Anseriformes Wagler, 1831
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publication ID |
https://doi.org/ 10.4202/app.00764.2020 |
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persistent identifier |
https://treatment.plazi.org/id/039D87AC-D95C-FFE2-FF40-FE2A329FF9BA |
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treatment provided by |
Felipe |
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scientific name |
Anseriformes Wagler, 1831 |
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Order Anseriformes Wagler, 1831 View in CoL View at ENA
Family incertae sedis
Remarks.—The new taxon( Fig.2 View Fig ) is referred to Anseriformes based on the following combination of characters: the medial angle of the proximal end is narrow and prominent, the shaft is mediolaterally compressed, the hypotarsus with one closed canal (for the tendon of m. flexor digitorum longus), the crista medialis hypotarsi is dorsoplantarly high and proximodistally elongate, the cotyla lateralis forms a characteristic distally extending “lip” on the dorsal surface of the bone, the plantar opening of the medial proximal vascular foramen is shifted proximally towards the proximal part of the hypotarsus. In particular, these features (except the structure of the hypotarsus) distinguish the new fossil from diving Alcidae . The structure of the hypotarsus is also more complicated in Alcidae . Yet another character of the new fossil that is shared with Anseriformes is the presence of a tubercle on the lateral surface of the bone just distal to the level of the hypotarsus. The hypotarsus of the new form is somewhat similar to that of some Galliformes, but aquatic forms with thick bone walls are not known for these ground and usually forest-dwelling birds. Galliformes further have well-developed fossae parahypotarsales.
The new taxon represents stem-Anatidae sensu lato ( Anatidae + Dendrocygnidae ) because it does not possess an apomorphic dorsoplantarly low hypotarsus with four crest and three well-defined sulci, which invariantly characterizes crown anatids ( Mayr 2016). Instead, the tarsometatarsus of the new form is high and has only two pronounced crests bordering one medial canal (for the tendon of m. flexor digitorum longus) together with a plantarly located sulcus. This structure of the hypotarsus is definitively more derived than in Anhimidae and fossil Presbyornithidae , which have only one medial sulcus ( Mayr and Smith 2017). The presence of closed medial hypotarsal canal distinguishes the new taxon from fossil Paranyroca Miller and Compton, 1939 ( Paranyrocidae, Mayr and Smith 2017 ), which otherwise have similar outlines of the hypotarsus, though a similarly-built hypotarsus with a canal might have been present in Saintandrea , a large-sized representative of Romainvilliidae, but the referred specimen is not sufficiently preserved to confirm it ( Mayr and De Pietri 2013). Although affinities of the new taxon with Romainvilliidae seem probable, the type genus Romainvillia Lebedinsky, 1927 has a morphologically rather different tarsometatarsus, more similar to that of Anatidae ( Mayr 2008) . Anseranatidae also have one closed medial hypotarsal canal, but otherwise are characterized by a more complex and an autapomorphically strongly laterally shifted hypotarsus, which might have evolved independently from Anatidae ( Mayr and Smith 2017) . Thus, the familiar assignment of the new taxon is unclear; it may represent a separate undescribed family of belong to either stem Anseranatidae , specialized Romainvilliidae or Paranyrocidae . The latter assignment appears to be most probable. The presence of a distinct distally extending lip of the cotyla lateralis (see below) indicates that the new genus occupies a more derived position than Anseranatidae .
Genus Cousteauvia nov.
ZooBank LSID: urn:lsid:zoobank.org:act:8C421BB2-4B4D-47F1-BAF0-74E3D2400964
Type species: Cousteauvia kustovia gen. et sp. nov., monotypic; see below.
Etymology: In honor of ocean explorer and prominent diver Jacques- Yves Cousteau (1910–1997), appealing to the fact that the new taxon is the oldest known (and presumably the first evolved) diving crownanseriform bird. The gender is feminine.
Diagnosis.—As for the type species, by monotypy.
Remarks.— Cousteauvia differs from all known anseriforms by having a highly prominent dorsomedial crest, running distally from the tip of the cotyla medialis, and further by the presence of a crista plantaris medialis, representing a continuation of the medial hypotarsal crest. Cousteauvia further differs from crown-group ducks ( Anatidae and Dendocygnidae) by the hypotarsus having only two (instead of four) crests and a common broad lateral sulcus.
Cousteauvia kustovia sp. nov.
Fig. 2A View Fig .
ZooBankLSID: urn:lsid:zoobank.org:act:45AFA67E-25E5-4A42-A066-204CFCA2CBDF
Etymology: In reference to the geological origin of the specimen (Kusto Svita), which is itself named after the Kusto river.
Holotype: PIN 2612 View Materials /4, proximal half of left tarsometatarsus.
Type locality: Kusto-Kyzylkain (“Plesh”), Kusto Svita, Zaysan Basin, Eastern Kazakhstan ( Fig. 1 View Fig ).
Type horizon: Late Priabonian (MP 19–MP 20); latest Eocene (see Emry et al. 1998; Tleuberdina 2017).
Diagnosis.—Medium sized anseriform, roughly similar in size to modern wild specimens of Anas platyrhynchos . Proximal tarsometatarsus with bulbous and proximally prominent eminentia intercotylaris; cotyla medialis oval-shaped, narrow and dorsally protruding; articular surface of the cotyla medialis does not extend on the medial surface of eminentia intercotylaris; cotyla lateralis wider and with cut dorsolateral angle; dorsomedial margin of the shaft forming prominent ridge; dorsolateral ridge vestigial; tuberositas m. tibialis cranialis short; hypotarsus moderately low, with closed medial canal for m. flexor digitorum longus and two plantar grooves, sulcus for m. fibularis longus absent; crista medialis hypotarsi is the best developed and extends moderately distally as a low crista medialis plantaris; caudal surface of the bone distal to hypotarsus slightly inclined medially (not flat); bone walls very thick.
Description.—The holotype represents a well-preserved proximal half of the left tarsometatarsus with complete proximal articular articular area and hypotarsus ( Fig. 2 View Fig ). The shaft is notably narrowed relative to the proximal end, being roughly similar to the condition in Presbyornithidae and Anseranatidae but unlike Anhimidae , Romainvillia and Anatidae sensu lato. A similarly widened proximal end might have also been present in large romainvilliid Saintandrea Mayr and De Pietri, 2013 ( Mayr and De Pietri 2013). The cross-sectional area of the mid-shaft is sub-trapezoid. The bone walls are very thick as in modern diving Anatidae and in contrast to thin bony walls of dabbling ducks ( Fig. 2 View Fig ).
The eminentia intercotylaris is roughly symmetrical and bulbous, and it protrudes further proximally than the medial border of the cotyla medialis, as in Saintandrea and some non-anseriform taxa (e.g., Palaelodidae ), but unlike all other fossil and modern Anseriformes . In Anatidae and Anseranatidae , the eminentia is asymmetrical and its more pointed tip is inclined medially. Anhimidae have an even bigger, but also symmetrical eminentia intercotylaris. In proximal view, the eminentia intercotylar is also prominent and extends plantarly approximately up to the mid-point of the cotylae, whereas it is restricted to the dorsal part of the articular area in Anatidae . The articular surface of the cotyla medialis does not expand on the medial wall of the eminentia, in contrast to the condition in Anatidae .
The cotyla medialis is oval-shaped and rather narrow; it protrudes more dorsally than the eminentia intercotylaris unlike the condition in all other Anseriformes except the supposed late presbyornithid Wilaru tedfordi Boles, Finch, Hofheins, Vickers-Rich, Walters, and Rich, 2013 , in which this cotyla is, however, unusually mediolaterally wide ( De Pietri et al. 2016). The dorsal margin of the cotyla medialis is distinctly convex, which is different from nearly straight margin in all other anseriforms except Anhimidae . The cotyla lateralis is wider than the cotyla medialis and is sub-circular in shape as in Paranyroca but unlike all other Anseriformes . The dorsomedial angle of the cotyla lateralis is prominent (as in Paranyroca ) because of the well-developed “lip” ( Fig. 2 View Fig : l), extending to the dorsal surface of the bone. This lip is positioned entirely on the dorsolateral edge of the bone in Anatidae , whereas in Cousteauvia it is strongly shifted medially. The condition in Romainvillia is unclear due to poor preservation. Such a “lip” (distal extension of the cotyla lateralis) is not present in Anhimidae , Presbyornithidae and Anseranatidae and hence may represent an apomorphy of Anatidae sensu lato + Cousteauvia . The exact state of this character in Romainvilliidae is unclear, but Paranyroca may have a similar morphology. Plantar parts of both cotylae medialis et lateralis are bordered by not high but distinct beads, which are present in Presbyornithidae , but are absent or at least indistinct in Anatidae and other Anseriformes . The condition in Romainvilliidae is unclear.
Dorsally, there are two distinct concavities in the proximal margin of the bone, formed by the cotylae. The lateral concavity protrudes distinctly more distally than the medial one, as in Presbyornithidae and many Anatidae , but unlike Paranyroca . The condition of this feature in Romainvilliidae is unclear, but Saintandrea appears to be similar to Paranyroca in this respect ( Mayr and De Pietri 2013). The fossa infracotylaris is deep proximally as in most Anseriformes except Anhimidae ( Anseranatidae have a moderately excavated fossa). The foramina vascularia proximalia are small and relatively widely separated, as in Anatidae . The tuberositas m. tibialis cranialis are short and proximally located, as in Anhimidae , Presbyornithidae , and Anseranatidae . In the more derived anseriforms, the tuberositas are notably elongate and shifted distally.
The most unusual feature of Cousteauvia kustovia gen. et sp. nov. is the relative development of the dorsal lateral and medial crests, which border the fossa infracotylaris. In all known Anseriformes except Anseranatidae , the lateral crest is more prominent (both in robustness and the degree of dorsal protrusion) than the medial one, and this asymmetry is especially well-pronounced in diving taxa (e.g., Oxyurini , Mergini ). Cousteauvia kustovia gen. et sp. nov. displays an alternative condition, with the medial crest being higher and more dorsally prominent than the lateral one. As a result, in medial view only the dorsomedial crest is visible in Cousteauvia kustovia gen. et sp. nov. ( Fig. 2A 2 View Fig : cdm) and Anseranatidae , whereas in other anseriforms the dorsolateral crest is also visible as it protrudes dorsally well above the medial one ( Fig. 2B 2 View Fig : cdl). This medial crest continues distally, forming a low medial wall of the dorsal sulcus (sulcus extensorius), as in Presbyornithidae and Anseranatidae , but not other Anseriformes . An apparently more poorly defined sulcus extensorius is visible in Cygnopterus alphonsi Cheneval, 1984 and Paranyroca magna Miller and Compton, 1939 ( Mayr and Smith 2017: fig. 1). Modern Anserini also have a well-developed (although less prominent) dorsomedial crest.
The medial surface of the bone is slightly concave, forming a rather shallow but still distinct fossa parahypotarsalis medialis, which is totally absent in Anatidae , but a relatively-well defined fossa is present in Anseranatidae and Presbyornithidae . A large vascular foramen is present in the middle area of the fossa. The fossa parahypotarsalis lateralis does not form a concavity, being nearly vestigial. However, the lateral side of the shaft is not flat proximally, but have a slightly sloping plantar part. Two muscular/ligamental scars are present in this area, one is located dorsoproximally, and the other one is shifted distally and plantarly. Distally the lateral surface of the tarsometatarsus is flat as in modern Anatidae .
The hypotarsus is low and in general proportions is most similar to that of Paranyroca (see Mayr and Smith 2017), from which it still differs in having a closed canal for the tendon of m. digitorum longus, as in Anseranatidae , Dendrocygnidae and most Anatidae . The medial hypotarsal crest, bordering this canal and a plantarly located sulcus, is prominent and continues distally as a gradually lowering crista medialis plantaris, a feature which is not present in any other Anseriformes (the medial hypotasal crest is still elongate in Anserini ). This crest distally borders a distinct sulcus for the tendon of m. digitorum longus, which is also lacking in all other Anseriformes . Lateral of the abovementioned canal, the hypotarsus forms one broad sulcus, as in Paranyroca . Unlike Paranyroca and Anatidae , the hypotarsus extends as much laterally as the lateral margin of the cotyla lateralis. In medial view, the straight proximal wall of the hypotarsus is oriented sub-perpendicular to the long axis of the bone, unlike Anatidae , where this wall is angled and sometimes concave. Distally to the hypotarsus, the plantar surface of the shaft slopes laterally more notably than in Anatidae due to the plantar prominence of the medial part of the shaft (as in modern Cereopsini).
Remarks.—The Kusto Svita has yielded a stem-anatid taxon Romainvillia kazakhstanesis (Zelenkov 2018) , which must be compared with Cousteauvia kustovia gen. et sp. nov. Romainvillia kazakhstanesis is known from a coracoid that is very similar to the coracoid of Romainvillia stehlini Lebedinsky, 1927 from the contemporary latest Eocene of France Mayr 2008). Given such a close similarity of the coracoids in two species, it would be reasonable to assume the same for their tarsometatarsi. However, the tarsometatarsus of R. stehlini significantly differs from that of Cousteauvia kustovia gen. et sp. nov., preventing any possible association of the new Kazakh specimen with Romainvillia . In R. stehlini , the tarsometatarsus is of typical anatid proportions and the shaft is not restricted relative to the proximal end, the dorsolateral margin of the proximal part of the shaft is thick and dorsally protruding, at least one visible tuberculum m. tibialis cranialis is elongate, the sulcus extensorius is poorly pronounced due to the absence of the dorsomedial ridge of the shaft, and the medial plantar ridge and a distally extending sulcus for the tendon of m. flexor digitorum longus are absent. These features thus clearly distinguish R. stehlini from Cousteauvia kustovia gen. et sp. nov. and strongly indicate closer affinities of Romainvillia with Anatidae . Additionally, in overall size, the tarsometatarsus of R. stehlini is comparable with modern small-sized teals ( Mayr 2008), whereas Cousteauvia kustovia gen. et sp. nov. was a larger bird approximating wild specimens of A. platyrhynchos , judging from the size of the articular surface.
Stratigraphic and geographic range.— Type locality and horizon only.
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