''Augustasaurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

sauropterygian Sauropterygia ("lizard Flipper (anatomy), flippers") is an extinct taxon of diverse, aquatic diapsid reptiles that developed from terrestrial ancestors soon after the Permian–Triassic extinction event, end-Permian extinction and flourished dur ...

s that lived during the

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

in what is now North America. Only one

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

is known, ''A. hagdorni'', described in 1997 from fossils discovered in the

Favret Formation The Favret Formation is a Triassic geologic formation. The Favret outcrops in the Augusta, New Pass and Fish Creek ranges of north central Nevada and consists of limestone, shale and siltstone. Fossil Hill Member The Favret Formation alon ...

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

, USA. ''Augustasaurus'' is a

pistosauroid Pistosauroidea is a group of marine reptiles within the superorder Sauropterygia that first appeared in the latter part of the Early Triassic and were the ancestors of plesiosaurs. Pistosauroids are rare in Triassic marine assemblages, and are re ...

estimated to be long. The

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

has fang-like teeth, indicating a diet of

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

and

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

. Its postcranial anatomy is similar to that of future

plesiosaur The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

s, with which it visibly shares a

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...

according to the most recent

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analyses. The Favret Formation, from which ''Augustasaurus'' is known, contains numerous fossils of

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including mari ...

s dating from the Middle Triassic. The fossils mainly include

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

s, ''Augustasaurus'' being the only sauropterygian to have been identified in the area.

Discovery and naming

The first known

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

of ''Augustasaurus'' was discovered in 1993 in Muller Canyon, in the

Augusta Mountains The Augusta Mountains are a small mountain range in Pershing, Churchill and Lander counties of Nevada.''Nevada Atlas and Gazetteer,'' DeLorme, 8th ed., 2012, p. 37. To the northeast the range merges with the Fish Creek Range. To the north acro ...

located in

, United States. It was excavated in the Fossil Hill Member of the

, a site dating from the Late

to the

. The fossil consists of a partial

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

, cataloged as

FMNH The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educationa ...

PR 1974, having been partly destroyed due to weathering. After analysis, paleontologists , Olivier Cedric Rieppel and Hugo Bucher established it as the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of a new

and

under the name ''Augustasaurus hagdorni''. The genus name is a combination of Augusta and the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

word (''saûros'', "lizard"), all meaning "Augusta lizard", in reference to its type locality. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

is named in honor of the German paleontologist Hans Hagdorn, who participated with the description team in the research of numerous European

s that lived during the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

. In the 1997 paper, the authors mention that the skeleton is not completely prepared and is therefore only partially described. A second study concerning the taxon was published in 2002 and this time concerned the

, which was recovered shortly after the discovery of the partial postcranial skeleton. The skull and the postcranial skeleton are also part of the same individual.

Description

''Augustasaurus'' measured long and weighed . Its

shares many general characteristics with its relative, ''Pistosaurus'', such as tall, blade-like upper temporal arches. The skull's elongated

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

tapers to a dull point, the anterior

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry and

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

have been described as "

fang A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fangs, ...

-like", and the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

makes a box-like suspensorium. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of ''Augustasaurus'' are low with

rugose Rugose means "wrinkled". It may refer to: * Rugosa, an extinct order of coral, whose rugose shape earned it the name * Rugose, adjectival form of rugae Species with "rugose" in their names * ''Idiosoma nigrum'', more commonly, a black rugose tra ...

tops. Its

coracoids A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is not ...

are large plates similar to those in other

plesiosaurs The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

. However, the coracoid foramina are missing from ''Agustasaurus'', in a way similar to those in the

Corosaurus ''Corosaurus'' is an extinct genus of pistosauroid known from Wyoming of the United States. The holotype measured about long, while larger specimens would have belonged to individuals measuring more than long. History of discovery ''Corosauru ...

''. Its

cervical ribs Cervical ribs are the ribs of the neck in many tetrapods. In most mammals, including humans, cervical ribs are not normally present as separate structures. They can, however, occur as a pathology. In humans, pathological cervical ribs are usually no ...

have anterior processes, and like most plesiosaurs, ''Augustasaurus

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e have "thickened transverse processes".

Classification

''Augustasaurus'' belongs to the

Pistosauroidea Pistosauroidea is a group of marine reptiles within the superorder (biology), superorder Sauropterygia that first appeared in the latter part of the Early Triassic and were the ancestors of plesiosaurs. Pistosauroids are rare in Triassic marine a ...

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

, a group of

s including the ancestors of the famous

s. Early descriptions placed ''Augustasaurus'' in the proposed

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Pistosauridae ''Pistosaurus'' (exact etymology uncertain) is an extinct genus of aquatic sauropterygian reptile closely related to plesiosaurs. Fossils have been found in France and Germany, and date to the Middle Triassic. It contains a single species, ''Pis ...

, classified as a

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

Pistosaurus ''Pistosaurus'' (exact etymology uncertain) is an extinct genus of aquatic sauropterygian reptile closely related to plesiosaurs. Fossils have been found in France and Germany, and date to the Middle Triassic. It contains a single species, ''Pi ...

''. However, the

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

between the two genera was no longer supported by Cheng ''et al.'' (2006), where it is now classified as the sister taxon of Plesiosauria. A 2011 study led by Hilary F. Ketchum and Roger B. J. Benson gives a similar

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

result. Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

of pistosauroid relationships from Ketchum & Benson, 2011:

Paleobiology

With its long

neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...

, small head and fang-like teeth, ''Augustasaurus'' would have fed on

and

, in the same way as other pistosauroids.

Palaeoecology

''Augustasaurus'' is known from the

, which, along with the

Prida Formation The Prida Formation is a geologic formation in northwestern Nevada. It preserves fossils dating back to the Triassic period. Fossil Hill Member The Prida Formation, along with the Favret Formation, constitute one of the recognized geologic ...

, constitutes one of the recognized

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

s of the Star Peak Group, located in Nevada. These two formations are linked by a single

member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

, known as the Fossil Hill Member. In the Prida Formation, this member outcrops west of the

Humboldt Range The Humboldt Range is a largely north-south running range of mountains in northwest Nevada, USA, that extend from the town of Imlay in the north to the junction with the West Humboldt Range in the south. It is bordered continuously by Intersta ...

, and extends to the Favret Formation,

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

ping in the Augusta Mountains, where it reaches up to more than wide. Although they are neighbors, the two formations do not share precisely the same age, the Prida one dating from the Middle

, while Favret dates from the Late Anisian, between approximately 244 and 242 million years ago. The significant presence of marine reptiles, ammonites and other

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s in the Fossil Hill Member indicates that the surface waters were well aerated, but there is little animal presence in the

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

zones, with the notable exception of

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

s of the family Halobiidae. The fossils found show that the

stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features ( facies) that characteriz ...

was once a

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

with a stable

food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Position in the food web, or trophic level, is used in ecology to broadly classify organisms as autotrophs or he ...

Bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

are little known and have currently only been discovered in the Favret Formation. Among the fish discovered are the

actinopterygian Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin ...

s ''

Saurichthys ''Saurichthys'' (from , 'lizard' and 'fish') is an extinct genus of predatory Actinopterygii, ray-finned fish from the Triassic period (geology), Period. It is the type genus of the family (taxonomy), family Saurichthyidae (Changhsingian-Ju ...

'' and an undetermined representative, while among the

sarcopterygian Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

s, numerous specimens of indeterminate

coelacanthid Coelacanthidae is an extinct family of coelacanths found in freshwater and marine strata throughout the world, originating during the Permian, and finally dying out during the Jurassic. The modern-day genus ''Latimeria'' is often erroneously tho ...

s are known. The most abundant

s of the Fossil Hill Member are the

s, including the

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

''Thalattoarchon'', ''

Phalarodon ''Phalarodon'' is an extinct genus of mixosaurid ichthyosaur known from the Middle Triassic (247.2-242.0 million years ago). Its name is derived from the Greek φάλαρα (''phálara'') ("boss on the cheek plate of a helmet") and ''odon'' ("to ...

'', '' Omphalosaurus'' and the large ''

Cymbospondylus ''Cymbospondylus'' (meaning "cupped vertebrae") is an extinct genus of large ichthyosaurs, of which it is among the oldest representatives, that lived from the Lower to Middle Triassic in what are now North America and Europe. The first known fo ...

''. Few other marine reptiles are known from the Fossil Hill Member, the only clearly identified being the sauropterygian ''Augustasaurus'' itself.

References

Bibliography

* * {{Authority control Triassic sauropterygians Fossil taxa described in 1997 Middle Triassic reptiles of North America Pistosaurs Aquatic reptiles Sauropterygian genera