Anatidae Ducks Geese and Swans

Most extant anseriform species belong to the Anatidae, which are widespread in all kinds of aquatic and semiaquatic environments. Anatids typically are short-legged birds. The crown group representatives are characterized by the reduction of the foramen for the supracoracoideus nerve on the coracoid, which in some extant representatives of early diverging lineages still forms a notch in the medial margin of the bone. The Paleogene fossil record of duck- or goose-like birds is very incomplete. The earliest unambiguously identified taxa are from late Eocene deposits of Europe. No representatives of the Anatidae are as yet known from the Paleogene of Africa.

Eonessa anaticula Wetmore, 1938 from the middle Eocene (Uinta Formation) of Utah is based on wing bones and was assigned to the Anatidae by Wetmore (1938a); this classification was disputed by Olson and Feduccia (1980a). Likewise, identification of "Anas" benedeni Sharpe, 1899 from the early Oligocene of Belgium as an anseriform was regarded incorrect by Brodkorb (1962); the material referred to this species consists of several incomplete bones of unknown whereabouts, including a humerus, an ulna, and a tibiotarsus.

Cygnopterus affinis (van Beneden, 1883) is known from several bones of a single individual from the early Oligocene (MP 23-24; Mlikovsky 2002) of Belgium. These were described by Lambrecht (1931a), who considered the fairly large species to be a representative of the Cygnini (swans). Another Paleogene species of Cygnopterus, C. lambrechti Kurochkin, 1968 from the late Oligocene (Indricotherium Beds) of Central Kazakhstan, whose holotype is the distal end of a humerus (Kurochkin 1968a), was synonymized with the phoenicopteriform bird "Agnopterus" turgaiensis Tugarinov, 1940 from the late Oligocene of Kazakhstan (Mlikovsky and Svec 1986). Mlikovsky and Svec (1986, p. 266) hypothesized that Cygnopterus may be a representative of the Phoenicopteriformes, and I also consider the phylogenetic affinities of the taxon to be uncertain and in need of a revision. Humerus, scapula, and coracoid of C. affinis are very similar to the corresponding bones of the coeval and similarly sized presumptive phoenicopteriform ?Agnopterus hantoniensis (Chap. 10; Mayr and Smith 2002a; Mayr 2005a, 2008f). The femur of C. affinis is, however, more slender than that of the Phoenicopteriformes and differs from a femur referred to ?A. hantoniensis in the low trochanteric crest.

The earliest unambiguously "duck-like" anseriform is Romainvillia stehlini Lebedinsky, 1927 from the late Eocene (MP 20; Mourer-Chauvire 1996) of France. Lebedinsky (1927) based the description of this species on a coracoid, furcula, carpometacarpus, and tarsometatarsus, but the material from the type locality also includes humeri that were not mentioned in the original description (Mayr 2008f). R. stehlini was a small species, the size of the extant Silver Teal (Anas versicolor), and is classified into the taxon Romainvilliinae. A record of Romainvillia sp. was also reported from the early Oligocene of Belgium (Mayr and Smith 2001). Paracygnopterus scotti Harrison and Walker, 1979, from the early Oligocene of England, is a further representative of the Romainvilliinae (Fig. 6.6; Mayr 2008f).

The coracoid of R. stehlini is distinguished from that of crown group Anatidae in that it still exhibits a small foramen for the supracoracoideus nerve, and in that the articulation facet for the furcula is ovate, essentially flat and in line with the medial margin of the coracoidal shaft (Fig. 6.6). The tip of the omal extremity of the furcula differs from that of crown group Anatidae in being wider and blunt. The elongate humerus is similar to that of the Presbyornithidae; as in the latter, the pneumotricipital fossa is very shallow and lacks pneumatic foramina. The short tarsometatarsus of R. stehlini is distinguished from that of crown group Anatidae in the shape of the trochlea for the second toe, which is mediolaterally narrow and lacks a proximally extending crest. The differences in the shape of the tarsometa-tarsal trochlea possibly suggest that Romainvillia was less adapted to a swimming way of living than extant Anatidae, which while paddling bring the toes together when moving the feet forward (Mayr 2008f).

Mlikovsky (2002) and Olson (1999b) assumed that R. stehlini belongs to the Anseranatidae, but a phylogenetic analysis supported the clade (Romainvillia + Anatidae), whose sister taxon are the Presbyornithidae (Mayr 2008f). Derived characters shared by Romainvillia and extant Anatidae but absent in the Presbyornithidae include the lack of a tarsometatarsal fossa for the first metatarsal, which indicates that the hallux was small as in extant Anatidae.

A putative anatid, Palaeopapia eous (Harrison and Walker, 1976), is known from a sternal fragment and a referred coracoid from the late Eocene and early Oligocene of England (Harrison and Walker 1976a, 1979a). The earliest moderntype anatids are from the earliest Oligocene of Belgium (Mayr and Smith 2001) and were tentatively assigned to Paracygnopterus in the original description. This identification is no longer upheld and the specimens are now regarded as indeterminate Anatidae (Mayr 2008f).

Crown group representatives of the Anatidae were reported from the late Oligocene of France and assigned to Mionetta blanchardi (Milne-Edwards, 1863) and M. natator (Milne-Edwards, 1867) (Hugueney et al. 2003). According to

Livezey and Martin (1988: 196), Mionetta "diverged from the rest of the Anatidae after Dendrocygna but before Stictonetta," but an analysis by Worthy and Lee (2008) resulted in a sister group relationship between this taxon and a clade including Stictonetta, Malacorhynchus, and Oxyura.

The holotype and only known specimen of the alleged swan Cygnavus formosus Kurochkin, 1968a from the early Oligocene of Kazakhstan is the distal end of a tibio-tarsus. Because this bone is damaged in C. senckenbergi Lambrecht, 1931, the early Miocene type species of the taxon Cygnavus, identification of the Kazakh specimen is arguable. Kurochkin (1968a) further assigned a distal ulna from the late Oligocene (Indricotherium Beds) of Kazakhstan to the extant taxon Somateria, but this assignment is likewise poorly founded. There is a greater possibility that the fragmentary bone belongs to one of the other taxa described by Kurochkin (1968a).

Louchart et al. (2005) detailed that Guguschia nailiae Aslanova and Burchak-Abramovich, 1968 from the Oligocene of Azerbaijan is not a swan (Cygnini), as that it was originally described (Aslanova and Burchak-Abramovich 1968). The species is known from wing remains, including a nearly complete humerus, and needs to be restudied. It is well possible that it is conspecific with the pelagornithid Caspiodontornis kobystanicus from the same locality (Aslanova and Burchak-Abramovich 1999; see Sect. 6.5).

In contradiction to Olson's (1989) assumption that the Anatidae originated in the Southern Hemisphere, the Southern Hemisphere fossil record of duck-like birds is rather scarce in the Southern Hemisphere and restricted to the late Oligocene. Teleornis impressus Ameghino, 1899 from the Deseadan of Patagonia (Argentina) was assumed to be a member of the Tadornini (shelducks) by Agnolin (2004). However, this species is represented by a distal humerus only, and although it indeed seems to be an anseriform, possibly even an anatid, additional specimens are required to establish its exact affinities. Agnolin (2004) also assigned to the Anseriformes another species from the Deseadan of Patagonia, Aminornis excavatus Ameghino, 1899, which is based on the omal extremity of a coracoid and was previously considered to be a representative of the Aramidae (limpkins; Sect. 9.3.4). The affinities of this species also have to be established with further material.

Worthy (2009) described crown group representatives of the Anatidae from the late Oligocene Etadunna Formation and Namba Formation of Australia. These were assigned to new taxa of the Oxyurini (stiff-tailed ducks) and Tadornini (shel-ducks), and are represented by many well-preserved limb bones.

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