Fact-checked by Grok 2 weeks ago

Austroraptor

Austroraptor cabazai is a large-bodied unenlagiine dromaeosaurid theropod dinosaur known from the Maastrichtian stage of the Late Cretaceous period in Patagonia, Argentina.^[1] The holotype specimen (MML-195), discovered in the Allen Formation at Bajo de Santa Rosa, Río Negro Province, consists of a partial skeleton including portions of the skull (e.g., maxillae, dentaries, frontals), vertebrae, ribs, a right humerus and manual ungual (forelimb elements), a left pubic shaft, and hindlimb bones (e.g., femur, tibia).^[1] Measuring approximately 5 meters in length with an estimated body mass of 368–460 kg, it represents the largest known dromaeosaurid from the Southern Hemisphere and the youngest record of a Gondwanan dromaeosaurid.^[1]^[2] The taxon is characterized by a long, low skull approximately 80 cm in length, featuring 24 maxillary teeth and 25 dentary teeth that are small, conical, slightly recurved, unserrated, and longitudinally fluted—morphology reminiscent of piscivorous theropods like spinosaurids.^[1] Its forelimbs are notably short, with a humerus measuring 26.2 cm (about 46% the length of the femur at 56 cm), the shortest relative arm length among known dromaeosaurids, though equipped with a robust manual claw.^[1] The hindlimbs are sturdy, with a tibia of 56.5 cm supporting bipedal locomotion, and the tail is elongated with chevron bones suggesting flexibility.^[1] A second specimen (MML-220), including additional hindlimb and forelimb elements from the same locality, confirms these proportions and provides further details on pneumaticity in cranial bones, such as wide recesses in the maxilla, lacrimal, and postorbital revealed by CT scans.^[3]^[2] Phylogenetically, Austroraptor belongs to Unenlagiidae, a clade of South American dromaeosaurids that may represent the sister group to Avialae (birds) or a basal subgroup within Dromaeosauridae, highlighting the morphological disparity among Gondwanan paravians.^[1]^[2] Its discovery underscores the evolutionary radiation of dromaeosaurids in the Southern Hemisphere, distinct from northern relatives like Velociraptor, and contributes to discussions on paravian paleoecology, including potential adaptations for aquatic prey capture based on cranial features.^[1] Named in 2008 by Fernando E. Novas and colleagues, Austroraptor cabazai honors Héctor Cabaza, founder of the Museo Municipal de Lamarque, and combines the Latin "auster" for "south" with "raptor" for "thief", emphasizing its Gondwanan affinity.^[1]

Discovery and naming

Discovery history

The holotype specimen of Austroraptor cabazai (MML-195), a partial skeleton preserving elements of the skull, vertebrae, ribs, and limbs, was discovered in December 2002 at the Bajo de Santa Rosa locality (40°03′28″ S, 66°48′03″ W) in the Allen Formation, Río Negro Province, Patagonia, Argentina.^[4] The specimen, loaned to researchers by local collector Daniel Cabaza and housed at the Museo Municipal de Lamarque (MML), includes the right frontal and postorbital bones, lacrimals, maxillae, dentaries with teeth, right surangular and prearticular, several cervical vertebrae (including the third, fifth, sixth, seventh, and eighth), two dorsal vertebrae (second and fourth), associated ribs and gastralia, the right humerus, a manual ungual phalanx from digit III, the left pubic shaft, left femur, right tibia, astragalus, calcaneum, metatarsal III, and various pedal phalanges.^[1] Initial fieldwork in the region, which revealed theropod remains amid eroded outcrops of the Maastrichtian-aged formation, was part of broader surveys documenting Late Cretaceous vertebrates in northern Patagonia.^[4] The holotype was formally described in 2008 by a team led by Fernando E. Novas from the Museo Paleontológico Egidio Feruglio (MPEF), along with Diego Pol, Juan I. Canale, Juan D. Porfiri, and Jorge O. Calvo, who identified it as a novel large-bodied dromaeosaurid based on its distinctive cranial and postcranial features.^[5] Preparation of the specimen was conducted by M. Isasi and S. Reuil at MPEF, highlighting collaborative efforts between local museums and paleontological institutions in Argentina.^[1] The discovery occurred in a semi-arid paleoenvironment where erosion naturally exposed fossil-bearing layers, allowing for the initial recognition of the material as theropod remains during prospecting.^[4] A referred specimen (MML-220), consisting of maxilla fragments, isolated teeth, an incomplete dorsal vertebra, caudal vertebrae, and additional postcranial elements such as the right humerus, radii, ulnae, metacarpal I, ischium, pubis, tibia, metatarsals, and pedal phalanges, was collected during a joint expedition in 2008 approximately 20 km east of the holotype site in the same formation.^[4] This material, slightly smaller than the holotype and representing an adult individual, was described in 2012 by Philip J. Currie and Ariana Paulina Carabajal, confirming its attribution to A. cabazai through shared morphology in the humerus, metatarsal III, and pedal phalanges. In November 2023, further fieldwork at the holotype quarry yielded an isolated gastralium and right pedal phalanx III-1, which were referred to MML-195 based on comparable size and proportions.^[4] Recent osteological analysis in 2025 by Matías J. Motta and Fernando E. Novas incorporated computed tomography (CT) scans of elements from both the holotype and MML-220, revealing internal pneumatic structures in the maxilla and lacrimal, and re-evaluating some fragments (e.g., maxillae from MML-220) as indeterminate while solidifying referrals for others like the right splenial.^[4] These updates, based on enhanced preparation and imaging, suggest potential for additional referrals from ongoing excavations in the Allen Formation, though no further complete specimens have been confirmed as of late 2025.^[4]

Etymology and taxonomy

The genus name Austroraptor is derived from the Latin australis (southern), in reference to its discovery in southern South America, combined with raptor (thief or plunderer), alluding to the predatory habits typical of dromaeosaurids.^[6] The specific epithet cabazai honors the late Héctor Cabaza, founder of the Museo Municipal de Lamarque in Río Negro Province, Argentina, where the holotype specimen is housed.^[6] Austroraptor cabazai was formally named and described in 2008 by Fernando E. Novas, Diego Pol, Juan I. Canale, Juan D. Porfiri, and Jorge O. Calvo, in a study published in Proceedings of the Royal Society B: Biological Sciences.^[6] The holotype (MML-195) comprises a partial skull, vertebrae, ribs, and limb elements collected from the Bajo de Santa Rosa locality in the lower section of the Allen Formation (Maastrichtian stage, approximately 70–66 million years ago), Río Negro Province, Argentina.^[6] In its original description, Austroraptor was classified as a member of Dromaeosauridae, nested within the subfamily Unenlagiinae, distinguishing it as one of the largest known Gondwanan dromaeosaurids and providing insights into southern hemisphere theropod evolution.^[6] Subsequent phylogenetic analyses have upheld this placement in Unenlagiinae while refining its position as a basal member of the clade, closer to taxa like Unenlagia and Buitreraptor.^[7]

Description

Cranial anatomy

The cranial remains of Austroraptor cabazai are primarily known from the holotype specimen (MML 195), which preserves a nearly complete left maxilla, fragmentary right maxilla, partial right lacrimal, right frontal, right postorbital, left and right dentaries, right surangular, and right quadrate, along with isolated teeth.^[5] A referred specimen (MML 220) adds fragmentary maxillae, dentary fragments, teeth, and a right splenial, providing additional insights into dental and mandibular variation.^[4] The skull is estimated to have measured approximately 80 cm in length, contributing to the animal's overall body length of 5–6 m.^[5] The maxilla is notably elongated anteroposteriorly but dorsoventrally low, with a length of 39 cm and height of 8.5 cm, yielding a height-to-length ratio of about 21%, which is lower than in most dromaeosaurids.^[5] It features a straight ventral margin bearing 24–25 tooth positions, a subtriangular antorbital fossa occupying roughly half its length, and a single large, elliptical maxillary fenestra, representing a reduced antorbital fenestral complex compared to the multiple fenestrae (including promaxillary) typical of Laurasian dromaeosaurids like Deinonychus.^[5] Recent analysis reveals pneumatic features, including a large paranasal recess and three small anterior chambers within the maxilla, potentially linked to diverticula invading the bone. This morphology closely resembles that of the South American unenlagiid Buitreraptor but contrasts with the deeper, shorter maxillae of basal paravians, suggesting derived elongation possibly influenced by troodontid-like traits.^[5] The jugal bone, partially preserved in the holotype, is robust with a prominent crest along its dorsal margin, indicating attachment sites for strong jaw adductor musculature; its suture with the postorbital is tightly interdigitated, and pneumatic invasion is evident in adjacent elements. The right quadrate is robust and dorsoventrally short, with a subtriangular lateral process, a broken pterygoid process, and a smaller lateral condyle relative to the medial one; its near-upright orientation lacks prominent pneumatic foramina, differing from the more slender, pneumatized quadrates of some troodontids, and may support limited prokinetic movement at the jaw joint. Other cranial elements exhibit distinctive pneumaticity and form. The lacrimal is T-shaped and highly pneumatized with five internal recesses, featuring an elongated anterior process, a ventrally curved descending process at approximately 45°, and a unique posterolateral projection; this configuration, including two foramina in a caudal excavation, sets it apart from the straighter, less pneumatized lacrimals of Laurasian dromaeosaurids.^[5] The right frontal is subtriangular, tapering rostrally with an anteromedial process comprising about 40% of its length and a deep notch for lacrimal articulation, lacking large pneumatic chambers but showing a straight oblique ridge in the supratemporal depression—traits echoing troodontids while differing from the caudolaterally expanded frontals of typical dromaeosaurids.^[5] The postorbital is dorsoventrally elongated with three pneumatic recesses (dorsal, medial, and lateral), lacking a dorsomedial process for frontal contact and exhibiting a quotation mark-like lateral profile, a configuration reduced relative to Laurasian forms.^[5] The mandible includes elongate, gracile dentaries with 24–25 alveoli, interdental plates, and an elongated nutrient groove with foramina, alongside a mid-length fenestra; teeth are small, conical, unserrated, and fluted, with anterior and middle teeth showing labiolingual compression and distal torsion up to 37° in the maxilla.^[5] The surangular features a hook-shaped shelf, wide adductor fossa, and absence of a surangular foramen, while the referred splenial is robust, subtriangular, and dorsoventrally tall with a ventral mylohyoid foramen. These mandibular traits align closely with Buitreraptor and basal paravians, highlighting shared unenlagiid specializations such as reduced serrations and enhanced pneumaticity in the skull roof.^[5]

Postcranial skeleton

The postcranial skeleton of Austroraptor cabazai is incompletely known from the holotype specimen MML 195 and a referred specimen MML 220, preserving elements of the axial column, ribs, pectoral girdle, pelvis, and both fore- and hindlimbs. These remains reveal a robust build consistent with large-bodied paravians, with adaptations for bipedal locomotion.^[8]^[9] The axial skeleton includes an incomplete cervical vertebra in the holotype, which is elongated with low neural spines that suggest enhanced neck flexibility compared to more rigid conditions in basal theropods. Dorsal vertebrae, represented by three partial elements in the holotype and an additional incomplete mid-posterior dorsal in the referred specimen, are robust with well-developed hyposphene-hypantrum articulations that interlock adjacent vertebrae for increased stability along the trunk. Pleurocoels are present in the dorsal centra, indicating pneumatization similar to other unenlagiids. Recent analyses provide detailed descriptions of the sacral vertebrae, comprising at least five fused elements with tall neural spines and robust sacral ribs that anchor the pelvis firmly, alongside tail morphology featuring elongate proximal caudals that taper distally over at least 10 preserved centra (lengths 32–82 mm), further supporting unenlagiid affinities through shared vertebral specializations; the caudals also exhibit pneumatic features with wide internal recesses.^[8]^[9]^[10]^[4] The 2025 study additionally describes previously undescribed elements including gastralia and more cervical vertebrae (e.g., possible CV3, CV5, CV9, CV10) with pneumatic fossae.^[4] The pelvis features a right ilium in the holotype with an elongated preacetabular process that exceeds the postacetabular wing in length, a condition approaching that seen in avian theropods and contributing to a bird-like pelvic profile. The pubis and left ischium are partially preserved, with the pubis showing a straight shaft typical of paravians.^[8]^[11] Hindlimb elements demonstrate cursorial proportions, with the left femur of the holotype measuring approximately 600 mm in length and the tibia (from the referred specimen) measuring approximately 600 mm, similar in length to the femur, accompanied by a reduced fibula that splints the tibia proximally but tapers distally. Metatarsals II–IV are slender and elongate, with the third metatarsal ginglymoid at the distal end, supporting agile terrestrial movement.^[8]^[9]^[12]^[4] Forelimb preservation is limited but includes the right humerus (232 mm long in the referred specimen; 265 mm in holotype), partial radius (161 mm), ulna, and several manual phalanges with large, recurved unguals (up to 67 mm), indicating robust but shortened arms relative to the hindlimbs (humerus ~46% of femur length). These features align with derived paravian manual morphology, though reduced in size compared to typical dromaeosaurids; the right metacarpal I is confirmed as authentic.^[8]^[9]^[4]

Size and distinguishing traits

Austroraptor cabazai was one of the largest known paravians from Gondwana, with body length estimates ranging from 5 to 6 meters based on the holotype femur (60 cm long) and comparative scaling with other dromaeosaurids.^[5] Weight estimates, derived from volumetric models, originally calculated at 368 kg in 2008 and later refined to approximately 460 kg in 2025 osteological analyses incorporating both known specimens, place it in the range of 300–500 kg overall.^[5]^[4] The holotype (MML 195) likely represents an adult individual, inferred from the advanced ontogenetic stage evident in bone morphology and preserved fusion patterns comparable to the second specimen (MML 220), which is explicitly identified as adult.^[9] No evidence of sexual dimorphism exists, as the two known specimens exhibit size differences consistent with intraspecific variation rather than sexual differences.^[9] Austroraptor cabazai is diagnosed by several autapomorphies, including a highly pneumatized lacrimal bone with a strongly rostrally curved descending process and a horizontally flaring caudal process, as well as a postorbital bone lacking a dorsomedial process for articulation with the frontal.^[5] Other distinguishing traits include proportionally short and robust forelimbs (humerus ~46% of femur length), a low and elongate skull with small, conical, unserrated teeth, and a narrow pedal phalanx II-2.^[5] Recent 2025 studies using CT scans have identified additional unique features, such as pneumatic caudal vertebrae with wide internal recesses.^[4]

Classification

Phylogenetic analysis

Austroraptor cabazai was initially placed within Dromaeosauridae, specifically in the subfamily Unenlagiinae, based on a phylogenetic analysis using an updated version of the dataset from Turner et al. (2007). This analysis employed equally weighted parsimony with TNT software and incorporated both cranial and postcranial synapomorphies, recovering Austroraptor as a member of a monophyletic Unenlagiinae alongside taxa such as Unenlagia and Buitreraptor. Key characters supporting this placement included reduced forelimbs, with the humerus measuring approximately 46% of femoral length, elongated hindlimbs evidenced by a tibia nearly equal in length to the femur, and features indicative of cranial kinesis such as a long, low skull with small conical teeth.^[5] A more recent phylogenetic analysis in 2025 incorporated new osteological data from additional specimens and utilized an expanded matrix derived from Pei et al. (2020), comprising over 150 characters across 175 operational taxonomic units. This study applied parsimony analysis using TNT v1.6 software, with bootstrap resampling to assess node support, confirming Austroraptor's position as a basal unenlagiid and reinforcing Unenlagiinae as the sister group to Dromaeosaurinae within Dromaeosauridae. The analysis highlighted Austroraptor's close affinities to Unenlagia comahuensis and Neuquenraptor argentinus, based on shared derived traits such as proportionally short upper limbs relative to hindlimb elongation. Bootstrap values provided moderate to strong support for the Unenlagiinae clade (above 70% at key nodes), underscoring the robustness of this topology despite ongoing debates on paravian interrelationships.^[4] The resulting strict consensus cladogram depicts Austroraptor as a basal member of Unenlagiinae, branching near the base of the subfamily alongside Unenlagia and Neuquenraptor, with the broader Unenlagiidae forming a southern Gondwanan radiation sister to northern hemisphere dromaeosaurines. This placement emphasizes the morphological divergence within unenlagiines, where Austroraptor's gigantism and specialized cranial features distinguish it while retaining core synapomorphies like the reduced forelimb condition. The updated matrix's inclusion of extensive character data, including newly scored postcranial elements, resolved previous ambiguities in southern paravian relationships, supporting Unenlagiinae's monophyly with high parsimony scores.^[4]

Relationship to other dromaeosaurids

Austroraptor cabazai is a member of the Unenlagiinae clade, a group of dromaeosaurid theropods characterized by a South American radiation that contrasts with the predominantly Laurasian distribution of other dromaeosaurid lineages, such as eudromaeosaurs.^[13]^[14] This Gondwanan endemism highlights an isolated evolutionary trajectory for unenlagiines, with fossils primarily from Patagonia during the Late Cretaceous.^[1] Within Unenlagiinae, Austroraptor is positioned as a basal taxon, larger than the contemporaneous Unenlagia comahuensis, which measured approximately 3 meters in length, while Austroraptor reached 5–6 meters.^[1]^[15] It shares a similar body size with the Asian Achillobator giganteus, estimated at around 5 meters long and 250–350 kilograms, though Austroraptor exhibits distinct adaptations suited to its southern habitat.^[1]^[16] The evolutionary implications of Austroraptor's position underscore a pattern of size variation among unenlagiines, with some taxa like Austroraptor exhibiting gigantism relative to smaller relatives, potentially influenced by isolation on the fragmenting Gondwanan continents.^[1] Known from Maastrichtian strata approximately 70 million years ago, unenlagiines represent a late divergence from northern dromaeosaurid lineages around 100 million years ago, following the separation of Laurasia and Gondwana.^[17] Recent analyses in 2025, including a study by Motta et al. that recovered Unenlagiidae as the sister group to Avialae (modern birds and their close relatives), have strengthened support for paravians encompassing unenlagiids as basal avialans rather than strictly within Dromaeosauridae, emphasizing their role in early bird evolution.^[13]

Paleobiology

Locomotion and adaptations

Austroraptor cabazai exhibited hindlimb proportions indicative of agile terrestrial locomotion, characterized by a femur-to-tibia ratio near 1:1 and a subarctometatarsalian foot structure similar to that of its relative Buitreraptor, which facilitated efficient cursorial movement on land.^[18] These features, combined with elongated metatarsals, suggest the dinosaur was adapted for pursuits in open Patagonian environments.^[18] In contrast to many northern dromaeosaurids with elongated forelimbs, Austroraptor displayed significant forelimb reduction, with arms notably shorter relative to hindlimb length and bearing robust manual claws suited for close-range grappling rather than slashing or prey manipulation at a distance.^[1] This morphology represents a departure from the typical "raptor" build, potentially reflecting adaptations for a larger body size where powerful but compact forelimbs aided in subduing prey during terrestrial hunts.^[19] Evidence for aquatic adaptations in Austroraptor is primarily from its conical teeth, consistent with semi-aquatic hypotheses for unenlagiids involving wading or shallow-water foraging.^[1] Recent osteological analysis reveals details of tail musculature in Austroraptor, with robust caudal vertebrae and associated attachment sites indicating enhanced lateral stability, likely aiding balance during maneuvers in water or on uneven terrain.^[2] Despite retaining paravian traits such as a furcula and possible feather impressions, Austroraptor's large size and robust postcranial skeleton preclude flight capability, positioning it firmly as a ground-dwelling predator.^[1]

Diet and behavior

The dentition of Austroraptor cabazai consists of small, conical, unserrated, and fluted teeth, a morphology that closely resembles that of spinosaurids and suggests a diet focused on piscivory or soft-bodied prey, rather than hard-shelled or heavily armored animals.^[1] This carnivorous, non-durophagous feeding strategy is further supported by recent osteological analyses (as of September 2025), which describe the teeth as adapted for grasping and piercing slippery aquatic prey, complemented by a long, low skull housing numerous teeth (24–25 maxillary and 24–25 dentary).^[4] The robust, dorsoventrally short quadrate and extensive cranial pneumaticity, including large paranasal recesses in the maxilla and multiple recesses in the lacrimal, indicate adaptations for rapid jaw closure and a lightweight structure potentially suited to capture fish or similar elusive prey near water surfaces.^[4] Additionally, the short forelimbs may have facilitated maneuvers in aquatic environments, aiding in the pursuit of underwater quarry.^[1] The claw morphology of A. cabazai features strongly curved manual unguals, particularly on digit III, which were likely used for slashing or securely holding slippery prey during feeding.^[1] These adaptations align with a predatory lifestyle involving close-range interactions with agile, aquatic targets, emphasizing precision over brute force. Although pack hunting has been inferred for some dromaeosaurid relatives based on gregarious bonebed assemblages, such behavior in A. cabazai remains speculative with no direct fossil evidence, such as multiple associated individuals.^[20] Sensory capabilities, inferred from impressions of cerebral hemispheres, olfactory tract, and bulb in the frontal bone, suggest enhanced sensory adaptations for detecting prey, potentially active during low-light conditions, though specific nocturnal adaptations are unconfirmed for this taxon.^[4]

Paleoecology

Geological context

The Allen Formation represents a key Late Cretaceous stratigraphic unit in northern Patagonia, Argentina, spanning the mid Campanian to early Maastrichtian stages and dated to approximately 73–66 Ma based on biostratigraphic evidence from foraminifera, palynomorphs, and vertebrate assemblages, as well as magnetostratigraphic correlations. This formation belongs to the lower portion of the Malargüe Group and outcrops extensively in Río Negro Province, including the Bajo de Santa Rosa locality (approximately 38°50′S, 68°00′W) where the holotype of Austroraptor cabazai was discovered. Although direct radiometric dating is limited, the unit's position above the dated Anacleto Formation (ca. 83–79 Ma) and below the early Paleogene Roca Formation supports its assignment to the late Late Cretaceous. Deposited in the northeastern Neuquén Basin, the Allen Formation records a mixed continental-marginal marine system dominated by fluvial and lacustrine sediments, indicative of riverine channels, floodplains, and shallow water bodies. The lithology includes interbedded medium- to fine-grained sandstones, siltstones, claystones, and occasional limestones and evaporites, reflecting low-energy depositional settings with tidal channels, intertidal flats, and shoreface environments influenced by the initial Atlantic ingression. This hybrid coastal plain setting transitioned from tidally dominated lower sections to wave-influenced upper strata, with clastic inputs from nearby continental sources. Taphonomic preservation in the formation favors rapid burial in sandy channel fills and overbank deposits, as evidenced by disarticulated but associated vertebrate remains embedded in cross-bedded sandstones at sites like Bajo de Santa Rosa. Such conditions minimized transport and weathering, preserving a mix of terrestrial, freshwater, and minor marine fossils in fine- to medium-grained sediments that suggest episodic high-energy fluvial events. Paleoenvironmental reconstructions indicate a warm, humid climate with seasonal precipitation and flooding, supported by palynological data showing thermophilous elements such as palm-like pollen (e.g., Spinizonocolpites), alongside conifers and ferns indicative of forested floodplains. The presence of freshwater taxa and fluvial features points to dynamic river systems prone to periodic inundation, while subtle marine incursions are inferred from evaporitic layers and rare elasmosaurid remains, reflecting proximity to a low-gradient epicontinental sea.

Contemporaneous fauna

The Allen Formation of Patagonia, Argentina, hosted a diverse vertebrate assemblage during the late Campanian to early Maastrichtian stages of the Late Cretaceous, including several theropod dinosaurs that coexisted with Austroraptor cabazai. Other theropods included the alvarezsaurid Bonapartenykus ultimus, known from partial skeletal remains indicating a small, specialized insectivore or omnivore adapted for digging behaviors,^[21] and the medium-sized abelisaurid Niebla antiqua represented by isolated cranial and postcranial elements suggestive of a robust, short-snouted predator potentially occupying an apex niche.^[22] Isolated theropod teeth associated with sauropod remains further indicate the presence of additional carnivorous or scavenging theropods, though their exact affinities remain uncertain.^[23] Ornithischian dinosaurs were relatively scarce in the Allen Formation compared to saurischians, with ornithopods represented by the hadrosaurid Bonapartesaurus rionegrensis, a medium-sized duck-billed herbivore known from well-preserved specimens showing evidence of healed pathologies possibly from intraspecific combat or predation attempts.^[24] Sauropod diversity was higher, dominated by saltasaurid titanosaurs such as Aeolosaurus sp., Bonatitan reigi, and Rocasaurus muniozi, which were armored, quadrupedal herbivores that likely browsed on floodplain vegetation and may have served as potential prey for large theropods like Austroraptor.^[25] Avifauna in the formation included early ornithurine birds, exemplified by Limenavis patagonica, a basal carinate known from fragmentary limb bones that suggest a terrestrial or semi-aquatic lifestyle similar to modern shorebirds, filling a niche as small, agile foragers. No enantiornithine remains have been definitively identified from the Allen Formation, though the overall bird record points to a developing diversity of crown-group avians in southern Gondwanan ecosystems. Potential prey items for Austroraptor encompassed a range of smaller vertebrates, including crocodyliforms such as notosuchians (indeterminate forms with adaptations for terrestrial or semi-aquatic lifestyles), possibly inhabiting rivers and wetlands. Abundant fish taxa, such as teleosts and chondrichthyans, populated the fluvial and lacustrine environments, providing opportunities for piscivory or opportunistic feeding.^[23] Smaller reptiles (e.g., turtles like Yaminuechelys gasperinii), amphibians, and early mammals further contributed to the prey base, supporting a food web in which Austroraptor likely functioned as a mid-tier predator, preying on juveniles of larger herbivores or competing with abelisaurids for carcasses. Marine reptiles like the elasmosaurid Kawanectes lafquenianum indicate occasional marine influence. The ecosystem of the Allen Formation represented a dynamic floodplain community with meandering rivers, seasonal flooding, and forested riparian zones, fostering interactions among these taxa; for instance, theropod bite marks on sauropod bones suggest scavenging or predatory behaviors involving multiple carnivores.^[23] Fossil preservation is characterized by isolated finds rather than mass death assemblages, reflecting low-energy depositional settings that favored disarticulated remains over concentrated bone beds.^[26] This scattered distribution underscores a stable, low-disturbance paleoenvironment where Austroraptor navigated a balanced trophic structure alongside diverse herbivores and smaller opportunists.

References

[1]
A bizarre Cretaceous theropod dinosaur from Patagonia and the ...
Austroraptor cabazai MML 195, holotype. (a) Skeletal reconstruction and body shape, indicating discovered bones. Body length was estimated following equations ...Missing: paper | Show results with:paper
[2]
a southern gigantic unenlagiid from the Late Cretaceous of Patagonia
CT scans of cranial bones and vertebrae of Austroraptor cabazai provided valuable information about internal anatomical features. Wide recesses were ...
[3]
(PDF) A New Specimen of Austroraptor cabazai Novas, Pol, Canale ...
A New Specimen of Austroraptor cabazai Novas, Pol, Canale, Porfiri and Calvo, 2008 (Dinosauria, Theropoda, Unenlagiidae) from the Latest Cretaceous ( ...
[4]
https://doi.org/10.1080/08912963.2025.2537843
[5]
https://doi.org/10.1098/rspb.2008.1554
[6]
A bizarre Cretaceous theropod dinosaur from Patagonia and the ...
Dec 16, 2008 · A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. Fernando E Novas. Fernando E Novas.Missing: Novas | Show results with:Novas
[7]
Unenlagiinae revisited: Dromaeosaurid theropods from South America
Aug 7, 2025 · The earliest and most complete South American dromaeosaurid is Buitreraptor gonzalezoru, whose preserved cranial remains, provides important ...Missing: classification | Show results with:classification
[8]
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2008.1554
[9]
A NEW SPECIMEN OF AUSTRORAPTOR CABAZAI NOVAS, POL ...
Currie, P. J., & Paulina Carabajal, A. (2013). A NEW SPECIMEN OF AUSTRORAPTOR CABAZAI NOVAS, POL, CANALE, PORFIRI AND CALVO, 2008 ...Missing: cabecensis | Show results with:cabecensis<|control11|><|separator|>
[10]
Postcranial skeletal anatomy of the holotype and referred specimens ...
Mar 26, 2018 · ... cervical vertebrae from the anterior, middle and posterior sections of the neck, some bearing cervical ribs; 15 dorsal vertebrae ... Forelimb.
[11]
Full article: Osteology of Austroraptor cabazai (Paraves: Theropoda)
Austroraptor is the only known unenlagiid in which the maxilla is almost entirely preserved, providing anatomical information from all anatomical perspectives (
[12]
Paravian Phylogeny and the Dinosaur-Bird Transition: An Overview
... Austroraptor cabazai (Novas and Puerta, 1997; Makovicky et ... preacetabular process of the ilium that is markedly longer than the postacetabular process.
[13]
The evolution and role of the hyposphene-hypantrum articulation in ...
Oct 2, 2019 · ... hyposphene-hypantrum and the largest taxon reported to lack the hyposphene-hypantrum. ... Austroraptor cabazai: FL = 560 mm [54]; Microraptor ...
[14]
Phylogenetic relationships of Unenlagiidae among Paraves ...
Our purpose is to test the hypotheses regarding the phylogenetic relationships of Unenlagiidae among Paraves. ... Motta, Citation2023, Motta et al., Citation2025a ...Missing: Motta | Show results with:Motta
[15]
[PDF] Unenlagiinae revisited: dromaeosaurid theropods from South America
Feb 10, 2011 · The most recently described, Austroraptor cabazai, also with cranial remains, allows further comparisons with Laurasian lineages and a better ...<|control11|><|separator|>
[16]
Osteology of Unenlagia comahuensis (Theropoda, Paraves ...
Apr 24, 2021 · ... sacral vertebrae with tall neural spines, nearly twice the height of ... Austroraptor, but absent in Buitreraptor (Gianechini ...
[17]
[PDF] The locomotor and predatory habits of unenlagiines (Theropoda ...
Feb 18, 2019 · Other unenlagiines, such as the large-sized Austroraptor cabazai and the medium-sized Neuquenraptor argentinus probably preyed on larger animals ...
[18]
A Review of Dromaeosaurid Systematics and Paravian Phylogeny
Aug 7, 2025 · Our study reviews and revises the membership of Dromaeosauridae and provides an apomorphy-based diagnosis for all valid taxa.
[19]
Eudromaeosauria - Wikipedia
This distribution suggests that eudroameosaurs evolved after Pangaea split into Laurasia and Gondwana, and they were therefore unable to colonize the Southern ...Bambiraptor · Dineobellator · Saurornitholestes · Yurgovuchia
[20]
Differential locomotor and predatory strategies of Gondwanan and ...
Feb 5, 2020 · During dromaeosaurid evolution, the different lineages seem to have diverged acquiring varied lifestyles, as documented by unenlagiines ...
[21]
Error
**Summary:**
[22]
A Review of Dromaeosaurid Systematics and Paravian Phylogeny
Aug 17, 2012 · ... Austroraptor), greatly increase the range of morphological ... Four additional characters—preacetabular process of ilium twice as ...<|separator|>
[23]
(PDF) A Reevaluation of Cooperative Pack Hunting and ...
Aug 3, 2025 · ... pack hunting behavior in these quin-. tessential pack hunters probably evolved no earlier ... Austroraptor cabazai from the Campanian– ...
[24]
New information on Bonapartenykus (Alvarezsauridae
Jan 30, 2025 · Alvarezsauria is a group of later-diverging coelurosaurian theropod dinosaurs of medium to small size, whose fossil record spans from the Late ...Missing: fauna ornithischians
[25]
A new medium-sized abelisaurid (Theropoda, Dinosauria) from the ...
Dinosaurs are well-known in Allen Formation, and include non-avian theropods ... Allen Formation of Northern Patagonia, Argentina.” declare that have not ...
[26]
[PDF] Isolated theropod teeth associated with a sauropod skeleton from ...
Jun 7, 2021 · Here, we describe and identify twelve theropod shed teeth associated with a partially complete skeleton of a titanosaur sauropod from the Allen ...
[27]
Osseous paleopathologies of Bonapartesaurus rionegrensis ...
Osseous paleopathologies of Bonapartesaurus rionegrensis (Ornithopoda, Hadrosauridae) from Allen Formation (Upper Cretaceous) of Patagonia Argentina.Missing: fauna | Show results with:fauna
[28]
The Titanosaur Sauropods from the Late Campanian ... - BioOne
Dec 1, 2012 · The Allen Formation is thought to be correlated with the Marília Formation in Brazil, and their faunas have certain elements in common such as ...
[29]
(PDF) New cranial remains of Comahuesuchus brachybuccalis ...
Aug 8, 2025 · Comahuesuchus ... This group has been reported in the Upper Cretaceous of the Lecho, Allen, and Anacleto formations of Argentina.
[30]
New mammals from the Upper Cretaceous Allen Formation ...
The age of Allen Formation can therefore be estimated as Campanian-Maastrichtian, likely Late Maastrichtian. This age is congruent with estimates based on ...Missing: depositional taphonomy