Maxakalisaurus

Maxakalisaurus topai inhabited the semi-arid environment of the Adamantina Formation during the Late Cretaceous, approximately 80–85 million years ago. The paleoenvironment was characterized by a braided river system with seasonal floods, sparse vegetation, and alternation between intense dry seasons and rainy periods. The Triângulo Mineiro region, where the fossils were found, corresponded to a low plain near temporary bodies of water. The ecosystem included crocodilians, turtles, and fish, along with theropods such as abelisaurids and carcharodontosaurids.

As a titanosaur sauropod, Maxakalisaurus topai was an obligate herbivore. Its ridged teeth, suboval in cross-section and described by França et al. (2016), are unusual among sauropods and suggest a specialized feeding strategy, possibly adapted to more fibrous or abrasive vegetation. The long neck allowed reaching vegetation both at ground level and at moderate heights. With a system of two replacement teeth per alveolus, the dentition was continuously renewed to compensate for wear caused by processing large amounts of plant material.

Direct fossil evidence about Maxakalisaurus topai behavior is limited. As an Aeolosaurini member, it plausibly exhibited gregarious behavior similar to that documented for other titanosaurs, with possible aggregations around water sources during dry seasons. The presence of osteoderms suggests a role in protection against predators or thermoregulation. Late Cretaceous South American titanosaurs coexisted with large theropods, implying predatory pressure on juveniles and possibly defensive group behavior.

As a derived titanosaur within Lithostrotia, Maxakalisaurus topai likely possessed endothermic or mesothermic metabolism, similar to that inferred for other titanosaurs based on bone histology. The osteoderms found in the holotype may have functioned as calcium reserves for egg production, a hypothesis raised for other titanosaurs with osteoderms. With an estimated weight of 5 tonnes and length of 13 meters, it was a mid-sized animal by titanosaur standards, but represented the largest herbivore in its ecosystem. The continuous dental replacement system indicates a high rate of tooth wear related to vegetation processing.

Founding paper naming and describing Maxakalisaurus topai based on holotype MN 5013-V, excavated over four field seasons between 1998 and 2002, 45 km west of Prata, Minas Gerais. Kellner and National Museum colleagues document a partial disarticulated skeleton including cranial elements, cervical and dorsal vertebrae, ribs, pectoral girdle elements, humeri, pelvic elements, caudal vertebrae, and osteoderms. The presence of ridged teeth is noted as unusual among sauropods. The authors position the taxon as a titanosaur and discuss its affinities with other South American titanosaurs, particularly Saltasaurinae and Aeolosaurini. The genus name honors the Maxakali indigenous people of the region, and the specific epithet refers to Topá, a deity of the Maxakali pantheon. This work established the taxonomic foundation for all subsequent studies on the species.

Scale model of Maxakalisaurus topai on display at the National Museum of UFRJ, Rio de Janeiro. The replica was produced to accompany the original holotype fossils MN 5013-V described by Kellner et al. (2006).

Map of sauropod collection localities in the Bauru Basin, including the Triângulo Mineiro region where Maxakalisaurus topai was found 45 km west of Prata, MG.

França and colleagues describe a dentary and teeth referred to Maxakalisaurus topai, substantially expanding knowledge of the species' cranial morphology. The dentary measures 8.2 cm anteroposteriorly with ten alveoli. Teeth exhibit high-angled planar facets and are suboval in cross-section, with two replacement teeth per alveolus. The phylogenetic analysis uses 42 taxa and 253 characters, recovering the Aeolosaurini clade with Maxakalisaurus as a basal member. Results confirm Gondwanatitan and Aelosaurus as sister taxa, and identify nine newly scored dental characters. The work demonstrated that dental material is informative for Brazilian titanosaur systematics and provided the most robust phylogenetic analysis published specifically on M. topai.

Skeleton of Gondwanatitan faustoi (MN 4111-V), sister taxon of Aelosaurus and close to Maxakalisaurus in the phylogenetic analysis of França et al. (2016). Both belong to the Aeolosaurini clade.

Reconstruction of Aeolosaurus, sister taxon of Gondwanatitan and member of the same Aeolosaurini clade to which Maxakalisaurus belongs, as per França et al. (2016).

Santucci and Arruda-Campos describe Aeolosaurus maximus, a new Aeolosaurini species from the Adamantina Formation of São Paulo state. The revised phylogenetic analysis, which includes Maxakalisaurus topai as a reference taxon, recovers Aeolosaurini as a South American endemic clade with members found only in Argentina and Brazil. The work discusses the group's synapomorphic characters, with emphasis on haemal processes, and repositions Maxakalisaurus relative to other clade members. The detailed description of A. maximus provided new comparative data for interpreting M. topai morphology, especially regarding caudal vertebrae and their haemal arches. This study consolidated Aeolosaurini's position as a coherent phylogenetic unit within Titanosauria.

Reconstruction of Aeolosaurus rionegrinus, the Argentine member of Aeolosaurini. Santucci and Arruda-Campos's (2011) analysis positioned Maxakalisaurus as a basal taxon within this clade.

Fauna of the Allen Formation (Late Cretaceous of Argentina), analogous to the Brazilian Adamantina Formation environment. Several Aeolosaurini members lived in similar South American ecosystems.

Candeiro and colleagues provide a systematic inventory of fossil vertebrates from the Adamantina Formation at the Prata paleontological district, Minas Gerais, precisely the site where Maxakalisaurus topai was excavated. The work documents associated fauna including lepisosteids, amiids, abelisaurid and carcharodontosaurid dinosaurs, and indeterminate titanosaurs, along with crocodilians and turtles. The Adamantina Formation sediments in the region are described as reddish sandstones with fluvio-lacustrine sediments deposited in a semi-arid environment. The Prata paleontological district, 45 km west of the town of Prata, is one of Brazil's most important fossil sites. This study established the biostratigraphic and paleoenvironmental context for the discovery of Maxakalisaurus topai.

Caudal vertebrae (S6, Ca1–Ca18) and haemal arches of Baurutitan britoi (MCT 1490-R) in lateral view, representative of the Bauru Group titanosaur fauna documented by Candeiro et al. (2006) in the Adamantina Formation context.

Axial vertebrae referred to Baurutitan britoi from the Serra da Galga Formation (Bauru Group). The Bauru Group, including the Adamantina Formation, preserves one of the most diverse titanosaur faunas of the Late Cretaceous of South America.

Salgado and Carvalho describe Uberabatitan ribeiroi, a new titanosaur from the Maastrichtian Bauru Group in Uberaba, Minas Gerais, the same state where Maxakalisaurus topai was found. The phylogenetic analysis places Uberabatitan within Titanosauria and discusses its relationships with other South American titanosaurs, including Adamantina Formation taxa. The material includes over sixty bones representing at least five individuals of varying ages and sizes, allowing discussion of ontogeny. Though distinct, Uberabatitan and Maxakalisaurus are contemporaneous Bauru Group titanosaurs from Minas Gerais, and this description offers valuable comparative anatomical context. The phylogenetic analysis, including Maxakalisaurus as a comparison taxon, helped clarify the internal relationships of Titanosauria.

Lateral life reconstruction of Baurutitan britoi, a Bauru Group titanosaur contemporary with Uberabatitan and Maxakalisaurus. All three are part of the diverse Late Cretaceous titanosaur fauna of Minas Gerais.

Size comparison between Gondwanatitan faustoi and a human. Together with Uberabatitan and Maxakalisaurus, it forms the group of mid-sized titanosaurs from the Late Cretaceous of Brazil.

Bandeira and colleagues, including Kellner, the same author who described Maxakalisaurus, describe Austroposeidon magnificus, the largest dinosaur found in Brazil at the time, from the Presidente Prudente Formation (Bauru Group) of São Paulo. The specimen, originally collected in 1953 by Llewelyn Ivor Price and stored for over 60 years at the Museum of Earth Sciences in Rio de Janeiro, consists of a partial vertebral column. The phylogenetic analysis reveals Austroposeidon as the sister group of Lognkosauria. CT scanning revealed previously undescribed internal bone structures in the cervical vertebrae. The work demonstrates the exceptional diversity of gigantic titanosaurs in the Bauru Group and provides a broader phylogenetic context within which Maxakalisaurus can be positioned as a mid-sized Aeolosaurini member.

Figure 1 from Bandeira et al. (2016): geological map showing the location of the Presidente Prudente Formation in the Bauru Group. The Bauru Group is the main Upper Cretaceous stratigraphic unit of Southeast Brazil preserving titanosaurs.

Figure 2 from Bandeira et al. (2016): cervical vertebra of the Austroposeidon magnificus holotype. The vertebral morphology of Bauru Group titanosaurs shares diagnostic features with Maxakalisaurus topai.

Silva Junior and colleagues reassess Baurutitan britoi based on new specimens from the Serra da Galga Formation (Bauru Group) and present a revised phylogenetic analysis of Late Cretaceous South American titanosaurs. The analysis includes Maxakalisaurus topai as a comparison taxon and helps clarify relationships among Bauru Group titanosaurs. The authors identify Trigonosaurus pricei as a junior synonym of Baurutitan britoi. The taxonomic reassessment demonstrates that titanosaur diversity in the Serra da Galga Formation is greater than previously thought. The work provides updated comparative data on vertebrae and other skeletal elements that complement knowledge of Bauru Group titanosaur anatomy, a direct context for interpreting Maxakalisaurus topai bones from the overlying Adamantina Formation.

Simplified Titanosauria cladogram based on Curry-Rogers (2005), showing phylogenetic relationships among major titanosaur groups. Maxakalisaurus belongs to Lithostrotia, within which Aeolosaurini is positioned.

Figure 3 from Bandeira et al. (2016): cervical vertebra Cv13 of Austroposeidon magnificus. The vertebral morphology of Bauru Group titanosaurs documents anatomical patterns shared by members of this fauna, including Maxakalisaurus topai.

Nascimento and colleagues, including British paleontologist Steve Brusatte, publish a comprehensive review of all titanosaur records from the Bauru Group in the Late Cretaceous of Brazil. The work analyzes eight recognized species, including Maxakalisaurus topai, and discusses their importance for understanding clade diversity in South America. The authors identify the Late Cretaceous environmental and geographic factors that controlled the life cycles of these giant herbivores and possible migration routes. Lithological characteristics suggest a braided river paleoenvironment in an arid climate with sparse vegetation. The study also highlights that the Adamantina and Serra da Galga formations represent the areas with the highest number of records collected, where environmental conditions were most favorable for titanosaur flourishing and preservation.

Sketch of the Gondwanatitan skull. Gondwanatitan is one of the eight Bauru Group titanosaurs reviewed by Nascimento et al. (2025) in their comprehensive synthesis of Titanosauria diversity in Brazil.

Figure 4 from Bandeira et al. (2016): CT analysis of an Austroposeidon magnificus vertebra. CT techniques applied to Bauru Group titanosaurs reveal internal anatomical details relevant to understanding the diversity of the group that includes Maxakalisaurus.

Bertini and colleagues conduct a pioneering review of Late Cretaceous vertebrate faunas from the Adamantina and Marília formations (Upper Bauru Group) in their stratigraphic and paleobiogeographic context. The work establishes the reference framework for understanding Bauru Group faunal diversity, including the titanosaur sauropods that would be described in the following decades, such as Maxakalisaurus topai. The paleobiogeographic analysis demonstrates connections between the Bauru Group fauna and contemporaneous South American faunas, especially from Argentina. The study defines the Turonian-Maastrichtian interval for the Bauru Group formations based on faunal correlation. This founding review remains essential for contextualizing any new species described from the Bauru Group, including Maxakalisaurus.

Calibrated neosauropod phylogeny published in 2011, showing positions of clades such as Titanosauria and Lithostrotia. Bertini et al.'s (1994) paleobiogeographic analysis anticipated relationships between Bauru Group titanosaurs and other South American taxa.

Size comparison of Saltasaurus loricatus, an Argentine Late Cretaceous titanosaur with osteoderms, similar in size to Maxakalisaurus. Bertini et al. (1994) identified paleobiogeographic connections between the Bauru Group fauna and contemporaneous Argentine dinosaurs.

Kellner and Azevedo describe Gondwanatitan faustoi, a new titanosaurid sauropod from the Late Cretaceous (Bauru Group) of São Paulo, representing the most complete sauropod skeleton from Brazil at the time. The material (MN 4111-V) includes cranial elements, cervical, dorsal, sacral, and caudal vertebrae, pectoral and pelvic girdles, and limbs. Kellner is the same author who would describe Maxakalisaurus topai seven years later, and Gondwanatitan was identified as a sister or close taxon to Maxakalisaurus in subsequent phylogenetic analyses. This work established the anatomical comparison baseline among Bauru Group titanosaurs and positioned the Brazilian fauna within South American Aeolosaurini.

Figure 2 from Zaher et al. (2011): skull of Tapuiasaurus macedoi. The elongated skull of Brazilian titanosaurs like Tapuiasaurus and Gondwanatitan provides morphological context for interpreting the fragmentary cranial elements of Maxakalisaurus topai described by Kellner and Azevedo.

Figure 3 from Zaher et al. (2011): views of the Tapuiasaurus macedoi skull from multiple perspectives. This skull is the most complete among titanosaurs and serves as a reference for understanding cranial morphology of Brazilian titanosaurs, including Maxakalisaurus.

Santucci and Bertini analyze the distribution of Late Cretaceous titanosaur sauropods from the Adamantina Formation and correlates of western São Paulo and Minas Gerais, with discussion of paleoenvironments and paleobiogeography. The work directly examines the geographic and stratigraphic context of Maxakalisaurus topai, describing the Adamantina Formation paleoenvironment as a braided river system in a semi-arid climate. The paleobiogeographic analysis points to relationships between Bauru Group titanosaurs and Argentine Aeolosaurini taxa, suggesting dispersal corridors along the Late Cretaceous of South America. This study helped establish the geographic distribution of Bauru Group titanosaurs and provided an occurrence map that contextualized the discovery of Maxakalisaurus.

Figure 4 from Zaher et al. (2011): teeth and mandible of Tapuiasaurus macedoi. The dental morphology of Brazilian titanosaurs is relevant to the paleobiogeographic comparisons of Santucci and Bertini (2006) and for contextualizing the ridged teeth of Maxakalisaurus topai.

Figure 5 from Zaher et al. (2011): post-cranial elements of Tapuiasaurus macedoi. The geographic distribution of Late Cretaceous Brazilian titanosaurs analyzed by Santucci and Bertini (2006) reveals a dispersal pattern connecting taxa from Minas Gerais, São Paulo, and other regions.

Upchurch, Barrett, and Dodson publish the most comprehensive systematic review of Sauropoda in the second edition of The Dinosauria, a fundamental reference work in dinosaur paleontology. The work formally defines the clade Lithostrotia (of which Maxakalisaurus is a member) as the most recent common ancestor of Malawisaurus and Saltasaurus and all their descendants. The monograph establishes standardized morphological terminology, diagnostic phylogenetic characters, and the classificatory framework within which Maxakalisaurus topai would be positioned by Kellner et al. in 2006 and subsequent analyses. The phylogenetic analysis of 309 taxa and over 200 characters remains the fundamental taxonomic reference for all work on titanosaurs, including Brazilian taxa.

Figure 5 from Bandeira et al. (2016): dorsal vertebra of Austroposeidon magnificus. Upchurch et al.'s (2004) Sauropoda monograph established anatomical criteria for interpreting dorsal vertebrae like these in phylogenetic context, enabling positioning of Bauru Group titanosaurs.

Figure 6 from Bandeira et al. (2016): sacral vertebra of Austroposeidon magnificus. Upchurch et al. (2004) defined the sacral and caudal characters that distinguish Lithostrotia, the clade to which Maxakalisaurus topai belongs.

González Riga and colleagues describe Notocolossus gonzalezparejasi, one of the largest dinosaurs ever found, from the Cretaceous of Mendoza, Argentina. The work includes a comprehensive phylogenetic analysis of Titanosauria that positions Notocolossus within Lithostrotia and recovers the Aeolosaurini clade, with Maxakalisaurus topai as a reference taxon. The analysis of the hind foot of giant titanosaurs revealed unique functional adaptations related to supporting enormous body weight. The work discusses the biogeography of giant South American titanosaurs and provides an updated phylogenetic context for interpreting Maxakalisaurus topai's position within Aeolosaurini.

Figure 6 from Zaher et al. (2011): skeletal elements of Tapuiasaurus macedoi. González Riga et al.'s (2016) phylogenetic analysis used similar limb and pelvis characters of titanosaurs, including Brazilian representatives like Maxakalisaurus, to position Notocolossus.

Figure 7 from Bandeira et al. (2016): caudal vertebra of Austroposeidon magnificus. González Riga et al. (2016) conducted a similar phylogenetic analysis of Titanosauria that positions Maxakalisaurus topai within Aeolosaurini, a South American endemic clade.

Apesteguía analyzes the evolution of the metacarpus in titanosaur sauropods, reviewing diagnostic characters distinguishing groups like Aeolosaurini from other titanosaurs. The work is relevant for interpreting the metacarpals of Maxakalisaurus topai, which are among the preserved elements in holotype MN 5013-V. Metacarpus morphology is discussed in evolutionary context, with comparisons between South American and African titanosaurs. The characteristics of the vertically arranged metacarpus, typical of derived titanosaurs, are analyzed in relation to the quadrupedal posture and locomotion of these giants. The work provides an anatomical framework for interpreting Maxakalisaurus hand elements within the morphological diversity of Aeolosaurini.

Figure 8 from Bandeira et al. (2016): scapula and coracoid of Austroposeidon magnificus. Apesteguía (2005) analyzed the titanosaur metacarpus in the context of the pectoral girdle, relevant for interpreting the forelimb skeletal elements of Maxakalisaurus topai.

Figure 9 from Bandeira et al. (2016): femur and tibia of Austroposeidon magnificus. Apesteguía's (2005) analysis of metacarpal evolution in titanosaurs includes comparisons with hind limbs that provide context for interpreting Maxakalisaurus post-cranial elements.

Zaher and colleagues describe Tapuiasaurus macedoi, a Lower Cretaceous titanosaur from Minas Gerais with a nearly complete skull, the most complete among titanosaurs. The phylogenetic analysis, published in PLOS ONE, places Tapuiasaurus in a trichotomy with Trigonosaurus and Maxakalisaurus topai, revealing direct phylogenetic relationships between the two Brazilian dinosaurs. The skull reveals that advanced titanosaurs developed an elongated diplodocid-like cranial morphology much earlier than previously imagined, 30–40 million years before their radiation in the Late Cretaceous. The open-access work includes a phylogenetic analysis of 42 taxa that is a reference for positioning Bauru Group titanosaurs, including Maxakalisaurus.

Figure 7 from Zaher et al. (2011): Titanosauria cladogram published in PLOS ONE, including Maxakalisaurus topai in a trichotomy with Trigonosaurus and Tapuiasaurus. This is the phylogenetic analysis that most directly positions Maxakalisaurus relative to other Brazilian titanosaurs.

Figure 1 from Zaher et al. (2011): geological map showing the location of the Quiricó Formation in Minas Gerais, where Tapuiasaurus macedoi was found. Minas Gerais is also the state where Maxakalisaurus topai was discovered in the Adamantina Formation.

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