strigiform fowl, this diagnostic function is exclusive to trogons, which additionally exhibit varied different derived morphological traits.”
An almost full skeleton of Daniatrogon kochi was present in 1989 on a seashore on the Danish island of Mors by the fossil collector Karsten Koch, for whom the fowl is called.
The fossil got here from rocks of the Early Eocene Fur Formation.
“Trogons have a relatively complete Early Paleogene document,” Dr. Mayr wrote.
“The oldest fossils stem from the Early Eocene Fur Formation in Denmark and the roughly coeval sediments of the London Clay of Walton-on-the-Naze in England.”
Reconstruction of the dwelling bar-tailed trogon (Apaloderma vittatum) within the Catalogue of the Birds within the British Museum.
Daniatrogon kochi overturns some assumptions about why trogons have their peculiar ft.
The heterodactyl foot has usually been thought-about a perching adaptation that compensated for a weak massive toe.
However the brand new species had a really lengthy massive toe, as did the Messel trogon Masillatrogon, suggesting that the toe shrank solely after trogons acquired their reversed second toe.
Dr. Mayr proposes that early trogons moved extra actively by way of branches and vegetation whereas foraging, a way of life by which a powerful greedy foot would assist.
“Residing trogons are somewhat sedentary birds, which forage by sallying flights from perches,” the researcher wrote within the paper.
“Stem-group trogoniforms could have been extra actively shifting within the branches and thru the vegetation whereas looking for meals — actions for which an enhanced greedy perform of the foot would have been advantageous.”
“Subsequently, dimension discount of the hallux (massive toe) in trogoniforms could have been associated to the acquisition of a extra sedentary way of life, as sallying substrate-gleaners, for which a single well-developed reversed toe — the second — is adequate for perching.”
Daniatrogon kochi and different early trogons had narrower, less-ossified beaks than dwelling species, which use their payments to excavate nesting cavities in comfortable, rotting wooden.
Dr. Mayr suggests the early species could have nested in present holes or dug in soil with their ft, as a few of their relations do.
The discovering signifies that the foot modified earlier than the beak widened.
“The narrower beak of Daniatrogon, Eotrogon and Primotrogon — as in comparison with extant Trogonidae — probably signifies that these stem-group trogoniforms constructed their nests in present holes or that they used their syndactyl ft to excavate nesting cavities in soil,” he wrote.
In accordance with the examine, early trogons had been extra ecologically different than their dwelling relations, with a larger variety of beak and foot shapes.
The trogon lineage is estimated to have break up from that of hornbills and hoopoes about 62 million years in the past, and early members of the 2 teams look strikingly alike under the neck.
“The primary variations between early Trogoniformes and the earliest Bucerotiformes (hoopoes, hornbills and allies) concern cranium options, which can point out that the divergence of the Trogoniformes and Bucerotiformes was initially pushed by disparate feeding specializations,” Dr. Mayr concluded.
His paper was revealed on September 21, 2026 within the Journal of Systematic Palaeontology.
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Gerald Mayr. 2026. Evolution of a morphological novelty: distinctive skeleton of an early Eocene trogon (Aves: Trogoniformes) elucidates the origin of a singular foot morphology. Journal of Systematic Palaeontology 24 (2): 2727037; doi: 10.1080/14772019.2026.2727037