Buteo dondasi, Scaglia, 2021

Scaglia, Fernando A., 2021, A new buzzard from the late Pliocene of Argentina, Acta Palaeontologica Polonica 66 (4), pp. 779-787 : 781-785

Buteo dondasi sp. nov.

Figs. 1–3 .

Zoobank LSID: urn:lsid:zoobank.org:pub:B1006830-A9FB-42A3-94DD-7BCD0A97FA37

Etymology: Named after Alejandro Dondas (1948–2016) who was the curator of the Paleontology Collection housed in the Museo Municipal de Ciencias Naturales Lorenzo Scaglia. At the age of 18, Alejandro established close relationships with Galileo Scaglia, director of the Scaglia Museum, and quickly began his first steps in curating his paleontological collection, until his death in 2016. He left a profound legacy on the responsibility of expanding, caring for and improving one of the most important paleontological collections in South America. The specific epithet is formed from the surname “Dondas,” taken as a noun in the genitive case, plus the Latin suffix “i” (according to the ICZN, 1999, article 31.1.2)

Holotype: MMP 5730 , an incomplete left hind limb consisting in a distal fragment of tibiotarsus, tarsometatarsus, fragmentary os metatarsale I, and toes I and II.

Type locality: La Estafeta Beach, Mar del Plata, Buenos Aires Province, Argentina ( Degrange et al. 2021: fig. 1); S38°10’1.21”, W57°38’3.83”. Type horizon: Chapadmalal Formation, lowest part of Playa Los Lobos Alloformation (Paleosoil 6 of Zárate and Fasano 1989; levels 9–10 of Kraglievich 1952), 3.0 million years ( Prevosti et al. 2021), Piacenzian, late Pliocene.

Material.— Holotype only.

Diagnosis.—A large buzzard with the following combination of characters (exclusive features are indicated with an *): tibiotarsus with a very marked elliptical scar on the medial side of the diaphysis, corresponding to one of the two scars of the tuberositas retinaculi extensoris, located on the medial side of the shaft; tarsometarsus with the lateral impressio retinaculi extensorii located more distally than the medial impression*, the medial foramen vasculare proximale, on ventral aspect, opens laterally to the crista medialis hypotarsi*, shallower notch for the nervus peroneus than other Buteoninae; the trochlea metatarsi III is more extended distally than the trochlea II; in the phalanx ungualis II both foramina opens into deep pits*.

The new species Buteo dondasi sp. nov. differs from Buteogallus , a genus commonly registered by several fossil species of large body size in the northern Neotropical region ( Campbell 1979; Emslie and Czaplewski 1999; Suárez 2004; Suárez and Olson 2007; Olson 2007, 2008; Steadman et al. 2019) in that the crista medialis hypotarsi forms an angle of 65° regarding the shaft, and it is not perpendicular as in the latter. Also, Buteo dondasi sp. nov. shares with species of Amplibuteo , the presence of a lateral impressio retinaculi extensorii located more distally than the medial, an uncommon feature among Accipitridae (FJD personal observations). However, it differs from species of Amplibuteo in having a less proximally extended eminentia intercotylatris, a markedly smaller foramen vasculare distale, and the trochlea metatarsi IV more extended distally. Buteo dondasi sp. nov. differs from species of Geranoaetus in having the medial impressio retinaculi extensorii located more proximally than the lateral, a shallower notch for the nervus peroneus, a wider furrow that continues proximally to the foramen vasculare distale, and by the presence of a foramen at the base of the middle prominence of the phalanx ungualis II. Parabuteo differs from Buteo dondasi sp. nov. in having the cotyla lateralis much narrower, the trochlea metatarsorum III and IV equally extended distally, the crista medialis hypotarsi more elongated proximodistally and by the presence of a narrow and elongated fossa, located medially to the fossa infracotylaris dorsalis. Species of Leucopternis possess an ossified retinaculi extensorii, the tuberositas m. tibialis cranialis is more medially located, the crista medialis hypotarsi is wider and poorly extended ventrally, the sulcus hypotarsis is narrower, and the trochlea metatarsi IV is more extended distally than the III. The holotype of Vinchinavis paka Tambussi, Degrange, Ciccioli and Prevosti, 2021 , does not have an overlap of materials with those of Buteo dondasi sp. nov., therefore, comparisons are not possible. Vinchinavis was considered similar to Buteogallus in the original description, which makes it unlikely the assignment of MMP 5730 to this fossil taxon.

Description.— Tibiotarsus: Only the left extremitas distalis tibiotarsi is preserved ( Fig. 1 ). The sulcus extensorius is narrow and deep (wider in species of Aquila , Gyps , Gypaetos , Gypohierax , and Buteo ). The canalis extensorius is narrow, opening medially, over the condylus medialis. This opening has a triangular shape as in species of Geranoaetus , Haliaeetus (except for Haliaeetus vocifer Daudin, 1800 ), Buteo and Harpia (rounded in species of Spilornis , Buteogallus , Gyps , Gypaetos , Torgos , Elanus , and Circus ). The pons supratendineus is stout (slender in species of Elanus , Gypaetos , Spilornis , Terathopius , and Gampsonax; stouter in Gyps and Gypohierax ), strongly slanted proximomedially, endowed with a small distal lip more developed in species of Circus ). Medially to the sulcus extensorius, there is an ovalated and well-marked scar as in species of Geranoaetus and Buteogallus , variable in Haliaeetus , more distally located in Sarcogyps and Torgos , proportionally longer in species of Gypohierax , rounded in species of Aquila , Buteo , Gyps , and Aegypius , placed on the medial margin of the shaft in species of Harpia , poorly marked in species of Gypaetus and Milvus ). This corresponds to one of the two scars of the tuberositas retinaculi extensoris. The second scar is broad and located on the base of the pons, laterodistally to it. The trochlea cartilaginis tibialis is wide and shallow (deeper in species of Aquila , Buteo , and Harpia , almost flat in species of Gyps ). The crista trochleae medialis is smooth, proximomedially directed, while the crista trochleae lateralis is vertically disposed, forming a proximally abruptly flange medially directed. The depressio epicondylaris lateralis is wide and deep. Proximally to this depressio, a laterally facing furrow is observed (more cranially facing in species of Buteo ), marked by a sharp cranial edge (strongly projected laterally in species of Stephanoaetus ) and a blunt caudal edge strongly projected laterally in species of Leucopternis ). The latter corresponds to the tuberculum retinaculi m. fibularis, which is vertically disposed. The sulcus m. fibularis is shallow and poorly marked as in species of Buteogallus and Buteo (deeper in species of Trigonoceps and Haliaeetus , shallower in species of Aquila ). The epicondylus medialis is elliptical and well developed (poorly developed in species of Gypohierax , Kaupifalco , and Ictinia ), distally located more proximally located in species of Aquila and Gyps , more cranially located in species of Buteo and Gypaetos ), strongly projected medially as is typical of Accipitridae . The condylus lateralis is subrounded when viewed laterally (more rounded in species of Accipiter and Aegypius ). The condylus medialis is low (taller in species of Aquila ), medially projected (strongly medially projected in species of Necrosyrtes ), and is more extended cranially than the condylus lateralis (almost equally extended in species of Morphnus and Torgos ). Both condyli are quite wide when viewed cranially and are delimited by stout and smooth edges. The incisura intercondylaris is wide and deep.

Tarsometatarsus: The tarsometatarsus resembles that of species of Buteo and Buteogallus , being proportionally sturdier than the tarsometatarsus of the latter two taxa, but not that much as in species of Aegypius , Gypaetus , Stephanoaetus , and Harpia or other Buteoninae such as Haliaeetus . The eminentia intercotylaris is poorly developed Fig. 2 , more developed proximally in species of Accipiter and Aquila ), as is typical of Accipitridae ( Mayr and Perner

2020). The cotyla medialis is a shallow concave depression that has a subcircular contour, medially bordered by a small flange proximo-medially directed. When viewed medially, this cotyla shows on its base a small conic tubercle, which separates it from the crista medialis hypotarsi. The cotyla lateralis is almost flat, subrectangular (deeper in species of Buteo ). It has a small flange directed ventro-laterally. This corresponds to the tuberculum m. fibularis brevis. The fossa infracotylaris dorsalis is shallow. The foramina vascularia proximalia are small (large in species of Aquila ), and open in this fossa at the same level (as in species of Accipiter , Buteo , and Buteogallus ). The impressiones retinaculi extensorii are paired, ridge-like and well-marked (this retinaculi is ossified in species of Pandion and Leucopternis ). The medial impressio is located more proximally than the lateral as in species of Buteo (and contrary to other Buteoninae species such as species of Buteogallus and Geranoaetus in which both are located proximally) and the fossil species of Amplibuteo (see Campbell 1979; Suárez 2004; Suárez and Olson 2007). The impressio lig. collateralis lateralis are partially preserved, but it is evident that they are very well marked and located on the lateral surface of the corpus tarsometatarsi. The corpus is elongated and stout as in species of Geranoaetus , Buteo regalis ( Gray, 1844) , B. jamaicensis ( Gmelin, 1788) , and species of Buteogallus (more elongated and slender in Accipitrinae and Buteo lineatus ( Gmelin, 1788) . The sulcus extensorius is concave, narrow and bordered laterally by the tuberositas m. tibialis cranialis, which is elliptical and prominent (more distomedially located in species of Accipiter ). The facies subcutanea lateralis is a stout and robust crest. The sulcus hypotarsi is deep, with a rounded dorsal margin. The crista lateralis hypotarsi is robust, with a stout laterally directed tubercle. This crista also presents a small sulcus ligamentosus on its base, poorly extended laterally. As is typical of Buteoninae, the notch for the nervus peroneus is very marked (see Jollie 1977; Mayr and Perner 2020), bounded by a stout and elongated tuberculum m. fibularis brevis (although it is also developed independently in fossil Gypaetinae , see Zhang et al. 2012). This notch, however, is shallower than in species of Buteogallus , Geranoaetus , and Buteo . The crista medialis hypotarsi is strongly projected ventrally, disposed at an angle of 65° posteriad in relation to the shaft, and endowed with a ventral expansion that also extends distally (more than in species of Buteo and Geranoaetus , not extended distally in species of Buteogallus ). However, this crista is less extended proximodistally than that species of Buteo , and similar to the condition observed in species of Buteogallus and Geranoaetus . The fossa parahypotarsalis lateralis is narrow, meanwhile the fossa parahypotarsalis medialis is wider. The foramina vascularia proximalia opens ventrally at the same level, but the medial foramen vasculare proximale opens laterally to the crista medialis hypotarsi as in the species of Buteo , Parabuteo , and Haliaeetus (this foramen opens medially in most accipitrids). The sulcus m. fibularis longus is shallow, medially delimited by a small crest. The sulcus flexorius is very deep, laterally bordered by a sharp crista plantaris lateralis strongly projected ventrally, and medially by a sturdier crista plantaris medialis less projected ventrally. The fossa metatarsi I is elliptical and deep. The fossa supratrochlearis plantaris is flat. In the facies dorsalis, the foramen vasculare distale is elliptical and proximally continued on the facies by a conspicuous, wide and deep furrow (shallow and narrow in species of Buteogallus , deep and narrow in Geranoaetus ), largely extended proximally as in species of Buteo . The incisurae intertrochlearis lateralis et medialis are narrow. The trochlea metatarsi II has a smooth and curved surface, not furrowed. It is expanded medially through a robust processus medioventrally directed, located ventrally to the conspicuous fovea lig. collateralium. The trochlea metatarsi III shows a shallow furrow (deeper in species of Buteo ), of subparallel edges, is slightly directed laterally and is more extended distally than the second as in Buteo regalis , but contrary to Buteo jamaicensis , B. lineatus , species of Buteogallus , and of Geranoaetus . The distal edge of the trochlea metatarsi IV is eroded, but the poorly marked fovea lig. collateralium can be appreciated. This trochlea is ventrally extended through a narrow ventral processus.

Os metatarsale I: The processus articularis tarsometatarsalis is lacking ( Fig. 3A ). It is a short and stout bone with a robust rounded trochlea metatarsi I (similar to Stephanoaetus ), strongly extended proximally (poorly extended in species of Aquila , Buteogallus , and of Harpia ), ventrally projected and bordered lateroproximally by a deep furrow. Both the tuberculum laterale et mediale are stout. On the dorsal surface, medially located, a conspicuous furrow (shallower in species of Geranoaetus ) delimited by two marked crest (stouter in species of Buteogallus ) is observed. Laterally to this furrow, the surface is completely concave.

Proximal phalanx I: The phalanx is stout, with a wide and depressed corpus phalangis, slightly curved dorsoventrally ( Fig. 3C ). The cotyla articularis is flat, wide, with a rounded dorsal edge, flexed distally. The facies dorsalis is convex, whereas the facies plantaris is slightly concave, with a shallow furrow located in the mid-plane. To both sides of the cotyla articularis, two stout tubercles can be identified, being the lateral one more extended distally (also projected distally through a stout accessory processus in species of Haliaeetus ). The trochlea articularis is narrow (wide in species of Aquila , Stephanoaetus , Harpia , and Haliaeetus ), deep, endowed with a small pit caudoventrally located (deeper in species of Geranoaetus and Buteogallus ). In dorsal view, the edges of the trochlea are equally divergent, but when viewed distally, the lateral margin is more directed ventrolaterally than the medial. In lateral view, the trochlea presents a dorsal straight margin and a ventral markedly rounded, projected ventrally. Both fovea lig. collateralium are deep and well-marked.

Phalanx ungualis I: The proximal articulation facet is slightly asymmetric, strongly concave (much more than in species of Harpia ), and deep, with a trapezoidal-shape contour ( Fig. 3E ). The medial cotyla is slightly narrower and less extended distally than the lateral cotyla. Separating both cotyla, a stout dorsoventral ridge can be appreciated. In the ventral area of this ridge, a middle prominence is located. The tuberculum extensorium is very well developed. Anteriorly and on the dorsal and lateral surfaces of the corpus, a strong scar of the position of the keratinous claw case is located. As is typical of Accipitridae ( Mosto and Tambussi 2013) , the tuberculum flexorium is very stout, ventrocranially directed (more ventrally directed in species of Haliaeetus and Gypaetus ). In B. dondasi sp. nov. it is, also, medially directed when viewed ventrally, being narrower than that of species of Aquila . On both sides of the tuberculum, conspicuous oval foramina are located at the same level both ventrally as distally. They are delimited dorsally by a thin bony bridge (thicker in species of Stephanoaetus , Harpia , and Aquila , absent in species of Haliaeetus ) that connects the cotylae articularis with the tuberculum flexorium, joining both at the midpoint, on the tuberculum (delimiting also the ventroproximal portion of the corneal case scar). The corpus phalangis is markedly curved ventrally, with a section markedly convex dorsally and straight ventrally. Ventral and dorsal surfaces of the corpus are separated by very sharp edges located on both sides. The sulci neurovasculares are absent. The apex phalangis is pointed.

Proximal phalanx II: It is a short and robust bone ( Fig. 3B ). The cotyla articularis is dorsoventrally convex and lateromedially concave. The cotyla projects laterally through a long lateral tubercle (more caudally directed in Buteogallus ), and medially through a flat distal end tubercle. The trochlea articularis is deep, with divergent margins, delimited dorsally and mediolaterally by a small sharp ridge (poorly marked in species of Buteogallus ).

Second phalanx II: It is a robust phalanx (markedly stouter in species of Stephanoaetus and Harpia ), with a straighter, narrower and taller corpus than the previous phalanx ( Fig. 3D ). It has a robust tuberculum extensorium, caudally directed. The facet of articulation is strongly concave and deep, with a sub-triangular outline. The cotyla medialis is more extended dorsally than the lateralis, while the lateralis is slightly more extended ventrally. Small tubercles are located on both sides of the articulation facet, on the ventral surface. Separating both cotylae there is a robust and blunt dorsoventral ridge. The facies dorsalis is convex, whereas the facies plantaris is flat. The trochlea articularis is deep and a small fossa is located both ventrocaudally and dorsocaudally to it. In dorsal view, the margins of the trochlea are divergent, while in distal view they are subparallel. The trochlea presents a straight dorsal margin and a rounded ventral margin, projected ventrally. Both fovea lig. collateralis are deep and well-marked.

Phalanx ungualis II: The articulation facet is asymmetrical, strongly concave and deep, with a trapezoidal outline ( Fig. 3F ). Both cotylae are located at the same level, separated by a blunt vertical dorsoventral ridge, located in the middle of the facet. A middle prominence is developed and a small foramen is located cranially to it, on the ventral surface of the phalanx (as in species of Stephanoaetus , two small foramina in species of Harpia , absent in species of Aquila , Geranoaetus , Buteogallus , and Haliaeetus ). The tuberculum extensorium is strongly developed. The tuberculum flexorium is very robust, strongly projected cranioventrally (more ventrally directed in species of Gypaetus ; more elongated distoproximally in species of Harpia and Stephanoaetus ), and medially directed in ventral view. The oval foramina are located at the same level in ventral view on both sides of the tuberculum, although the lateral one is more dorsally. Both foramina open into deep pits (less marked in species of Stephanoaetus ), an exclusive feature of this taxon. They are delimited dorsally by a slender bony bridge (thick in species of Stephanoaetus , Harpia , and Aquila , absent in species of Halieetus) that connects the cotylae and borders the tuberculum flexorium dorsally, joining at the midpoint, on top of the tuberculum. The corpus phalangis is markedly curved, with a section markedly convex dorsally and slightly convex ventrally, separated by sharp edges projected to the sides. The sulci neurovasculares are absent.

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig. 1. Left fragmentary tibiotarsus of the buzzard Buteo dondasi sp. nov. (MMP 5730) from Chapadmalal Formation (late Pliocene), La Estafeta Beach, Mar del Plata,Argentina; in cranial (A1), lateral (A2), caudal (A3), medial (A4), and distal (A5) views.

Fig. 2. Left tarsometatarsus of the buzzard Buteo dondasi sp. nov. (MMP 5730) from Chapadmalal Formation (late Pliocene), La Estafeta Beach, Mar del Plata, Argentina; in dorsal (A1), lateral (A2), ventral (A3), medial (A4), proximal (A5), and distal (A6) views.

Fig. 3. Partial left pes of the buzzard Buteo dondasi sp. nov. (MMP 5730) from Chapadmalal Formation (late Pliocene), La Estafeta Beach, Mar del Plata, Argentina. A. Left os metatarsale I in dorsal (A1) and distal (A2) views. B. First phalanx of toe I, in lateral (B1), dorsal (B2), medial (B3), ventral (B4), proximal (B5), and distal (B6), views. C. Ungual phalanx of toe I, in proximal (C1), dorsal (C2), medial (C3), and ventral (C4) views. D. First phalanx of toe II, in proximal (D1), lateral (D2), dorsal (D3), medial (D4), ventral (D5), and distal (D6) views. E. Second phalanx of toe II in medial (E1), dorsal (E2), lateral (E3), ventral (E4), proximal (E5), and distal (E6) views.F. Ungual phalanx of toe II, in proximal (F1), dorsal (F2), medial (F3), and ventral (F4) views.