Genus
Selenonetta Zelenkov, gen. nov.
Etymology. From Selene (ancient Greek Goddess of the moon) and Netta (the modern duck genus).
Type species. Selenonetta lacustrina sp. nov.
Diagnosis. In the humerus, incisura capitis does not form a notch in the ventroproximal profile of
the bone (between the caput humeri and the ventral margin of the tuberculum ventrale); the distance from the dorsal margins of the crus dorsale fossae to the caudal shaft ridge is noticeably smaller than the dorsoventral width of the fossa pneumotricipitalis at this level; the caudal shaft ridge is fairly well defined and oriented between the tuberculum dorsale and caput humeri; the cross section of the shaft is subtriangular; tuberculum dorsale is clearly elongated; its distal corner is sharp and “lowered” to the shaft level; crista deltopectoralis is short (its length is comparable with the dorsoventral width of the proximal end); its dorsal surface is moderately concave; crus dorsale fossae is dorsoventrally oriented and tuberculum ventrale is caudally oriented; fossa pneumotricipitalis is nonpneumatized; caput humeri moderately overhangs the dorsal surface of the shaft.
Species composition. Type species.
Comparison. The humerus of
Selenonetta is characterized by the combination (unique to Anatidae) of an elongated tuberculum brachiale, the absence of the notch of the incisura capitis in the ventroproximal profile of the bone, as well as by a nonpneumatized fossa pneumotricipitalis and a narrow distance between the crus dorsale fossae and caudal shaft ridge (narrow dorsal tricipital fossa). The absence of the incisura capitis notch is apparently a plesiomorphic feature for Anatidae, which is characteristic, in particular, of the Oligocene genus
Pinpanetta (Worthy, 2009). At the same time,
Pinpanetta has a long crista deltopectoralis and a short and high (caudally protruding) tuberculum dorsale (as in modern Dendrocygninae), while the crista deltopectoralis in
Selenonetta is shortened and its tuberculum dorsale is elongated and has a pointed and lowered distal angle. The latter feature is an advanced one characterizing Anatinae. With respect to the width of the dorsal tricipital fossa and the whole outline of the proximal end, Selenonetta is closest to
Nettapus, from which it differs in the non-pneumatized fossa pneumotricipitalis (pneumatized in
Nettapus) and the above-mentioned absence of the incisura capitis notch. The caudal shaft ridge is noticeably less pronounced in
Nettapus than in
Selenonetta.
Selenonetta differs from the fossil genus
Helonetta (which is also similar to
Nettapus Emslie,
1992)) in the absence of the incisura capitis notch and an elongated tuberculum dorsale. As can be judged from the description (Emslie, 1992),
Helonetta does not differ from
Nettapus in the structure of the fossa pneumotricipitalis.
The combination of an elongated tuberculum dorsale and a non-pneumatized fossa pneumotricipitalis
is present in modern Mergini (except
Mergus, in which this fossa is pneumatized), from which
Selenonetta differs in a narrow dorsal tricipital fossa, the absence of the notch of the incisura capitis, and the caudal orientation of the tuberculum ventrale (in Mergini, this tubercle is oriented more distally and overhangs the fossa pneumotricipitalis). It also differs from the fossil genus
Protomelanitta (supposed basal Mergini; Zelenkov, 2011; Stidham and Zelenkov, 2017) in a narrow dorsal tricipal fossa and the absence of the incisura capitis notch, an expanded caput humeri, and an elongated tuberculum dorsale.
Remarks. The diagnosis of the genus is based on the proximal end of the humerus, which is a highly diagnostic element of the skeleton of Anatidae and, in particular, has a characteristic morphology in
Selenonetta. See the description of other bones below in the description of the type species.
The humerus of Selenonetta demonstrates a combination of plesiomorphic and progressive traits, which
is not characteristic of other modern and fossil ducks, thereby making it difficult to assess the phylogenetic position of this taxon. The combination of the elongated tuberculum brachiale and closed (non-pneumatized) fossa pneumotricipitalis brings
Selenonetta close with Mergini and
Aythya; however, the absence of the notch of the incisura capitis indicates the basal position of this fossil genus not only with respect to Mergini but also with respect to all Anatinae. The absence of the pneumatization of the fossa pneumotricipitalis may also prove to be a plesiomorphic feature characterizing, in addition to Mergini (apparently, the basal representatives of Anatinae; Sun et al., 2017), also Oxyurinae and
Malacorhynchus. At the same time, the general structural similarity with
Nettapus can be considered as an advanced feature indicating the attribution of
Selenonetta to the basalmost radiation of Anatinae. The humerus of
Mioquerquedula minutissima, the type species of the genus
Mioquerquedula, is unknown (Zelenkov, 2023); however, the humerus of the somewhat larger species
M. soporata morphologically significantly differs in the presence of a distinct notch of the incisura capitis (an advanced feature with respect to
Selenonetta) and a short subtriangular tuberculum dorsale (a primitive
character with respect to
Selenonetta).
Very small coracoids from Tagay, which are here assigned to
Selenonetta lacustrina, differ from similarly
sized
M. minutissima in general outlines. As in modern Anatini, the caudal (sternal) expansion of the shaft in
M. minutissima is moderately developed, while it is distinct in
S. lacustrina, which is expressed in a noticeable concavity of both margins (in particular, the medial one) of the central part of the coracoid. The outlines of the coracoid shaft indicate that, with respect to the morphology of the sternal expansion, the coracoid of
S. lacustrina was closer to
Malacorhynchus and early Miocene
“Mionetta” natator than to Anatini and
Mioquerquedula soporata. In turn, this indicates a distinct evolutionary level of the
Selenonetta coracoid and confirms the separate generic status of the smallest duck from Tagay. The structure of the carpometacarpus also distinguishes
Selenonetta from
Mioquerquedula.
Selenonetta lacustrina Zelenkov sp. nov.
Mioquerquedula sp.: Zelenkov, Martynovich, 2012, p. 14; 2013, p. 80; Gorobets, 2013, p. 72; Zelenkov and Kurochkin, 2015, p. 170.
Etymology. From Latin lacustris (lacustrine).
Holotype. NMNHU-P No Av-52, proximal fragment of the left humerus; Baikal Region, Tagay locality; Lower–Middle Miocene; material collected by N.A. Logachev, 1957–1958.
Material. In addition to the holotype, specimens from the type locality: specimen PIN, nos. 2614/198, proximal fragment of the right humerus, horizon “E”; 2614/181, 193, two incomplete coracoids; 2614/180, left scapula (all from horizon “A”); 2614/385, proximal fragment of the right carpometacarpus, horizon “E”; 2614/396, proximal fragment of the left carpometacarpus, horizon “A”; 2614/392, distal end of the right tibiotarsus, horizon “E”; and 2614/365, fragmentary shaft of the left tarsometatarsus, horizon “C”.
Species composition. The genus
Selenonetta includes one species.
Remarks. The remains of the tiniest duck among the small ducks from Tagay (on the lower size limit for the family Anatidae) were assigned to this species. With respect to the absolute dimensions, this form is comparable to modern
Nettapus auritus or
Spatula hottentota, but distinctly smaller than
Anas crecca and, apparently, slightly smaller than
M. minutissima. This form was previously designated as
Mioquerquedula sp. 2 (Zelenkov and Martynovich, 2013; Zelenkov and Kurochkin, 2015); however, the morphology of the humerus and coracoids of the smallest duck from Tagay indicates its separate generic status (see above).
In addition to the holotype, another very small proximal humerus is known from Tagay (specimen
PIN, no. 2614/198), which is assigned here to
S. lacustrina. In specimen PIN, no. 2614/198, tuberculum
dorsale is incompletely preserved; however, one can clearly see its general elongation, a progressive feature that is characteristic of the holotype and distinguishes
S. lacustrina from
Mioquerquedula soporata (examplified by specimen PIN, no. 4869/107 from Sharga) and specimen PIN, no. 2614/342, assigned to
T. palaeobaikalensis. The ventral margin of the tubercle in specimen PIN, no. 2614/198 is largely oriented along the long axis of the bone, while it is oriented approximately at an angle of 45° in specimen PIN, no. 4869/107 and specimen PIN, no. 2614/342. Modern
Nettapus also have a slightly more shortened tuberculum. The dorsal surface of the crista deltopectoralis is nonconcave (also a progressive feature); there is a moderately pronounced caudal ridge on the caudal surface of the shaft. The degree of development of this ridge is comparable to that in specimen PIN, no. 4869/107 from Sharga, which is assigned to
Mioquerquedula, but somewhat lower than that in
Tagayanetta. The base of the crus dorsale fossae is preserved, which shows that the area between the crus and caudal ridge was very narrow, as in the holotype and in contrast to the wide area (“dorsal tricipital fossa”) in
Malacorhynchus, Oxyurinae, and Mergini. The width of this area corresponds to the configuration in
Nettapus and Anatini, although the latter have an indistinct caudal crest. The cross section of the shaft at the level of the distal part of the crista deltopectoralis is subtriangular. The inner (dorsal) wall of the fossa pneumotricipitalis is solid and non-pneumatized; a medium-sized pneumatic foramen is visible in its deep part. This region is morphologically most similar to that of modern
Aythya, which have no defined pneumatization of the fossa pneumotricipitalis and, at the same time, may also have foramens in the solid dorsal wall of the fossa. While the absolute thickness of the shaft is similar to that of
N. auritus, the crista deltopectoralis is longer; its distal part is oriented more cranially than dorsally (unlike
Nettapus but similarly to Anatini).
Two incomplete coracoids (specimen PIN, nos. 2614/181, 193) were also assigned to this taxon; they
are similar to the coracoids of
M. minutissima in general dimensions and, at the same time, differ from
them in smaller facies articularis humeralis (at a similar length of the glenoid articular part and with the
same size of the cotyla scapularis) and the presence of a ventrally defined fossa inside the sulcus m. supracoracoidei (in
Mioquerquedula, the surface of the sulcus is flat or slightly concave, but without a defined fossa). A characteristic feature of these coracoids that distinguishes them from
M. minutissima is the narrowing of the middle part of the shaft, which is formed by the concavity of its lateral and medial margins. In
Mioquerquedula, the margins of the shaft have a more parallel orientation in the middle part. These coracoids are also characterized by a convex medial margin of the shaft at the level of the facies articularis humeralis (between the processus procoracoideus and proc. acrocoracoideus), which is absent in
Mioquerquedula. These coracoids are very similar to those of the smallest duck, Anatidae gen. indet., from Sansan (Zelenkov, 2023).
The left scapula (specimen PIN, no. 2614/180) corresponds in size to
N. auritus and is also assigned here to this taxon. This specimen is smaller than the other scapula fragments from Tagay; it is characterized
by an elongated acromion, which, in contrast to specimen PIN, no. 2614/463 (assigned to T
. palaeobai-
kalensis), is oriented noticeably more cranially than dorsally. Facies articularis humeralis is elongated; the
general curvature of the bone is weakly pronounced. Morphologically, specimen PIN, no. 2614/180 is close to modern Anatini.
Two fragmentary carpometacarpi from Tagay (specimens PIN, nos. 2614/385, proximal fragment of the right carpometacarpus, and 2614/396, proximal fragment of the left carpometacarpus) are assigned to
this taxon; they differ from
M. palaeotagaica in a small size and a lower processus exensorius, as well as in an unpronounced depressio muscularis externa, a rather large and concave fossa infratrochlearis (in Anatini, this fossa is usually very small and forms a punctate depression), a proximally protruding dorsal semitrochlea of the trochlea carpalis, and a distinct fovea carpalis cranialis. On the whole, these carpometacarpi are closer to modern Mergini. They differ from the smallest carpometacarpus from Sansan in a somewhat smaller size, the presence of a distinct saddle-shaped notch in the distocranial contour of the os metacarpale alulare, a lower processus extensorius, and a shortened proximal part of the proximal end (proximal to the processus pisiformis).
Other materials are represented by the distal end of the right tibiotarsus (specimen PIN, no. 2614/392)
and the fragmentary shaft of the left tarsometatarsus of a subadult individual (specimen PIN, no. 2614/365), corresponding in size to modern
N. auritus. In the tibiotarsus, the condylus medialis is oriented subparallel to the condylus lateralis (as in
Nettapus) and is medially not inclined (unlike Anatini). Tibiotarsus is craniocaudally low in distal view; it is somewhat lower than that in Anatini and noticeably lower than in
Nettapus; incisura intercondylaris is narrow at its base, as in
Nettapus. Tarsometatarsus has a uniform thickness of the shaft; i.e. it is not narrowed in the central part.
Fred
Coracoids (1–8), tibiotarsus (9), maxillary rostrum (fig. 10), carpometacarpus (11–14), scapulae (15–17), humeri (18–20)), and tarsometatarsi (21–23) of Early–Middle Miocene and modern Anatidae in dorsal (1, 2, 3a–8a, 10b, 21a, 22a, 23b), ventral (3b‒8b, 10c, 11–14, 21b, 22b), distal (fig. 9a), cranial (9b, 20b), lateral (10a, 15–17, 21c–23c), caudal (18, 19, 20a), and medial (3c, 4c, 21d) views.
Figs. 1 and 19. Mioquerquedula soporata (Kurochkin, 1976): (1) specimen MNHN, no. SA 10283; France, Sansan locality; Middle Miocene; (19) specimen PIN, no. 4869/107; Mongolia, Sharga locality; Middle Miocene.
Figs. 2, 3, 10, 14, 16, 18, and 21. Tagayanetta palaeobaikalensis gen. et sp. nov.: (2) specimen PIN, no. 2614/338; (3) holotype PIN, no. 2614/337 (reflected); (10) specimen PIN, no. 2614/393; (14) specimen PIN, no. 2614/389; (16) specimen PIN, no. 2614/463; (18) specimen PIN, no. 2614/342; (21) specimen. PIN, no. 2614/340; Baikal Region, Tagay locality; uppermost Lower Miocene.
Figs. 4, 9, 13, 15, and 22. Mioquerquedula palaeotagaica sp. nov.: (4) holotype PIN, no. 2614/177; (9) specimen PIN, no. 2614/386; (13) specimen PIN, no. 2614/458; (15) specimen PIN, no. 2614/454 (reflected); (22) specimen PIN, no. 2614/339; Baikal Region, Tagay locality; uppermost Lower Miocene.
Fig. 5. Mioquerquedula integra (Miller, 1944) comb. nov., specimen UCMP, no. 37370; United States, South Dakota, Flint Hill locality; Lower Miocene.
Figs. 6, 12, 17, 20, and 23. Selenonetta lacustrina gen. et sp. nov.: (6) specimen PIN, no. 2614/181; (12) specimen PIN, no. 2614/385; (17) specimen PIN, no. 2614/180; (20) holotype NMNHU-P No Av-52; (23) specimen PIN, no. 2614/365 (reflected); Baikal Region, Tagay locality; uppermost Lower Miocene.
Fig. 7. Mioquerquedula minutissima Zelenkov et Kurochkin, 2012, holotype PIN, no. 4869/193; Mongolia, Sharga locality; Middle Miocene.
Fig. 8. Anatidae gen. indet. (
?Selenonetta lacustrina gen. et sp. nov.), specimen MNHN, no. SA 14006; France, Sansan locality; Middle Miocene.
Fig. 11. Nettapus coromandelianus Gmelin, 1789, specimen from the osteological collection of PIN RAS, no. 40-7-1, modern. Designations: ca, crista acrocoracoidea; cdp, crista deltopectoralis; ch, caput humeri; cl, cotyla lateralis; clh, crista lateralis hypotarsi; cm, cotyla medialis; cs, cotyla scapularis; csr, caudal shaft ridge of the humerus; dtf, dorsal tricipital fossa; eic, eminentia intercotylaris; fac, facies articularis clavicularis; fah, facies articularis humeralis; fas, facies articularis sternalis; fic, fossa infracotylaris; fpl, fossa parahypotarsalis lateralis; fpt, fossa pneumotricipitalis; iic1, developed notch of the incisura capitis in the ventroproximal profile of the humerus; iic2, undeveloped notch of the incisura capitis in the ventroproximal profile of the humerus; mm, medial margin of the coracoid shaft; pa, processus acrocoracoideus; pp, processus procoracoideus; sms, sulcus m. supracoracoidei; td, tuberculum dorsale.
Scale bar, 10 mm; (21d and 22d) out of scale.
