''Dynamosuchus'' 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 ...

pseudosuchian Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...

archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

s from the family

Ornithosuchidae Ornithosuchidae is an extinct family (biology), family of Pseudosuchia, pseudosuchian archosaurs (distant relatives of modern Crocodilia, crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like ...

. It is known from a single species, ''Dynamosuchus collisensis'', which is based on a partial skeleton from the

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, " rauisuchian" pseudosuchians, and early dinosaurs and othe ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. ''Dynamosuchus'' is considered a close relative of '' Venaticosuchus'', which is known from the

Ischigualasto Formation The Ischigualasto Formation is a Late Triassic geological formation in the Ischigualasto-Villa Unión Basin of southwestern La Rioja Province, Argentina, La Rioja Province and northeastern San Juan Province, Argentina, San Juan Province in northw ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. Ornithosuchids are one of many groups which lived in the Santa Maria and Ischigualasto Formations, which formed at approximately the same time (the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

stage of the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

) and were ecologically similar. As a large

scavenging Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding be ...

reptile, ''Dynamosuchus'' helps to illuminate the trophic structure of the Santa Maria Formation. It also supports the hypothesis that ornithosuchids had diversified throughout

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

by the start of the Carnian, and were not originally endemic to the

Ischigualasto-Villa Unión Basin The Ischigualasto-Villa Unión Basin () is a small sedimentary basin located in the Argentine Northwest, Argentina. It is located in the southwestern part of La Rioja Province and the northeastern part of San Juan Province. The basin borders the ...

Discovery

''Dynamosuchus'' is known from a single partial skeleton, CAPPA/UFSM 0248, stored at the Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia (CAPPA) of the

Federal University of Santa Maria The Federal University of Santa Maria (, UFSM) is a Brazilian public university located in Santa Maria, in the state of Rio Grande do Sul, funded by the federal government of Brazil. It was founded in 1960, by Professor José Mariano da Rocha ...

(UFSM). This specimen consists of parts of the skull, several cervical and dorsal vertebrae, and a large portion of the limbs. It was discovered at the Janner site near the town of Agudo in

Rio Grande do Sul Rio Grande do Sul (, ; ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative units of Brazil#List, fifth-most populous state and the List of Brazilian s ...

. The Janner site preserves late Triassic sediments of the

. Based on the abundance of '' Exaerotodon'' (a large herbivorous

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

) and ''

Hyperodapedon ''Hyperodapedon'' (from , 'above' and , 'pavement') is an extinct genus of rhynchosaur reptiles which lived during Triassic, Late Triassic period. Like other rhynchosaurs, it was an heavily built Archosauromorpha, archosauromorph, distantly rel ...

'' (a

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

), it was probably equivalent in age and environment to the

-age

. Other animals known from the Janner site include basal

sauropodomorphs Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

('' Pampadromaeus'' and '' Bagualosaurus'') and large carnivorous cynodonts (''

Trucidocynodon ''Trucidocynodon'' is an extinct genus of ecteniniid cynodonts from the Upper Triassic (Carnian) of Brazil. It contains a single species, ''Trucidocynodon riograndensis''. Fossils of ''Trucidocynodon'' were discovered in outcrops of the Upper Sa ...

''). The generic name ''Dynamosuchus'' is

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

for "powerful crocodile", in reference to its

heritage and strong bite force, as proposed for other ornithosuchids. The specific name ''collisensis'' is based on ''collis'', the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

term for hill, which references the fact that the Janner site is located at the base of a hill. The holotype skeleton was discovered in March 2019 and described in 2020 by

Rodrigo T. Müller Rodrigo () is a Spanish, Portuguese and Italian name derived from the Germanic name ''Roderick'' ( Gothic ''*Hroþareiks'', via Latinized ''Rodericus'' or ''Rudericus''), given specifically in reference to either King Roderic (d. 712), the last ...

(CAPPA/UFSM), M. Belén Von Baczko (

Museo de la Plata The La Plata Museum () is a natural history museum in La Plata, Argentina. It is part of the (Natural Sciences School) of the National University of La Plata. The building, long, today houses three million fossils and relics (including 44,000 bo ...

), Julia B. Desojo (Museo de la Plata), and Sterling J. Nesbitt (

Virginia Tech The Virginia Polytechnic Institute and State University, commonly referred to as Virginia Tech (VT), is a Public university, public Land-grant college, land-grant research university with its main campus in Blacksburg, Virginia, United States ...

Description

Skull

Like other ornithosuchids, the snout of ''Dynamosuchus'' had a hooked

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 ...

with three teeth, followed by a gap (a

diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...

) and a deep

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 ...

with six to eight teeth. The maxilla was similar to that of ''Ornithosuchus'' due to possessing pitting on its outer surface (absent in ''Venaticosuchus'' and ''Riojasuchus'') and a not particularly deep antorbital fossa (unlike ''Riojasuchus''). Preserved skull bones generally reconstruct a skull with small

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

and temporal fenestration like ''Riojasuchus'', but 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 ...

is not as thick as in that taxon. The

quadratojugal bone The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

was roughly textured and L-shaped, not as acute in angle as ''Riojasuchus''. A hole known as a quadrate foramen separates the quadratojugal from the quadrate, and an additional smaller hole on the quadrate opens up into the quadrate foramen. The additional hole is an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a Synapomorphy, derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or Outgroup (cladistics), outgroup taxa, not ...

(unique characteristic) of ''Dynamosuchus'' absent in other ornithosuchids. The parabasisphenoid bone at the bottom of the braincase has a semilunar depression like that of ''Venaticosuchus'', but the gap between its basipterygoid processes and basitubera is less acute than in that taxon. ''Dynamosuchus'''s basipterygoid processes are also more closely spaced and pointed further rearwards compared to ''Venaticosuchus''. The

surangular The surangular or suprangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular bone, angular, splenial and articular. It is o ...

is similar to that of ''Riojasuchus'', with a pronounced blade-like crest on its outer surface and a large hole (a surangular foramen) at the rear of the jaw. The jaw as a whole deepens towards the chin and has a long mandibular fenestra.

Postcrania

The cervical (neck) vertebrae have a variety of features shared with various pseudosuchians, such as pits below the postzygapophyses (rear connecting plates), expanded neural spines, and a strong keel on the underside.

Dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

near the shoulder have a pair of centrodiapophyseal laminae, buttress-like crests connecting the diapophyses (rib facets) to the centrum (spool-shaped lower portion of each vertebra). These crests are shared with ''Ornithosuchus'' but absent in ''Riojasuchus'' and unknown in ''Venaticosuchus''. In most other respects, the dorsal vertebrae of ''Dynamosuchus'' are more similar to ''Riojasuchus'' than ''Ornithosuchus''. For example, ''Dynamosuchus'' lacks prezygodiapophyseal and postzygodiapophyseal laminae. These crests, present in ''Ornithosuchus'', connect the diapophyses to the zygapophyses (vertebral connecting plates). ''Dynamosuchus'''s

osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...

are set in two rows along the back, are somewhat square-shaped, and are densely textured by radiating ridges and grooves. Osteoderms at the front of the body often have a sideways-oriented peak-like projection. The forelimb bones are thick and generally strongly built. The

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

expands towards the wrist more so than ''Ornithosuchus'', while the humeral head is not as developed as that of ''Riojasuchus''. The hip has an overall shape like that of ''Ornithosuchus'', with a smooth and straight upper portion of the ilium, a long pubis, and three

sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

. Like other ornithosuchids, the hindlimb bones are large and have prominent and/or unusual muscle scars. These include an anterior trochanter at the top of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

, and a knob-like scar for the iliofibularis muscle on the shaft of the

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

. The iliofibularis attachment is located about 1/3rd down the shaft of the fibula in ''Dynamosuchus'', while it is about halfway down in ''Riojasuchus''.

Classification

The relations of ''Dynamosuchus'' were investigated using a

phylogenetic analysis 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 data ...

adapted from

Ezcurra Ezcurra is a surname. Notable people with the surname include: * Alma Ezcurra (born 1986), Spanish politician * Bautista Ezcurra (born 1995), Argentine rugby union player * Encarnación Ezcurra (1795–1838), Argentine political activist * Exequiel ...

''et al.'' (2017). The analysis found ''Dynamosuchus'' 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 '' Venaticosuchus'' based on a semilunar depression on the parabasisphenoid and an L-shaped

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

. The ''Dynamosuchus'' + ''Venaticosuchus'' clade is itself sister to '' Riojasuchus'' based on a strongly downturned

and expanded outer

. '' Ornithosuchus'' is found to be the most basal ornithosuchid, and ornithosuchids are related to erpetosuchids and

aetosaurs Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...

, replicating the results of Ezcurra ''et al.'' (2017). The following

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 ...

is based on the results of the phylogenetic analysis:

References

{{Taxonbar, from=Q85758069 Ornithosuchidae Triassic archosaurs Carnian genera Late Triassic reptiles of South America Triassic Brazil Fossils of Brazil Santa Maria Formation Fossil taxa described in 2020 Prehistoric pseudosuchian genera Taxa named by Rodrigo T. Müller