Monster of Aramberri
The "Monster of Aramberri" is an informal name given to a fossil skeleton of a very large pliosaur since numbered as UANL-FCT-R2, of which the first remains were discovered in 1985 near the town of Aramberri, Mexico. In scientific literature, some authors also refer to it as the Aramberri pliosaur or the Aramberri specimen. Initially interpreted as a dinosaur in 1988, it was formally reidentified as a marine reptile of the family Pliosauridae in a short 2001 publication. Initially, two concretions only containing the animal's fossils were discovered, with one of the two—containing the fossils of a rostrum and teeth—later noted as lost in the first in-depth study conducted on the specimen in 2003. During the 2000s, a new excavation campaign unearthed several additional fossils of the animal. Subsequently, most of these fossils were sent to Karlsruhe State Museum of Natural History, Germany, to be prepared, before returning them in 2012 to the Autonomous University of Nuevo León, where they are mainly stored. Another significant portion of the fossils are currently stored in the Desert Museum of Saltillo.
The "Monster of Aramberri" is one of the largest pliosaurs ever discovered, but estimates of its size have dropped considerably over the years. Initial estimates set a length of around, with maximum proposals going up to or even according to some media. Its former interpretation as a juvenile as well as its incorrect attribution with Liopleurodon—then incorrectly portrayed in the 1999 BBC documentary series Walking with Dinosaurs—would probably have been the origin of the over-exaggeration of its size. Most recent accurate size estimates put fixes the specimen at around. Nevertheless, the animal would have an approximately long mandible, and the large teeth, since lost, would have possessed two sharp edges.
Since 2013, the "Monster of Aramberri" is viewed as a representative of the Thalassophonea, a derived clade of pliosaurids characterized by a short neck and a large, elongated skull. The gastralia of the Aramberri pliosaur possess traits that could be diagnostic for a distinct pliosaurid lineage that may soon be described. In the trunk, the Aramberri pliosaur preserves fossils of what appears to be an ichthyosaur, suggesting that this was its last prey consumed before its death. Two known cranial fragments of the animal also preserve bite marks that would have been made by another, more imposing pliosaur. The La Caja Formation, where the "Monster of Aramberri" was discovered, contains abundant marine fossils from a shallow environment dating from the Kimmeridgian stage of the Late Jurassic. It shared its habitat with a variety of other animals, including invertebrates, fish, thalattosuchians, ichthyosaurs, and other plesiosaurs.
History of discovery
During an excursion conducted in the fall of 1985, in the Mexican state of Nuevo León, a geology student of the Autonomous University of Nuevo León reported the discovery of a large concretion of fossils in the Sierra Madre Oriental, at around northwest of the municipality of Aramberri. During the exhumation, a second, equally large concretion was discovered by paleontologists. The inaccessibility of the place and the fossils collected at the time weighing around in total, prevented researchers from moving it immediately. The following year, the discovered material was finally moved over via fairly complex technical processes before reaching a road facilitating transport. Subsequently, the two large concretions were sent to the Faculty of Earth Sciences of the Autonomous University of Nuevo León, where the fossils concerned are all cataloged under the specimen number UANL-FCT-R2. The preparation of the first fossil concretion lasted two months, and when this was finalized, it was fixed vertically on a poured concrete base. The first concretion contained numerous postcranial elements which include, among other elements, seven pectoral vertebrae, fragments of coracoids and a left scapula, ribs as well as gastralia. The second concretion contained a rostrum with teeth. These fossils were first mentioned in the scientific literature in 1988 by German geologist Walter Hähnel, one of the researchers who participated in their exhumations. In his paper, he indicated that the discovery had been made stratigraphically within the La Casita Formation, a Late Jurassic geological formation more precisely dated to the late Kimmeridgian. Despite the fact that the specimen was discovered in marine sediments, Hähnel identified it as a carnivorous dinosaur with a length ranging between.The main fossils of the specimen were rediscovered during the autumn 2000 and, based on their vertebral morphology, were reidentified as belonging to a large marine reptile of the family Pliosauridae. The discovery was announced in September 2001 by German paleontologist and colleagues in a brief publication, in which they gived to this specimen the informal nickname of the "Monster of Aramberri". On December 28, 2002, the German magazine Der Spiegel published an article about the discovery, adopting this nickname and highlighting the completeness and remarkable size of the marine reptile. This coverage drew the attention of international media, to the point that the nickname has since been widely used by both journalists and scientists. The announced study describing the fossils in more detail was finally published in 2003 and was led by French paleontologist Marie-Céline Buchy and her colleagues. In the 2001 publication, the authors note that the second concretion was not relocated to the university, but it is since the 2003 study where it is noted as lost. Based on the stratigraphic position of various ammonite specimens at the site, the authors of the latter study also revealed that the Aramberri pliosaur was in fact discovered in the La Caja Formation, which dates to the "middle" Kimmeridgian.
From 2001 to 2007, new expeditions carried out in the type locality by Mexican, French and German paleontologists helped by residents of the city, made it possible to exhume the cranial, and caudal|caudal] part of the specimen, and two thirds of the skeleton. Cranial fragments have also been discovered although most of them 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, it seems that 70% of the animal's skeleton is known. In 2003, in order to help paleontologists, the newly elected mayor of Nuevo León sent a helicopter to transport a fossil block weighing a total of. During his campaign the following year, the mayor 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 in Karlsruhe were 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 expressed 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. Although the entire skeleton of the animal has not received detailed descriptions at present, authors have nevertheless described certain parts of the animal. Plesiosaurs are usually categorized as belonging to the small-headed, long-necked "plesiosauromorph" morphotype or the large-headed, short-necked "pliosauromorph" morphotype, the "Monster of Aramberri" belonging to the latter category. Like all plesiosaurs, it had a short tail, a massive trunk and two pairs of large flippers.Size estimates
The "Monster of Aramberri", as its nickname suggests, is also one of the largest pliosaurs identified to date, but its size estimates have declined considerably over years. Initial estimates putted the size at around long at least, although maximum estimates of up to with a body mass of was also proposed. In 2008, British paleontologist Adam S. Smith and his Irish colleague Gareth J. Dyke, citing the 2003 paper, give a maximum length of. In his 2009 thesis, Australian paleontologist Colin McHenry criticized the initial interpretations, which he finds 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 does not give a precise estimate of the measurements of the specimen. He suggests 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 even been lost like the rostrum and teeth. However, using one of the photographs presented in the 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 have three broken teeth. The teeth are described as massive, reaching about in diameter and being bicarinate. The fossil would also contain an additional tooth probably coming from an opposite jaw. Therefore, it is uncertain whether the rostrum would represents a dentary, a maxilla or premaxilla. Based on a mandible of a large pliosaur preserved at the Oxford University Museum of Natural History in England, the authors estimate that the "Monster of Aramberri" should have a mandible and a skull up to long. The animal's teeth would be conical in shape and the largest ones would have reached in length.Postcranial skeleton
Currently, the majority of the postcranial material of the Aramberri pliosaur has not yet been described due to the fact that preparations are not currently finalized. 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. The latter 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 us from saying more about their morphology. The rare 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
The "Monster of Aramberri" was initially described as a large dinosaur by Hähnel in 1988 without more precise classifications, its carnivorous nature suggesting a probable theropod. Paleontologists discovered that it was actually a pliosaur from the family Pliosauridae in the early 2000s. According to Buchy et al., its affiliation is based on the presence of two vertebral characteristics unique to this group. The first feature is the foramina that are present on the ventral side of each vertebra, vertebrae that are pulley-shaped. The second is the rib joints on the lateral side of some vertebrae located near the neural arches, typical of the pectoral vertebrae of plesiosaurs. The lack of proper cranial diagnosis and remaining undescribed fossils prevent it from being assigned to any European pliosaurid taxon.In 2013, British paleontologist Roger B. J. Benson and his American colleague Patrick S. Druckenmiller named a new clade within Pliosauridae, Thalassophonea. This clade included the "classic", short-necked pliosaurids while excluding the earlier, long-necked, more gracile forms. 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 would be related to Kronosaurus. The group that currently includes Kronosaurus, known as Brachaucheninae, only includes representatives that lived during the Cretaceous, the Aramberri specimen being dated to the Upper Jurassic. In 2009, based on its vertebral morphology, McHenry did not consider the Aramberri specimen to be close to Kronosaurus, casting doubt on the classification later proposed by Frey and Stinnesbeck. Nevertheless, both authors note that the notable anatomy of the gastralia could be diagnostic for the specimen and therefore establish it within a distinct taxon for future studies.
Paleobiology
Ontogeny
In their 2003 study, Buchy and his colleagues noted that the seventh neural arch is not fused with the vertebrae, the other neural arches being incomplete to allow similar observations. Plesiosaur specimens with neural arches not fused to the vertebrae are generally seen as juveniles, and the authors therefore consider the Aramberri specimen to be one as well. However, Buchy questioned this interpretation in 2007, citing that very few pliosaur fossils have been found with neural arches fused to the vertebrae, and that these were most likely juvenile traits carried over into adulthood. Many subsequent works share identical conclusions. Based on these observations, Frey and Stinnesbeck then interpreted the specimen as being a subadult in 2014. Ten years later, Zhao, sharing the same observations, considers the specimen as an adult due to its rather imposing size.Bite marks
Some cranial fragments of the Aramberri pliosaur, the jugal and the pterygoid, show bite marks showing that the specimen would have been attacked at the back of the head. The bite mark present on the pterygoid shows that it would have been made by a tooth whose crown is estimated according to sources at 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 would have been perforated by a tooth which would have reached two-thirds of that which had touched the pterygoid, but which would have probably been fatal because there are no signs of healing. The animal that would have injured or even 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
At the trunk level, the Aramberri specimen shows what appear to be poorly preserved bones with etching traces from a possible ichthyosaur. The ichthyosaur in question would likely have been the specimen's last meal before its death, but further studies are needed to confirm this.Paleoecology
The La Caja Formation, where the "Monster of Aramberri" was discovered, would have been 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 imposing pliosaurid in this region is an argument in favor of 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 formation contains a number of other marine reptiles from various groups. Among the plesiosaurs, in addition to the "Monster of Aramberri", two other additional specimens of indeterminate pliosaurids are known. Apart from these three pliosaurids, the only known plesiosaurian is an possible elasmosaurid also noted as indeterminate. Thalattosuchians include one unattributed specimen and Cricosaurus saltillensis. The first thalattosuchian cited 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
Most media put the size of the Aramberri pliosaur at 19-20 meters long and consider it as a representative of Liopleurodon. The depiction of Liopleurodon in the 1999 BBC documentary series Walking with Dinosaurs, where it is depicted as reaching in length and weighing 150 metric tons, and its former juvenile interpretation, are possible causes of these erroneous estimates and attributions. However, the largest known specimen of Liopleurodon would have reached in length with a body mass of 6.2 metric tons, and it is admitted that the Aramberri specimen is not a representative of this genus. Some authors humorously referred this tendency to over-exaggerate the size of Liopleurodon and the Aramberri specimen as "godzillaisation".In 2017, a life-sized restoration of the "Monster of Aramberri" was carried out on the basis of the dimensions of the preserved fossils. It has since been exhibited at the Papalote Museo del Niño, in Monterrey.