Eocene London Clay Research Articles

A new species of the Prophaethontidae (Aves, Phaethontiformes) from the early Eocene London Clay

ABSTRACT We report new specimens of the stem group phaethontiform Prophaethon from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The two partial skeletons are distinctly smaller than a previously described record of Prophaethon from this locality, which was assigned to P. shrubsolei. Even though some extant aquatic birds show a pronounced sexual dimorphism in size, this is considered unlikely to explain the size disparity of the Prophaethon fossils from Walton-on-the-Naze and the new specimens are here described as P. waltonensis, sp. nov. The distal end of the humerus of the new species differs from that of other Phaethontiformes in the presence of a small but well-defined processus supracondylaris dorsalis. With regard to this feature, it shows a resemblance to the humerus of the Procellariiformes, which is unexpected in light of the recently proposed hypothesis that the sister taxon of the Phaethontiformes are the terrestrial Eurypygiformes. Finally, we comment on prophaethontid remains from the late Paleocene of Kazakhstan, which were assigned to the taxa Zhylgaia Nessov, 1988 and Tshulia Nessov, 1988. We synonymise the latter with the former taxon and also consider it possible that Zhylgaia Nessov, 1988 is a junior synonym of Prophaethon Andrews, 1899.

Two distinctive, but difficult-to-classify, avian species and a new trogon (Trogoniformes) from the early Eocene London Clay

Two distinctive, but difficult-to-classify, avian species and a new trogon (Trogoniformes) from the early Eocene London Clay

Messelornithids and messelornithid-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

We describe gruiform and gruiform-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). One species belongs to the Messelornithidae and is classified as Nasiornis messelornithoides nov. gen., nov. sp.; the coracoid of this species resembles that of Bumbaniralla from the early Eocene of Mongolia. Another possible messelornithid species is tentatively assigned to the poorly known taxon Parvirallus Harrison and Walker, 1979, as ?P. incertus nov. sp. A further species is referred to the taxon Walbeckornis Mayr, 2007, as W. waltonensis nov. sp., and extends the geographical and temporal range of this taxon, which so far was only known from the Paleocene of Germany. Even though similarities between Walbeckornis and messelornithids were previously noted, a plesiomorphic morphology of the quadrate suggests a position of Walbeckornis outside crown group Gruiformes. Furthermore, all fossil taxa described in the present study lack a deeply concave facies articularis alularis (carpometacarpus), which we identify as a previously overlooked apomorphy of crown group Ralloidea. Therefore, resemblances between Walbeckornis and the Messelornithidae, which are the sister taxon of crown group Ralloidea, are likely to be plesiomorphic for a more inclusive clade.

The non-apodiform Strisores (potoos, nightjars and allied birds) from the early Eocene London Clay of Walton-on-the-Naze

The non-apodiform Strisores (potoos, nightjars and allied birds) from the early Eocene London Clay of Walton-on-the-Naze

The Picocoraciades (hoopoes, rollers, woodpeckers, and allies) from the early Eocene London Clay of Walton-on-the-Naze

We describe upupiform, coraciiform, and possible piciform birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The material includes partial skeletons of a new species of a small upupiform bird, Waltonirrisor tendringensis, gen. et sp. nov., which is the earliest known representative of the Upupiformes. Three very similar species of stem group rollers are assigned to Laputavis robusta, Septencoracias morsensis, and S. simillimus, sp. nov. These species only differ in minor features, which raises the possibility that the taxon Sepencoracias Bourdon, 2016 is a junior synonym of Laputavis Dyke, 2001. A smaller stem group roller from Walton-on-the-Naze resembles the North American primobucconid species Primobucco mcgrewi. We also describe two species of a new genus-level taxon, Pristineanis, gen. nov., which shows close affinities to the North American “Neanis” kistneri and may be a stem group representative of the Piciformes. In many aspects of their postcranial osteology, the stem group Coracii from Walton-on-the-Naze, as well as the new taxon Pristineanis, resemble coeval Trogoniformes from this fossil site. Because trogons are the extant sister taxon of the Picocoraciades – the clade including the Upupiformes, Coraciiformes, and Piciformes –, the shared similarities are likely to be plesiomorphic for this latter clade. Early Cenozoic representatives of the Upupiformes and Coraciiformes were much smaller than their extant relatives, which suggests that the Picocoraciades are an avian example of Cope’s Rule that postulates a tendency for size increase in evolutionary lineages over time.

New fossils of Eocypselus and Primapus from the British London Clay reveal a high taxonomic and ecological diversity of early Eocene swift‐like apodiform birds

We describe new specimens and species of apodiform birds from the early Eocene London Clay of Walton‐on‐the Naze (Essex, UK). In addition to multiple partial skeletons of Eocypselus vincenti Harrison, 1984, three new species of Eocypselus are described as Eocypselus geminus, sp. nov., Eocypselus paulomajor, sp. nov. and Eocypselus grandissimus, sp. nov. The previously unknown quadrate of Eocypselus shares a characteristic derived morphology with the quadrate of the Aegothelidae, Hemiprocnidae and Apodidae, whereas the quadrate of the Trochilidae is very different. We also report a striking disparity of the shapes of the axis vertebra of apodiform birds, which is likely to be of functional significance. Eocypselus and extant Hemiprocnidae and Cypseloidini (Apodidae) exhibit the plesiomorphic morphology, whereas a derived shape characterizes extant Aegothelidae, Apodini and Trochilidae. Furthermore, we describe the first partial skeleton of the earliest aegialornithid species, Primapus lacki Harrison & Walker, 1975, which was previously only known from the humeri of the type series that stem from different sites of the London Clay. The apodiform birds from Walton‐on‐the‐Naze show a considerable taxonomic and ecomorphological diversity, and whereas Eocypselus may have inhabited forest edges and caught insects by sallying flights from perches, Primapus probably was a fast‐flying and more aerial bird.

The galliform birds from the Lower Eocene London Clay of Walton-on-the-Naze (Essex, U.K.): New species suggest faunal connections to Asia

ABSTRACT We report stem group Galliformes from the lower Eocene (Ypresian) London Clay of Walton-on-the-Naze (Essex, U.K.), which are among the oldest known fossils of galliform birds. The specimens are assigned to two new species, ?Paraortygoides argillae, sp. nov. and Waltonortyx bumbanipodiides, gen. et sp. nov. The latter is classified in a new family-level taxon, Waltonortygidae, fam. nov., which differs from other higher-level clades of stem group Galliformes in a proximo-distally narrow caput humeri and a short tuberculum dorsale of the humerus. With regard to these plesiomorphic features and a characteristic morphology of the coracoid, Waltonortyx is similar to early Eocene stem group Galliformes from Mongolia. Wing and pectoral girdle bones of a third, undetermined galliform from Walton-on-the-Naze resemble the Quercymegapodiidae; this fossil also shows a similarity to early Eocene galliforms from Mongolia. The affinities of “Paraortygoides” radagasti Dyke and Gulas, 2002, the only previously described putative galliform from Walton-on-the-Naze, are uncertain and neither its classification in the Galliformes nor its assignment to the taxon Paraortygoides are unequivocally established. For the first time we subjected a larger taxonomic sample of early Paleogene Galliformes to a formal analysis, and even though the resulting phylogenies were poorly resolved, they supported paraphyly of the Quercymegapodiidae, with the Early Miocene taxon Ameripodius being more closely related to the crown group than the late Eocene species of Quercymegapodius. Waltonortyx bumbanipodiides was recovered as the sister taxon of the Mongolian Bumbanipodius transitoria, which indicates early Paleogene dispersal events across the Turgai Strait.

The Halcyornithidae from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK): A species complex of Paleogene arboreal birds

We report fossils of the Halcyornithidae from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The material includes remains of nine individuals of these small zygodactyl birds, which belong to at least seven different species, two of which are newly described. This documents a high species richness of halcyornithids in the London Clay, and these birds apparently underwent a significant radiation in the early Paleogene. One of the specimens includes a skull with a proportionally much smaller neurocranium than in Pseudasturides macrocephalus from Messel, suggesting an increased encephalization of halcyornithids towards the middle Eocene. A previously undescribed variation in sternum morphology of halcyornithids distinguishes the fossils we assign to the taxa Pulchrapollia and Cyrilavis and indicates that halcyornithids occupied disparate ecological niches. Furthermore, sternum morphology supports a sister group relationship between the halcyornithid taxa Pulchrapollia and Pseudasturides. The closest extant relatives of the Halcyornithidae remain elusive, but our new osteological data substantiate the hypothesis of a sister group relationship to the Messelasturidae, another group of Eocene birds with zygodactyl feet.[http://zoobank.org/urn:lsid:zoobank.org:pub:DDC1768F-1389-4F36-92F6-46DA318A0C19].

Partial skeleton from the Paleocene of New Zealand illuminates the early evolutionary history of the Phaethontiformes (tropicbirds)

We describe a new stem group representative of the Phaethontiformes (tropicbirds) from the Paleocene Waipara Greensand in New Zealand. The fossil consists of a partial skeleton with a nearly complete skull and represents the first unambiguous record of the Phaethontiformes from the Paleocene of the Southern Hemisphere. Clymenoptilon novaezealandicum gen. et sp. nov. has a proportionally shorter pelvis than Prophaethon shrubsolei from the early Eocene London Clay and appears to have been less adapted to foraging in an aquatic environment at or below sea-level. It is furthermore distinguished from P. shrubsolei and Lithoptila abdounensis from the late Paleocene/early Eocene of Morocco in a proportionally smaller foramen magnum of the skull. Together with other plesiomorphic features, this suggests that C. novaezealandicum is the sister taxon of a clade including Lithoptila, Prophaethon and crown group Phaethontiformes, and as one of the oldest stem group phaethontiforms the new species may indicate a Southern Hemispheric centre of origin of tropicbirds. After a recently described bony-toothed bird, C. novaezealandicum is the second seabird species from the Waipara Greensand to show affinities to taxa from the early Paleogene of the Northern Hemisphere. The wide early Paleogene distribution of the Phaethontiformes stands in sharp contrast to the geographic restriction of coeval diving seabirds, and different factors appear to have limited the dispersal of aquatic and pelagic seabird taxa in the early Paleogene. Gerald Mayr [Gerald.Mayr@senckenberg.de], Senckenberg Research Institute and Natural History Museum Frankfurt, Ornithological Section, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany; Vanesa L. De Pietri [vanesa.depietri@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; Al Mannering [alman@slingshot.co.nz], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand; Leigh Love [lvlove@xtra.co.nz], PO Box 49, Waipara 7483, New Zealand; Erica Crouch [e.crouch@gns.cri.nz], GNS Science, 1 Fairway Drive, Lower Hutt 5040, New Zealand; Catherine Reid [catherine.reid@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; R. Paul Scofield [pscofield@canterburymuseum.com], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand, and University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand.

Early Eocene fossils elucidate the evolutionary history of the Charadriiformes (shorebirds and allies)

AbstractWe report charadriiform and charadriiform-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). A partial skeleton of a small modern-type charadriiform is described as a new species, Charadriisimilis essexensis n. gen. n. sp., and most closely resembles taxa of the Charadrii (plovers, stilts, oystercatchers, and other “wader-like” shorebirds). Affinities to this clade were also supported by phylogenetic analyses, which placed the fossil as the sister taxon of either the Burhinidae or all crown group Charadrii. In addition, we identify specimens of the charadriiform-like taxon Scandiavis, which was before known only from the early Eocene Fur Formation in Denmark. Associated limb elements of two individuals are classified as Scandiavis cf. mikkelseni Bertelli et al., 2013, and remains of two further individuals are tentatively assigned to Scandiavis. The presence of a processus supracondylaris dorsalis on the previously unknown humerus corroborates charadriiform affinities of Scandiavis, whereas a plesiomorphic hypotarsus morphology indicates a position outside crown group Charadriiformes. Charadriisimilis essexensis is one of the earliest modern-type charadriiforms, and the holotype of the species is the most substantial early Paleogene fossil record of a charadriiform bird. Together with Scandiavis, as the best-represented taxon to be considered as a stem group charadriiform, it provides the basis for an improved understanding of the evolutionary history of charadriiform birds.UUID: http://zoobank.org/ca15ee81-09e8-4577-8beb-a362debf6636

Narrow-beaked trogons from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

We describe multiple partial skeletons of a new trogon species from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK), which are among the oldest fossils of the Trogoniformes. Eotrogon stenorhynchus, gen. et sp. nov. has a much narrower and more gracile beak than extant trogons, which denotes different ecological attributes of the fossil species. Eotrogon stenorhynchus already had the heterodactyl foot characterising extant trogons, even though the trochlea for the second toe is smaller than in crown group Trogoniformes. Differences to extant trogons in the wing and pectoral girdle elements suggest that E. stenorhynchus was less adapted to short-term hovering, which may indicate different foraging techniques. We also report a partial tarsometatarsus from the early Miocene of France that is likely to belong to Paratrogon gallicus, a species previously only known from humeri. P. gallicus is the earliest modern-type trogon, and we show that the newly identified tarsometatarsus does not support the proposed referral of this species to the African taxon Apaloderma. We identify skeletal features that suggest a sister group relationship between Apaloderma and all other crown group Trogoniformes, but the exact affinities of Paratrogon remain poorly resolved. (http://zoobank.org/urn:lsid:zoobank.org:pub:73B64B84-11C2-4D50-8540-099CF86B6CA1).

The Vastanavidae and Messelasturidae (Aves) from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

The Vastanavidae and Messelasturidae (Aves) from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

Multiple skeletons of Rhynchaeites from the London Clay reveal the osteology of early Eocene ibises (Aves, Threskiornithidae)

We describe a new species of Rhynchaeites from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK), which is represented by a partial skeleton comprising a skull and most major postcranial bones. Multiple further partial skeletons are assigned to Rhynchaeites sp. and include skeletal elements that are rarely preserved in Paleogene birds. Rhynchaeites is for the first time included in a phylogenetic analysis, which did not unambiguously resolve its affinities, but provided weak support for a sister group relationship to the Threskiornithidae. If Rhynchaeites is a stem group representative of ibises, its skeletal morphology indicates significant homoplasy in the evolution of Aequornithes, the higher level clade including the Threskiornithidae and most other aquatic or semi-aquatic birds. In particular, Rhynchaeites has much shorter legs than extant ibises and the new fossils show that its palate was schizognathous. Current phylogenies suggest that a desmognathous palate as well as long legs evolved multiple times independently within Aequornithes. Unlike in extant ibises, the tip of the beak of Rhynchaeites lacks a densely pitted surface. We hypothesize that vision played a greater role in the foraging strategy of Rhynchaeites, whereas extant ibises are tactile probers and use their beaks for “remote sensing”.

New species from the early Eocene London Clay suggest an undetected early Eocene diversity of the Leptosomiformes, an avian clade that includes a living fossil from Madagascar

We report the first records of the leptosomiform taxon Plesiocathartes from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). Two species could be distinguished, one of which is described as Plesiocathartes insolitipes, sp. nov. (the other is classified as Plesiocathartes sp.). We furthermore describe two small leptosomiform-like birds from Walton-on-the-Naze, Waltonavis paraleptosomus, gen. et sp. nov. and W. danielsi, gen. et sp. nov., which are represented by partial skeletons of multiple individuals. In plesiomorphic characters of the coracoid and furcula, the new taxon Waltonavis is distinguished from Plesiocathartes and the extant Leptosomus; the skull of Waltonavis furthermore exhibits basipterygoid processes, which are absent in Leptosomus. Another new species, Lutavis platypelvis, gen. et sp. nov., is based on a partial skeleton from Walton-on-the-Naze and closely resembles Plesiocathartes in the overall shape of the tarsometatarsus. However, L. platypelvis is clearly distinguished from leptosomiform birds in the morphology of the hypotarsus, the more massive coracoid, and other skeletal features. Although we consider close affinities to Plesiocathartes and, hence, the Leptosomiformes to be possible, we could not identify derived characters that enable an unambiguous phylogenetic placement of L. platypelvis. In any case, the new species document an unexpected diversity of Plesiocathartes-like fossil in the London Clay and may open a new perspective for a reconstruction of the ancestral morphology of the avian clade Afroaves, which includes the Leptosomiformes and other arboreal landbirds.

Psittacopedids and zygodactylids: The diverse and species-rich psittacopasserine birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

ABSTRACT The Daniels collection of fossil birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK) contains multiple specimens of the Psittacopedidae and Zygodactylidae, which are here for the first time studied in detail. The Psittacopedidae include Parapsittacopes bergdahli, Psittacomimus eos, gen. et sp. nov., ?Psittacopes occidentalis, sp. nov., and at least one further unnamed species. The Zygodactylidae comprise Primozygodactylus cf. danielsi, Primoscens cf. minutus, Primoscens carolinae, sp. nov., as well as several unnamed species, which are represented by fragmentary remains. A very small zygodactylid-like species, which was previously identified as P. minutus, is described as Minutornis primoscenoides, gen. et sp. nov. A phylogenetic analysis showed the Zygodactylidae and Psittacopedidae to be stem group representatives of the Passeriformes (passerines), but the exact interrelationships of the fossil taxa are poorly resolved. In particular, no compelling character evidence supports a monophyletic Zygodactylidae, with distinctive features of these birds being likely to be plesiomorphic for Psittacopasseres or also found in crown group Passeriformes. In the majority rule consensus tree of our analysis, Minutornis is the sister taxon of a clade including the Zygodactylidae and Passeriformes, whereas the affinities of the Psittacopedidae were insufficiently resolvedhttp://zoobank.org/urn:lsid:zoobank.org:pub:81800349-5DE9-468B-81D7-6A5664526DF1.

Early Eocene fossil illuminates the ancestral (diurnal) ecomorphology of owls and documents a mosaic evolution of the strigiform body plan

We describe a partial skeleton of a fossil owl (Strigiformes) from the early Eocene London Clay of Walton‐on‐the‐Naze (Essex, UK). The holotype ofYpresiglaux michaeldanielsi, gen. et sp. nov. is one of the most complete specimens of a Palaeogene owl and elucidates the poorly known ecomorphology of stem group Strigiformes. Whereas most of the postcranial bones show the characteristic strigiform morphology, the new species exhibits plesiomorphic features of the skull and cervical vertebrae that differ distinctly from extant owls. A well‐developed supraorbital process of the lacrimal bone suggests that the eyes were not as greatly enlarged and forward‐facing as in extant owls. A plesiomorphic quadrate morphology indicates differences in the otic region, and a proportionally longer axis suggests that the fossil species was not able to rotate its head to the degree found in crown group Strigiformes. Therefore, the fossil documents a mosaic evolution of the strigiform body plan, with owls developing raptorial adaptations before specializations of the visual and acoustic systems evolved. Because the latter relate to a crespuscular or nocturnal activity pattern, we hypothesize thatYpresiglauxwas diurnal. Nocturnality in owls may have evolved in response to the emergence of evolutionary opportunities, which enabled owls to exploit new ecological niches, or owls may have been driven into nocturnal habits by ecological competition.

Oldest fossil loon documents a pronounced ecomorphological shift in the evolution of gaviiform birds

Abstract We describe a stem group representative of Gaviiformes (loons or divers) from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The holotype of Nasidytes ypresianus gen. et sp. nov. is a partial skeleton including the mandible and all major limb bones. The new species is the oldest unambiguously identified loon and the most substantial Palaeogene fossil record of Gaviiformes. The mandible of Nasidytes is proportionally wider than that of extant loons and resembles that of extant coots (Fulica spp.), which indicates that the new taxon was less piscivorous than crown group Gaviiformes. Hypotarsus morphology suggests that N. ypresianus is the sister taxon of a clade including all other Cenozoic fossil loons and crown group Gaviiformes. According to its plesiomorphic leg morphology, and unlike extant loons, the new species was not a specialized pursuit predator of fishes. The evolution of advanced diving capabilities in the stem lineage of Gaviiformes is likely to have been correlated with an increased piscivory of loons, and the skeletal morphology of Nasidytes conforms to multiple independent origins of specialized piscivory and a highly aquatic ecology in the waterbird clade (Aequornithes).

Mastixioid fruits (Cornales) from the early Eocene London Clay Flora: morphology, anatomy and nomenclatural revision

Following on the seminal works of Reid and Chandler in 1933 and Chandler in 1961, morphology and anatomy of fossil mastixioid fruits from the early Eocene London Clay of southern England were reanalyzed with the benefit of new methods in comparison with extant genera of Mastixiaceae and with other fossil representatives from Europe and North America. The species named Mastixia cantiensis E.Reid et M.Chandler was based on a heterogeneous assemblage of specimens, all representing Mastixiaceae, some of which truly represent Mastixia whilst others correspond to Diplopanax and Mastixiopsis The holotype of M. cantiensis E.Reid et M.Chandler corresponds to extant Diplopanax rather than Mastixia. Therefore, this species is moved out of Mastixia and is treated as Diplopanax cacaoides (Zenker) comb. nov. Nine species of mastixioid fruits are currently recognized in the London Clay flora: Mastixia parva E.Reid et M.Chandler, M. cf. oregonensis (R.A.Scott) Tiffney et Haggard, Diplopanax cacaoides, Tectocarya grandis (E.Reid et M.Chandler) comb. nov., Mastixiopsis nyssoides Kirchh., Exbeckettia mastixioides (E.Reid et M.Chandler) gen. et comb. nov., Lanfrancia subglobosa E.Reid et M.Chandler, Portnallia bognorensis M.Chandler, and Langtonia bisulcata E.Reid et M.Chandler. These include the oldest known representatives of the genera Diplopanax, Tectocarya and Mastixiopsis and contribute to our understanding of the former morphological diversity and palaeobiogeography of the Mastixiaceae.

A partial skeleton of Septencoracias from the early Eocene London Clay reveals derived features of bee-eaters (Meropidae) in a putative stem group roller (Aves, Coracii)

A partial skeleton of the putative stem group roller Septencoracias is described from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). With an age of about 55 million years, the bones represent one of the earliest fossil records of a coraciiform bird. The new fossil reveals that the proximal pedal phalanges of the three anterior toes of Septencoracias exhibit markedly widened distal ends. This distinctive trait is not found in other representatives of the Coracii, but occurs in the Meropidae (bee-eaters). The quadrate likewise exhibit a derived characteristic of the Meropidae, and the beak is narrower than in rollers. These previously unnoticed features are of particular interest, because the Meropidae result as the sister taxon of the Coracii in sequence-based analyses. Calibrated molecular data suggest that the divergence between the Coracii and the Meropidae occurred at 55.6 Ma, with the new fossil being only slightly younger than this date. However, phylogenetic analyses recovered Septencoracias within the Coracii, so that the derived features shared with the Meropidae most likely are either plesiomorphic and were lost in the Coracii, or they represent parallelisms that evolved convergently in Septencoracias and the Meropidae. In any case, these traits suggest that Septencoracias differed from extant rollers in its ecological preferences and foraging mode.

An early Eocene fossil from the British London Clay elucidates the evolutionary history of the enigmatic Archaeotrogonidae (Aves, Strisores)

AbstractArchaeotrogons have long been known from late Eocene and Oligocene localities in France, where limb bones are abundantly represented. The phylogenetic affinities of these birds, however, have remained elusive. Although archaeotrogons are now considered to be representatives of the Strisores, the clade including ‘caprimulgiform’ and apodiform birds, their exact position in this clade is unresolved. Here, a partial skeleton of a new species of the Archaeotrogonidae is described from the early Eocene London Clay of Walton‐on‐the‐Naze (Essex, UK). In addition, a new specimen of the archaeotrogon Hassiavis from the latest early or earliest middle Eocene of the Messel fossil site in Germany is reported, which is the best preserved skeleton of this species. Archaeodromus anglicus gen. et sp. nov. from the London Clay is the earliest archaeotrogon known to date, and the holotype shows previously unknown skeletal characteristics of archaeotrogons that bear on the phylogenetic affinities of these birds. The quadrate in particular exhibits a distinctive morphology and shows derived morphological characteristics of the Strisores. Although the primary analysis did not conclusively resolve the affinities of archaeotrogons, analyses constrained to a molecular scaffold resulted in a sister group relationship to the Caprimulgidae (nightjars). The evolutionary history of this most species‐rich group of nocturnal Strisores is virtually unknown, and recognition of archaeotrogons as archaic stem group representatives of the Caprimulgidae would fill a striking gap in the fossil record.