Type species: Noriegavis santacrucensis (Noriega, Vizcaíno, and Bargo, 2009); Santa Cruz Province, Argentina; early Miocene Estancia La Costa member of the Santa Cruz Formation.

Emended diagnosis. —Distinguished from the two extant taxa of Cariamidae, Cariama and Chunga, in the following features: (i) prominentia cerebellaris more conspicuous and globose (Noriega et al. 2009); (ii) foramen magnum dorsally bordered by well-developed crests (Noriega et al. 2009); (iii) dorsal surface of cranium forming two elevated areas that are each separated by a depression from the orbital rim (Fig. 2A₅); (iv) processus supraorbitalis proportionally larger; (v) carina sterni proportionally deeper (Fig. 3); pelvis with (vi) postacetabular region proportionally shorter (Fig. 4), and (vii) cristae iliacae dorsales not fused on level of crista spinosa (Fig. 4A₂); femur with (viii) narrower proximal end, and (ix) less medially inflected distal end (Fig. 5); (x) cristae cnemiales of tibiotarsus less proximally protruding (Fig. 5); (xi) medial flange of trochlea metatarsi II better developed plantarly (Fig. 5A₁₄). Three of the five characters listed in the original diagnosis of Noriega et al. (2009), i.e., the length and orientation of the postorbital and zygomaticus processes and the shape of the foramen magnum, are revised below and no longer considered to be diagnostic.

Stratigraphic and geographic range. —Early Miocene Estancia La Costa member of the Santa Cruz Formation; Santa Cruz Province, Argentina.

Material.—MPM-PV 15049, consisting of associated skeletal elements of a single individual including the skull, left os lacrimale, caudal portion of right ramus mandibulae, partial sternum and pelvis, fragmentary proximal half of left humerus, proximal end of right ulna, distal end of left ulna, right phalanx proximalis digiti majoris, left femur, nearly complete right tibiotarsus (broken in two pieces), distal end of right tarsometatarsus, midsection of shaft and distal end of left tarsometatarsus, as well as four pedal phalanges. Specimen collected from Monte Tigre locality, between Coyle and Gallegos rivers (approximately at 51º20' S and 69º02' W), 20 km south of the type locality, Santa Cruz Province, Argentina (Fig. 1). Estancia La Costa Member of the Santa Cruz Formation, early Miocene, 16 million years ago (Vizcaíno et al. 2012; Fleagle et al. 2012).

Dimensions (in mm). —Skull: length as preserved, ∼95.6; width on level of processus postorbitales, ∼36.1; length of beak as preserved, ∼47.2; greatest width of beak, 14.0; length of nostril, 21.3; greatest depth of beak, 7.6. Humerus: width of shaft at distal end of crista deltopectoralis; 8.6. Ulna: proximal width, 13.3; distal width, 8.7. Femur: length, 78.6; proximal width, 16.5; distal width, 17.1. Tibiotarsus: length as preserved, ∼175.0; proximal width of cranial portion, from facies articularis medialis to crista cnemialis lateralis, 24.2; proximal width of caudal portion, from facies articularis medialis to facies articularis lateralis, 13.3; width of mid section of shaft, 8.5; depth of mid section of shaft, 6.6; depth of condylus lateralis, 12.2. Tarsometatarsus: width of mid section of shaft, 5.9; depth of mid section of shaft, 6.3 (medial portion), 6.6 (lateral portion); distal width, 13.4; width of trochlea metatarsi III, 5.6.

Description and comparisons. —The cranium of Noriegavis santacrucensis was described by Noriega et al. (2009), who noted the following differences to extant Cariamidae: (i) shorter and more vertically oriented processus postorbitalis, (ii) shorter and less cranially protruding processus zygomaticus, (iii) better developed prominentia cerebellaris, and (iv) elliptical foramen magnum, which is (v) dorsally bordered by well-developed crests. The comments on the orientation of the postorbital and zygomatic processes in the original diagnosis of N. santacrucensis (Noriega et al. 2009: 621) need to be revised, however, based on the information provided by specimen MPM-PV 15049, whose better preserved cranium allows a more accurate assessment of the relative inclinations of the postorbital and zygomatic processes. The correct orientation of these processes can be obtained if the holotype skull figured in lateral view by Noriega et al. (2009: fig. 3A, B) is slightly rotated counterclockwise towards its true horizontal position, in which case it becomes evident that the processus postorbitalis is not more vertically oriented and the processus zygomaticus is not less cranially protruding than in extant seriemas. In MPM-PV 15049 the tip of the processus postorbitalis is broken, but the remaining portion shows that it was mediolaterally thin as in Chunga burmeisteri, whereas it is somewhat broader in Cariama cristata. The processus zygomaticus is damaged in both, the holotype and the new specimen MPM-PV 15049, but appears to have had a similar length to that of modern Cariamidae. Both, the postorbital and zygomatic processes of N. santacrucensis exhibit similar angles to those of C. cristata and Ch. burmeisteri, with the tip of the processus zygomaticus reaching the vertical level of the processus postorbitalis.

The prominentia cerebellaris is poorly preserved, but exhibits two lateral depressions on both sides, as in the holotype. Although the prominentia itself is badly crushed in the new specimen, its fragments overlie a “sedimentary cast” that allows to infer its prominent condition. As in C. cristata, the fossa temporalis is ventrally bordered by a faintly marked crista nuchalis transversa, whereas this crest forms a distinctly arched ridge in Ch. burmeisteri, which runs obliquely across the squamosum and joins the processus zygomaticus. The impression of the origin of musculus adductor mandibulae externus, pars rostralis, in the fossa temporalis is similar to that of C. cristata, i.e., is relatively wide and shallow with a rounded medial margin, whereas it forms a more elongated, more confined, and deeper mark in Ch. burmeisteri.

The right margin of the foramen magnum is damaged, but the remaining parts indicate that it was less dorsoventrally elongated than in the holotype and more closely corresponded in its shape with the foramen magnum of extant Cariamidae. We consider these differences to be due to distortion of the holotype, in which the foramen has an asymmetric shape, and the new specimen presumably better reflects the true morphology of the foramen magnum of N. santacrucensis.

The dorsal surface of the cranium forms two elevated areas, which are each separated by a depression from the orbital rim (Fig. 2A₅). This condition is approached by Ch. burmeisteri where those bulges and the depression are, however, less marked. As in modern seriemas, the skull roof bears numerous impressions of blood vessels, which are particularly pronounced along the orbital rims. The interorbital section of the skull roof is of similar width to Chunga, whereas it is wider in Cariama (Fig. 2). The processus supraorbitalis of the os lacrimale is proportionally larger than in both species of extant seriemas (Fig. 2). The processus orbitalis of the os lacrimale is thin and laterally notched, being more slender than in Ch. burmeisteri and much more so than in C. cristata. The preserved neurovascular foramina on the left os exoccipitale show the same pattern as in the holotype, but other details of the basicranial and palatal areas cannot be recognized.

The beak is broken from the cranium and angled in an unnatural position. In its overall proportions, with a straight culmen and a slightly deflected tip, it resembles that of modern Cariamidae, but the nostrils are proportionally larger than in the two extant species (Fig. 2). The processus frontales of the ossa praemaxillaria are unfused, of similar width to those of C. cristata and somewhat broader than in Ch. burmeisteri. Of the mandible only the caudal portion of the right ramus is preserved, which has similar proportions to modern seriemas, but is not well enough preserved for meaningful comparisons (Fig. 2A₄).

The sternum preserves the cranial portion and much of the carina sterni, which, however, lacks the ventral rim and the apex carinae (the latter being cranially prominent in modern Cariamidae). The preserved part of the carina still shows that it was proportionally deeper dorsoventrally than in extant seriemas, and whereas the margo cranialis carinae, i.e., the cranial margin dorsal to the apex carinae, measures only slightly more than the distance across the sulci articulares coracoidei in extant Cariamidae, it is more than two-thirds of the width across the sulci articulares coracoidei in Noriegavis (Fig. 3). The preserved margo cranialis of the carina is further steeper, i.e., less curved, than in extant Cariamidae, which may indicate that the apex may did not form a marked overhang. The sulci articulares coracoidei are narrower than in extant Cariamidae, and the medial section of the labrum internum is dorsoventrally narrower (Fig. 3). The spina externa is broken.

Only the fragmentary proximal half of the left humerus is preserved, which, as far as comparisons are possible, resembles the corresponding part of the humerus of extant seriemas. The cranial surface of the distal section of the shaft is, however, more flattened than in extant Cariamidae, with the craniodorsal margin forming a sharp edge.

The preserved fragments of the proximal right ulna and the distal left ulna correspond with extant seriemas in shape and proportions, but the condylus dorsalis has a somewhat more rounded outline than in the modern species. On the caudal surface of the proximal end, there is a projection, just distal to the olecranon (Fig. 3A₂), which is also present in extant seriemas and Elaphrocnemus (Mourer-Chauviré 1983: pl. 1: 7). The phalanx proximalis digiti majoris resembles that of extant Chunga in its shape, whereas the caudal margin of this phalanx is more bulged in Cariama (Fig. 3).

The pelvis differs in its proportions and some morphological characters from that of modern seriemas. In particular, and as can be deduced from the proportions of the ala postacetabularis ilii, the medial margin of which is preserved (Fig. 4A₁), the caudal part is proportionally shorter. The cristae iliacae dorsales contact each other and the crista spinosa of the synsacrum, but unlike in extant Cariamidae these crests do not fuse and a suture is still visible (Fig. 4A₄). As in modern seriemas and Phorusrhacidae but unlike the bathornithid Paracrax wetmorei (Cracraft 1968: fig. 10), there is a well-defined, laterally prominent process dorsal of the antitrochanter (Fig. 4). The suturae iliosynsacrales are less obliterated than in extant C. cristata (Fig. 4A₂), and further unlike the latter the synsacrum forms a midline bulge on the dorsal surface of the caudal part of the pelvis; with regard to the degree of sutural obliteration and bulging of the synsacrum, Noriegavis is more similar to Ch. burmeisteri. As in extant Cariamidae there is a curved linea intermuscularis along the ventral section of the alae praeacetabularis ilii (Fig. 4A₃). The foramen ilioischiadicum is of similar relative size to that of modern seriemas, with a distinct ridge, which runs from its cranial margin ventrally across the ala ischii (Fig. 4A₃). Of the foramen obturatum only the dorsal rim is preserved, and it can thus not be said whether the processus obturatorius only contacted the pubis as in extant Cariamidae, or was fused with it as in Paracrax (Bathornithidae) and Phorusrhacidae (Cracraft 1968: fig. 10; Sinclair and Farr 1932: pl. 28). Unlike in Paracrax, there is no well-defined tuberculum praeacetabulare, and as in extant seriemas, the alae postacetabulares ilii form a laterally projecting bulge in their midsection (Fig. 4). The processus costales of the synsacral vertebra cranial to the vertebra acetabularis are narrower than in extant seriemas, the intervertebral openings are thus larger. Whether there was a marked recessus caudalis fossae as in extant Cariamidae cannot be ascertained.

The femur, the shaft of which is damaged in the lateral section of the proximal end, is also distinguished from that of extant seriemas in some features. Like in extant Cariamidae there is a marked trochanter with a well-developed crista trochanteris. The proximal and distal ends of the bone are, however, proportionally narrower than in extant seriemas (Fig. 5A₂, B). The distal end, and the condylus medialis in particular, is less medially inflected, and the trochlea fibularis is less strongly laterally projected. The sulcus intercondylaris is narrower than in modern seriemas and the fossa poplitea is less marked. The latter feature also distinguishes the bone from the femur of Dynamopterus (Idiornithidae), in which the fossa poplitea is more marked and in which the femur shaft is more slender.

The right tibiotarsus has similar overall proportions to that of the two living species of Cariamidae. In proximal view, the bone also corresponds well with extant seriemas. As in the latter and Dynamopterus (Mourer-Chauviré 1983: fig. 3), there is a marked incisura tibialis, which is somewhat wider in the fossil than in the two living species (Fig. 5A₈, C₂). In proximal view, and as in extant Cariamidae, there is further a prominent projection medial to the fossa retropatellaris, which is steeply sloping towards facies gastrocnemialis (Fig. 5A₈). The cristae cnemiales are better developed than in Dynamopterus. Although only the base of the crista cnemialis cranialis is preserved, the cristae appear to have been less strongly proximally protruding than the cristae cnemiales of extant seriemas (Fig. 5A₃, C₁). The distal end of the bone is damaged, but corresponds in size to specimen MPM-PV 3510, the larger of the two distal tibiotarsi figured by Noriega et al. (2009). These authors noted that in lateral view the condylus lateralis has a more rounded outline than in extant seriemas.

Of the tarsometatarsus only the distal ends and part of the left shaft are preserved. The proportions of the latter indicate that the bone was long and slender like in extant seriemas. On the plantar surface, three ossified tendons are preserved in situ (Fig. 5A₅). As in modern Cariamidae there is a sulcus for musculus extensor hallucis longus on the medial surface of the distal shaft, which terminates at the proximal end of the fossa metatarsi I. The fossa metatarsi I itself is a well-defined concavity as in the fossil species Chunga incerta and extant seriemas. The foramen vasculare distale is proportionally larger and situated farther distally than in extant seriemas. The distal end closely resembles the distal tarsometatarsus of extant seriemas, but the trochleae metatarsorum III and IV are mediolaterally narrower, the medial flange on the plantar surface of the trochlea metatarsi II is better developed (Fig. 5A₁₄), and the incisura intertrochlearis medialis is wider (Fig. 5A₁₄). The lateral portion of the trochlea metatarsi IV reaches as far distally as the medial one, whereas it is shorter in extant seriemas. Compared to fossil Cariamiformes, the distal tarsometatarsus of Noriegavis more closely resembles that of Phorusrhacidae than that of Dynamopterus (Idiornithidae), and the trochleae metatarsorum II and IV of Noriegavis are less plantarly deflected and reach farther distally (beyond the middle of the trochlea metatarsi III) than in Dynamopterus. The distal end of the trochlea metatarsi IV is further oriented rectangular to the longitudinal axis of the shaft and not laterally tilted. The phalanges (Fig. 5A₁₃) correspond with those of extant Cariamidae.

Stratigraphic and geographic range. —Early Miocene Estancia La Costa member of the Santa Cruz Formation; Santa Cruz Province, Argentina.