Puertasaurus

Puertasaurus reuili is a genus and species of titanosaurian sauropod dinosaur known from the Late Cretaceous (Campanian–Maastrichtian) of southwestern Patagonia, Argentina.^[1] The holotype specimen (MPM-PV 10002) consists of four articulated vertebrae—a posterior cervical, an anterior dorsal, and two mid-caudal vertebrae—recovered from the Cerro Fortaleza Formation (formerly known as the Pari Aike Formation) near Río Gallegos in Santa Cruz Province.^[1] These remains indicate an exceptionally large animal, with the second dorsal vertebra measuring 1.68 meters in transverse width across the centrum, making Puertasaurus one of the largest known sauropod dinosaurs.^[1] The specimen was discovered in January 2001 by Argentine paleontologists Pablo Puerta and Santiago Reuili during fieldwork in the Cerro Fortaleza Formation, which dates to approximately 83–66 million years ago.^[2] Named in 2005 by Fernando E. Novas, Leonardo Salgado, José O. Calvo, and Federico L. Agnolín, the genus Puertasaurus honors Puerta ("puerta" meaning "door" in Spanish, alluding to his nickname "El Puerta"), while the species reuili commemorates Reuili's role in the discovery.^[1] Distinctive features include an inflated neural spine on the cervical vertebra and a notably short centrum on the second dorsal vertebra, supporting its classification within Titanosauria.^[1] Size estimates for Puertasaurus reuili vary due to the fragmentary nature of the remains, but based on vertebral proportions, it likely reached lengths of 30–35 meters and weighed around 50 metric tons, rivaling or exceeding other gigantic titanosaurs in scale.^[2] This dinosaur represents one of the last giant sauropods before the end-Cretaceous extinction, highlighting the persistence of enormous herbivores in southern Gondwana during the final stages of the Mesozoic era.^[2] Its discovery provides critical insights into the anatomy of late titanosaurs, particularly the structure of their necks and trunks, which were adapted for browsing high vegetation in a forested, riverine environment.^[1]

Discovery and Taxonomy

Discovery

The holotype specimen of Puertasaurus reuili, cataloged as MPM 10002, consists of four articulated vertebrae (the ninth cervical, second dorsal, and two middle caudal vertebrae) from a single individual. It was discovered in January 2001 by Argentine fossil collectors Pablo Puerta and Santiago Reuil during fieldwork in southern Patagonia.^[2] The fossils were unearthed at Cerro Los Hornos, near the locality of La Leona in Santa Cruz Province, Argentina, within the lower section of the Cerro Fortaleza Formation (formerly known as the Pari Aike Formation). The remains were preserved in situ in a fine-grained, gray sandstone lens associated with carbonized plant debris, including fragments of cycads and conifers, suggesting deposition in a fluvial or floodplain setting during the Campanian-Maastrichtian stages of the Late Cretaceous, approximately 84–66 million years ago. Puerta and Reuil, experienced preparators, initially excavated and conserved the bones before notifying professional paleontologists. The specimen was then analyzed by a team including Fernando E. Novas, Leonardo Salgado, Jorge Calvo, and Federico L. Agnolin at the Museo Paleontológico Egidio Feruglio. Their description, establishing Puertasaurus as a new giant titanosaurian sauropod, was published in 2005, marking the first report of cervical vertebral material for such a large-bodied titanosaur from Patagonia. The holotype is currently housed at the Museo Padre Molina (Regional Provincial Museum Padre Jesús Molina) in Río Gallegos, Santa Cruz Province, Argentina.

Naming and Etymology

Puertasaurus was named and described in 2005 by a team of Argentine paleontologists including Fernando E. Novas, Leonardo Salgado, Jorge Calvo, and Federico L. Agnolin, based on fossil material recovered from the Late Cretaceous Cerro Fortaleza Formation (formerly Pari Aike Formation) at Cerro Los Hornos in Patagonia.^[3] The description was published in the Revista del Museo Argentino de Ciencias Naturales, marking it as a new genus and species of titanosaurian sauropod.^[3] The genus name Puertasaurus derives from the surname of Pablo Puerta, a skilled fossil hunter who co-discovered the type specimen, combined with the Ancient Greek sauros (σαῦρος), meaning "lizard" or "reptile," following standard paleontological nomenclature for dinosaurs.^[3] The specific epithet reuili honors Santiago Reuil, Puerta's collaborator, who not only participated in the discovery but also meticulously prepared the fossils for study.^[3] This naming convention recognizes their pivotal roles in unearthing and preserving the remains in January 2001 near Cerro Los Hornos, Santa Cruz Province, Argentina.^[3]

Type Specimen and Material

The type specimen of Puertasaurus reuili is catalogued as MPM 10002 and is housed at the Museo Padre Molina in Río Gallegos, Santa Cruz Province, Argentina.^[4] It consists of four well-preserved vertebral elements: the ninth cervical vertebra (the most complete element), the second dorsal vertebra, and the centra of two mid-caudal vertebrae.^[4] These remains were collected from the Cerro Fortaleza Formation (formerly Pari Aike Formation; Campanian-Maastrichtian stages of the Late Cretaceous) at Cerro Los Hornos, approximately 10 km southwest of the La Leona Ranch in Santa Cruz Province, Argentina.^[4] The ninth cervical vertebra measures 118 cm in length from prezygapophysis to postzygapophysis and 140 cm in transverse width, including the fused ribs; it features an inflated neural spine and robust, elongated neural arch, indicative of the taxon's massive size.^[4] The second dorsal vertebra is notably short and wide, with dimensions of 168 cm in transverse width and 106 cm in height, characterized by a low neural spine and deep pleurocoels.^[4] The two caudal centra are subrectangular in outline, measuring approximately 30 cm in length and 40 cm in width, with shallow pneumatic foramina.^[4] No additional skeletal elements or referred specimens have been formally assigned to Puertasaurus reuili, making MPM 10002 the sole known material for the taxon.^[4]

Classification

Puertasaurus reuili is classified within the clade Sauropoda, specifically as a member of Titanosauriformes and Titanosauria. It exhibits several synapomorphies of Titanosauriformes, including deep pre- and postspinal fossae on the neural arches, elongated cervical centra, reduced lamination of the cervical neural arches, and the presence of prespinal laminae in the dorsal vertebrae.^[3] Within Titanosauria, Puertasaurus shares derived features such as laterally projecting diapophyses and parapophyses on the cervical vertebrae, a low neural arch with a relatively high neural spine, and robust pre- and postspinal laminae on the dorsal vertebrae. These traits support its placement as a titanosaurid, initially interpreted as basal within Titanosauridae due to features like vertical neural spines and transverse processes perpendicular to the centrum in the dorsal vertebrae.^[3] Subsequent phylogenetic analyses have refined this position, recovering Puertasaurus within the non-lithostrotian titanosaur clade Lognkosauria, a group characterized by gigantic body sizes and specific vertebral morphologies, such as elongated neural spines in anterior dorsal vertebrae. In a cladistic analysis of 87 sauropodomorph taxa using 405 osteological characters, Puertasaurus was positioned as sister taxon to Argentinosaurus within Lognkosauria, which itself forms part of a broader radiation of massive South American titanosaurs.^[5] This placement highlights its affinities with other Patagonian giants like Patagotitan and Notocolossus, though its fragmentary remains contribute to some instability in the topology, with alternative positions possible under minimal additional steps.^[5] More recent studies have incorporated Puertasaurus into the clade Colossosauria, defined as the most inclusive group containing Mendozasaurus neguyelap but excluding Saltasaurus loricatus, encompassing lineages such as Lognkosauria and Rinconsauria. This clade represents a distinct titanosaurian radiation in South America, diverging from the Saltasaurinae line and characterized by extreme size and robust appendicular elements. Phylogenetic analyses supporting Colossosauria emphasize shared autapomorphies in the limb bones, such as expanded proximal humeri and robust femora, aligning Puertasaurus with other colossal forms from the Late Cretaceous of Patagonia.^[6] Ongoing discoveries continue to test these relationships, but Puertasaurus remains a key taxon illustrating the diversity and gigantism within South American Titanosauria.^[7]

Description

Size and Morphology

Puertasaurus reuili is known from a fragmentary holotype consisting of four well-preserved vertebrae: the ninth cervical, the second dorsal, and two mid-caudal vertebrae, recovered from the Pari Aike Formation in southern Patagonia, Argentina. These elements exhibit characteristics typical of titanosaurian sauropods, including procoelous to opisthocoelous centra and robust neural arches, but stand out due to their exceptional size. The cervical vertebra measures 118 cm in length (between the pre- and postzygapophyses) and 140 cm in transverse width (including the fused ribs), with an inflated neural spine that is wider than the centrum and features strong dorsolateral ridges separating deep pre- and postspinal fossae. The diapophyses and parapophyses project laterally, the neural arch is low, and the centrum lacks pleurocoels, indicating limited pneumatization. The anterior dorsal vertebra is particularly notable for its massive dimensions, reaching 106 cm in height and 168 cm in transverse width across the wing-like transverse processes, making it the widest known vertebral element among sauropods. Its centrum is strongly opisthocoelous and short relative to its width (width/length ratio greater than 1), with perpendicular transverse processes and a low, dorsoventrally expanded neural spine reinforced by robust pre- and postspinal laminae; notably, it lacks hyposphene-hypantrum articulations. The mid-caudal vertebrae have procoelous centra but are less detailed in description due to their smaller relative size and simpler morphology, lacking the extreme expansions seen in the anterior elements. Based on the proportions of these vertebrae and comparisons to better-known titanosaurs like Argentinosaurus huinculensis, Puertasaurus reuili is estimated to have reached a total body length of approximately 30 meters, with a body mass around 50–80 metric tons, placing it among the largest known dinosaurs. The extreme transverse width of the dorsal vertebra exceeds that of Argentinosaurus (approximately 123 cm) and other titanosaurs such as Brachiosaurus and Neuquensaurus, suggesting a broad thoracic region and pillar-like limb support adapted for supporting immense weight. No postcranial elements beyond the vertebrae are known, limiting detailed inferences on limb morphology or overall skeletal proportions, but the preserved material indicates a robust, gigantic build consistent with advanced titanosaurs from the Late Cretaceous of Patagonia.

Axial Skeleton

The axial skeleton of Puertasaurus reuili is represented by four well-preserved vertebrae from the type specimen (MPM-PV 10002), including the ninth cervical, the second dorsal, and two middle caudal vertebrae, providing key insights into the construction of this gigantic titanosaur. These elements exhibit extreme transverse expansion, a hallmark of derived somphospondylan titanosaurs, with the dorsal vertebra achieving an unprecedented width that underscores the animal's massive body proportions. No ribs or other axial elements are preserved in the known material, limiting detailed analysis of the thoracic basket, but the vertebrae alone indicate a robust, pneumatized structure adapted for supporting immense weight.^[4] The ninth cervical vertebra measures 118 cm in length from prezygapophysis to postzygapophysis and 140 cm in transverse width, including the fused ribs, with an inflated neural spine that is broader than the centrum itself. It features strong dorsolateral ridges extending from the prezygapophyses to the diapophyses, deep and wide pre- and postspinal fossae, a low neural arch positioned posteriorly, and a depressed centrum with minimal pneumatization and no pleurocoels. These traits align with those of other titanosaurs like Saltasaurus but are scaled up dramatically, marking the first reported cervical vertebra for a giant member of the clade. The second dorsal vertebra is notably short anteroposteriorly, with an opisthocoelous centrum, wing-like transverse processes perpendicular to the axial plane, a low neural spine that is dorsoventrally expanded, and robust pre- and postspinal laminae; it lacks a hyposphene-hypantrum articulation and measures 106 cm in height and 168 cm in transverse width, exceeding the width of the corresponding element in Argentinosaurus huinculensis.^[4] The two preserved middle caudal vertebrae possess procoelous centra, a condition typical of titanosaurs, though specific measurements are not detailed in the description; their robust build suggests continuity in the broadened morphology seen anteriorly. Overall, the axial elements of Puertasaurus demonstrate enhanced lateral expansion of the neural arches and transverse processes compared to basal titanosaurs, contributing to a wider body cavity that may have accommodated expanded viscera in this enormous sauropod, estimated to reach over 30 meters in total length. This configuration parallels features in related taxa such as Euhelopus but is amplified in scale, highlighting evolutionary trends toward gigantism in Late Cretaceous South American titanosaurs.^[4]

Postcranial Skeleton

The postcranial skeleton of Puertasaurus reuili is incompletely known, with the holotype (MPM 10002) preserving only a limited portion of the axial column and no appendicular elements such as limb bones, girdles, or ribs beyond those fused to the cervical vertebra.^[4] No additional specimens or referred material have been described that include post-axial postcranial bones, limiting detailed morphological analysis to inferences from the preserved vertebrae and comparisons with other titanosaurs.^[3] This scarcity of material underscores the challenges in reconstructing the full body plan of this gigantic sauropod, though its vertebral proportions suggest robust support for an enormous body mass estimated at over 70 tons.^[4]

Paleobiology and Paleoecology

Geological Context

The holotype specimen of Puertasaurus reuili (MPM 10002) was recovered from the Cerro Fortaleza Formation in Santa Cruz Province, southern Patagonia, Argentina, specifically at the Cerro Los Hornos locality near the La Leona River. This formation, formerly referred to as the Pari Aike Formation in earlier literature, represents a key Late Cretaceous stratigraphic unit in the Austral Basin. The discovery site consists of a fine-grained gray sandstone lens embedded within the formation's upper levels, where the vertebrae were found in situ alongside highly carbonized plant debris.^[3] The Cerro Fortaleza Formation spans the Campanian to Maastrichtian stages of the Late Cretaceous, roughly 83 to 66 million years ago, with detrital zircon maximum depositional ages confirming a predominantly Campanian timeframe for much of the unit; however, the Puertasaurus horizon is interpreted as early Maastrichtian based on biostratigraphic correlations and associated fauna. Lithologically, it is dominated by fluvial sandstones, overbank mudstones, and carbonaceous shales, reflecting deposition in a low-gradient, alluvial plain system with periodic fluvial channels and floodplain wetlands. These sediments indicate a stable tectonic setting within the foreland basin of the Andean orogeny, with provenance from eroding Paleozoic and Mesozoic highlands to the west.^[8]^[9]^[3] Paleoenvironmentally, the formation records a warm, humid subtropical climate with seasonal rainfall, supporting dense forests of gymnosperms such as cycads, conifers, and ferns, as evidenced by abundant silicified wood and leaf impressions in the fossil-bearing layers. The Puertasaurus site, in particular, preserves evidence of a vegetated riparian zone along ancient rivers, where large-bodied herbivores could access ample foliage; associated microfossils and sedimentary structures suggest low-energy depositional conditions with minimal marine influence, consistent with a fully continental inland setting far from the proto-Atlantic coastline. This environment facilitated the coexistence of megafaunal titanosaurs with other vertebrates, highlighting the ecological richness of Patagonia's Late Cretaceous floodplains.^[8]^[10]^[3]

Associated Fauna

The Cerro Fortaleza Formation (Campanian–Maastrichtian) of southern Patagonia, Argentina, from which Puertasaurus reuili was recovered, preserves a diverse vertebrate fauna indicative of a fluvial-lacustrine paleoenvironment supporting large-bodied herbivores and a variety of predators and aquatic forms.^[4]^[11] Dinosaur remains dominate the terrestrial component, with multiple titanosaurian sauropods co-occurring alongside P. reuili, including the exceptionally complete Dreadnoughtus schrani and indeterminate titanosaurs represented by isolated teeth and caudal vertebrae.^[11] Smaller titanosaurs are also present, as evidenced by partial tails, suggesting niche partitioning among sauropods in this ecosystem.^[11] Theropod diversity includes abelisauroids, known from ziphodont teeth up to 11 mm in length, and megaraptorids such as Orkoraptor burkei.^[11] Carcharodontosaurids are represented by Austrocheirus isasii, identified through partial ulnae, manual phalanges, and metatarsals, highlighting the presence of large carnivores capable of preying on or scavenging giant sauropods like Puertasaurus.^[11] Ornithischian remains are less common but include the ornithopod Talenkauen santacrucensis and indeterminate nodosaurid ankylosaurs, documented by leaf-shaped teeth (8.5 mm high) and small osteoderms (approximately 6 mm in diameter). Aquatic and semi-aquatic vertebrates further enrich the assemblage, with peirosaurid crocodyliforms being prominent, as shown by multiple tooth morphotypes including conical and ziphodont forms, marking one of the southernmost records of this group.^[11] Chelid turtles occur alongside fish taxa such as lamniform sharks, lepisosteiform gars, the dipnoan lungfish Atlantoceratodus iheringi, and mosasaurs (from isolated teeth), indicating well-oxygenated freshwater bodies connected to marine influences.^[11] This faunal association reflects a stable, resource-rich habitat supporting megafaunal dinosaurs amid a broader Gondwanan vertebrate community during the Late Cretaceous.

Ecological Inferences

Puertasaurus reuili inhabited a subtropical forested environment characterized by seasonal rainfall, fluvial depositional settings with sandstones, mudstones, and paleosols indicative of riverine and coastal plain habitats.^[8] The presence of carbonized plant remains, including cycads and conifers, in the fine-grained sandstones of the Pari Aike Formation (now recognized as part of the Cerro Fortaleza Formation) suggests a vegetated landscape supporting diverse flora suitable for large herbivores.^[3] This early Maastrichtian ecosystem in southern Patagonia provided abundant resources, as evidenced by the co-occurrence of multiple titanosaurian taxa, enabling the evolution and sustenance of gigantic sauropods like Puertasaurus.^[8] As a herbivorous titanosaurid, Puertasaurus likely adopted a high-browsing feeding strategy, utilizing its elongated neck—exemplified by the ninth cervical vertebra measuring 118 cm in length—to access elevated vegetation such as conifer branches and treetops beyond the reach of smaller herbivores.^[3] The robust neck musculature and ligamentous structures inferred from preserved vertebrae indicate adaptations for efficient foraging in a forested setting, minimizing competition for ground-level plants with ornithopods like Talenkauen santacrucensis.^[3] Its enormous body size, estimated to exceed 30 meters in length, positioned it as a dominant primary consumer in a resource-rich niche, potentially influencing vegetation structure through selective browsing.^[8] Ecological interactions within this community included potential predation pressure from large abelisaurid theropods and competition with sympatric titanosaurs such as Dreadnoughtus schrani, alongside armored nodosaurs and crocodyliforms like peirosaurids in the aquatic margins.^[8] The diverse archosaur assemblage reflects a stable, humid habitat supporting high biomass, where Puertasaurus's gigantism may have served as a defense against predators while facilitating access to a broad foraging range in the floodplain forests.^[3]