SYSTEMATIC PALEONTOLOGY
Order INCERTAE SEDIS
Family TERATORNITHIDAE Miller, 1925
TERATORNITHIDAE gen. et sp. indet.
Referred Material—Complete left tarsometatarsus (MFA-GPV w/no.; i.e., without collection number). Due to the current pandemic situation in Argentina, the final cataloging of the specimen in the Museo Provincial de Ciencias Naturales ‘Florentino Ameghino’ (Santa Fe Province, Argentina) is pending.
Locality and Stratigraphic Context—The tarsometatarsus MFA-G-PV w/no. was recovered from outcrops of the left cliffs of northern Salado River, 100 m downstream of the road bridge of the provincial route No. 4 (31°15′16.98″S–60°53′ 32.82″W, Fig. 1), near to Manucho locality, Santa Fe Province, Argentina. Outcrops display a fluvial–shallow lacustrine stratigraphic succession exposed along 25 km of the river cliffs with a thickness up to 5 m (Vezzosi et al., 2017). MFA-G-PV w/no. comes from deposits of the basal section informally named Esperanza Lithostratigraphic Unit (ELU, Fig. 1), which are composed of fine laminated pale-olive sandy-silts of tabular geometry with frequent iron oxide nodules, corresponding to a channel facies generated in a low energy flow regime (Vezzosi et al., 2017). Infrared stimulated luminescence dates (ISRL) of 96.5 ± 5.6, 91.6 ± 7.6 and 84.9 ± 6.7 ka BP obtained from ELU correlated deposits exposed in a nearby locality at ∼24 km NE (Autódromo Emilia; Kruck et al., 2011) indicate an early late Pleistocene age. Available geomorphological, sedimentary, geochronological and paleofaunistic proxies support a relationship with the Last Interglacial Stage (Marine Isotopic Stage 5, MIS 5) for the fossilbearing unit (e.g., Vezzosi et al., 2017; Brandoni and Vezzosi, 2019).
Description and Comparison—The tarsometatarsus MFA-GPV w/no. (Fig. 2) is well preserved, only its distal and proximal ends are slightly eroded. The presence of a large-sized tarsometatarsus with an asulcate block-like hypotarsus is a character only shared by the terrestrial taxa Cariamiformes (i.e., Cariamidae and Phorusrhacidae), Cathartidae and Teratornithidae. The new specimen lacks the characteristic cursorial adaptations displayed in the tarsometatarsi of extant and fossil Cariamiformes (e.g., reduced fossa metatarsi I and general pneumaticity, different arrangement of the trochleae). On the other hand, MFA-G-PV w/no. clearly agrees with comparable elements known for Teratornithidae and differs from Cathartidae in the following characters: (1) corpus tarsometatarsi with nearly square cross section of the shaft (vs. dorsoplantarly compressed section); (2) dorsal view, quadrangular proximal end (i.e., lateral and medial profiles abruptly expanded on both sides and nearly parallel to the sagittal plane; vs. triangular, i.e., both profiles gradually diverge from the sagittal plane); (3) relatively inconspicuous eminentia intercotylaris, very low and almost symmetrical in all directions (vs. more prominent, higher and asymmetrical, except Sarcoramphus papa [Linnaeus, 1758]); (4) proximal view, similar-sized cotylae (vs. cotyla medialis usually somewhat larger than the cotyla lateralis); (5) more reduced and shallower area intercotylaris; (6) wider and deeper sulcus ligamentosus (except C. gracilis); (7) on the proximomedial side of the fossa infracotylaris dorsalis, lateral impression of the retinaculum extensorium developed like a small, sharp papilla (vs. absent or reduced); (8) proximal view, stouter and more plantarly extended hypotarsus; (9) plantar view, higher, wider, and quadrangular hypotarsus with a well-defined distal transverse ridge distinctly elevated above the crista medianoplantaris (10) stouter crista medianoplantaris; (11) wider fossae parahypotarsalis lateralis and medialis, mainly the latter; (12) shallower fossa infracotylaris dorsalis; (13) foramina vascularia proximalia more closely positioned to each other; (14) extremitas distalis widens very gradually with an almost symmetrical curvature of both lateral and medial profiles (vs. slightly asymmetric condition due to the more mediodistal projection of the trochlea metatarsi II); (15) distal end of the sulcus extensorius leading to the foramen vasculare distale deeper and slightly laterally rotated (vs. more superficial and straighter); (16) plantarly incomplete canalis interosseous distalis (i.e., reduced to a sulcus or to a very short osseous bridge; vs. complete); (17) two excavated surfaces on the fossa supratrochlearis plantaris (one between the fossa metatarsi I and the trochlea metatarsi III, and other between the trochlea metatarsi IV and the plantar opening of foramen vasculare distale) creating a crista proximally extended from the trochlea metatarsi III (vs. almost flat fossa); (18) one or more small foramina on the medial surface of fossa supratrochlearis plantaris (vs. minimal or absent); (19) dorsal view, both trochleae metatarsorum II and IV equal or slightly more distally extended; and (20) proximal view, four very prominent tubercula present around both cotylae (vs. individual tubercula variably present, but never all four). The first tuberculum is a round headed structure observed on the dorsal edge of the cotyla lateralis, which is broken in MFA-G-PV w/no. but appears to have been present. Among cathartids, only some specimens of Gymnogyps californianus (Shaw, 1797) show a small tuberculum in this location. Another two tubercula located on the laterodorsal (broken in MFA-GPV w/no.) and lateroplantar corners of the cotyla lateralis in teratorns are also present in cathartids, but reduced. A fourth tuberculum found on the medial edge of the cotyla medialis of MFA-G- PV w/no. and other teratorns is absent or very poorly developed in Cathartidae. Despite their lesser development, some of these four tubercula are usually present in Cathartidae, but never all together as in Teratornithidae. Among teratornithids, the complete tarsometatarsus is only known for T (Teratornis). merriami, C. gracilis, and partially for O. olsoni (distal end) and A. magnificens (very fragmentary distal end lacking trochleae). The general measurements of MFA-G-PV w/no., slightly larger than those of C. (Cathartornis) gracilis, are within the size-range observed in T. (Teratornis) merriam, suggesting that it belonged to a bird clearly larger than T.(Teratornis) campbelli and O. (Oscaravis) olsoni, but smaller than A. (Aiolornis) incredibilis and A. (Argentavis) magnificens.
Referred Material—Right fragmentary proximal radius (MACN Pv 13717,
Locality and Stratigraphic Context—The referred specimen was collected by Osvaldo Coronel between 1934 and 1946 from ‘stratified sands’ at the cliffs of the Carcarañá River near to the homonym city and the national route No. 9 (32°51′30.7″S–61° 10′42.2″W, Fig. 1), Santa Fe Province, Argentina. Upper Pleistocene units are regionally recognized, which include fluvial facies of the Timbúes Formation and the overlying lacustrine to aeolian Tezanos Pintos Formation, outcropping along with the Holocene fluvial terraces (e.g., Vezzosi et al., 2019; Fig. 1). With a local thickness of 2–4 m, the Timbúes Formation is segregated into two facies. The basal Facies 1 consists of sandy silts with low-angle cross-stratification corresponding to downstream accretion bars built-up as banks inside sinuous channels. The overlying Facies 2 is constituted by poorly structured and massive reddish brown sandy silts with abundant iron oxide coatings. The latter, together with the presence of faintly stratified deposits with dispersed carbonate, suggests a floodplain environment deposited under drier climatic cycles alternating diachronically with more humid periods (Vezzosi et al., 2019). According to the geological context indicated by the collector (i.e., ‘stratified sands’) and the taphonomic attributes typical of subaqueous burial observed in MACN Pv 13717 (i.e., complete dark staining by manganese impregnation, absent in specimens of the overlying Tezanos Pintos, Caracarañá and Palo Negro Formations), the provenance of the specimen can be referred with relative certainty to Facies 1 of the Timbués Formation. An early late Pleistocene age has been proposed for the Timbúes Formation based on its relative stratigraphic position along various sections in the Paraná River cliffs near Carcarañá River (Vezzosi et al., 2019), and the OSL and TL dates of 118–67.4 ka BPobtained from putative coeval regional outcrops (e.g., Palo Negro Formation; Brunetto et al., 2017). However, it is important to note that the upper levels may be younger if the facies described as the ‘Carcarañá Formation’ (OSL and TL dates of 68–52 ka BP; Brunetto
et al., 2017) are incorporated as part of the Timbúes Formation. Referred ages and additional paleoclimatic data are consistent with the Last Interglacial Stage (MIS 5) environmental conditions for the fossil-bearing unit (Ferrero et al., 2017; Vezzosi and Kerber, 2018). Finally, ISRL, TL and C14 dating from the overlying Tezanos Pintos Formation show a final late Pleistocene age (ca. 35–9 ka BP; Brunetto et al., 2017), including terminal MIS 3 and MIS 2 (Last Glacial Maximum).
Description and Comparison— The fragmentary radius MACN Pv 13717 shows its proximal end slightly eroded on the caudal surface. This specimen agrees with Teratornithidae (radius only known in T. merriami) and differs from Cathartidae in the following combination of characters (Fig. 3): (1) fovea ligamentum radioulnare transversum lacking large pneumatic foramen (vs. present; except in Breagyps clarki [Miller, 1910] and Coragyps atratus [Bechstein, 1793]); (2) on the tuberculum bicipitale, more elongated and distally extended scar for the musculus biceps brachii (vs. wider and shorter scar); (3) from the tuberculum bicipitale to the edge of the cotyla humeralis, two ligamentous scars are well delimited, excavated and close to each other (vs. one or two poorly defined and more spaced ligamentous scars, sometimes on a proximal tubercle); and (4) more excavated sulcus proximalis (vs. shallower, with a large foramen in C. atratus). The size of MACN Pv 13717 is consistent with the expected proportions of the radius in T. merriami (slightly larger than the homologous bone in V. (Vultur) gryphus).
Referred Material—Right fragmentary proximal end and shaft
ulnae, right section of margo cranialis sterni, and right pedal
phalanx proximalis digiti II (MPH-P 0227)
Referred Material—Incomplete ventral section of synsacrum
(MD-PDB 05-25,)
Fred
Figure 1. Left tarsometarsus assigned to Teratornithidae gen. et sp. indet. (MFA-G-PV w/no.) from the early late Pleistocene of Salado R iver (Santa Fe Province, Argentina) and homologous elements in select Teratornithidae and extant Cathartidae. Teratornithidae gen. et sp.
indet. (MFA-G-PV w/no.), in A, dorsal, D, plantar, G, proximal, and J, distal views. Teratornis merriami (holotype, UCMP 12599, Teratornithidae), in B, dorsal, E, plantar, H, proximal, and K, distal views. Vultur gryphus (MLP-PV-OR 367, Cathartidae), in C, dorsal, F, plantar, I, proximal, and L, distal views. Abbreviations: aic, area intercotylaris; cmp,
crista medianoplantaris; cst, crista supratrochlearis; dtr, distal transverse ridge; eic, eminentia intercotylaris; fhl, fossa parahypotarsalis lateralis; fhm, fossa parahypotarsalis medialis; fid, fossa infracotylaris dorsalis; fst, foramina supratrochleares; fvd, foramen vasculare distale; fvp, foramina vacularia proximalia; lpw, lateroplantar wing of the trochlea IV; rel, lateral impressio of the retinaculum extensorium; sid, sulcus interosseous distalis; sle, sulcus extensorius; slg, sulcus ligamentosus; tbI, tuberculum I; tbII, tuberculum II; tbIII, tuberculum III; tbIV, tuberculum IV; I, fossa metatarsi I; II, trochlea metatarsi II; III, trochlea metatarsi III; IV, trochlea metatarsi IV.
Scale bars equal 30 mm in A–F, and 10 mm in G–L.
