Suchosaurus

localities of southeast England; 3 is the Tilgate Forest quarry where Suchosaurus was found The taxonomic history of Suchosaurus begins in 1822, when British palaeontologist Gideon Mantell and his partner Mary Ann mentioned, in their book The Fossils of the South Downs, teeth that had been discovered by Mantell in a quarry in Tilgate Forest, near Cuckfield in Sussex, England. Based on their morphology, characterized by well-defined lateral ridges, Mantell's mentor William Clift, then curator of the Hunterian Museum, London, suggested that these fossils might belong either to a crocodile or to a monitor lizard, the couple favoring the former interpretation. In June 1823, Scottish geologist Charles Lyell brought the fossils described by the Mantell couple to Paris, France, so that they could be examined by French naturalist Georges Cuvier. In 1827, Mantell redescribed these fossils in greater detail, distinguishing them as belonging to two types of crocodilians, separating the blunt- teeth from the more slender and recurved ones, which he considered comparable to those of gharials. Although he did not erect any scientific name to formalize this observation, he attributed the teeth of the second category to a crocodilian that he referred to by the common name "gavial of Tilgate Forest". of the holotype tooth of S. cultridens In 1841, British palaeontologist Richard Owen established, within the genus Crocodilus, a subgenus and species he named Crocodilus (Suchosaurus) cultridens, based on the fossils discovered by Mantell. The name Suchosaurus comes from the Ancient Greek σοῦχος (souchos, "crocodile"), and σαῦρος (saûros, "lizard"), reflecting its then-accepted affinities with crocodilians. In his work published the following year (the same work in which he first coined the term Dinosauria), Owen retained Suchosaurus at the rank of subgenus and also referred to it two fossil vertebrae collected by Mantell, without, however, providing any justification for this association. He further considered the expression "gavial of Tilgate Forest" to be the vernacular name of this taxon. The holotype, cited in the scientific literature since the Cuvier's work, consists of a single tooth broken at the upper third of the crown. Like many fossils discovered at Tilgate, this tooth is now housed in the palaeontological collections of the Natural History Museum, London. The original specimen number was BMNH R36536, In the years following the publication of Owen’s two works, Suchosaurus was elevated to the rank of a distinct genus by Owen himself as well as by other authors. In a work published posthumously in 1867, the French naturalist Charles Léopold Laurillard nevertheless made a taxonomic error regarding this animal: although he acknowledged that Suchosaurus had been named by Owen, he nonetheless attributed the origin of the species name cultridens to Mantell. In the second volume of his 1884 work, when he figured again this latter, Owen named it as S. laevidens. This designation was probably a lapsus calami, as he did not use this specific epithet elsewhere in the same publication. a position likewise adopted in 1890 by British palaeontologists Arthur Smith Woodward and Charles Davies Sherborn. In 1897, French palaeontologist Henri-Émile Sauvage erected the second species, Suchosaurus girardi, on the basis of two jaw fragments and a single tooth discovered by Swiss geologist Paul Choffat at Boca do Chapim, in Portugal. The specific epithet honors the Portuguese naturalist Albert Girard. The two jaw fragments are currently numbered as MG 324 at the in Lisbon. In a conference abstract published in 2013, Portuguese palaeontologist Elisabete Malafaia and her colleagues reported the rediscovery of the isolated tooth in the palaeontological collections of the National Museum of Natural History and Science, Lisbon. Now catalogued as MNHN/UL.I.F2.176, the tooth is among the fossils that were saved from a fire that destroyed a significant part of the museum in 1978. After certain fossil teeth collected in Sussex and on the Isle of Wight were routinely labelled to Suchosaurus, the taxon—then still classified among crocodilians—was only rarely mentioned in the scientific literature after the late 19th century, probably due to the very limited nature of the fossil material. However, these specimens were never described in detail afterwards and appear to have been lost during the Spanish Civil War. at the National Museum of Nature and Science, Tokyo. Based on its dental characteristics, Suchosaurus'' has been reinterpreted as a spinosaurid, and a possible synonymy with the latter has even been suggested In 1986, British palaeontologists Alan Charig and Angela Milner described the theropod dinosaur Baryonyx walkeri on the basis of a relatively well-preserved partial skeleton discovered near the Ockley, in Surrey. Its initial descriptions highlighted distinctive dental characters, which led some authors to assign several isolated teeth uncovered in the Wealden Supergroup of England to this genus. In his 2007 study, Buffetaut considered the teeth of S. girardi very similar to those of Baryonyx (and S. cultridens) except for the stronger development of the tooth crown flutes (or "ribs"; lengthwise ridges), suggesting that the remains belonged to the same genus. Buffetaut agreed with Milner that the teeth of S. cultridens were almost identical to those of B. walkeri, but with a ribbier surface. The former taxon might be a senior synonym of the latter (since it was published first), depending on whether the differences were within a taxon or between different ones. According to Buffetaut, since the holotype specimen of S. cultridens is a single tooth and that of B. walkeri is a skeleton, it would be more practical to retain the newer name. In 2011, Portuguese paleontologist Octávio Mateus and colleagues agreed that Suchosaurus was closely related to Baryonyx, but considered both species in the former genus nomina dubia (dubious names) since their holotype specimens were not considered diagnostic (lacking distinguishing features) and could not be definitely equated with other taxa. However, following its formal reidentification in the early 21st century, Suchosaurus is recognized as the first spinosaurid to have been named, as well as one of the earliest dinosaurs described in the history of paleontology, although it was not initially identified as such. Furthermore, the illustration of the holotype tooth published by Cuvier in 1824 is now regarded as the first printed depiction of a spinosaurid fossil, and as one of the oldest dinosaur figures in general, even though these groups had neither been defined nor named at the time of its publication. == Description ==

of S. cultridens Although known only from very fragmentary fossil remains, Suchosaurus would likely have had an overall morphology broadly similar to that of many other spinosaurids, i. e. large bipedal carnivore with robust forelimbs and an elongated skull resembling that of crocodiles. In 2012, American vertebrate palaeontologist Thomas R. Holtz Jr. tentatively estimated Suchosaurus at around in length and weighing between . And in 2016, Spanish palaeontologists Rubén Molina-Pérez and Asier Larramendi estimated S. cultridens at approximately long, tall at the hips and weighing . When Mantell described in 1827 the assemblage of teeth of the "gavial of Tilgate Forest", now recognized as chimeric, he stated that the largest of these teeth would have belonged to an animal of comparable length, estimated between in length. The dentition of Suchosaurus shows some notable differences between the two species. However, the teeth display only the basic characteristics typical of baryonychines and do not exhibit any diagnostic traits allowing distinction at the generic level, which has led the taxon to be regarded as a nomen dubium. Like Baryonyx, the holotype tooth of S. cultridens is round in cross-section, slightly recurved, and bears numerous flutes on the crown. It differs, however, in having more pronounced fluting and an apparent absence of serrations on the carinae (the anterior and posterior cutting edges of a tooth). Because the carina is strongly worn, it remains difficult to determine whether the tooth was truly devoid of serrations or whether their absence simply results from this wear. The teeth of S. girardi are , being subcircular in cross-section and bearing seven denticles per millimetre, a number comparable to that observed in Baryonyx. The roots, very long and slender, exceed half the length of the crown. The teeth of S. girardi are just as strongly fluted as the holotype of S. cultridens, showing eight longitudinal ridges on their inner surface and an texture that is microscopically wrinkled. Nevertheless, unlike the type species, at least one tooth of S. girardi appears to possess a serrated anterior carina. Little information has been reported about the rare fossil jaw fragments of the holotype of S. girardi because of their very incomplete preservation, but they are understood to represent the right portion of the (the largest bone of the lower jaw in diapsids). ==Classification==

Early classifications Suchosaurus is among the fossil animals that have one longest cases of taxonomic misidentification, having been frequently interpreted as a crocodilian for nearly two centuries. This situation is largely explained by the very limited fossil material then known for spinosaurids, as well as by the morphological similarities between their teeth and those of crocodilians. However, the position of this taxon within crocodilians itself varied repeatedly throughout its taxonomic history. In 1842, one year after Suchosaurus was formally named, Owen rejected von Meyer's classification, citing the absence of skeletal remains attributable to teleosaurians in the Wealden deposits to support his interpretation. During the 19th and 20th centuries, the majority of the scientific community followed Owen's view regarding the crocodilian nature of Suchosaurus. Depending on the classification, the genus was assigned to the Goniopholididae (or considered close to Goniopholis), to the Pholidosauridae, or treated as incertae sedis, with the second assignment being the most widely accepted during the 20th century. Nevertheless, some 19th century authors did not adopt this interpretation. This now-obsolete group included numerous archosaurs that are today assigned to phytosaurs, rauisuchians, and dinosaurs. However, he later reclassified it among crocodilians, in accordance with the view that had become widely accepted within the scientific community. In 1879, the British geologist John Whitaker Hulke also expressed doubts about the crocodilian nature of Suchosaurus. In describing the ornithopod Vectisaurus (now regarded as a synonym of Mantellisaurus), he compared its vertebrae to those attributed to Suchosaurus by Owen, suggesting that the latter might in fact be a dinosaur. One year earlier, in a new description of Suchosaurus, Owen himself had mentioned possible affinities with dinosaurs. One of the main characteristics used to distinguish baryonychines from spinosaurines is the frequent presence of fine serrations on their teeth. Nevertheless, in 2010, the British palaeontologist Roger Benson regarded Spinosauroidea as a junior synonym of Megalosauroidea, which had been established earlier, although he retained the traditional classification of the Spinosauridae. A 2017 study by the Brazilian palaeontologists Marcos A. F. Sales and Cesar L. Schultz found that the clade Baryonychinae was not well supported, since serrated teeth may be an ancestral trait among spinosaurids. Nevertheless, the validity of this group is still maintained in many subsequent studies. == Palaeobiology ==

Though few skull material has been discovered for Suchosaurus, Most theropod dinosaurs have recurved, blade-like teeth with serrated carinae for slicing through flesh, whereas spinosaurid teeth evolved to be straighter, more conical, and have small or nonexistent serrations. Such dentition is seen in living piscivorous predators such as gharials, as it is better suited for piercing and maintaining grip on slippery aquatic prey so it can be swallowed whole, rather than torn apart. == Palaeoecology ==

England The original stratigraphic position of the holotype tooth of S. cultridens does not appear to be unanimously agreed upon among geologists. The specimen comes from the Grinstead Clay, a unit dated to the late Valanginian of the Early Cretaceous, whose status varies according to authors: it is considered either as a distinct geological formation or a member of the Tunbridge Wells Sand Formation. In any case, it originates from the fossil record of the Wealden Supergroup of England, a geological group divided into numerous formations with ages that are both older and younger. Portugal S. girardi is known from the Papo Seco Formation, which dates to the early Barremian age of the Early Cretaceous epoch. Many other fossil taxa have been found in localities of the Papo Seco Formation. and a coelurosaurian. Two theropod footprint types have been found, one that is smaller with narrow digits, belonging to an indeterminate theropod, and another referrable to the ichnogenus Megalosauripus, likely produced by a carnosaurian theropod such as a spinosaurid. The other dinosaurs present in the formation are sauropods and ornithopods. Sauropod material includes the remains of indeterminate sauropods, eusauropods, titanosauriforms, and titanosaurs. The only formally described ornithopod genus is Cariocecus, A probable ornithopod footprint has also been described from the formation. Non-dinosaurian vertebrate fossils from the Papo Seco Formation include teeth referred to ornithocheirid and ctenochasmatoid pterosaurs, cf. Anteophthalmosuchus sp. (a goniopholidid crocodyliform), and cf. Lepidotes sp. (a semionotiform actinopterygian) and carapace fragments and a partial radius of pancheloniids (sea turtles). == References ==