DOI: 10.15468/yfrz6k
title: A new mousebird (Aves, Coliiformes) from the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom) constitutes a morphological link between sandcoleids and coliids

description: This dataset contains the digitized treatments in Plazi based on the original journal article Mayr, Gerald, Kitchener, Andrew C. (2024): A new mousebird (Aves, Coliiformes) from the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom) constitutes a morphological link between sandcoleids and coliids. Geodiversitas 46 (20): 979-993, DOI: 10.5252/geodiversitas2024v46a20, URL: https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2024v46a20.pdfABSTRACTWe describe a new species of the Coliiformes from the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom). Ypresicolius sandcoleiformis n. gen., n. sp. is represented by two partial skeletons and shows an overall resemblance to the Sandcoleidae in the preserved bones. However, the hypotarsus of the tarsometatarsus exhibits a characteristic derived morphology that is different from sandcoleids and closely resembles the hypotarsus of crown group Coliiformes (Coliidae). A phylogenetic analysis supported a sister group between Ypresicolius n. gen. and Pan-Coliidae, the total group including stem and crown group members of the Coliidae. We conclude that the similarities between Ypresicolius n. gen. and sandcoleids are plesiomorphic for the Coliiformes, and the low degree of morphological disparity between Ypresicolius n. gen. and sandcoleids indicates that the divergence of the sandcoleid and coliid lineages did not occur long before the earliest Eocene. The length proportions of the pedal phalanges of Ypresicolius n. gen. and sandcoleid Coliiformes are strikingly similar to those of Paleogene stem group representatives of the Strigiformes. The significance of this resemblance depends on the relationships of coliiform birds. Most current analyses do not recover owls and mousebirds as sister taxa, in which case the similar foot morphology of stem group Coliiformes and Strigiformes is either plesiomorphic for a more inclusive clade or evolved convergently in mousebirds and owls.RÉSUMÉUn coliou nouveau (Aves, Coliiformes) de l’argile de Londres de l’Éocène inferieur de Walton-on-the-Naze (Essex, Royaume-Uni) constitue un lien morphologique entre les sandcoléides et les coliides.Nous décrivons une nouvelle espèce de Coliiformes de l’argile de Londres de l’Éocène inferieur de Walton-on-the-Naze (Essex, Royaume-Uni). Ypresicolius sandcoleiformis n. gen., n. sp. est représenté par deux squelettes partiels et présente une ressemblance avec les Sandcoleidae. Cependant, l’hypotarse du tarsométatarse présente une morphologie dérivée caractéristique qui est différente de celle des Sandcoleidae et ressemble beaucoup à l’hypotarse du groupe-couronne des Coliiformes (Coliidae). Une analyse phylogénétique soutient Ypresicolius n. gen. comme groupe frère des Pan-Coliidae, le groupe total comprenant les membres du groupe-souche et du groupe-couronne des Coliidae. Nous concluons que les similitudes entre Ypresicolius n. gen. et les Sandcoleidae sont plésiomorphes pour les Coliiformes, et que le faible degré de disparité morphologique entre Ypresicolius n. gen. et les Sandcoleidae indique que la divergence des lignées des Sandcoleidae et des Coliidae ne s’est pas produite longtemps avant l’Éocène inférieur. Les proportions en longueur des phalanges des doigts d’ Ypresicolius n. gen. et des Sandcoleidae sont étonnamment similaires à celles des représentants du groupe-souche paléogène des Strigiformes. L’importance de cette ressemblance dépend des relations entre les Coliiformes. La plupart des analyses actuelles ne considèrent pas les hiboux et les colious en tant que taxons frères, auquel cas la morphologie similaire du pied des groupes-souches des Coliiformes et des Strigiformes est soit plésiomorphe, pour un clade plus inclusif, soit dérivé de manière convergente chez les colious et les hiboux.MOTS CLÉSAves,évolution,phylogénie,genre nouveau,espèce nouvelle. INTRODUCTION Mousebirds (Coliiformes) today include six very similar species of small, long-tailed birds, whose distribution is restricted to Africa south of the Sahara. The crown group representatives are classified in the taxon Coliidae and are predominantly herbivorous. However, coliiform birds had a more diversified ecology and much wider distribution in the past and are well represented in Paleogene fossils sites of Europe and North America (Mayr 2022). The earliest unequivocal coliiform birds belong to the Sandcoleidae, which include the taxa Sandcoleus, Anneavis, and Eobucco from the late Paleocene and Eocene of North America (Houde & Olson 1992) and the taxon Eoglaucidium from the middle Eocene of Germany (Mayr & Peters 1998; Mayr 2000, 2002, 2018, 2020). As detailed by Mayr (2018), the taxa Anneavis and Eoglaucidium are poorly differentiated from each other and there exists a possibility that Anneavis Houde & Olson, 1992 is a junior synonym of Eoglaucidium Fischer, 1987. In any case, the interrelationships of sandcoleid Coliiformes are unresolved, and the four taxa Sandcoleus, Anneavis, Eobucco, and Eoglaucidium were placed in a polytomy in all analyses (Mayr & Mourer-Chauviré 2004; Ksepka & Clarke 2009, 2010; Mayr 2013, 2015). Houde & Olson (1992) referred three further North American taxa to the Sandcoleidae, namely the early Eocene Chascacocolius as well as the middle Eocene Botauroides and Uintornis. Mayr & Peters (1998) proposed that Chascacocolius is more closely related to crown group Coliiformes than to the Sandcoleidae, and this hypothesis was supported by subsequent analyses (Zelenkov & Dyke 2008; Ksepka & Clarke 2009, 2010; Mayr 2013, 2015). The two species referred to Uintornis as well as the single species of Botauroides are known from distal portions of the tarsometatarsus. As noted byMayr (2018), these bones differ from the tarsometatarsus of typical sandcoleids, and at least Uintornis more likely represents a stem group representative of the Coliidae (the affinities of the poorly known Botauroides, of which no photographs have been published, need to be restudied). Another putative sandcoleid is Tsidiiyazhi abini from the mid-Paleocene of New Mexico (United States), which was described by Ksepka et al. (2017). However, this species is likewise distinguished from unequivocal representatives of the Sandcoleidae in various features (see discussion). Other early or middle Eocene Coliiformes belong to the Coliidae, the clade including crown group Coliiformes. These include the European taxa Selmes and Masillacolius from the latest early or earliest middle Eocene of Messel in Germany (Mayr & Peters 1998; Peters 1999; Mayr 2001; 2015) as well as the North American taxon Celericolius from the early Eocene Green River Formation (Ksepka & Clarke 2010). A record of Selmes also exists from the early Eocene of France (Mayr & Mourer-Chauviré 2004). A partial skeleton of an unidentified coliiform-like bird was reported from the early Eocene of the Okanagan highlands in British Columbia (Canada; Mayr et al. 2019), and associated wing and pectoral girdle bones from the early Eocene Danish Fur Formation were tentatively assigned to Chascacocolius oscitans by Dyke et al. (2004). A putative coliiform species, Eocolius walkeri, was furthermore identified in the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom) by Dyke & Waterhouse (2001), but coliiform affinities of this species have since been contested (Mayr 2009, 2022; Ksepka & Clarke 2009). Also from Walton-on-the-Naze, Mayr & Kitchener (2023a) described a bird with a mousebird-like tarsometatarsus as Sororavis solitarius (because the Latin term “avis” is feminine, this name is here corrected to Sororavis solitaria; the same considerations apply to Avolatavis europaeus described by Mayr & Kitchener 2023b, which should be A. europaea). Sororavis solitaria was assigned to the Morsoravidae, with this taxon being regarded as nested within Psittacopasseres, the clade including the Passeriformes and Psittaciformes, and therefore being only very distantly related to mousebirds (Mayr & Kitchener 2023a). FIG. 1. — Overview of the two fossils of Ypresicolius sandcoleiformis n. gen., n. sp. from the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom): A, holotype, NMS.Z.2021.40.181; B, referred specimen NMS.Z.2021.40.182. Scale bars: 5 mm. Here we report the first unequivocal coliiform birds from Walton-on-the-Naze.These fossils are among the oldest records of the Coliiformes from outside North America and exhibit a previously unrecorded character mosaic, which bridges the morphological gap between the two major coliiform clades, the Sandcoleidae and the Coliidae.Mousebirds (Coliiformes) today include six very similar species of small, long-tailed birds, whose distribution is restricted to Africa south of the Sahara. The crown group representatives are classified in the taxon Coliidae and are predominantly herbivorous. However, coliiform birds had a more diversified ecology and much wider distribution in the past and are well represented in Paleogene fossils sites of Europe and North America (Mayr 2022).The earliest unequivocal coliiform birds belong to the Sandcoleidae, which include the taxa Sandcoleus, Anneavis, and Eobucco from the late Paleocene and Eocene of North America (Houde & Olson 1992) and the taxon Eoglaucidium from the middle Eocene of Germany (Mayr & Peters 1998; Mayr 2000, 2002, 2018, 2020). As detailed by Mayr (2018), the taxa Anneavis and Eoglaucidium are poorly differentiated from each other and there exists a possibility that Anneavis Houde & Olson, 1992 is a junior synonym of Eoglaucidium Fischer, 1987. In any case, the interrelationships of sandcoleid Coliiformes are unresolved, and the four taxa Sandcoleus, Anneavis, Eobucco, and Eoglaucidium were placed in a polytomy in all analyses (Mayr & Mourer-Chauviré 2004; Ksepka & Clarke 2009, 2010; Mayr 2013, 2015).Houde & Olson (1992) referred three further North American taxa to the Sandcoleidae, namely the early Eocene Chascacocolius as well as the middle Eocene Botauroides and Uintornis. Mayr & Peters (1998) proposed that Chascacocolius is more closely related to crown group Coliiformes than to the Sandcoleidae, and this hypothesis was supported by subsequent analyses (Zelenkov & Dyke 2008; Ksepka & Clarke 2009, 2010; Mayr 2013, 2015). The two species referred to Uintornis as well as the single species of Botauroides are known from distal portions of the tarsometatarsus. As noted byMayr (2018), these bones differ from the tarsometatarsus of typical sandcoleids, and at least Uintornis more likely represents a stem group representative of the Coliidae (the affinities of the poorly known Botauroides, of which no photographs have been published, need to be restudied).Another putative sandcoleid is Tsidiiyazhi abini from the mid-Paleocene of New Mexico (United States), which was described by Ksepka et al. (2017). However, this species is likewise distinguished from unequivocal representatives of the Sandcoleidae in various features (see discussion).Other early or middle Eocene Coliiformes belong to the Coliidae, the clade including crown group Coliiformes. These include the European taxa Selmes and Masillacolius from the latest early or earliest middle Eocene of Messel in Germany (Mayr & Peters 1998; Peters 1999; Mayr 2001; 2015) as well as the North American taxon Celericolius from the early Eocene Green River Formation (Ksepka & Clarke 2010). A record of Selmes also exists from the early Eocene of France (Mayr & Mourer-Chauviré 2004).A partial skeleton of an unidentified coliiform-like bird was reported from the early Eocene of the Okanagan highlands in British Columbia (Canada; Mayr et al. 2019), and associated wing and pectoral girdle bones from the early Eocene Danish Fur Formation were tentatively assigned to Chascacocolius oscitans by Dyke et al. (2004). A putative coliiform species, Eocolius walkeri, was furthermore identified in the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom) by Dyke & Waterhouse (2001), but coliiform affinities of this species have since been contested (Mayr 2009, 2022; Ksepka & Clarke 2009). Also from Walton-on-the-Naze, Mayr & Kitchener (2023a) described a bird with a mousebird-like tarsometatarsus as Sororavis solitarius (because the Latin term “avis” is feminine, this name is here corrected to Sororavis solitaria; the same considerations apply to Avolatavis europaeus described by Mayr & Kitchener 2023b, which should be A. europaea). Sororavis solitaria was assigned to the Morsoravidae, with this taxon being regarded as nested within Psittacopasseres, the clade including the Passeriformes and Psittaciformes, and therefore being only very distantly related to mousebirds (Mayr & Kitchener 2023a).FIG. 1. — Overview of the two fossils of Ypresicolius sandcoleiformis n. gen., n. sp. from the early Eocene London Clay of Walton-on-the-Naze (Essex, United Kingdom): A, holotype, NMS.Z.2021.40.181; B, referred specimen NMS.Z.2021.40.182. Scale bars: 5 mm.Here we report the first unequivocal coliiform birds from Walton-on-the-Naze.These fossils are among the oldest records of the Coliiformes from outside North America and exhibit a previously unrecorded character mosaic, which bridges the morphological gap between the two major coliiform clades, the Sandcoleidae and the Coliidae.