Mapusaurus ( 'earth lizard') is a genus of giant carcharodontosaurid dinosaur that lived in Argentina during the Albian age of the Early Cretaceous. It is known from a bonebed of between seven and nine specimens, excavated from the strata of the Huincul Formation between 1997 and 2001 as part of the Argentinian-Canadian Dinosaur Project. In 2006, Rodolfo Coria and Philip J. Currie scientifically described Mapusaurus. Only one species of Mapusaurus, M. roseae, has been described, named after the rose-colored rocks in which it was discovered and sponsor Rose Letwin. Another carcharodontosaurid, Taurovenator, was once believed to be a synonym of Mapusaurus. However, the description of a more complete specimen of Taurovenator demonstrated that they are separate taxa.
Mapusaurus was one of the largest carcharodontosaurids. Based on the biggest specimen known from the bonebed, represented by a left femur, it was originally estimated to have reached a maximum body length of and a mass of . Subsequent works have given maximum size estimates of and , respectively. Mapusaurus generally resembled Giganotosaurus, though had a deeper skull, a more rugose maxilla, a rougher surface to its lacrimal bone, differently proportioned neck vertebrae, and various other minor differences. The arms of Mapusaurus were very small, similar in terms of proportional size to those of tyrannosaurids and abelisaurids. During the Cretaceous, Argentina underwent an explosion in carcharodontosaurid and titanosaur size and diversity. Mapusaurus itself coexisted with the giant titanosaurs Argentinosaurus and Choconsaurus, as well as a menagerie of rebbachisaurids, unenlagiids, and ceratosaurs.
Discovery and naming
The first fossils of this taxon were discovered in 1997 by members of the Argentinian-Canadian Dinosaur Project in an exposure of the Huincul Formation at Cañadón del Gato, a site south of Plaza Huincul in Neuquén Province, Argentina. In 1997, crews from the Project began excavating the fossils, which they believed to belong to a single skeleton of a large theropod dinosaur. However, during preparation of the remains it was realized that they came from several individuals of differing sizes and ontogenetic stages. That same year, Argentine paleontologist Rodolfo Coria and Canadian paleontologist Philip Currie, the leaders of the Project, announced the discovery of the theropod at a meeting of the Society of Vertebrate Paleontology, stating that the team had unearthed a single skeleton of a new carcharodontosaurid theropod similar to Giganotosaurus. By that time, an isolated tooth, a , a (tail) vertebra, a manual , an incomplete pelvis, femora, tibiae, a fibula, a metatarsal and several pedal (foot) phalanges had been collected. Excavations of the fossils at Cañadón del Gato lasted from 1997 to 2001, wherein hundreds of fossils from at least seven to nine individuals of Mapusaurus were discovered. These fossils were mentioned in conference abstracts in 2000 and 2001, which noted the possibility of pack behavior or gregariousness in large theropods based on the quantity and age range of the theropod fossils found.
In 2006, Coria and Currie scientifically described the remains, and identified them as belonging to a new genus and species of giant carcharodontosaurid theropod, which they named Mapusaurus roseae. The generic name Mapusaurus derives from the Mapuche word Mapu, meaning "Earth", and the Greek σαῦρος (saûros), meaning "lizard", and thus translates as "Earth lizard". The specific name roseae is named for both the rose-colored rocks, in which the fossils were found, and for Rose Letwin, who sponsored the expeditions which recovered the fossils. Coria and Currie designated an isolated right (MCF-PVPH-108.1, Museo Carmen Funes, Paleontología de Vertebrados) as the holotype (name-bearing) specimen of M. roseae. Prortions of the skull, limbs, pelvis and vertebrae were designated as paratypes. In total, Mapusaurus is known from parts of the skull and mandible, teeth, some cervical (neck), (back) and caudal vertebrae, much of the sacrum and pelvis, some ribs, parts of the , much of the hindlimbs, many pedal phalanges, and fragments of the forelimb and manus. Later studies have reidentified some of the elements described by Coria and Currie (2006), such as a that American paleontologist Matthew Carrano and colleagues (2012) stated is the distal (away from body) end of a humerus and a partial fibula that Canadian paleontologist Phil Bell and Coria (2013) identified as a pathological dorsal rib.
Taurovenator
In 2005, a right (the skull bone located behind the eye socket) and an associated partial skeleton of a theropod dinosaur were unearthed by Argentine paleontologist Matias Motta from sandstones at Violante Farm in Río Negro Province, Argentina deriving from the lower member of the Huincul Formation. The postorbital was deposited at the Museo Provincial "Carlos Ameghino" and cataloged as MPCA-Pv 803. In 2016, Motta and colleagues described MPCA-Pv 803 as the holotype of a new genus and species of carcharodontosaurid dinosaur, Taurovenator violantei. Taurovenator went largely unnoticed in scientific literature because of its fragmentary nature. Coria and colleagues (2019) suggested that Taurovenator is a synonym of Mapusaurus, as they found no autapomorphies (distinguishing traits) unique to MPCA-Pv 803. Additionally, the authors stated that the two genera were likely coeval. However, Taurovenator is actually from the lower unit of the Huincul Formation, while Mapusaurus is from the upper unit of the formation, suggesting they could be distinct genera. In 2022, another carcharodontosaurid from the Huincul Formation, Meraxes, was named on the basis of a skull and skeleton from the same sandstones as Taurovenator. The authors who described Meraxes stated that Taurovenator lacked autapomorphies and may be coeval with Meraxes.
Although an associated skeleton was discovered alongside the Taurovenator holotype, Motta and colleagues (2016) stated it came from an indeterminate carcharodontosaurid. In 2024, this specimen was described in detail and assigned to Taurovenator. The authors noted that the Huincul Formation is separated into two distinct sequences; a lower section of thin, multicolored sandstones and an upper section of thick conglomeratic sediments. Mapusaurus derives from the upper sequence of the formation, whereas Meraxes and Taurovenator are exclusive to the lower rock layers. Meraxes was collected in strata close to the Candeleros-Huincul Formation boundary, but Taurovenator was found over above the Candeleros-Huincul Formation limit. It is for these reasons that the three carcharodontosaurids found at Huincul were potentially not coeval, supporting the argument for Taurovenator validity. A new host of diagnostic traits were found on the bones of MPCA-Pv 803, properly demonstrating its distinctiveness.
Description
In their paper describing Mapusaurus, Coria and Currie estimated that the specimens found in the bonebed measured between in length. The smallest specimen is represented by an left dentary, while the largest is known from a left femur. Subsequent maximum size estimates vary from around , and weight estimates range from .
Skull and dentition
While most carcharodontosaurids are known from few or fragmentary skull remains, Mapusaurus' is relatively complete. The skull of Mapusaurus was deeper and narrower than that of Giganotosaurus, due to the comparative shortness of the maxillae and slenderness of the . These nasals were very rugose, as in Carcharodontosaurus, Giganotosaurus, Meraxes and Tameryraptor, though lack any expansion of the narial (a depression in the nasal bone). The lateral (external, or outer) surface of the maxilla in many carcharodontosaurids (i.e. Carcharodontosaurus, Giganotosaurus, Meraxes and Tameryraptor) had a rough texture, and the same is true of Mapusaurus. Whereas the rugosity of Giganotosaurus maxilla stopped shortly posterior to (behind) the nasal opening, that of Mapusaurus continued for most of the bone's length. The bar between the antorbital (an opening in the skull in front of the orbit) and , the so-called interfenestral strut, was fairly wide in comparison to other carcharodontosaurids. Whereas many derived carnosaurs had several openings in the maxilla anterior to (in front of) the antorbital fenestra, in Mapusaurus, the maxillary fenestra was the only one, and it disappeared with growth. A long sinuous ridge running horizontally across the outer face of the maxilla is known in Mapusaurus, as well as carcharodontosaurids like Acrocanthosaurus. The antorbital fossa was about equal in size to that of Carcharodontosaurus and Giganotosaurus. The orbit was partly divided into upper and lower sections by projections of the lacrimal and postorbital bones. Like in many derived carcharodontosaurids, such as Meraxes, the lateral postorbital surface bore a robust brow horn. The lacrimals and prefrontal bones were fused, as in many theropods, including Giganotosaurus. The lacrimals of the two genera differed in that Mapusaurus lacrimal had a rugose dorsal (upper) surface, whereas that of Giganotosaurus bore deep grooves. Mapusaurus teeth were similar to those of other carcharodontosaurids, being flat, narrow and blade-like and bearing 10–12 denticles per , as opposed to 13–15 denticles per 5 mm in Acrocanthosaurus. There were 12 alveoli (tooth sockets) in each maxilla, as opposed to 14 in Carcharodontosaurus.
The (tooth-bearing part of the lower jaw) of Mapusaurus was similar to that of Giganotosaurus in that it wider at the anterior end than in most other theropods; this was partially composed of a large flange (growth of bone) on the mandibular symphysis (the area where the mandibles meet). While loosely similar expansions are seen in other groups and genera, such as Tyrannosaurus, in Mapusaurus (and by extension, presumably, other carcharodontosaurids), the presence of this distinctive flange in a juvenile suggests that it was not controlled by ontogeny. In both Mapusaurus and Giganotosaurus, the Meckelian groove is fairly shallow, though that of the former genus was positioned more dorsally. A partial surangular is known from a juvenile Mapusaurus specimen, which is identical to the corresponding bone in Giganotosaurus. The angular bone was strengthened by a thick ventral margin, which contributed to the ventral portion of the mandible. Each dentary appears to have had fifteen teeth.
Axial skeleton