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We report a tarsometatarsus and an associated pedal phalanx from the lower Eocene London Clay of Walton-on-the-Naze (Essex, UK). The specimen resembles the tarsometatarsus of the taxonLimnofregata (Fregatidae), but it belongsto a species that is distinctly larger than any other, extinct or extant, frigatebird, from which it also differs in some morphologicalfeatures. Because of a close stratigraphical and geographical provenance, as well as a similar large size andfrigatebird-like morphology, we consider it possible that the fossil belongs toMarinavis longirostris. This large seabirdwas initially described from the London Clay of Abbey Wood and is based on fragments of the rostrum, which likewiseshow a resemblance to the Fregatidae. If correctly assigned to the Fregatidae, the fossils would be among the earliestrecords of frigatebirds and the first fossils of this group of birds from the Paleogene of Europe, but we note that ourtentative classification is still afflicted with considerable uncertainty.

Key words: Aves, Fregatidae,Marinavis longirostris evolution, taxonomy.

Gerald Mayr [Gerald.Mayr@senckenberg.de; ORCID:https://orcid.org/0000-0001-9808-748X], Ornithological Section,Senckenberg Research Institute and Natural History Museum Frankfurt, Senckenberganlage 25, 60325 Frankfurtam Main, Germany.Andrew C. Kitchener [a.kitchener@nms.ac.uk; ORCID:https://orcid.org/0000-0003-2594-0827] , Department of NaturalSciences, National Museums Scotland, Chambers Street, Edinburgh EH1 1JF, UK and School of Geosciences,University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, UK.

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