A crown‐group galliform bird from the Middle Eocene Bridger Formation of Wyoming

Abstract

ABSTRACT. Despite an extensive described fossil record of Galliformes (Aves:`landfowl'), very few specimens have been considered within a phylogenetic context. Here we present a cladistic analysis and description of a new, well-preserved and well-dated fossil specimen from the Middle Eocene Bridger Formation of Wyoming (c. 50 Ma). Amitabha urbsinterdictensis gen. et. sp. nov. is assigned to Galliformes on the basis of the presence of derived characters including double, and open, incisurae laterales on the sternum and an incisura capitis of the proximal humerus that is enclosed from the crus dorsale fossa by a distinct ridge. Amitabha is considered to be a member of the large and diverse`phasianoid' clade of Galliformes (including, for example, the pheasants, peafowl and turkeys) owing to a lack of extensive pneumaticity in the sternal plate. The age of this avian taxon and degree of preservation allow for a discussion of the use of fossil birds for the calibration of`molecular clock' hypotheses and dating divergences within Neornithes in general, and Galliformes in particular.KEY WORDS: Eocene,`landfowl', Galliformes, Wyoming, cladistics, phylogeny.T H E avian order Galliformes (`landfowl') includes such familiar taxa as junglefowl, peacocks and turkeys and generally has been considered to be one of the more basal clades of modern birds ( Neornithes sensu Cracraft 1988,`crown-clade' Aves of others; Gauthier 1986; Gauthier and de Queiroz 2001). Existing systematic treatments of these birds (e.g. Sibley and Monroe 1990;McGowan 1994) suggest that the order comprises at least ®ve distinct families, the Megapodiidae (megapodes and relatives), Numididae (guineafowl), Phasianidae (pheasants and relatives), Odontophoridae (New World quails), and Cracidae (curassows and relatives;Wetmore 1960;Cracraft 1981;Sibley and Ahlquist 1990). Recent cladistic analysis of over 100 morphological characters (Dyke and Gulas 2002;Dyke et al. 2003) found a basalmost, monophyletic Megapodiidae to be the sister-group to all other Galliformes, followed by Cracidae as the sister-group to the`phasianoids' (Text-®g. 1).Upon initial inspection, the described fossil record of this avian order appears extensive: reputed remains of galliform birds are described from deposits that range in age from the latest Cretaceous to the Recent (Brodkorb 1964;Unwin 1993; Hope in press). However, the fragmentary nature of supposed fossil galliform' records from the Cretaceous (Hope in press) as well as problems resulting from the polarization of the few phylogenetically informative characters preserved in these specimens (Clarke 1999) places the oldest certain record of the order (described to date) in the Lower Eocene Green River Formation of the United States (Grande 1984). This taxon, Gallinuloides wyomingensis Eastman, 1900, was placed within the family Gallinuloididae by Lucas (1900), now also considered to contain a number of somewhat younger and incompletely known specimens (Milne-Edwards 1867±71;Tordoff and Macdonald 1957;Crowe and Short 1992;. A num...

Broken gears in the avian molecular clock: new phylogenetic analyses support stem galliform status forGallinuloides wyomingensisand rallid affinities forAmitabha urbsinterdictensis

“…Gulas‐Wroblewski and Wroblewski (2003, p. 1272) listed two characters supporting referral of A. urbsinterdictensis to Galliformes: (i) “double, and open, incisurae laterales on the sternum” and (ii) “incisura capitis of proximal humerus enclosed from crus dorsale fossae by a distinct ridge”. The status of the first character cannot be determined because the caudal half of the sternum is broken off in the holotype.…”

“…The phylogenetic analysis conducted by Gulas‐Wroblewski and Wroblewski (2003) placed A. urbsinterdictensis as part of a clade including Odontophoridae and Phasianidae. However, this analysis provided no test of the higher‐level relationships of the fossil because only crown species of Galliformes were included in the ingroup.…”

“…Amitabha urbsinterdictensis was originally described by Gulas‐Wroblewski and Wroblewski (2003) as a crown galliform belonging to a clade including Odontophoridae and Phasianidae, a more exclusive placement within crown Galliformes than that proposed for G. wyomingensis . This assignment was immediately criticized by Mayr and Weidig (2004), who argued that there were several flaws in the phylogenetic analysis and that the fossil lacked convincing galliform apomorphies.…”

“…2E) and Messelornithidae. Absence of an elongate scar for accessory attachment of the tendon of m. supracoracoideus (see Baumel and Witmer, 1993). Gulas‐Wroblewski and Wroblewski (2003) coded an elongate supracoracoideus scar as present in A. urbsinterdictensis and extant Galliformes, but absent in outgroups. This coding conflates the accessory attachment scar (characteristic of Galliformes) with the tuberculum dorsale (the primary insertion site of the tendon of m. supracoracoideus, a feature present in all extant birds).…”

Bird Evolution Across the K–Pg Boundary and the Basal Neornithine Diversification

“…Use of fossil taxa is usually restricted to outgroups (Mayr & Clarke, 2003;Livezey & Zusi, 2006 or included in analyses restricted to less inclusive clades, often at "ordinal" level (e.g. Ericson, 1997;Livezey, 1997;Dyke & Gulas, 2002;Mayr, 2002Mayr, , 2003Mayr, , 2005bDyke, 2003b;Gulas-Wroblewski & Wroblewski, 2003;Mayr & Mourer-Chauviré , 2004). However, recent phylogenetic analyses have employed several fossil and extant taxa, but unfortunately only sampled for single extinct clades (Odontopterygiformes or Sphenisciformes) and had somewhat skewed taxonomic distributions (e.g.…”