New fossil birds from the miocene of Patagonia, Argentina

Anhimidae Stejneger, 1885

Genus Chainkanas nov. gen.

Diagnosis. Large anseriform diagnosed on the basis of the following combination of characters: 1- procoracoid extensive and dorsally hooked (shorter and not dorsally tilted in Chauna, Anhima and Chaunoides); 2- humeral facet strongly medially tilted (not tilted in Chauna, Anhima and Chaunoides); 3- humeral facet nearly reaching the level of the distal end of the scapular facet (more proximally placed in Chauna, Anhima and Chaunoides); 4- scapular facet subcircular in contour and deeply excavated, and slightly distally oriented (strongly laterally oriented in Chauna, Chaunoides and Anhima); and 5- acrocoracoid process elongated (shared with Chaunoides; much wider and stouter in Chauna and Anhima).

Etymology. Chaink, meaning large in Aonikenk language; anas, meaning duck in Latin.

Type and only known species. Chainkanas koshon nov. sp.

Chainkanas koshon nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 3306, right coracoid with incomplete distal end (Figure 4).

Locality and horizon. Loma de la Lluvia fossil site, Pinturas river, Santa Cruz province, Argentina. The specimen comes from beds belonging to the Early-Middle Miocene Pinturas Formation.

Etymology. Koshon, from the Aonikenk language meaning scream; members of the family Anhimidae are popularly known as “screamers” in English language.

Description. Relatively elongate coracoid, especially the acrocoracoid process (68 millimeters of maximum preserved length). Poorly excavated triosseal concavity, with well-defined margins. Ventral fossa deep and well-defined. The scapular facet is deeply excavated, subcircular in contour, and with well-raised margins. It is distolaterally oriented, and is connected with the acrocoracoid by menas of a thick and rounded ridge. The humeral facet is roughly ovoidal in contour. It distally extends for almost three quarters the proximodistal height of the scapular facet. It is strongly medially tilted and, consequently, its lateral exposure is relatively narrow. Its margins are delimited by a very narrow, but well-raised minute ridge. Procoracoid process prominent and thick, strongly proximally curved and hook-like. The base of this process shows an ellipsoidal-shaped and relatively wide procoracoid foramen.

The coracoid body is transversely wide and shows a nearly flat lateral surface that is only interrupted by obliquely oriented muscle scars. The distal end preserves the margin that delimited a very large distal pneumatic foramen.

Remarks. Chainkanas nov. gen. can be included among anhimids by having very large size, robust coracoid with a large procoracoid process, procoracoid foramen extensive and ellipsoidal in contour, and the presence of a large pneumatic foramen at its distal end (Alvarenga, 1999Alvarenga, H.M. (1999). A Fossil Screamer (Anseriformes: Anhimidae) from the Middle Tertiary of Southeastern Brazil. Smithsonian Contributions to Paleobiology, 89, 223-230.). As indicated in the diagnosis, Chainkanas can be clearly distinguished by other extant and extinct anhimids, especially by its procoracoid shape. Among anhimids, it is more similar to the Oligocene genus Chaunoides from Brazil than to extant genera Anhima and Chauna, by having a relatively elongate coracoid, narrow acrocoracoid process, and very wide and deep scapular fossa (Alvarenga, 1999Alvarenga, H.M. (1999). A Fossil Screamer (Anseriformes: Anhimidae) from the Middle Tertiary of Southeastern Brazil. Smithsonian Contributions to Paleobiology, 89, 223-230.).

Loxornis clivus is a bird species based on a distal tibiotarsus with eroded distal condyles coming from the Deseadan beds (Oligocene) of Santa Cruz province. The only known specimen. It was originally described by Ameghino (1895)Ameghino, F. (1895). Sur les oiseaux fossiles de Patagonie. Boletín del Instituto Geográfico Argentino, 15, 501- 602. as an uncertain anseriform (Tonni, 1980Tonni, E.P. (1980). The present state of knowledge of the Cenozoic birds of Argentina. Natural History Museum of Los Angeles County, Contributions in Science, 330, 105-114.), and more recently it was regarded as a possible anhimid by Alvarenga (1999Alvarenga, H.M. (1999). A Fossil Screamer (Anseriformes: Anhimidae) from the Middle Tertiary of Southeastern Brazil. Smithsonian Contributions to Paleobiology, 89, 223-230.; see Cenizo and Agnolín, 2010Cenizo, M.M., and Agnolín, F.L. (2010). The southernmost records of Anhingidae and a new basal species of Anatidae (Aves) from the lower-middle Miocene of Patagonia, Argentina. Alcheringa, 34(4), 493-514.). Because Loxornis and Chainkanas are based on different materials, a direct comparison between them is not possible. However, it should be pointed out, that both come from distant stratigraphical units that show strong faunal differences. Furthermore, as pointed out by Alvarenga (1999)Alvarenga, H.M. (1999). A Fossil Screamer (Anseriformes: Anhimidae) from the Middle Tertiary of Southeastern Brazil. Smithsonian Contributions to Paleobiology, 89, 223-230. the phylogenetic position of Loxornis is not clear, and it is not entirely certain that it belongs to Anhimidae.

Anatidae Leach, 1820

Tadorninae Reichenbach, 1850

Genus Kaikenia nov. gen.

Diagnosis. Relatively large anatid, very similar in size and shape to Miotadorna, having the following unique combination of characters: 1- lateral margin of the shaft nearly straight; 2- attachment of the pronator muscle distally located with respect to the proximal margin of the anterior articular ligamental facet (at the same level in remaining tadornines; Worthy et al., 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.); 3- scapulotricipital groove deep, but does not extend around the distal end of the bone (in contrast to remaining tadornines; Worthy et al., 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.); 4- flexor process poorly extended distally; and 5- olecranal fossa in distal view, laterally delimited by a thick ridge.

Etymology. Kaiken, meaning members of the goose genus Chloephaga in Aonikenk language.

Type and only included species. Kaikenia mourerchauvirea nov. sp.

Kaikenia mourerchauvirea nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 4506, right humerus lacking its proximal third (Figure 5).

Locality and horizon. The specimen comes from the Santa Cruz Formation (Early-Middle Miocene), at the well-known fossiliferous locality of Monte Observación (the label of the specimen indicates “Estaca 7”), Monte León National Park, Santa Cruz province, Argentina. Collected in 1991.

Referred material. MACN SC 3431, proximal end of left carpometacarpus (Figure 6).

Locality and horizon. The referred specimen comes from the Santa Cruz Formation (Early-Middle Miocene), Monte Observación locality, Monte León National Park, Santa Cruz province, Argentina.

Etymology. The specific epithet honors Cécile Mourer-Chauviré, a leading paleontologist from France, who greatly contributed to our current knowledge on palaeornithology.

Description. Kaikenia nov. gen. is a relatively large anatid, the size of Chloephaga, but having more gracile proportions (20 millimeters of maximum distal width). The preserved shaft indicates that the humerus was narrow and with nearly straight lateral and medial margins, lacking the remarkable sigmoid curvature present in some genera such as Anabernicula and Tadorna (Howard, 1964Howard, H. (1964). A new species of the “pygmy goose” Anabernicula, from the Oregon Pleistocene, with a discussion of the genus. American Museum Novitates, 2200, 1-14.).

The anterior surface of the shaft is nearly flat, with an ellipsoidal-shaped but shallow and poorly defined brachial fossa. This fossa is proximally placed, and its distal end does not reach the level of the proximal end of the ectepicondylar prominence. This latter prominence is well-defined but proximodistally low and shows a well defined concavity for attachment of the dorsal collateral ligament. The facet of the attachment for the anterior articular ligament is very wide and not well-raised from the surface surrounding it. The surface for the attachment of the m. carpi ulnaris is very deep, prominent, and distally located. The flexor process is poorly distally extended and is level with the distal margin of the dorsal condyle.

Dorsal and ventral condyles are prominent and well-defined, the latter being smaller than the former, and ovoidal in contour.

In posterior view the olecranal fossa is shallow and is not dorsally delimited by a subhorizontally oriented ridge. The scapulotricipital groove is well defined but shallow and does not extend around the distal end of the bone.

In distal view the olecranal fossa is delimited along its lateral margin by a thick ridge. This ridge is continuous with the distal edge of the dorsal condyle extending posteriorly and ending in a subtriangular bump.

The proximal end of the carpometacarpus is referred to Kaikenia because of its size and corresponding characteristics. It shows a shallow infratrochlear fossa and relatively deep anterior and cuneiform fossae. The posterior fossa is notably deep and forms a strong notch at the base of the carpal trochlea. The proximal synostosis is proximodistally short. The minor metacarpal is medially grooved.

Remarks. Kaikenia nov. gen. may be referred to Tadorninae on the basis of the following combination of characteristics: tendence to narrowing of the humeral shaft, distinct ectepicondylar prominence and scapulotricipital groove, distal margin of flexor process level with distal margin of dorsal condyle, and shallow brachial fossa (Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.; Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.).

Its large size easily distinguishes Kaikenia from several small tadornines, such as Nannonetta, Pleistoanser and Anabernicula. The North America Pleistocene genus Brantadorna lacks overlaping material with Kaikenia, and thus, comparisons are not possible (Howard, 1963Howard, H. (1963). Fossil birds from the Anza-Borrego desert. Contributions in Science, Natural History Museum of los Angeles County, 73, 3-33).

Kaikenia differs from members of the genera Chloephaga, Neochen, Anabernicula, Australotadorna, Pleistoanser and Alopochen in having a straight shafted and narrow humerus, with poorly developed flexor tubercle, and much less prominent ectepicondylar prominence (see Agnolín, 2006aAgnolín, F.L. (2006a). Dos nuevos Anatidae (Aves, Anseriformes) del Pleistoceno inferior-medio de Argentina. Studia Geologica Salmanticensia, 42, 81-95.; Howard, 1964Howard, H. (1964). A new species of the “pygmy goose” Anabernicula, from the Oregon Pleistocene, with a discussion of the genus. American Museum Novitates, 2200, 1-14.; Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.). In these features, Kaikenia resembles tadorninines of the genera Tadorna and Miotadorna. However, it differs from both by having a prominent entepicondylar process and the attachment for the m. carpi ulnaris very deep and medially oriented (Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.). Particularly, Kaikenia is similar in shape and development of the ectepicondylar process, flexor process, and facet for the anterior articular attachment to the extinct Miocene genus Miotadorna (Worthy and Lee, 2008Worthy, T.H., and Lee, M.S. (2008). Affinities of Miocene waterfowl (Anatidae: Manuherikia, Dunstanetta and Miotadorna) from the St Bathans Fauna, New Zealand. Palaeontology, 51(3), 677-708.; Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.). However, it differs in several important anatomical features (as indicated above), including a shallower brachial fossa (distally very deep in Miotadorna, Alopochen and Australotadorna; Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.) and having a poorly distally oriented flexor process (Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.). A feature that occurs in Kaikenia, that is unknown in other tardornines, is the presence in distal view of a ridge that delimits the olecranal fossa. This feature may be regarded as autapomorphic of Kaikenia.

Teleornis impressus is an anatid named by Ameghino 1899Ameghino, F. (1899). Sinopsis geologico-paleontologica... En segundo censo nacional de la República Argentina... 1898... Suplemento (adiciones y correcciones), Julio de 1899. Imp. Encuadernacion “La Libertad”, 19 pp. on the basis of an incomplete forelimb coming from Deseadan Oligocene beds at Santa Cruz province. Teleornis was later considered as belonging to Tadorninae (Agnolín, 2004Agnolín, F.L. (2004). Revisión sistemática de algunas aves deseadenses (Oligoceno Medio) descriptas por Ameghino en 1899. Revista del Museo Argentino de Ciencias Naturales Nueva Serie, 6(2), 239-244.). Kaikenia differs from Teleornis in being much larger and in having the distal end of the bone transversely wider and more anteroposteriorly flattened. Furthermore, Kaikenia differs in having a much thicker and less distally extended flexor process, and by the shallower humerotricipital groove.

Genus Tamtamia nov. gen.

Diagnosis. Mid-sized and relatively gracile tadornine diagnosable on the basis of the following combination of characteristics: distal end of humerus: 1- very low ectepicondylar prominence that is distally located level with the dorsal margin of the dorsal condyle; 2- very prominent and large attachment for the anterior articular ligament, which is very prominent and medially displaced; 3- attachment for the anterior articular ligament ventrally delimited by a strongly concave fossa for the m. carpi ulnaris; 4- small flexor process that is not distally extended and is located close to the dorsal margin of the ventral condyle; proximal end of humerus: 5- transversely expanded and anteroposteriorly flattened; 6- shallow pneumotricipital fossa; 7- ventral pneumotricipital fossa pneumatic, and delimited by lateral and well-raised ridge (dorsal crus commune); 8- bicipital crest extensive and strongly flared; and 9- capital ridge located between the humeral head and the dorsal tubercle.

Etymology. Támtam, meaning female members of the goose genus Chloephaga in Aonikenk language.

Type and only included species. Tamtamia yzurietai nov. sp.

Tamtamia yzurietai nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 4507, distal end of right humerus and proximal end of left humerus from the same individual (Figure 7 A-E, I-M).

Paratypes. MACN SC, 4508, distal end of left humerus (Figure 7 N-R); MACN SC 3309, proximal end of right humerus (Figure 7 F-H).

Locality and horizon. Loma de la Lluvia fossil site, Pinturas river, Santa Cruz province, Argentina. The specimen comes from beds belonging to the Early-Middle Miocene Pinturas Formation.

Etymology. Yzurietai, honouring the naturalist, birdwatcher and artist Dario Yzurieta (1931-1996). Together with “Tito” Narosky they published the most useful Bird Guide Identification of the Neotropics. Due to their conjoined efforts, hundreds of young people become birdwatchers (including the author of the present contribution).

Description. Tamtamia nov. gen. is a relatively gracile tadornine (maximum transverse width of proximal end 14 milimeters; maximum transverse width of distal end 12 milimeters). The preserved shaft of humerus indicates that it was narrow and with nearly straight lateral and medial margins, lacking the strong sigmoid curvature present in some genera such as Anabernicula, Australotadorna and Tadorna (Howard, 1964Howard, H. (1964). A new species of the “pygmy goose” Anabernicula, from the Oregon Pleistocene, with a discussion of the genus. American Museum Novitates, 2200, 1-14.; Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.).

The ventral pneumotricipital fossa is relatively wide and deep. Despite being partially covered by matrix, it is clear that it was pneumatized. It is strongly medially extended along a flat surface formed by the bicipital crest. It is laterally delimited by the dorsal crus commune which extends distally as a ridge. The ventral tubercle is subtriangular in contour and relatively low. It is laterally delimited by a very wide and deeply excavated capital groove. The dorsal pneumotricipital fossa is wide and deep. The humeral head is relatively low and not very prominent; it is well-separated from the dorsal tubercle by a concavity. The capital ridge is prominent and is located between the humeral head and the dorsal tubercle. The dorsal tubercle is very wide, proximally extended and notably prominent. The deltopectoral crest is incomplete, but its surface is notably concave in posterior view.

In anterior view, the transverse ligamental groove is represented by a shallow and poorly defined excavation that distally delimits the humeral head.

The anterior surface of the shaft shows a well-defined and ellipsoidal shaped brachial fossa which deepens towards its disto-medial margin. This fossa is proximally placed, and its distal end does not reach the level of the proximal end of the ectepicondylar prominence. This prominence is well-defined, distally located (at the same level as the dorsal margin of the dorsal condyle) and is mound-shaped in anterior view. It shows a well-defined concavity for the attachment of the m. pronator superficialis. The facet for the attachment of the anterior articular ligament is very wide and very well-raised from the surface surrounding it. It is anterodistally oriented. It is strongly medially located and is far from the medial margin of the ventral condyle. It is ventrally delimited by a very deep and wide m. carpi ulnaris fossa. The flexor process is poorly developed and slightly extended distally, being close to the proximal margin of the ventral condyle.

Dorsal and ventral condyles are prominent and well-defined. The latter is much smaller than the former, ovoidal in contour, and is subhorizontally oriented.

In posterior view the olecranal fossa is well-excavated and dorsally delimited by a subhorizontally oriented ridge. The scapulotricipital and humerotricipital grooves are relatively wide and shallow.

Remarks. The distal end of the humerus of Tamtamia nov. gen. is very different from basal forms such as anseranatids, anhimids, dendrocygnines and romainvilliines by being anteroposteriorly thicker and transversely narrow, and by the poorly excavated distal end of the bone proximal to the ventral and dorsal condyles (Agnolín and Tomassini, 2012Agnolín, F.L., and Tomassini, R.L. (2012). A fossil Dendrocygninae (Aves, Anatidae) from the early Pliocene of the Argentine Pampas and its paleobiogeographical implications. Annales de Paléontologie, 98, 191-201.; Mayr, 2008Mayr, G. (2008). Phylogenetic affinities and morphology of the late Eocene anseriform bird Romainvillia stehlini Lebedinsky, 1927. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 248, 365-380.).

Tamtamia is assigned to Tadorninae on the basis of the following combination of characteristics: prominent capital shaft ridge located close to the level of the dorsal tubercle, elevated and elongate dorsal tubercle, dorsal pneumotricipital fossa narrow and not strongly excavated under the humeral head, large ventral pneumotricipital fossa, deltoid crest concave in posterior view, and strongly raised and distally oriented facet for the anterior articular ligament (Woolfenden, 1961Woolfenden, G.E. (1961). Postcranial osteology of the waterfowl. Bulletin of the Florida State Museum, Biological Sciences, 6(1), 1-129.; Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.).

Tamtamia differs from Chloephaga in that it lacks the very weak capital ridge and the shaft compression adjacent to the angle of the deltoid crest, but well rounded from there, a condition unique to this genus (Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.). It also differs in the more proximodistally narrow and less prominent humeral head. It differs from Pleistocene Anabernicula, Pleistoanser and Nannonetta in the poorly distally extended flexor process and in the distally positioned ectepicondylar prominence, among several other anatomical details (Agnolín, 2006aAgnolín, F.L. (2006a). Dos nuevos Anatidae (Aves, Anseriformes) del Pleistoceno inferior-medio de Argentina. Studia Geologica Salmanticensia, 42, 81-95.; Howard, 1964Howard, H. (1964). A new species of the “pygmy goose” Anabernicula, from the Oregon Pleistocene, with a discussion of the genus. American Museum Novitates, 2200, 1-14.). From Neochen, Alopochen and Brantadorna it differs in the much more gracile proportions, narrower shaft, and smaller and less prominent humeral head (see Howard, 1963Howard, H. (1963). Fossil birds from the Anza-Borrego desert. Contributions in Science, Natural History Museum of los Angeles County, 73, 3-33; Short, 1970Short, L.L. (1970). Mid-Pleistocene birds from western Nebraska, including a new species of sheldgoose. The Condor, 72(2), 147-152.). It differs from Australotadorna in having a more gracile construction, with a less prominent humeral head, ventral pneumotricipital fossa delimited by a ridge, and rounded and relatively low ventral tubercle, among several other anatomical traits (see Worthy, 2009Worthy, T.H. (2009). Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia. Zoological Journal of the Linnean Society, 156(2), 411-454.).

In size and proportions, Tamtamia is reminiscent to the extant genus Tadorna and extinct Miocene genus Miotadorna (see Worthy and Lee, 2008Worthy, T.H., and Lee, M.S. (2008). Affinities of Miocene waterfowl (Anatidae: Manuherikia, Dunstanetta and Miotadorna) from the St Bathans Fauna, New Zealand. Palaeontology, 51(3), 677-708.; Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.). It differs from Tadorna in having a much wider and excavated ventral pneumotricipital fossa that is laterally delimited by a subvertical ridge, by having a more prominent but distally located ectepicondylar prominence, and a proximally positioned flexor process. It differs from Miotadorna in having a notably wider and more excavated ventral pneumotricipital fossa, and a prominent and distally located ectepicondylar prominence (Worthy and Lee, 2008Worthy, T.H., and Lee, M.S. (2008). Affinities of Miocene waterfowl (Anatidae: Manuherikia, Dunstanetta and Miotadorna) from the St Bathans Fauna, New Zealand. Palaeontology, 51(3), 677-708.; Worthy et al., 2007Worthy, T.H., Tennyson, A.J., Jones, C., McNamara, J.A., and Douglas, B.J. (2007). Miocene waterfowl and other birds from Central Otago, New Zealand. Journal of Systematic Palaeontology, 5(1), 1-39.).

Tamtamia differs from Kaikenia (described above) in several features, including a deeper and more extensive humerotricipital groove, a well-raised facet for the anterior articular ligament, a deep brachial fossa, and different development of the ectepicondylar process and flexor process. Tamtamia differs from Teleornis (Ameghino, 1899Ameghino, F. (1899). Sinopsis geologico-paleontologica... En segundo censo nacional de la República Argentina... 1898... Suplemento (adiciones y correcciones), Julio de 1899. Imp. Encuadernacion “La Libertad”, 19 pp.; Agnolín, 2004Agnolín, F.L. (2004). Revisión sistemática de algunas aves deseadenses (Oligoceno Medio) descriptas por Ameghino en 1899. Revista del Museo Argentino de Ciencias Naturales Nueva Serie, 6(2), 239-244.) in that the latter has a prominent and distally extended flexor process, whereas in Tamtamia it is much shorter and more proximally positioned with respect to the distal end of the ventral condyle. The ventral condyle in Tamtamia is subhorizontally oriented, whereas in Teleornis it is strongly oblique, forming an angle of about 90° with the main axis of the dorsal condyle (see Agnolín, 2004Agnolín, F.L. (2004). Revisión sistemática de algunas aves deseadenses (Oligoceno Medio) descriptas por Ameghino en 1899. Revista del Museo Argentino de Ciencias Naturales Nueva Serie, 6(2), 239-244.).

Tamtamia comes from beds that are probably coeval with those that yielded the basal anatid Ankonetta larriestrai (Cenizo and Agnolín, 2010Cenizo, M.M., and Agnolín, F.L. (2010). The southernmost records of Anhingidae and a new basal species of Anatidae (Aves) from the lower-middle Miocene of Patagonia, Argentina. Alcheringa, 34(4), 493-514.). Regrettably, Ankonetta is based on an incomplete tarsometatarsus, and thus, there is no overlapping material with Tamtamia. As described by Cenizo and Agnolín (2010)Cenizo, M.M., and Agnolín, F.L. (2010). The southernmost records of Anhingidae and a new basal species of Anatidae (Aves) from the lower-middle Miocene of Patagonia, Argentina. Alcheringa, 34(4), 493-514., Ankonetta is a basal dendrocygnine-like anatid, and in all probability larger in size than that inferred for Tamtamia. It is not improbable that after the finding of new materials, Tamtamia may result in being a junior synonym for Ankonetta.

Gruoidea sensu Wetmore, 1960

Gruidae Vigors, 1825

?Gruinae Vigors, 1825

Genus Patagogrus nov. gen.

Diagnosis. Medium-sized gruid diagnosed on the basis of the following combination of characters: 1- distal end of the bone with its anteroposterior length subequal to transverse width (shared with Palaeogrus; much transversely wider than anteroposteriorly long in Grus); 2- intercondylar groove in distal view narrow and with subparallel lateral and medial margins (relatively wide and forming an opened “V” or “U” in Grus and Palaeogrus); 3- distal end of lateral condyle with a well-developed notch (shared with Grus, nearly absent in Palaeogrus); 4- medial condyle strongly anteriorly projected and with its anterior end acute and transversely narrow (shared with Palaeogrus; narrower in Grus); 5- medial epicondyle poorly developed (well-developed and exposed when viewed distally in Grus and Palaeogrus); 6- tubercle lateral to supratendinal bridge poorly developed (shared with Palaeogrus, in Grus the tubercle is very strong); and 7- proximodistally extended supratendinal bridge (shared with Grus).

Etymology. Patago, from Patagonia, and Grus, the type genus of Gruidae.

Type and only included species. Patagogrus olsoni nov. sp.

Patagogrus olsoni nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 1423, distal end of right tibiotarsus (Figure 10).

Locality and horizon. Loma de la Lluvia fossil site, Pinturas river, Santa Cruz province, Argentina. The specimen comes from beds belonging to the Early-Middle Miocene Pinturas Formation.

Etymology. The specific epithet honours Storrs L. Olson (1944-2020), one of the most important paleornithologists from the XX and XXI centuries.

Description. Cross-section of the shaft roughly crescent-shaped, with a flattened anterior surface. Distal end with lateral condyle much larger than the medial one, with a thicker base and anteroposteriorly shorter (21 milimeters of maximum transverse width through the distal condyles). Distal margin of lateral condyle with a poorly-developed notch. Medial epicondyle present but not strongly developed and not surpassing the medial condyle medially. In distal view the distal trochlea do not strongly taper posteriorly. Intercondylar groove transverselly narrow and subrectangular in contour, with nearly straight medial and lateral margins and with a distinct sub-horizontal scar anteriorly. Presence of a well-developed tubercle located at the lateral edge of the supratendinal bridge and not in contact with lateral condyle. Distal opening of extensor groove proximodistally narrow and transversely wide, located at the medial half of the bone. Supratendinal bridge proximodistally extensive and with a concave anterior surface. Lateral retinacular tubercle ridge-like, strongly developed and subvertically oriented. It is placed medially to the fibularis muscle groove and is separated from the tubercle located at the lateral surface of the supratendinal bridge by a shallow subvertical groove. The medial retinacular tubercle is obliquely oriented with respect to the main axis of the extensor groove; it is poorly developed and ridge-like. This tubercle is located medially with respect to the medial margin of the extensor groove.

In posterior view the distal trochlea is relatively proximodistally low and shows shallow rings and a poorly developed transverse ridge.

Remarks. Patagogrus nov.gen. shows a unique combination of characteristics shared with Gruidae, including flat anterior face of the tibiotarsus, proximodistally low distal trochlea in posterior view, anteriorly divergent condyles, lateral condyle anteroposteriorly long, with a shallow notch on its distal margin, medial condyle more anteriorly projected than the lateral one, anterior end of medial condyle transversely narrow, the presence of a tubercle lateral to the base of the supratendinal bridge, well developed ridge delimiting the lateral margin of the extensor groove, and supratendinal bridge proximodistally tall (Clarke et al., 2005Clarke, J.A., Norell, M.A., and Dashzeveg, D. (2005). New avian remains from the Eocene of Mongolia and the phylogenetic position of the Eogruidae (Aves, Gruoidea). American Museum Novitates, 2005(3494), 1-17.; Cracraft, 1973aCracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127.; Livezey, 1998Livezey, B.C. (1998). A phylogenetic analysis of the Gruiformes (Aves) based on morphological characters, with an emphasis on the rails (Rallidae). Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 353(1378), 2077-2151.; Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.). Patagogrus differs from psilopterine phorusrhacids by having a slimmer configuration, more dorsoventrally lower and transversely wider distal condyles, by having a subelliptical external rim on the lateral condyle, a medial condyle much more deflected medially, not alligned with the medial margin of the shaft, an anterior intercondylar fossa, and a poorly excavated extensor groove, among other anatomical details (see Noriega et al. 2009Noriega, J.I., Vizcaíno, S.F., and Bargo, M.S. (2009). First record and a new species of seriema (Aves: Ralliformes: Cariamidae) from santacrucian (Early-Middle Miocene) beds of Patagonia. Journal of Vertebrate Paleontology, 29(2), 620-626.).

Patagogrus clearly differs from cariamids in having the lateral condyle not anteriorly projected and with a reduced epicondyle, a proximodistally high supratendinal bridge, a transversely wide and proximodistally low distal opening of the supratendinal bridge, the presence of a tubercle lateral to the supratendinal bridge, and absence of a ridge connecting the lateral edge of the supratendinal bridge with the medial margin of the lateral condyle, among other features (Cracraft, 1968Cracraft, J. (1968). A review of the Bathornithidae (Aves, Gruiformes), with remarks on the relationships of the suborder Cariamae. American Museum Novitates, 2326, 1-46.; Noriega et al., 2009Noriega, J.I., Vizcaíno, S.F., and Bargo, M.S. (2009). First record and a new species of seriema (Aves: Ralliformes: Cariamidae) from santacrucian (Early-Middle Miocene) beds of Patagonia. Journal of Vertebrate Paleontology, 29(2), 620-626.).

Among gruids, Patagogrus clearly differs from Balearica and extinct Balearicinae, previously referred to as Probalearica (Mourer Chauviré, 2001Mourer-Chauvire, C. (2001). The systematic position of the genus Basityto Mlikovsky, 1998 (Aves: Gruiformes: Gruidae). Proceedings of the Biological Society of Washington, 114(4), 964-971.), in that balearicines exhibit a robust distal end of the tibiotarsus with a strongly anteroposteriorly flattened shaft, a strongly medially deflected medial condyle, and a transversely expanded extensor groove (Feduccia and Voorhies, 1992Feduccia, A., and Voorhies, M.R. (1992). Crowned cranes (Gruidae: Balearica) in the Miocene of Nebraska. Natural History Museum of Los Angeles County, Science Series, 36, 239-248.; Mourer Chauviré, 2001Mourer-Chauvire, C. (2001). The systematic position of the genus Basityto Mlikovsky, 1998 (Aves: Gruiformes: Gruidae). Proceedings of the Biological Society of Washington, 114(4), 964-971.). On the other side, Patagogrus resembles gruines in having a progressive (not abrupt) widening of the distal end of the bone, in the presence of a strong tubercle lateral to the supratendinal bridge, a relatively long lateral condyle, a transversely narrow extensor groove occupying only the medial part of the cranial face of the bone, and a notch at the distal edge of lateral condyle forming an indentation that is much less pronounced in the Balearicinae (Göhlich, 2003Göhlich, U.B. (2003). A new crane (Aves: Gruidae) from the Miocene of Germany. Journal of Vertebrate Paleontology, 23(2), 387-393.; Mourer Chauviré, 2001Mourer-Chauvire, C. (2001). The systematic position of the genus Basityto Mlikovsky, 1998 (Aves: Gruiformes: Gruidae). Proceedings of the Biological Society of Washington, 114(4), 964-971.).

Tertiary gruines are still poorly known. Several previously published records rest on weak evidence and they are considered to be of uncertain phylogenetic affinities (Cracraft, 1973aCracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127.; Göhlich, 2003Göhlich, U.B. (2003). A new crane (Aves: Gruidae) from the Miocene of Germany. Journal of Vertebrate Paleontology, 23(2), 387-393.), which makes comparisons of Patagogrus with other fossil gruines difficult. The only Tertiary extinct gruine genera that rest on relatively robust evidence are Palaeogrus and Camusia (e.g., Göhlich, 2003Göhlich, U.B. (2003). A new crane (Aves: Gruidae) from the Miocene of Germany. Journal of Vertebrate Paleontology, 23(2), 387-393.; Mayr et al., 2020bMayr, G., Lechner, T., and Böhme, M. (2020b). A skull of a very large crane from the late Miocene of Southern Germany, with notes on the phylogenetic interrelationships of extant Gruinae. Journal of Ornithology, 161(4), 923-933.; Mourer-Chauviré, 2001Mourer-Chauvire, C. (2001). The systematic position of the genus Basityto Mlikovsky, 1998 (Aves: Gruiformes: Gruidae). Proceedings of the Biological Society of Washington, 114(4), 964-971.; Seguí, 2002Seguí, B. (2002). A new genus of crane (Aves: Gruiformes) from the Late Tertiary of the Balearic Islands, Western Mediterranean. Ibis, 144, 411−422.; Zelenkov, 2015Zelenkov, N.V. (2015) The fossil record and evolutionary history of cranes. In: Ilyashenko EI, Winter SV (eds) Cranes of Eurasia (biology, distribution, captive breeding). 5. Proceedings of the International Scientific Conference “Cranes of Eurasia: biology, conservation, management”, Daursky Nature Reserve, Transbaikalia, Russia, 1‒4 September 2015. Crane Working Group of Eurasia, Moscow and Nizhny Tsasuchei, Russia, pp. 88-90). Comparisons between Patagogrus, Palaeogrus and the extant genus Grus were made in the diagnosis of Patagogrus following characteristics noted by previous authors (Cracraft, 1973aCracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127.; Göhlich, 2003Göhlich, U.B. (2003). A new crane (Aves: Gruidae) from the Miocene of Germany. Journal of Vertebrate Paleontology, 23(2), 387-393.; Northcote and Mourer-Chauviré, 1988Northcote, E. M., and Mourer-Chauviré, C. (1988). The extinct crane Grus primigenia Milne-Edwards in Majorca (Spain). Geobios, 21(2), 201-208.). Camusia is very different from Patagogrus and any other gruid genus (Seguí, 2002Seguí, B. (2002). A new genus of crane (Aves: Gruiformes) from the Late Tertiary of the Balearic Islands, Western Mediterranean. Ibis, 144, 411−422.). It differs from Patagogrus in several anatomical details, including a tibiotarsus with a much transversely wider and anteroposteriorly flattened distal end, by having narrower and a more medially projected medial condyle and a prominent and elongate medial epicondyle.

The combination of characteristics enumerated above indicates that Patagogrus is a valid gruid genus. Among other anatomical details, it is distinctive in having a transversely narrow distal end of the tibiotarsus, as is shown by the shape of the intercondylar groove in distal view.

Psophiidae Bonaparte 1831

Genus Archaeopsophia nov. gen.

Diagnosis. A medium-sized gruoid closely related to psophiids and parvigruids from which it differs in the following combination of characteristics: 1- proximally extended and well-defined intercotylar eminence (condition similar to Psophiidae; much lower in Parvigruidae); 2- hypotarsus distally located (very proximally located in Parvigruidae, close to the level of the proximal cotyles; similar condition to Archaeopsophia is present in Psophiidae); 3- medial crest for the flexor digitorum longus anteroposteriorly short (long in Psophiidae; condition similar to Parvigruidae); 4- hypotarsus lateral to the flexor digitorum longus groove forming a nearly subparallel surface with respect to the main transverse axis of the bone (disposed on an oblique angle in Psophiidae; condition similar to Parvigruidae); 5- groove for the fibularis longus shallower than in Psophiidae; and 6- groove for the flexor hallucis longus notably transversely wide (very narrow in Parvigruidae).

Etymology. Archaeo, from the Greek, meaining ancient; Psophia, the type genus of Psophiidae.

Type and only included species. Archaeopsophia aoni nov. sp.

Archaeopsophia aoni nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 3422, proximal end of right tarsometatarsus (Figure 11).

Locality and horizon. The specimen comes from the Santa Cruz Formation (Early-Middle Miocene), at the well-known fossiliferous locality of Monte Observación, Monte León National Park, Santa Cruz province, Argentina. Collected in 1991.

Etymology. Aoni, from the Aonikenk, meaning south.

Description. Proximal end of tarsometatarsus poorly transversely expanded (21 milimeters of maximum transverse width). The intercotylar eminence is distinctly proximally extended and anteroposteriorly narrow. Proximal cotyles strongly concave and delimited by rising outside margins. The medial cotyle is situated farther proximally than the lateral one. The infracotylar fossa is deep and well-defined, and shows three very small proximal vascular foramina.

In proximal view the medial cotyle is much larger than the lateral one, and exhibits a subrectangular contour. Intercotylar area relatively wide, subrectangular in contour and deeply excavated.

In posterior view the hypotarsus is distally displaced and is separated from the proximal cotyles by a very deep and well-defined subhorizontally oriented excavation. The hypotarsus is relatively complex and is not strongly posteriorly projected. It does not enclose bony canals. Its most prominent crest is the medial crest for the flexor digitorum longus, which is not strongly posteriorly extended and is close in size to the lateral crest for the flexor digitorum longus. The medial crest for the flexor digitorum longus is proximodistally long. The grooves for the flexor digitorum longus and flexor hallucis longus are well-defined, especially when viewed posteriorly. The lateral crest for the flexor hallucis longus is thick and blunt, but not prominent.

The fossa parahypotarsalis lateralis appears to have been poorly developed. There is a low crista plantaris lateralis along the midsection of the shaft.

Remarks. Archaeopsophia aoni nov. sp. shows a hypotarsal morphology exclusive to Gruoidea: there is a lateral sulcus for the tendon of musculus fibularis longus, the hypotarsus forms a laterally slanted embossment, there is a groove for the flexor digitorum longus tendon, and a proximodistally long crista medialis partially or entirely enclosing such a groove (Cracraft, 1973aCracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127.; Mayr, 2016aMayr, G. (2016a). Variations in the hypotarsus morphology of birds and their evolutionary significance. Acta Zoologica, 97(2), 196-210.). Among gruoids, Archaeopsophia exhibits a hypotarsal morphology that only fits with that of the Psophiidae and Parvigruidae. In most ralloids, and in all gruids and aramids, the canal for the flexor digitorum longus is entirely closed, whereas in Archaeopsophia, Psophiidae, and Parvigruidae it is represented by an opened groove (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89., 2016aMayr, G. (2016a). Variations in the hypotarsus morphology of birds and their evolutionary significance. Acta Zoologica, 97(2), 196-210.). Furthermore, in Archaeopsophia, Psophia, and gruoids more derived than parvigruids the medial crest for the flexoris digitorum longus is proximodistally extensive, whereas in Parvigrus it is notably shorter (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.). In addition, Archaeopsophia resembles psophiids and differs from parvigruids in having a proximally extended and well-defined intercotylar eminence, a distally displaced hypotarsus, and a groove for the flexor hallucis longus that is notably transversely wide. Furthermore, as in Psophiidae and Aramidae, there exits a well-defined groove for the flexor hallucis longus lateral to the medial hypotarsal crest. The hypotarsus of Archaeopsophia is very different from the condition exhibited by cariamiforms, which share a block-like hypotarsus lacking deep grooves and crests (Alvarenga and Hofling, 2003Alvarenga, H.M., and Höfling, E. (2003). Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia, 43(4), 55-91.; De Pietri and Mayr, 2014De Pietri, V.L., and Mayr, G. (2014). The enigmatic Ibidopodia from the early Miocene of France-the first Neogene record of Cariamiformes (Aves) in Europe. Journal of Vertebrate Paleontology, 34(6), 1470-1475.). On the basis of this combination of characters, Archaeopsophia is referred here to the Psophiidae.

Anisolornis excavatus is an enigmatic bird coming from early Miocene Santacrucian beds at the Karaiken fossil site in Santa Cruz province. The specimen was originally considered by Ameghino as being a phororhacoid bird (1891)Ameghino, F. (1891). Enumeración de las aves fósiles de la República Argentina. Revista Argentina de Historia Natural, 1, 441- 453. and later as a galliform bird (1895Ameghino, F. (1895). Sur les oiseaux fossiles de Patagonie. Boletín del Instituto Geográfico Argentino, 15, 501- 602.). More recently, Cracraft (1973a)Cracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127. included it among aramids and Olson (1985)Olson, S. L. (1985). The fossil record of birds. In: Farner DS, King JR, Parkes KC (eds) Avian biology, vol 8. Academic Press, New York, pp 79-238 noted resemblances to Psophiidae. However, the affinities of Anisolornis with psophiids, and even gruiformes, are far from being well-settled (Tambussi and Degrange, 2013). Anisolornis is based on a distal tarsometatarsus, and thus, direct comparisons with Archaeopsophia are not possible. In any case, Anisolornis belongs to a relatively large bird, much bigger than Archaeopsophia (see Cracraft, 1973aCracraft, J. (1973a). Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History, 151, 1-127.).

Parvigruidae Mayr, 2005Mayr, G. (2005). A chicken-sized crane precursor from the early Oligocene of France. Naturwissenschaften, 92(8), 389-393.

Genus Alhuenia nov. gen.

Diagnosis. Small-sized gruoid closely related to psophiids and parvigruids from which it differs in the following combination of characteristics: 1- distal end of the humerus anteroposteriorly flattened (similar to Psophia and gruids, thicker in Parvigrus); 2- robust dorsal condyle with a bulbous distal end (narrower in Parvigrus and narrow and ventrally excavated in Psophia); 3- attachment of the tendon of the m. carpi radialis represented by low and elongate scar (more prominent in Parvigrus); 4- proximal margin of the brachial fossa poorly delimited (similar to Parvigrus, more excavated and delimited by a ridge in Psophia); 5- flexor tubercle not distally extended (similar to Parvigrus, strongly distally projected in Psophia); 6- distal end of the humerus not ventrally slanted (slanted in Parvigrus and ralloids); and 7- humerotricipital groove not delimited by subvertical ridges (ridges present in Parvigrus).

Etymology. Alhue, from the Mapundugún, meaning phantom.

Type and only included species. Alhuenia eduardotonnii nov. sp.

Alhuenia eduardotonnii nov. sp.

Diagnosis. The same as for genus by monotypy.

Holotype. MACN SC 1439, distal end of right humerus (Figure 12).

Locality and horizon. Loma de la Lluvia fossil site, Pinturas river, Santa Cruz province, Argentina. The specimen comes from beds belonging to the Early-Middle Miocene Pinturas Formation.

Description. The distal end of the humerus of Alhuenia is not strongly transversely expanded (13 milimeters of maximum transverse width). In spite of being not entirely preserved, the flexor process was not strongly ventrally projected, a condition shared with gruoids and different from ralloids (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.). This results in the ventral edge of the bone being straight and not ventrally slanted.

The entepicondylar process is strongly anteriorly projected and is proximally continuous with a ridge that delimits the medial margin of the bone, a condition shared with gruoids excluding parvigruids (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.). The attachment scar for the tendon of the anterior articular ligament, distal to the entepicondylar process, is prominent. The brachial fossa is not well-excavated and roughly ellipsoidal in contour. It is centrally positioned, as occurs in most gruoids (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.), and is not distally displaced. Both dorsal and ventral condyles are prominent and rounded, and are separated by a deep and wide intercondylar groove. The ventral condyle is roughly subcircular in contour. Proximal to the dorsal condyle, there is a thick attachment area for the tendon of m. carpi radialis. This area is elongate and is not prominent.

In posterior view, both scapulotricipitalis and humerotricipitalis grooves are wide and shallow. The olecranal fossa is relatively deep and well-defined.

Remarks. The distal end of the humerus of Alhuenia nov. gen. clearly differs from other gruiforms and cariamiforms, and resembles parvigruids in the following unique combination of characteristics: distal end of the bone not ventrally slanted (a condition shared with gruoids and contrasting with rallids, messelornithids and other gruiforms and cariamiforms; Mourer-Chauviré, 1983Mourer-Chauviré, C. (1983). Les Gruiformes (Aves) Des Phosphorites Du Quercy (France): 1, Sous-ordre Cariamae (Cariamidae Et Phorusrhacidae): Systématique et Biostratigraphie. Palæovertebrata, 13, 83-143.; 1995Mourer-Chauviré, C. (1995): The Messelornithidae (Aves: Gruiformes) from the Paleogene of France. Courier Forschungsinstitut Senckenberg, 181, 95-105.) and not strongly transversely expanded (notably expanded in Psophia), the proximal end of the ectepicondylar process is markedly projected anteriorly (weakly elevated in gruoids, including psophiids; Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.), attachment for anterior articular ligament prominent (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.), brachial fossa shallow and not proximally delimited by a ridge (more excavated in psophiids and gruids; Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.); brachial fossa intermediate in position between the centrally located position of gruoids and the ventrally situated position of ralloids (Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.), dorsal condyle robust and not strongly compressed (shared also with gruids; strongly compressed in Psophia; Mayr, 2002Mayr, G. (2002). A new specimen of Salmila robusta (Aves: Gruiformes: Salmilidae n. fam.) from the Middle Eocene of Messel. Paläontologische Zeitschrift, 76(2), 305-316., 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.), ventral condyle globular and distally extended beyond the level of the flexor process and dorsal condyle (Mayr and Smith, 2001Mayr, G., and Smith, R. (2001). Ducks, rails, and limicoline waders (Aves: Anseriformes, Gruiformes, Charadriiformes) from the lowermost Oligocene of Belgium. Geobios, 34(5), 547-561.), and ventral condyle separated from the dorsal one by a deep groove (groove shallower and ventral condyle elongate in cariamiforms; Mayr, 2002Mayr, G. (2002). A new specimen of Salmila robusta (Aves: Gruiformes: Salmilidae n. fam.) from the Middle Eocene of Messel. Paläontologische Zeitschrift, 76(2), 305-316.). Furthermore, Alhuenia shows important differences with Psophia which include a very different shape of the dorsal condyle and much narrower and not strongly distally divergent humeral margins (see Mayr, 2013aMayr, G. (2013a). Parvigruidae (Aves, core Gruiformes) from the early Oligocene of Belgium. Palaeobiodiversity and Palaeoenvironments, 93(1), 77-89.).

As indicated in the diagnosis, Alhuenia shows several features that distinguish it from the parvigruids Parvigrus and Rupelrallus, particularly the less distally extensive flexor tubercle and the more robust and globose dorsal condyle, among other anatomical details (see Mayr, 2005Mayr, G. (2005). A chicken-sized crane precursor from the early Oligocene of France. Naturwissenschaften, 92(8), 389-393.; 2013). In spite of not being directly compared to the psophiid Archaeopsophia and the enigmatic Anisolornis, the distal humerus of Alhuenia belongs to a much smaller bird than expected for Archaeopsophia and Anisolornis, as inferred by their tarsometatarsi.

Herpetotheriinae Lesson, 1842

Genus ThegornisAmeghino, 1895Ameghino, F. (1895). Sur les oiseaux fossiles de Patagonie. Boletín del Instituto Geográfico Argentino, 15, 501- 602.

Thegornis spivacowi nov. sp.

Diagnosis. Very small Thegornis species distinguishable by the following combination of characters: 1- tarsometatarsus in distal view with metatarsal IV trochlea having the posterior wing well-separated from the main body of the trochlea, resulting in a sigmoidal outer margin of the trochlea IV; 2- trochlea II robust and rounded, with a distal notch separating the anterior articular surface from the posterior wing; and 3- proximal ridge resulting in a medial prominence dorsal to the articular surface of trochlea II.

Holotype. MACN-SC 1407, distal end of right tarsometatarsus (Figure 14).

Paratypes. MACN-SC 1390, distal end of left tarsometatarsus lacking II trochlea (Figure 15 A-F); MACN-SC 1393, distal end of left tarsometatarsus lacking IV trochlea (Figure 15 J-M); MACN-SC 1396, distal end of left tarsometatarsus lacking IV trochlea (Figure 15 Q-S); MACN-SC 4510, distal end of right tarsometatarsus lacking IV trochlea (Figure 15 G-I); MACN-SC 4511, distal end of left tarsometatarsus with partially eroded distal trochleae (Figure 15 N-P).

Locality and horizon. Loma de la Lluvia fossil site, Pinturas river, Santa Cruz province, Argentina. The specimen comes from beds belonging to the Early-Middle Miocene Pinturas Formation. The specimen MACN-SC 4511 comes from the Portezuelo Sumich locality (see Bown and Larriestra, 1990Bown, T.M., and Larriestra, C.N. (1990). Sedimentary paleoenvironments of fossil platyrrhine localities, Miocene Pinturas Formation, Santa Cruz Province, Argentina. In The Platyrrhine Fossil Record (pp. 87-119). Academic Press.).

Etymology. Honouring José Boris Spivacow (1915-1994), editor of EUDEBA and Centro Editor de América Latina. Due to his efforts, more than 5000 titles were published, and without any doubt his projects have been of capital importance for Argentine cultural heritage.

Description. Small-sized Thegornis species (the largest tarsometatarsus, MACN-SC 1407, having 1.7 cm. of maximum distal transverse width). The metatarsal shaft is roughly “H”-shaped in cross-section. It shows a well defined, but shallow anterior metatarsal groove that is delimited by longitudinal ridges, the lateral one much more prominent than the medial one, resulting in the lateral half being more anteroposteriorly extended than the medial half of the bone. The extensor groove ends on a large and proximodistally extended distal vascular foramen. This groove forms a well-defined and deep canal.

In posterior view the metatarsal shaft is deeply excavated and delimited by two longitudinal plantar ridges. Metatarsal I impression is deep and crescent-shaped, with a proximal margin delimited by a prominent ridge.

The second metatarsal trochlea has a distinctively-formed articular body, which is rounded and ovoidal in contour. The posteromedial wing is well-defined and separated from the main body of the trochlea by a groove and a smooth depression. Metatarsal III trochlea is separated from the II trochlea by a well-defined and narrow intertrochlear incisure. The outer rim of trochlea III is more prominent than the inner rim.

The articular surface of trochlea IV is relatively transversely narrow and subrectangular in contour. In distal view it is laterally inclined. The posterior wing is slightly medially oriented and is separated from the main body of the trochlea by a transverse constriction. This also grades into a concave lateral margin of the main body of the trochlea, which results in a sigmoidal outline.

Remarks. The material belonging to T. spivacowi nov. sp. was previously identified as a caracarine falconid by Chiappe (1991)Chiappe, L.M. (1991). Fossil birds from the Miocene Pinturas Formation of southern Argentina. Journal of Vertebrate Paleontology, 11(Suppl), R21-22.. On the contrary, Thegornis spivacowi nov. can be nested among herpetotheriine falconids based on having the following combination of features, including the roughly “H” shaped metatarsal shaft with a prominent lateral anterior ridge, resulting in a nearly subtriangular general contour and in a very wide and extended impression of the m abductor digiti II, metatarsal II trochlea with posteromedial wing slightly medially oriented, rounded and prominent articular surface of trochlea II, the lateral trochlear rim of metatarsal III trochlea more posteriorly extended than the medial one, relatively thin trochlea IV and extensive posterior wing of metatarsal IV trochlea (Noriega et al., 2011Noriega, J.I., Areta, J.I., Vizcaíno, S.F., and Bargo, M.S. (2011). Phylogeny and taxonomy of the patagonian Miocene falcon Thegornis musculosus Ameghino, 1895 (Aves: Falconidae). Journal of Paleontology, 85(6), 1089-1104.; Cenizo et al., 2013). Thegornis spivacowi comfortably fits within the genus Thegornis, with which it shares a tarsometatarsus with the anterior surface excavated and delimited by sharp ridges intermediate in size between Micrastur and Herpetotheres, an anterolateral margin of shaft elevated as a prominent border, resulting in a roughly subtriangular contour of the shaft, a relatively low posterior lateral metatarsal ridge, large and deep metatarsal I fossa that it is proximally delimited by a prominent ridge, trochlea II slightly grooved, and posteromedial wing of trochlea II relatively thin, well-defined and strongly medially tilted.

Ameghino (1895)Ameghino, F. (1895). Sur les oiseaux fossiles de Patagonie. Boletín del Instituto Geográfico Argentino, 15, 501- 602. coined the falconid genus Thegornis with the aim of including the Santacrucian species Thegornis musculosus and T. debilis, which were distinguished mostly by their disparate size. Later, Thegornis was assigned to Accipitridae (Brodkorb, 1964Brodkorb, P. (1964). Catalogue of Fossil Birds: Part 2: Anseriformes Through Galliformes. Bulletin of the Florida State Museum, 8, 1-150.; Agnolín, 2006bAgnolín, F.L. (2006b). Notas sobre el registro de Accipitridae (Aves, Accipitriformes) fósiles argentinos. Studia Geologica Salmanticensia, 42, 67-80.). However more recently, Noriega et al. (2011)Noriega, J.I., Areta, J.I., Vizcaíno, S.F., and Bargo, M.S. (2011). Phylogeny and taxonomy of the patagonian Miocene falcon Thegornis musculosus Ameghino, 1895 (Aves: Falconidae). Journal of Paleontology, 85(6), 1089-1104. based on newly collected specimens, including a nearly complete skeleton, referred Thegornis to the family Falconidae, Subfamily Herpetotherinae. They also sustained that the size difference between T. debilis and T. musculosus may fit the sexual dimorphism present in extant falconids and considered that the only valid species is T. musculosus, a criterion with which I concur.

T. spivacowi comes from younger beds than those which yielded T. musculosus. In spite of their similarities, T. spivacowi is a smaller species that can be distinguished by details of the distal trochleae of tarsometatarsus. These include a different shape of metatarsal IV trochlea with a well-defined posterior wing and strongly sigmoidal lateral margin. The prominent and rounded metatarsal II articular surface of T. spivacowi nov. resembles the condition of buteonine accipitrids (Noriega et al., 2011Noriega, J.I., Areta, J.I., Vizcaíno, S.F., and Bargo, M.S. (2011). Phylogeny and taxonomy of the patagonian Miocene falcon Thegornis musculosus Ameghino, 1895 (Aves: Falconidae). Journal of Paleontology, 85(6), 1089-1104.). However, in contrast with Thegornis musculosus the ventral margin of the trochlea II is not complete, with the anterior articular surface being separated from the posteromedial wing by a distal notch.