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Saltasauridae
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Saltasaurids
Temporal range: Late Cretaceous, 85.8–66 Ma
Life restoration of Saltasaurus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Clade: †Macronaria
Clade: †Titanosauria
Clade: †Lohuecosauria
Family: †Saltasauridae
Powell, 1992
Genera
Synonyms
  • Balochisauridae Malkani, 2003[3]

Saltasauridae (named after the Salta region of Argentina where they were first found) is a family of armored herbivorous sauropods from the Upper Cretaceous. They are known from fossils found in South America, Africa,[4] Asia, North America, and Europe. They are characterized by their vertebrae and feet, which are similar to those of Saltasaurus, the first of the group to be discovered and the source of the name. The last and largest of the group and only one found in North America, Alamosaurus, was thirty-four metres (112 feet) in length and one of the last sauropods to go extinct.

Most of the saltasaurids were smaller, around fifteen metres (49 feet) in length, and one, Rocasaurus, was only eight metres (26 feet) long. Like all sauropods, the saltasaurids were quadrupeds, their necks and tails were held almost parallel to the ground, and their small heads had only tiny, peg-like teeth. They were herbivorous, stripping leaves off plants and digesting them in their enormous guts.[5] Although large animals, they were smaller than other sauropods of their time, and many possessed distinctive additional defenses in the form of scutes along their backs.

Description

[edit]

As sauropods, the Saltasauridae are herbivorous saurischians with the characteristic body plan of a small head, long neck, four erect legs, and a counterbalancing tail. Most sauropods are from the clade Neosauropoda, which is further split into the narrow-toothed Diplodocoidea and the broad-toothed Macronaria. The Macronarians emerged in the Jurassic and a subclade, the Titanosauria, survived into the Cretaceous and spread across the continents. Because of their diversity, wide distribution, and the fragmentary or incomplete nature of most specimens, little is known about the titanosaurs beyond their size and tendency to have scutes.[6]

The saltasaurids, one of the several titanosaur families, are recognized by the convexities in certain caudal vertebrae and the markings on their coracoid bones.[7] All saltasaurids have thirty-five or fewer caudal vertebrae,[8] each of which is convex on both sides of its centrum, and the one closest to the tail is shorter than the others.[9] Their coracoid bones have rectangular margins on the anteroventral side, as well as a lip where they meet the infraglenoid. The Opisthocoelicaudiinae, a subfamily of the saltasaurids, are unique in that they lack phalanges in their forelimbs.[8][10] Although Saltasaurus is known to possess dorsal osteoderms, scutes have not been discovered in all saltasaurids, and it is unclear when and where the evolution of osteoderms occurred in saltasaurids and titanosaurs in general.[11]

History of study

[edit]

The first saltasaurid to be discovered was Alamosaurus, found by paleontologist Charles Gilmore in Utah in 1922. The next species would not be described until Opisthocoelicaudia was named by Magdalena Borsuk-Bialynicka from a postcranial material in Mongolia in 1977. In 1980, Jose Bonaparte and Jaime Powell discovered Saltasaurus in Argentina. This was the first sauropod to be discovered with armor and proved that sauropods had thrived in Cretaceous South America. Paul Sereno eventually recognized a cladistic relationship between Opisthocoelicauda and Saltasaurus to create the family Saltasauridae.[12]

Classification

[edit]

The group is defined by the characteristics shared by all with the two best-known members, Saltasaurus and Opisthocoelicaudia. Paleontologists J Wilson and P Upchurch defined the Saltasauridae in 2003 as the least inclusive clade containing Opisthocoelicaudia skarzynskii, and Saltasaurus loricatus, their most recent common ancestor, and all that species’ descendants.

Taxonomy

[edit]

This taxonomy is based on those of González Riga et al. (2009) and Curry Rogers & Wilson (2005).[13][14]

Phylogeny

[edit]

The family is then further divided into two subfamilies. Wilson and Upchurch defined Saltasaurinae in 2003 as the least-inclusive clade containing Saltasaurus but not Opisthocoelicaudia. The same paleontologists defined Opisthocoelicaudiinae as the inverse: the least-inclusive clade containing Opisthocoelicaudia but not Saltasaurus. Some species, due to the incompleteness of their skeletons, cannot yet be placed in either subfamily.

Saltasauridae in a cladogram after Navarro et al., 2022:[15]

Saltasauridae

Paleobiology

[edit]

Geographic range

[edit]

Many fragmentary saltasaurids have been discovered since 1980, placing members of the family in territories as widely dispersed as today's Australia, Madagascar, and France, in addition to their earlier-known residencies in North and South America. Like the other titanosaurs, the saltasaurids where a widespread, successful group that colonized all continents in the Cretaceous.[16]

Feeding habits

[edit]

Like all titanosaurs, the saltasaurids possessed small, peg-like teeth that were not usable for chewing. Coproliths from an unidentified titanosaur found in India suggest a diet of conifers, cycads, and early species of grasses.[17] Unable to chew and probably lacking gastroliths, sauropods survived by retaining plant matter in their stomachs for long periods of time, fermenting it to extract as many resources as possible. Their long necks allowed them to graze over a large area while standing, reducing energy use.

Osteoderms

[edit]

The osteoderms of Saltasaurus consisted of numerous, large bony plates embedded in the dorsal skin, each surrounded by a pattern of smaller plates. The large osteoderms contained some hollow spaces for blood vessels and spongy trabecular bone, while the small ones were solid.[18] Patches of skin from unidentified Cretaceous titanosaurs have revealed similar scale patterns in embryos (a large scale surrounded by ten smaller ones) but no bone or mineralized structure, suggesting that, like crocodiles, those saltasaurids that possessed armor only developed it some time after hatching. Analysis of the osteoderms of the titanosaur Rapetosaurus revealed that the bones were hollow in adults, while those of juveniles were solid pieces similar to those in crocodiles. Paleontologist Kristina Curry Rogers, who made this discovery, theorized that the adult animals used their hollow osteoderms to store minerals during lean times. It is unknown whether any of the Saltasauridae used their osteoderms in a similar manner.[14]

Reproduction and development

[edit]

The same Argentine dig site, Auca Mahuevo, that provided information on embryonic skin, has also yielded information on the nesting habits of titanosaurs, but not saltasaurids specifically. The nests were constructed on the surface by piling debris in a ring around the eggs, with the eggs themselves left uncovered. Each egg was porous and spherical, about 14 cm in diameter, and they were laid in clutches. The embryos show smaller rostrum and nares close to the anterior portion of the face compared to adult titanosaurs, suggesting that the nostrils may have moved towards the back of the head as the animal grew.[19]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Saltasauridae

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from Grokipedia
Saltasauridae is a family of lithostrotian titanosaurian sauropod dinosaurs, defined as the most inclusive clade containing Opisthocoelicaudia skarzynskii and Saltasaurus loricatus and all descendants of their . This clade is known from the epochs of the to stages (approximately 83 to 66 million years ago), with fossils primarily discovered in but also reported from , , , and . Members of Saltasauridae are distinguished by derived skeletal features such as procoelous caudal vertebrae, biconvex middle caudal centra, and in several genera, dermal armor consisting of osteoderms embedded in the skin. The family was originally established by José F. Bonaparte and Jaime E. Powell in 1980 with the description of the Saltasaurus loricatus from the Lecho Formation in , Argentina, marking the first unambiguous record of osteoderms in a sauropod . Saltasaurus, a small-bodied form reaching about 12 meters in length, exemplifies the family's typical morphology, including a robust build, short neck, and stubby limbs adapted for a quadrupedal, herbivorous lifestyle. Subsequent discoveries have expanded the known diversity, with phylogenetic analyses placing Saltasauridae within the broader clade as a derived group of Titanosauriformes, often subdivided into subfamilies like Saltasaurinae (e.g., Saltasaurus, Neuquensaurus) and Opisthocoelicaudiinae (e.g., , ). Dermal armor, a hallmark of many saltasaurids, consists of polygonal plates and small ossicles formed through metaplastic ossification in the dermis, providing potential protection against predators. Histological studies reveal that these osteoderms in Saltasaurus feature woven-fibered bone with lines of arrested growth indicating longevity, and similar structures occur in related genera like Neuquensaurus and Aeolosaurus, suggesting armor evolved convergently or was widespread in the lineage. The global distribution of Saltasauridae reflects the widespread dispersal of titanosaurs during the Late Cretaceous, with recent finds such as Qunkasaura pintiquiniestra from Spain highlighting Europe as a biogeographic crossroads for Gondwanan and Laurasian forms. These dinosaurs represent some of the last surviving sauropods before the end-Cretaceous extinction, contributing to our understanding of sauropod evolution and paleoecology in the final stages of the Mesozoic Era.

Description

General morphology

Saltasauridae comprises herbivorous, quadrupedal sauropod dinosaurs characterized by the typical of the group, including a small head, elongated , robust trunk, pillar-like limbs for weight support, and a tail comprising 35 or fewer vertebrae. These features enabled efficient locomotion and foraging among high vegetation, with the long facilitating access to elevated plant matter while the columnar limbs provided stability for their massive bodies. Body sizes within Saltasauridae varied significantly, ranging from approximately 8 m in length for the smallest known member, Rocasaurus muniozi, to up to 34 m for the largest, , though most genera measured around 10–15 m. Relative to other titanosaurians, saltasaurids exhibited a lightweight build, achieved through extensive vertebral pneumaticity where presacral, sacral, and proximal caudal vertebrae feature camellate internal structures—numerous small, irregular chambers separated by thin bony septa—reducing skeletal mass while maintaining structural integrity. A defining external feature of Saltasauridae is the presence of dermal armor, consisting of embedded bony osteoderms that provided protection, though the extent and density of coverage differed among genera; for instance, loricatus bore both large oval plates and numerous small forming a pattern, while evidence in other taxa like remains fragmentary. This armor, often lightweight with internal cavities, contributed to the family's overall reduced body density compared to non-armored titanosaurs.

Diagnostic skeletal features

Saltasauridae is characterized by a suite of diagnostic osteological traits that distinguish it from other titanosaurian clades, particularly in the axial and . These features, initially outlined by Powell (1992) based on the Saltasaurus loricatus, include reduced pleurocoels in the centra of cervical and dorsal vertebrae, reflecting a shift toward more complex internal pneumaticity while maintaining procoelous articulation in the dorsal vertebrae—a synapomorphy shared more broadly within but refined in Saltasauridae through reduced external fossae. Caudal centra are broader transversely than tall, filled with extensive pneumatic chambers rather than solid tissue, which Powell (1992) identified as a defining synapomorphy enhancing skeletal lightness. Neural spines in the caudal vertebrae are low, posteriorly inclined, and often expanded transversely, contributing to a robust yet lightweight tail structure; in certain members, these spines exhibit bifurcation, further distinguishing the . Presacral vertebrae display specific pneumatic foramina patterns, with foramina on the lateral surfaces of neural arches and centra forming interconnected camerate structures, an advancement over the simpler pleurocoels of basal titanosaurs as updated in phylogenetic revisions. In the , the features a prominent acromial process that articulates closely with the , while the blade is notably reduced in length relative to the overall glenoid contribution, optimizing support in smaller-bodied forms. elements show reduction, particularly in subfamilies like Opisthocoelicaudiinae, where manual phalanges are absent or vestigial, with only rudimentary remnants fused to metacarpals in genera such as Opisthocoelicaudia skarzynskii. These traits, refined by Salgado et al. (1997) in their analysis of basal titanosaur relationships, emphasize Saltasauridae's derived position within through enhanced pneumaticity and limb miniaturization.

History of discovery

Initial discoveries

The initial recognition of saltasaurid dinosaurs began with the discovery of fragmentary remains in during the early . In June 1921, geologist John B. Reeside, Jr., of the U.S. Geological Survey unearthed a well-preserved left and a nearby right in Barrel Spring Arroyo, approximately one mile south of Ojo Alamo in , from the Upper . These specimens were described the following year by Charles W. Gilmore as the new genus and species Alamosaurus sanjuanensis, classified within due to its large size and general resemblances to sauropods such as and , though distinct enough to warrant a separate ; Gilmore noted its unique features but did not assign it to a specific family at the time. This find represented one of the first sauropod discoveries in , though its titanosaurian affinities, including potential saltasaurid relations, were not recognized until decades later. Further early insights into Asian saltasaurid-like forms emerged from the . In 1965, the Polish-Mongolian Palaeontological Expedition excavated a partial postcranial (lacking ) from the Upper at Altan Ula IV in the Nemegt Basin, . This material, cataloged as ZPAL MgD-I/48 and housed at the Institute of Paleobiology of the Polish Academy of Sciences in , was formally described in 1977 by Magdalena Borsuk-Białynicka as the new and Opisthocoelicaudia skarzynskii, tentatively placed within Camarasauridae (subfamily Euhelopodinae) based on vertebral morphology and pelvic similarities to and . The description highlighted the specimen's opisthocoelous caudal vertebrae and robust build, marking an early indication of titanosaurian diversity in , though its saltasaurid placement was not established until subsequent analyses. The pivotal breakthrough in identifying armored saltasaurids occurred in during the late 1970s. Between 1975 and 1977, paleontologists José F. Bonaparte, Martín D. Vince, and Juan C. Leal excavated multiple partial skeletons, including vertebrae, limb bones, and notably osteoderms, from the Lecho Formation (Upper , Upper Campanian-Lower ) at Estancia El Brete in , northwestern . These remains were named and described in 1980 by Bonaparte and Jaime E. Powell as Saltasaurus loricatus, the of a new within Titanosauridae, representing the first unequivocal evidence of dermal armor in a titanosaurian sauropod and thus a foundational saltasaurid . The discovery underscored the group's Gondwanan origins and distinctive osteoderm-bearing morphology. Concurrent with these finds, scattered fragmentary saltasaurid material began surfacing in Patagonia during the 1990s, often initially misattributed to other titanosaurs. For instance, partial skeletons including vertebrae, ribs, and appendicular elements from the Upper Cretaceous Anacleto Formation near Cinco Saltos, Río Negro Province, Argentina, were collected in the late 1980s and early 1990s but preliminarily classified as Saltasaurus sp. or referred to broader Titanosaurus species in contemporary reviews, such as those by John S. McIntosh in 1990, due to shared vertebral and limb features without full contextual analysis. These specimens, later integral to the 1992 naming and description of Neuquensaurus, highlighted the challenges of distinguishing saltasaurine taxa from isolated remains amid the era's limited understanding of titanosaur diversity.

Family definition and expansions

The family Saltasauridae was originally established by José F. Bonaparte and Jaime E. Powell in 1980. It was phylogenetically defined by Paul Sereno in 1998 as the most inclusive clade containing Opisthocoelicaudia skarzynskii and loricatus. This definition highlighted the distinctive presence of osteoderms and advanced pneumatic features in the , distinguishing saltasaurids from other sauropod groups. In the early 2000s, the family underwent significant expansions with the recognition of additional South American taxa sharing key saltasaurid synapomorphies, such as extreme vertebral pneumatization and armor; these included Neuquensaurus from the Anacleto Formation, Rocasaurus from the , and Bonatitan from the , all in . These inclusions, supported by analyses in González Riga (2003) and subsequent works, reinforced Saltasauridae's Gondwanan origins while emphasizing shared traits like keeled and robust limb elements. The definition was further refined by Jaime E. Powell in 2003, who emphasized the diagnostic role of osteoderms—small, polygonal plates with vascular foramina—and specific vertebral morphology, including procoelous caudals and deeply excavated neural arches, in distinguishing saltasaurids from basal titanosaurs. More recent phylogenetic studies have confirmed additional members, such as the North American Alamosaurus sanjuanensis as a derived saltasaurid based on shared appendicular and axial features (D'Emic 2012), and the European Qunkasaura pintiquiniestra from the Lo Hueco Formation in Spain (Company et al. 2024), extending the family's distribution beyond Gondwana for the first time.

Systematics

Classification

Saltasauridae is a family of titanosaurian sauropod dinosaurs classified within the clade . It occupies a derived position in the sauropod phylogenetic tree, following the sequence > > Titanosauriformes > > > Saltasauridae. Recent phylogenetic analyses confirm Saltasauridae's status as a lithostrotian , often positioned as sister to within broader titanosaurian groupings such as . The family comprises two subfamilies: Saltasaurinae, consisting of South American armored forms such as , and Opisthocoelicaudiinae, including Asian and North American forms like and .

Taxonomy

Saltasauridae is a family of titanosaurian sauropod dinosaurs characterized by the possession of osteoderms and other derived features, with Saltasaurus loricatus serving as the type genus and species. This taxon, the first saltasaurid recognized, was described from multiple partial skeletons including vertebrae, limb bones, and osteoderms recovered from the Upper Cretaceous Lecho Formation in Salta Province, Argentina. Several other genera are firmly placed within Saltasauridae based on shared synapomorphies such as procoelous caudal vertebrae and specific osteoderm morphologies. Neuquensaurus australis, from the Anacleto and Allen formations in northern Patagonia, Argentina, was originally classified as Titanosaurus australis before being reassigned to a new genus; T. robustus, based on fragmentary appendicular elements from the same region, is now considered a junior synonym of N. australis. Rocasaurus muniozi, known from a partial skeleton including dorsal vertebrae and a partial pelvis from the Allen Formation in Río Negro Province, Argentina, represents a small-bodied saltasaurine closely allied to Saltasaurus. Bonatitan reigi, described from disarticulated postcranial bones such as a humerus and tibia from the lower Allen Formation in Río Negro Province, Argentina, is another diminutive saltasaurine, though its exact intrafamilial position remains basal within the group. Outside , Alamosaurus sanjuanensis is the sole North American representative, known from extensive skeletal material including vertebrae, girdle elements, and limbs from the Naashoibito Member of the and equivalent units in the and ; it forms a with South American saltasaurines in multiple analyses. In , Opisthocoelicaudia skarzynskii from the in is a well-preserved saltasaurid, represented by an articulated posterior lacking the and neck, featuring opisthocoelous middle caudals diagnostic of the family. Borealosaurus wimani, based on a single opisthocoelous middle caudal vertebra from the Early Sunjiawan Formation in Province, , has been tentatively referred to Saltasauridae but its placement is debated due to limited material and potential convergence in vertebral morphology. A recent European addition expands the family's known distribution: Qunkasaura pintiquiniestra, described in 2024 from a nearly complete including cervical, dorsal, and caudal vertebrae, ribs, and appendicular elements from the Lo Hueco fossil site in the Villalba de la Sierra Formation (late –early ), Cuenca Province, , is positioned within Saltasauridae, potentially in Opisthocoelicaudiinae. Several junior synonyms and invalid taxa have been reassigned or excluded from Saltasauridae over time, including Titanosaurus nanus () and various indeterminate titanosaurs from that lack distinguishing saltasaurid features.

Phylogeny

Phylogenetic analyses of Saltasauridae have consistently recovered it as a derived clade within Lithostrotia, the group of titanosaurs characterized by advanced skeletal pneumaticity and the presence of osteoderms as a key synapomorphy. Within Saltasauridae, a major analysis by Navarro et al. (2022) supports a topology dividing the family into two subfamilies: Opisthocoelicaudiinae and Saltasaurinae. Opisthocoelicaudiinae includes Opisthocoelicaudia and Nemegtosaurus as basal members, while Saltasaurinae encompasses Alamosaurus, Saltasaurus, Neuquensaurus, and additional taxa such as the recently described nanoid form Ibirania parva. This arrangement is supported by shared features in the character matrix, including high vertebral convexity indices in anterior caudals (exceeding 0.6 in some metrics) and extreme postcranial pneumaticity, which distinguish saltasaurids from other lithostrotians. Recent discoveries have refined intra-familial relationships and biogeographic implications. The 2024 description of Qunkasaura pintiquiniestra from the Lo Hueco fossil site in the Villalba de la Sierra Formation (late –early ), Cuenca Province, places it within Opisthocoelicaudiinae in implied weighting analyses, as the sister to Abditosaurus, with shared synapomorphies such as elongated dorsal diapophyses and neural spines of constant anteroposterior width. This European , alongside North American and Asian , bolsters evidence for a Gondwanan origin of saltasauroids followed by dispersal to via northern routes during the , highlighting intercontinental faunal exchange in the final stages of sauropod evolution. Debates persist regarding the of Saltasauridae, particularly the placement of . While many cladistic matrices recover it firmly within Saltasaurinae, alternative analyses have positioned Alamosaurus outside the family as a basal lithostrotian or sister to Saltasauridae, based on differences in cervical vertebral morphology and the absence of definitive in known specimens. These discrepancies underscore ongoing uncertainties in titanosaurian character scoring, such as the interpretation of osteoderm presence as a reversal or convergence within , where it evolved independently or was secondarily lost in some lineages.

Paleobiology

Temporal and geographic distribution

Saltasaurids are a family of titanosaurian sauropods primarily known from the , spanning the to stages (approximately 83 to 66 million years ago). The earliest potential records of the group may date to the stage (around 89-86 million years ago) in , based on fragmentary material attributed to early-branching members such as Jiangshanosaurus from the Jinhua Formation in , though its placement within Saltasauridae remains debated. Most definitive fossils, however, come from later deposits, reflecting the family's diversification toward the end of the . The core geographic distribution of Saltasauridae centers on , particularly in and , where multiple genera such as , Neuquensaurus, and Rocasaurus are documented from formations like the Lecho and Allen, indicating a Gondwanan origin. Fossils are also widespread in Laurasian continents, including ( region, southwestern ) with Alamosaurus from the Ojo Alamo and Javelina Formations, and (, and ) represented by Opisthocoelicaudia from the . These distributions highlight the family's presence across both northern and southern hemispheres during the late to . Recent discoveries have expanded the known range to include and , underscoring a more than previously recognized. In , Qunkasaura pintiquiniestra from the Lo Hueco site in (late , ~75 million years ago), represents a saltasauroid titanosaur in the . In , unnamed saltasaurid remains from the middle Quseir Formation in the , , provide the first definitive record on the continent. No saltasaurid fossils have been reported from or , consistent with biogeographic barriers in the southern high latitudes. These patterns suggest dispersal facilitated by Late Cretaceous land bridges and faunal exchanges, particularly between South America and North America via proto-Caribbean connections, and northward into Eurasia and Africa through Laurasian corridors, allowing saltasaurids to achieve a near-global presence before the end-Cretaceous extinction.

Diet and locomotion

Members of Saltasauridae, like other titanosaurian sauropods, were high-browser herbivores that primarily consumed foliage from tall vegetation, including conifers, cycads, ferns, and possibly early angiosperms or grasses in the Late Cretaceous. Their peg-like teeth, adapted for stripping rather than chewing, show microwear patterns consistent with abrasive vegetation, likely influenced by silica phytoliths in plants or ingested grit such as sand, indicating a diet of tough, fibrous material. Tooth replacement rates in titanosaurs were relatively low compared to other herbivorous dinosaurs, typically around 35–76 days per tooth, allowing for functional wear before substitution, a trait shared across Sauropoda that supported their inefficient oral processing. Evidence from associated gastroliths in titanosaur specimens, such as polished pebbles found near skeletons, suggests these dinosaurs ingested stones to aid digestion in a crop-like , grinding tough matter that their simple could not masticate effectively. This gastric milling complemented their reliance on for breaking down cellulose-rich foods. Carbon analyses of titanosaur and bones confirm an exclusive diet of C3 plants, with δ¹³C values indicating consumption of non-grass vegetation in humid, forested environments during the . For instance, isotopic data from Neuquensaurus specimens align with a C3-dominated diet in wetter paleoenvironments, reflecting niche partitioning where saltasaurids targeted higher canopy layers. Saltasaurids employed a quadrupedal locomotion with a wide-gauge posture, characterized by robust, arched hind limbs that enhanced lateral stability for supporting their multi-tonne bodies over uneven . Limb proportions, including elongated femora and narrow tibiae in genera like and Neuquensaurus, favored an efficient, energy-conserving prioritizing endurance over speed, with estimated stride lengths suited to slow movements. The hyper-robust hind limb morphology in Saltasauridae likely permitted occasional rearing onto the hind legs to access elevated foliage, combining stability for quadrupedal with flexibility for high . This adaptation reflects an for , where wide-gauge stances improved balance during locomotion in dense, humid habitats.

Osteoderms

The dermal armor of saltasaurids consists of two main types of osteoderms: larger bony plates and smaller dermal , primarily distributed along the flanks, back, and possibly the anterior tail. In Saltasaurus loricatus, the plates are oval-shaped with a conical external surface and a concave basal face, measuring up to 12 cm in diameter and 5.5 cm in thickness, while the ossicles are sub-spherical to lenticular and polygonal when arranged in a dense , with dimensions of 7–10 mm along their longest axis and a of 18–25 per 10 cm². These elements covered much of the posterior body in a protective layer, forming an irregular that embedded within the . In contrast, osteoderms in Neuquensaurus exhibit greater morphological irregularity and variability in size and shape compared to Saltasaurus, including at least two distinct morphotypes, though specific dimensions remain less precisely documented. Histological analysis reveals that saltasaurid osteoderms formed through dermal , involving direct mineralization of collagenous fiber bundles, with evidence of rapid periosteal deposition indicated by highly vascularized, uninterrupted fibrolamellar tissue and the presence of lines of arrested growth. The plates show reconstructed cancellous internal structure with woven-fibered and secondary remodeling, while are more compact without significant resorption, suggesting a primary role in structural support and protection against predation. Possible secondary functions include , as the vascularization and porous texture could facilitate heat exchange, though this remains speculative based on comparative dermal structures. The presence of osteoderms represents an evolutionary novelty within , marking a reversal to armored in an otherwise unarmored of derived sauropods, and was first recognized in Saltasaurus loricatus from Upper deposits in . This armor is absent in the closely related Opisthocoelicaudiinae, such as Opisthocoelicaudia, where nearly complete skeletons lack any dermal ossifications. Recent studies highlight variability across saltasaurids, with osteoderms showing diverse microanatomies from compact to highly cancellous bone, supporting their role in both defense and potential mineral storage.

Reproduction and growth

Saltasaurids were oviparous, laying eggs in clutches buried shallowly in substrate on ancient floodplains. The Auca Mahuevo site in Patagonia, Argentina, provides the primary evidence of their reproductive behavior, yielding over 500 eggs from the Anacleto Formation, dated to approximately 80 million years ago. These subspherical eggs measured 13–15 cm in diameter and contained well-preserved embryos of titanosaurian sauropods morphologically similar to Saltasaurus, featuring elongated necks and limb proportions indicative of the Saltasauridae family. The embryos, at an advanced developmental stage, were unhatched, preserved by rapid burial in fine-grained overbank sediments following flooding events that inundated the nesting area. Nesting occurred in colonial assemblages, with clutches distributed across an area exceeding 1 km² in mudstones, suggesting gregarious breeding among adult saltasaurids. Each typically comprised 15–34 eggs arranged in two or three layers within simple, unlined depressions about 50–60 cm in diameter and 20–30 cm deep, covered by a thin layer of . This strategy implies with limited post-hatching , as no traces of brooding, nest guarding, or juvenile aggregation with adults have been identified at the site. Bone histology from juvenile titanosaur specimens, including those referable to saltasaurids, indicates rapid early growth, characterized by fibrolamellar cortical bone with plexiform vascularization and minimal lines of arrested growth. In osteoderms, parallel-fibered tissue and cyclical growth lines reflect sustained but moderating growth rates through ontogeny, with extensive secondary remodeling in mature individuals. These patterns suggest saltasaurids achieved subadult body sizes quickly, potentially within a few years, before transitioning to slower adult growth. Ontogenetic shifts in saltasaurids are documented through embryonic and juvenile material from Auca Mahuevo, where skulls exhibit more robust proportions, including a deeper and larger orbits relative to adults. A 2019 study on juvenile Alamosaurus specimens, a North American saltasaurid relative, further supports these changes, revealing unfused neurocentral sutures and proportionally sturdier cranial elements in early growth stages compared to mature individuals. Sexual dimorphism remains debated, with potential differences in osteoderm density suggested by variability in armor distribution, though confirmatory evidence is lacking.

References

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