Langstonia

Langstonia (meaning "[crocodile] of Langston", in honor of paleontologist Wann Langston, Jr.) is an extinct genus of notosuchian crocodylomorph of the family Sebecidae. It lived in the middle Miocene (specifically in the Laventan land-mammal age), in the "Monkey Beds" of the Colombian Villavieja Formation. "Langstonia" was named in 2007 by Alfredo Paolillo and Omar Linares for fossils originally described by Langston in 1965 as "Sebecus huilensis". Thus, the type species is "L. huilensis".
Discovery and naming.
The first fossils of "Langstonia" were discovered in the province of Huila in Colombia by the Spanish geologist José Royo y Gómez, during the expeditions in the region by the American paleontologist Robert Stirton. They were found in the area called the Tatacoa Desert at the locality V-4517, characterized by gray claystone overlying sandstone sediments. These have been named the Honda Group, of the La Venta fauna, the geological formation named the "lechos de monos" (Monkey Beds) in 1945. Many of the remains discovered were then be sent to the collections of the Museum of Paleontology at the University of California, Berkeley (UCMP), where they are still housed. The description of the specimens did not come until 1965, when the American paleontologist Wann Langston Jr. published his monograph "Fossil Crocodylians from Colombia", in which he made a detailed analysis of several fossils of crocodylomorphs in Colombia, including the remains of other species as "Purussaurus neivensis", "Mourasuchus atopus", "Gryposuchus colombianus" and "Charactosuchus fieldsi" (plus a possible dyrosaurid) As for the sebecid material he designated the dentary UCMP 37877 as the holotype of a new species a fragmentary taxon, which he called "Sebecus huilensis"; thus extending the time range of this genus and the family, hitherto known only from remains of the Eocene of Argentina. Langston gave the taxon a new species considering that besides being larger, as the dentary fragment is 68% larger than the Argentine species, "S. icaeorhinus", it was also proportionally thinner, and had with more recurved teeth being laterally compressed. Additionally Langston referred a series of zyphodont teeth in the area found this species, with some teeth referred to as similar but classified generally to "Sebecus" sp., which do not come from the Miocene but the Eocene, found in the department of Santander in Colombia.
Subsequently, Éric Buffetaut and Robert Hoffstetter (1977) reported from the Ipururo Formation in the Amazon region of Peru the presence of a huge cranial portion (area of the snout), referring it to this genus, and although its age coincides with "S. huilensis", distinguished it through it being larger and more robust.
Arthur Busbey (1986) later brought new remains of the species also from the "Monkey Beds" of Huila in Colombia, this time a fragment of premaxilla, smaller than " S. icaeorhinus", and equally thin. He also described the first remains of the jugal bone, the suspensory and retroarticular joint in the jaw, and a fragment of bone scute (osteoderm), which were the earliest known for this family. Busbey also ruled out the Peruvian fossil belonging to "S. huilensis", based on its unique anatomy, less spaced teeth and a wider nose.
Langston, along with the Argentine paleontologist Zulma Gasparini, reported new remains of the species in a contribution on fossil crocodylomorphs of Colombia for the book "Vertebrate Paleontology of the Neotropics: The Miocene Fauna of La Venta" (1997). In this case it would be new specimens of teeth, a somewhat fuller premaxilla, an anterior fragment of dentary, and two vertebrae: a sacral and a caudal, which also were unknown to this group. The specimens discovered on this occasion were deposited in the Geological Museum of Ingeominas (previous name of Colombian Geological Service).
Moreover, Alfredo Paolillo and Omar Linares described a new genus of a large Venezuelan Miocene sebecid, "Barinasuchus" of Venezuela. In their article they considered that the traits of two species of "Sebecus", "S. huilensis" and "S. querejazus" of Paleocene of Bolivia, and their age justified the creation of separate genres for both: "S. huilensis" was given the genus "Langstonia", in honor of its initial descriptor and his "(..)advances in knowledge of crocodylians of Tertiary Colombia in particular and South America in general", while "S. querejazus" was renamed "Zulmasuchus", although some authors (, and ) still maintain both species within "Sebecus". Paolillo and Linares also clarified the status of the Peruvian fossil before assigned to the species, assigning it to "Barinasuchus", although this does not rule out its presence in more southern areas; in the area of the Peruvian Amazon known as the Fitzcarrald Arch has been found a characteristically flattened tooth from the middle Miocene therefore assigned to "Langstonia".
Finally, a premaxilla and maxilla fragment found in Itaboraí Basin in Brazil dating from the Middle Paleocene (and where have been found fossils of other sebecids) has been classified as related to this species, under the name of "Sebecus" cf. "huilensis", whose main features are very similar to "Langstonia", suggesting that the latter is part of a lineage of sebecids with an extensive temporal and geographical record.
Specimens known.
Here is a list of specimens assigned to the species, with a brief description of these. They are grouped according to the institution in which they are preserved:
Museum of Paleontology at the University of California.
Not all materials from this collection were assigned to " Langstonia huilensis " but are included because of their similar morphology.
Paleobiology.
Due to the fragmentary remains generally known for this family, its possible only describe some general aspects of the appearance and biology of "Langstonia". As mentioned above, the fossil type of the species is larger than "Sebecus icaeorhinus" with jaws and teeth even more flattened, although its general proportions are reminiscent of this species, which suggests that their skull would be higher and laterally flattened, in contrast to modern crocodilians, which generally have a horizontally flattened skull with conical teeth. Teeth are of the zyphodont kind, with very flattened sides, slightly curved back and with serrated edges with small denticles (between 5-6 denticles per millimeter in the teeth of this genus) and also without any grooves on its surface. This type of teeth appears in the close relatives of sebecids, the peirosaurids and baurusuchids of the Cretaceous and some crocodilians of the Cenozoic as the pristichampsids and some mekosuchines. These forms were land animals that used their teeth to cut and tear their prey, because the traditional method of capture of the crocodiles, using its pressure force to retain and drown his victims is not viable on land; these crocodylomorphs also had more elongated limbs, stiff back, ideal to hold the weight and give strength to run. Langston had already suggested that these teeth were indicative that this animal had more terrestrial habits than those of existing species and the Miocene contemporary crocodylians, and in the modern world only could be vaguely compared with the less aquatic habits of the caimans of the genus "Paleosuchus", which have a higher muzzle and a higher degree of ossification around the eye socket, so that they partially resemble sebecids. Busbey suggested the fact that his skull was high implied that these animals seek not to make pressure during the bite indefinitely, but to produce cuts then back quickly so that the bleeding weakens their prey slowly up to devour, similar to what has been thought to be the case for the extant Komodo dragon, thereby adopting a strategy of stalking in areas where prey transit frequently.
Since in the fauna of La Venta, although there were some large mammalian predators (sparassodonts, "Lycopsis longirostrus" and "Dukecynus"), neither of them equated in size to the contemporary crocodylomorphs, , and given the absence of large predatory birds phorusrhacids as in the southern part of the continent, these sebecids were probably the terrestrial apex predators in its ecosystem. The fossils found of other species - big fishes, manatees, large browsing meridiungulates as "Granastrapotherium" and "Huilatherium", and some grazers as "Pericotoxodon" - indicate that the climate was warm and humid with heavy rainfall and with droughts periods no extending beyond 3–4 months, consisting of watersheds, forests and certain adjacent areas of open grasslands where it could hunt down a large variety of megafauna.
The disappearance of the system of large rivers of the Amazon lake system and the gradual uplift of the Andes caused major ecological changes in South America in the mid-Miocene. The last sebecids, "Langstonia" and "Barinasuchus" were likely apex predators in their environment, and as an effect they would be particularly susceptible to ecological changes that caused other lineages, particularly hoofed mammals (such as groups Astrapotheria, Leontiniidae, Adianthidae and Notohippidae) to die out, thus leading to extinction to the last notosuchians crocodilomorphs of the world.
Phylogeny.
"Langstonia" is considered part of Sebecosuchia, a lineage of ziphodont terrestrial crocodylomorphs forming part of a separate lineage of the southern continent of Gondwana. As noted earlier, this species formerly part of the genus "Sebecus" and phylogenetic analyzes have consistently shown that these forms a clade within Sebecidae next to "S. icaeorhinus" and "Zulmasuchus", not so closely related to "Barinasuchus" and "Bretesuchus". Cladogram based on .