Monster of Aramberri

, the Mexican mountain range in which the "Monster of Aramberri" was discovered. In the fall of 1985, a geology student from the Autonomous University of Nuevo León discovered a large concretion of fossils during an excursion in the Sierra Madre Oriental, approximately northwest of Aramberri, Nuevo León. During the exhumation, a second, equally large concretion was discovered by paleontologists. The site's inaccessibility and the weight of the collected fossils prevented researchers from moving them immediately. The following year, the discovered material was finally moved over via fairly complex technical processes before reaching a road facilitating transport. A detailed study of the fossils, led by French paleontologist Marie-Céline Buchy and colleagues, was published in 2003. In the 2001 publication, the authors noted that the second concretion was not relocated to the university, and the 2003 study later noted it as lost. Based on the stratigraphic position of various ammonite specimens at the site, the authors of the latter study determined the Aramberri pliosaur was discovered in the La Caja Formation, which dates to the "middle" Kimmeridgian. From 2001 to 2007, new expeditions carried out in the original locality by Mexican, French and German paleontologists helped by residents of the city, made it possible to exhume the caudal part of the specimen, and two thirds of the skeleton. Cranial fragments were also discovered, although most are unidentifiable. Field data even suggested that the fossil specimen would have been technically complete before the erosion of the skull and its exhumation for phosphorite. Ultimately, approximately 70% of the skeleton has been recovered. In 2003, in order to help paleontologists, the newly elected governor of Nuevo León sent a helicopter to transport a fossil block weighing a total of . During his campaign the following year, the governor approved and even completed the construction of a road leading to the excavation site. Once exhumed, most of the fossils were transferred to the Natural History Museum in Karlsruhe, Germany, for preparation. The Karlsruhe Museum could not accommodate more fossils due to the size of the animal, so the remaining material was transferred to the Desert Museum in Saltillo, Coahuila. When the material sent to Karlsruhe was prepared, they were returned to the Faculty of Earth Sciences of the Autonomous University of Nuevo León in 2012, where they have since been stored. Some fossils were temporarily exhibited in 2007 at the Mexican History Museum in Mexico City. The newly discovered and prepared fossils consisted of nine cervical vertebrae preserved on three blocks, additional dorsal vertebrae, ribs and gastralia, a femoral joint head, as well as an almost complete pelvic girdle. The cranial elements identified included a pterygoid, a jugal and part of a maxilla preserving a dental alveolus. The new fossils are still being prepared and should receive much more detailed descriptions in future work. In 2012, Mexican paleontologist Javier Aguilar Pérez suggested that the specimen should receive a skeletal mount formed from the fossils once their preparations are completed. Furthermore, he also expressed that new cranial fragments should be found in the field where the specimen was discovered, but no expedition has apparently been sent since. ==Description==

The Aramberri specimen is one of the most complete large pliosaurs ever discovered. In his 2009 thesis, Australian paleontologist Colin McHenry criticized the initial interpretations, which he found very exaggerated. Comparing the Aramberri specimen with the fossil material attributed to the Australian pliosaurid Kronosaurus, he reduced its size to between for a body mass of between . In 2014, Frey and Wolfgang Stinnesbeck increased the length of the specimen slightly to between . In 2021, German paleontologists Frederik Spindler and Martin Mattes further reduced the size of this specimen to between long. In 2024, Chinese paleontologist Ruizhe Jackevan Zhao did not give a precise estimate of the measurements of the specimen. He suggested instead, based on vertebral dimensions, that it would have been similar in size to Pliosaurus funkei, which according to his model was approximately long with a body mass of . The same year, Australian biologist Joel H. Gayford and his colleagues estimated that the animal would have reached approximately in length. Skull Relatively few of the animal's cranial bones have been discovered, and some of them have been lost, such as the rostrum and teeth. However, using one of the photographs presented in Hähnel's 1988 publication, Buchy and colleagues gave some comments in their first re-examination of the specimen in 2003. The rostrum is long and has three broken teeth. The teeth are described as massive, reaching about in diameter and being bicarinate (possessing two sharp edges). The fossil also contains an additional tooth probably coming from an opposite jaw. Therefore, it is uncertain whether the rostrum represents a dentary (one bone of the mandible), a maxilla or premaxilla (two bones of the upper jaw). Based on a mandible of a large pliosaur preserved at the Oxford University Museum of Natural History in England, the authors estimated that the "Monster of Aramberri" had a mandible and a skull up to long. The animal's teeth were conical in shape and the largest ones would have reached in length. Postcranial skeleton Much of the postcranial material remains undescribed as its preparation is ongoing. However, much of the material initially discovered and some fossils exhumed and subsequently prepared have been described. The front and back parts of the centra are slightly convex. They are pulley-shaped and vary in length from . The neural spines of the vertebrae are quadrangular in shape in lateral view, reaching high with a length ranging from . The neural tubes are oval in shape, reaching high and wide. The preserved proximal parts of the ribs measure up to , but their state of preservation prevents further description of their morphology. The few ribs associated with the vertebrae have a curved dorsal margin. The femoral head of the "Monster of Aramberri" measures wide; for comparison, a specimen of Liopleurodon measuring long has a femoral head which only reaches . The gastralia have deep, almost circular grooves that are irregularly spaced. These features are not bite marks, and they could prove to be a diagnostic trait of the animal in future studies. ==Classification==

n Liopleurodon, a pliosaurid regularly compared to the "Monster of Aramberri". The "Monster of Aramberri" was initially described as a large dinosaur by Hähnel in 1988 without more precise classifications, Although no study addressing its phylogenetic position has yet been published, the "Monster of Aramberri" has since been considered as a large representative of the group. In 2014, Frey and Stinnesbeck provided a brief description of the Aramberri pliosaur and commented on its hypothetical affinities within the pliosaurid family. The small size of the flippers relative to the body of the animal indicates that the specimen was related to Kronosaurus. The group that currently includes Kronosaurus, known as Brachaucheninae, lived during the Cretaceous, whereas the Aramberri specimen dates to the Late Jurassic. Although Frey and Stinnesbeck later proposed this relationship in 2014, McHenry had already concluded in 2009 that the specimen was not closely related. ==Paleobiology==

Ontogeny In their 2003 study, Buchy and her colleagues noted that the seventh neural arch is not fused with the vertebrae, while the other neural arches were too incomplete to allow for similar observations. Plesiosaur specimens with neural arches not fused to the vertebrae are generally seen as juveniles, and the authors therefore considered the Aramberri specimen to be one as well. In 2014, based on these observations, Frey and Stinnesbeck interpreted the specimen as a subadult. Ten years later, Zhao, sharing the same observations, considered the specimen as an adult due to its large size. Bite marks Some cranial fragments of the Aramberri pliosaur, the jugal and the pterygoid, show bite marks suggesting that the specimen was attacked at the back of the head. The bite mark on the pterygoid indicates the attacking tooth had a crown estimated between , suggesting a total length of the tooth of approximately . Despite the significant injury, the pterygoid shows the presence of a callus, suggesting that the animal may have survived the incident. Conversely, the jugal was perforated by a tooth two-thirds the size of the one that struck the pterygoid, but which was probably fatal because there are no signs of healing. The animal that injured or killed the Aramberri pliosaur would probably have been larger, but the authors did not give estimates of its size in order to avoid speculations. Stomach contents Within the trunk region, the Aramberri specimen shows what appear to be poorly preserved bones, possibly from an ichthyosaur, that exhibit acid etching. The ichthyosaur in question would likely have been the specimen's last meal, though further study is required for confirmation. ==Paleoecology==

The La Caja Formation, where the "Monster of Aramberri" was discovered, was a calm marine environment of shallow depth estimated between , although the proximity of an island is attested by plant deposits probably torn away during rare storms. The presence of this large pliosaurid in the region supports the existence of a connection between the northern Tethyan domain where most of the fossils were found, and the epicontinental seas which covered South America at that time. The formation, dating from the "middle" Kimmeridgian, contains numerous invertebrate fossils, ammonites being the most abundant. Other invertebrates present include belemnites, bivalves, brachiopods, serpulids, radiolarians, and calpionellids. Fossil remains of fish are also known. The unattributed specimen was also discovered during the excavation of the Aramberri pliosaur. The ichthyopterygians known from the La Caja Formation include an indeterminate specimen as well as the ophthalmosaurid Parrassaurus. ==In popular culture==

documentary series Walking with Dinosaurs, where it is depicted as reaching in length and weighing 150 metric tons (165.3 short tons), and its former juvenile interpretation (thus suggesting that contemporary adult specimens would have been much larger), are possible causes of these erroneous estimates and attributions. However, the largest known specimen of Liopleurodon is estimated to have reached in length with a body mass of 6.2 metric tons, and it is now recognized that the Aramberri specimen is not a representative of this genus. ==Notes==