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Mapusaurus
Carcharodontosaurid dinosaur genus from the Late Cretaceous From Wikipedia, the free encyclopedia
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Mapusaurus (lit. 'earth lizard') is a genus of giant carcharodontosaurid carnosaurian dinosaur that lived in Argentina during the Cenomanian–Turonian ages of the Late 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.
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 10.2 m (33 ft) and a mass of 3 t (6,600 lb). Subsequent works have given maximum size estimates of 10.2–12.6 metres (33–41 ft) and 3–6 t (6,600–13,200 lb) 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.
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Discovery
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Mapusaurus was excavated between 1997 and 2001, by the Argentinian-Canadian Dinosaur Project, from an exposure of the Huincul Formation (late Cenomanian–Turonian[2]) at Cañadón del Gato. Initially, it was believed that the remains of a single large theropod were present at the site, though in time, it was determined that between seven and nine were present. All were identified as belonging to a single species, which was described by paleontologists Rodolfo Coria and Philip J.Currie in 2006,[3][4][5][6][7] and named Mapusaurus roseae. The name Mapusaurus is derived from the Mapuche word mapu, meaning 'of the Land' or 'of the Earth' and the Greek sauros, meaning 'lizard'. The type species, Mapusaurus 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 these fossils.[3]
The designated holotype for the genus and type species, Mapusaurus roseae, is an isolated right nasal (MCF-PVPH-108.1, Museo Carmen Funes, Paleontología de Vertebrados, Plaza Huincul, Neuquén). Twelve paratypes have been designated, based on additional isolated skeletal elements. Taken together, the many individual elements recovered from the Mapusaurus bone bed represent most of the skeleton.[3]
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Description
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In their paper describing Mapusaurus, Coria and Currie estimated that the specimens found in the bonebed measured between 5.5–10.2 m (18–33 ft) in length, with the former being based on a left dentary (MCF PVPH-108.3) and the latter being based on a left femur (MCF-PVPH-108.203).[3] Subsequent maximum size estimates vary from around 10.2–12.6 metres (33–41 ft), and weight estimates range from 3–6 t (6,600–13,200 lb).[3][8][9][10]
Skull and dentition
The skull of Mapusaurus was deeper and narrower than that of Giganotosaurus, due to the comparative shortness of the maxillae and slenderness of the nasal bones.[3] The nasals were very rugose, as in Carcharodontosaurus, Giganotosaurus, Meraxes, and Tameryraptor. The lateral (external, or outer) surface of the maxilla in many carcharodontosaurids (i.e. Carcharodontosaurus, Giganotosaurus, Meraxes, and Tameryraptor) had a rough texture,[11] and the same is true of Mapusaurus.[3][12] 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 and maxillary fenestrae, 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,[3] and it disappeared with growth.[12] The antorbital fossa was about equal in size to that of Carcharodontosaurus and Giganotosaurus. The orbit, or eye socket, was partly divided into upper and lower sections by projections of the lacrimal and postorbital bones.[3] Like in many derived carcharodontosaurids, such as Meraxes, the lateral postorbital surface bore a robust brow horn.[2] 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 5 mm (0.20 in), 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.[3]
The dentary of Mapusaurus, the part of the lower jaw which bore teeth in life, was similar to that of Giganotosaurus in that it expanded anteriorly more than in most other theropods; this is contributed to by a ventral flange on the mandibular symphysis. 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.[3]
Axial skeleton
The vertebral column of Mapusaurus closely resembled that of Giganotosaurus. As in most carnosaurs, the neural arches, the masses of bone or cartilage posterior to the main vertebral bodies, were inclined posterodorsally (rearward and upward). The neural spine (the tall projections at the top of each vertebra) of the axis, the second cervical (neck) vertebra, appears to have been longer and more gracile than those of Mapusaurus. There were well-developed laminae between the neural spine and vertebral epiphysis, which are not observed in more basal taxa such as Acrocanthosaurus and Allosaurus. Further back in the cervical column, the neck vertebrae were proportionally shorter and slimmer than those of Giganotosaurus, more closely resembling abelisaurids in their proportions. The neural spines of the dorsal (back) vertebrae were relatively tall and were inclined posteriorly. The more posterior dorsal vertebrae were amphiplatyan, meaning that both anterior and posterior surfaces were flat. Mapusaurus' caudal (tail) vertebrae are well known from various specimens. The neural spines of the mid-caudal vertebrae were low and anteroposteriorly (from front-to-back) elongated. The most posterior one had a low regular neural spine and a second, accessory one anterior to it. The anatomy of the preserved ribs, which resemble those of many other large theropods, suggests that the chest of Mapusaurus would have been deeper than it was wide. Various fragmented gastralia, the bones which would have supported the abdominal organs and served as muscle attachment points, are known, and do not seem to have meaningfully differed from those of other big theropods.[3]
Appendicular skeleton
Mapusaurus' scapula (shoulder blade) was long and gently curved, with a pronounced, sharply offset acromial process, similar to other carnosaurs and tyrannosaurids. It is less robust than that of large ceratosaurs and megalosaurids. The scapula and coracoid were distinct bones, and did not co-ossify into a scapulocoracoid. One partial coracoid is known. A possible furcula is preserved, though there is a possibility that it is a fused pair of gastralia. What is known of the humerus (upper arm bone) based on a right humerus, MCF-PVPH-108.45, was fairly robust. The humerus was around a quarter of the length of the femur, and its arms were thus relatively short. The radius (one of the two forearm bones) was relatively massive. Little is preserved of the manus (hand). The second and third metacarpals (hand bones) appear to have been partly fused, though there is no indication that the first metacarpal had fused with the others. A single manual phalanx (finger bone) is known, as well as a probable ungual phalanx (the bone which would have supported a claw) which may be from the second digit.[3]
The pelvis and hind limbs are very well preserved in comparison to the pectoral girdle and forelimbs. The ratio between the preacetabular and postacetabular lengths of the ilium (the parts before and after the acetabulum) is about the same as in the holotype of Giganotosaurus. At the back of the ilium, near the base of the peduncle where the ischium articulated, there were a series of shallow pits, likely attachment sites for the iliofemoralis and caudofemoralis muscles. Three femora (thigh bones) are known. Unlike most other carnosaurs, the fourth trochanter, one of the structures to which the caudofemoralis muscles would have attached, was prominent. It was similar in size to that of Giganotosaurus, though both were exceeded by that of Carcharodontosaurus. Like in Giganotosaurus, the lateral (outer) side of the tibia (one of the lower leg bones) of Mapusaurus extends further down than the medial (inner) side. The fibula, the other lower leg bone, was slightly more gracile than in the holotype of Giganotosaurus. The metatarsals (foot bones) of Mapusaurus were fundamentally to those of other carnosaurs. Eight pedal (foot) phalanges are represented, though no pedal unguals are preserved.[3]
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Paleobiology
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The fossil remains of Mapusaurus were discovered in a bone bed containing at least seven to possibly up to nine individuals of various growth stages.[3][13][12] Coria and Currie speculated that this may represent a long term, possibly coincidental accumulation of carcasses (some sort of predator trap) and may provide clues about Mapusaurus behavior.[3] Other known theropod bone beds and fossil graveyards include those of dromaeosaurids Deinonychus and Utahraptor,[14][15] those of Allosaurus from the Cleveland-Lloyd Dinosaur Quarry of Utah,[16] and those of tyrannosaurids Teratophoneus, Albertosaurus and Daspletosaurus.[17]
Paleontologist Rodolfo Coria, of the Museo Carmen Funes, contrary to his published article, repeated in a press-conference earlier suggestions that this congregation of fossil bones may indicate that Mapusaurus like Giganotosaurus also hunted in groups and worked together to take down large prey, such as the immense sauropod Argentinosaurus.[18][19]: 206–207 If so, this would be the first substantive evidence of gregarious behavior by large theropods other than Tyrannosaurus rex, although whether they might have hunted in organized packs (as wolves and lions do) or simply attacked in a mob, is unknown. Through the study of bonebed of at least nine Mapusaurus individuals from the Canadon Del Gato site in Neuquén Province, Argentina, researchers have discovered that their skeletal abnormalities were rare but present, containing trauma being the most common cause. meaning that the predatory animal was living in that of a hazardous and perilous lifestyle.[20] The authors interpreted the depositional environment of the Huincul Formation at the Cañadón del Gato locality as a freshwater paleochannel deposit, "laid down by an ephemeral or seasonal stream in a region with arid or semi-arid climate".[3] This bone bed is especially interesting, in light of the overall scarcity of fossilized bone within the Huincul Formation. An ontogenetic study by Juan Ignacio Canale and colleagues in 2014 found that Mapusaurus displayed heterochrony, an evolutionary condition in which the animals may retain an ancestral characteristic during one stage of their life, but lose it as they develop. In Mapusaurus, the maxillary fenestrae are present in younger individuals, but gradually disappear as they mature.[12]
A biomechanical model of Tyrannosaurus presented by William I. Sellers and colleagues in 2017 suggested that speeds above 11 mph (18 km/h) would probably have shattered the leg bones of Tyrannosaurus. The finding may mean that running was also not possible for other giant theropod dinosaurs like Giganotosaurus, Mapusaurus and Acrocanthosaurus.[21]
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Classification
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Cladistic analysis carried out by Coria and Currie definitively showed that Mapusaurus is nested within the clade Carcharodontosauridae. The authors noted that the structure of the femur suggests a closer relationship with Giganotosaurus than either taxon shares with Carcharodontosaurus. They created a new monophyletic taxon based on this relationship, the subfamily Giganotosaurinae, defined as all carcharodontosaurids closer to Giganotosaurus and Mapusaurus than to Carcharodontosaurus. They tentatively included the genus Tyrannotitan in this new subfamily, pending publication of more detailed descriptions of the known specimens of that form.[3]
In their 2022 description of the large carcharodontosaurine Meraxes, Juan I. Canale and colleagues recovered the following relationships for Mapusaurus and the Giganotosaurini.[22]
In his 2024 review of theropod relationships, Cau recovered similar results, with Tyrannotitan as the sister taxon to the clade formed by Mapusaurus and Giganotosaurus. His results are displayed in the cladogram below:[23]
| Carcharodontosauridae |
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Paleoenvironment
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Taurovenator was discovered in the Argentine Province of Neuquén. It was found in the Huincul Formation, a rock formation bordering the Río Limay Subgroup, the latter of which is a subdivision of the Neuquén Group. This unit is located in the Neuquén Basin in Patagonia. The Huincul Formation is composed of yellowish and greenish sandstones of fine-to-medium grain, some of which are tuffaceous.[24] These deposits were laid down during the Upper Cretaceous, either in the middle Cenomanian to early Turonian stages[25] or the early Turonian to late Santonian.[26] The deposits represent the drainage system of a braided river.[27]
Fossilised pollen indicates a wide variety of plants were present in the Huincul Formation. A study of the El Zampal section of the formation found hornworts, liverworts, ferns, Selaginellales, possible Noeggerathiales, gymnosperms (including gnetophytes and conifers), and angiosperms (flowering plants), in addition to several pollen grains of unknown affinities.[28] The Huincul Formation is among the richest Patagonian vertebrate associations, preserving fish including dipnoans and gar, chelid turtles, squamates, sphenodonts, neosuchian crocodilians, and a wide variety of dinosaurs.[25][29] Vertebrates are most commonly found in the lower, and therefore older, part of the formation.[30]
In addition to Mapusaurus, the theropods of the Huincul Formation are represented by the other giant carcharodontosaurids Meraxes and Taurovenator, abelisaurids including Skorpiovenator,[31] Ilokelesia, and Tralkasaurus,[32] noasaurids such as Huinculsaurus,[33] paravians such as Overoraptor,[34] and other theropods such as Aoniraptor and Gualicho[35] have also been discovered there.[25] Several iguanodonts are also present in the Huincul Formation.[24] The sauropods of the Huincul Formation are represented by the titanosaurs Argentinosaurus and Choconsaurus,[36] and several rebbachisaurids including Cathartesaura,[37] Limaysaurus,[38][39] and some unnamed species.[30]
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References
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