Chanaresuchus
Encyclopedia
Chanaresuchus is an extinct genus
of proterochampsia
n archosauriform. It was of modest size for a proterochampsian, being on average just over a meter in length. Fossil
s have been found from the Chañares Formation
in La Rioja Provence
, Argentina
, dating back to the Ladinian
stage of the Middle Triassic
. Chanaresuchus appears to be one of the most common archosauriforms from the formation due to the abundance of specimens referred to the genus. Much of the material has been found by the La Plata-Harvard expedition of 1964-65. Chanaresuchus was originally classified in the family Proterochampsidae
, although it has been placed in the family Rhadinosuchidae
in more recent studies (both families belong to Proterochampsia).
, farther up the skull. The premaxilla
is slightly down-curved. The skull table is highly ornamented in larger specimens, with the dermal bone
s well sculptured. The palate of Chanaresuchus has two elongate choana
e. Two small openings anterior to the choanae may be anterior palatine foramina that could have been used for access to vomeronasal organ
s. The secondary palate
formed between these two sets of openings may have been an adaptation for breathing through the snout while underwater.
Unlike other proterochampsians and early archosaurs, Chanaresuchus had little body armor. The only osteoderm
s found are small and scale-like, forming a single row down the neural spines. They run from the neck to the last presacral
, and most likely continue on down the tail, although no specimens have been shown that suggest this. There are roughly three scales per vertebra.
The foot of Chanaresuchus differs from other related archosaurs in that there is an emphasis on an enlargement of the inner phalanges
, whereas other primitive archosaurs retain a somewhat more symmetrical pattern. The first digit is reduced but quite robust. The second digit is clearly the most massive, yet the third digit is the longest, although somewhat slender in comparison. The fourth digit is very slim and the fifth consists of only a metatarsal spur.
s and modern day crocodilia
ns has been proposed for Chanaresuchus, as is suggested by the secondary palate, dorsally facing orbits, dorsally positioned nostrils, and many other characteristics. However, some evidence, such as a lack of aquatic amphibian
s found from the Chañares Formation, suggests that the area was relatively dry during the time of deposition. A terrestrial lifestyle is possible for the genus, as extreme differences in the size of the forelimbs relative to the hind limbs in comparison to other "thecodonts" may be considered a characteristic of bipedalism. However, this is most likely not the case for Chanaresuchus, and the evidence still remains in favor of a semiaquatic animal.
The depositional environment
of the locality from which specimens of Chanaresuchus have been found was in close proximity to an area of high volcanic
activity, due to the fact that it was in an active rift basin
. It is thought that all of the recovered specimens had died in a single event of mass mortality and may have been buried on a fluvial
strandline
. The mortality-causing event was most likely linked to regional volcanic activity.
The locality from which specimens of Chanaresuchus have been found is well known for its abundance of tetrapods. Theraspids
include the kannemeyeriid
Dinodontosaurus
, and cynodonts such as Probainognathus
and Massetognathus
, the latter being the most abundant taxon of the locality. However, the most common group of tetrapods present from the formation are the archosaurs. Ornithodirans include Lewisuchus
, Lagerpeton
, Marasuchus
, and Pseudolagosuchus
. Other archosaurs include Gracilisuchus
and Luperosuchus
. Another proterochampsian, which was named alongside Chanaresuchus in 1971, is Gualosuchus. It is very similar in appearance to Chanaresuchus, differing only in size and cranial proportions.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of proterochampsia
Proterochampsia
Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the genera Proterochampsa, Cerritosaurus, Chanaresuchus, Gualosuchus, Rhadinosuchus, and Tropidosuchus...
n archosauriform. It was of modest size for a proterochampsian, being on average just over a meter in length. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from the Chañares Formation
Chañares Formation
The Chañares Formation in La Rioja Provence, Argentina, dates to the Anisian stage of the early Middle Triassic.Some localities are well known for their abundance of tetrapods. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter...
in La Rioja Provence
La Rioja Province (Argentina)
La Rioja is a one of the provinces of Argentina and is located in the west of the country. Neighboring provinces are from the north clockwise Catamarca, Córdoba, San Luis and San Juan.-History:...
, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, dating back to the Ladinian
Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...
stage of the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
. Chanaresuchus appears to be one of the most common archosauriforms from the formation due to the abundance of specimens referred to the genus. Much of the material has been found by the La Plata-Harvard expedition of 1964-65. Chanaresuchus was originally classified in the family Proterochampsidae
Proterochampsidae
Proterochampsidae is a family of archosauriforms. Proterochampsids may have filled an ecological niche similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now South America in the Middle and Late Triassic....
, although it has been placed in the family Rhadinosuchidae
Rhadinosuchidae
Rhadinosuchidae is an extinct family of archosauriforms. It includes the proterochampsians Gualosuchus, Chanaresuchus, and Rhadinosuchus, all of which are from the Middle and Late Triassic of Brazil. Rhadinosuchus, the type genus of the family, was originally described as a rauisuchian in 1942...
in more recent studies (both families belong to Proterochampsia).
Description
Chanaresuchus had a low, elongate skull that is characteristic of proterochampsians. The skull is quite broad posteriorly with a narrow snout, varying in length from around 165mm to 260mm in the largest individuals. The nares are slit-like and positioned away from the tip of the rostrumRostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
, farther up the skull. The premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
is slightly down-curved. The skull table is highly ornamented in larger specimens, with the dermal bone
Dermal bone
A dermal bone - bony structures derived from intramembranous ossification that form components of the vertebrate skeleton including the skull, jaws, gills, fins and exoskeleton. In contrast to endochondral bone, dermal bone does not form from cartilage first and then calcify...
s well sculptured. The palate of Chanaresuchus has two elongate choana
Choana
Choana is the posterior nasal aperture.The choanae are separated by the vomer.- Boundaries :It is the opening between the nasal cavity and the nasopharynx....
e. Two small openings anterior to the choanae may be anterior palatine foramina that could have been used for access to vomeronasal organ
Vomeronasal organ
The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....
s. The secondary palate
Secondary palate
The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates.In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medially and their mutual fusion in the midline...
formed between these two sets of openings may have been an adaptation for breathing through the snout while underwater.
Unlike other proterochampsians and early archosaurs, Chanaresuchus had little body armor. The only osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
s found are small and scale-like, forming a single row down the neural spines. They run from the neck to the last presacral
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
, and most likely continue on down the tail, although no specimens have been shown that suggest this. There are roughly three scales per vertebra.
The foot of Chanaresuchus differs from other related archosaurs in that there is an emphasis on an enlargement of the inner phalanges
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
, whereas other primitive archosaurs retain a somewhat more symmetrical pattern. The first digit is reduced but quite robust. The second digit is clearly the most massive, yet the third digit is the longest, although somewhat slender in comparison. The fourth digit is very slim and the fifth consists of only a metatarsal spur.
Paleobiology
A semiaquatic lifestyle similar to phytosaurPhytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
s and modern day crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns has been proposed for Chanaresuchus, as is suggested by the secondary palate, dorsally facing orbits, dorsally positioned nostrils, and many other characteristics. However, some evidence, such as a lack of aquatic amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s found from the Chañares Formation, suggests that the area was relatively dry during the time of deposition. A terrestrial lifestyle is possible for the genus, as extreme differences in the size of the forelimbs relative to the hind limbs in comparison to other "thecodonts" may be considered a characteristic of bipedalism. However, this is most likely not the case for Chanaresuchus, and the evidence still remains in favor of a semiaquatic animal.
The depositional environment
Sedimentary depositional environment
In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock...
of the locality from which specimens of Chanaresuchus have been found was in close proximity to an area of high volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
activity, due to the fact that it was in an active rift basin
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
. It is thought that all of the recovered specimens had died in a single event of mass mortality and may have been buried on a fluvial
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
strandline
Strandline
The strandline, or high water mark, is the area at the top of a beach where debris is deposited. Where there are tides, this line is formed by the highest position of the tide, and moves up and down the beach on a fortnightly cycle...
. The mortality-causing event was most likely linked to regional volcanic activity.
The locality from which specimens of Chanaresuchus have been found is well known for its abundance of tetrapods. Theraspids
Therapsida
Therapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be...
include the kannemeyeriid
Kannemeyeriidae
Kannemeyeriidae is a family of large, stocky, beaked and sometimes tusked dicynodonts. They were the dominant large terrestrial herbivores through most of the Triassic period...
Dinodontosaurus
Dinodontosaurus
Dinodontosaurus is a genus of dicynodont therapsid. It was one of the largest herbivores of the Triassic and had a beak corneum...
, and cynodonts such as Probainognathus
Probainognathus
Probainognathus is a genus of meat-eating mammal-like reptile that lived during the lower Upper Triassic of South America. This creature had an incipient squamosal-dentary jaw-cranium joint, which is a clearly mammalian anatomical feature. It was at the very least closely related to the family of...
and Massetognathus
Massetognathus
A relative of Cynognathus, Massetognathus was a plant-eating cynodont belonging to the Traversodontid family. This cynodont lived in what is now South America, in Brazil and Argentina during the Middle Triassic period .Massetognathus was about long. It had cheek teeth specially adapted to...
, the latter being the most abundant taxon of the locality. However, the most common group of tetrapods present from the formation are the archosaurs. Ornithodirans include Lewisuchus
Lewisuchus
Lewisuchus is a genus of archosaur that lived during the Middle Triassic ; it was a silesaurid dinosauriform, a member of the group of reptiles which lead to the dinosaurs. Lewisuchus was about three feet long. Fossils have been found in Argentina...
, Lagerpeton
Lagerpeton
Lagerpeton is a genus of basal dinosauromorph from the Ladinian . Lagerpeton is known from several specimens of hindlimbs, hips, vertebrae, and feet. It was about 0.7 metres long and was found in the Chañares Formation of Argentina. It has unique feet, with an unusually long fourth toe...
, Marasuchus
Marasuchus
Marasuchus is a genus of dinosaur-like ornithodiran from the middle Triassic Chañares Formation of Argentina. The species Marasuchus lilloensis was originally described as a second species of Lagosuchus, L. lilloensis...
, and Pseudolagosuchus
Pseudolagosuchus
Pseudolagosuchus is a genus of dinosauromorph from the Middle Triassic Chañares Formation of Argentina. It may be a junior synonym of Lewisuchus, but there is very little overlapping material...
. Other archosaurs include Gracilisuchus
Gracilisuchus
Gracilisuchus is an extinct genus of tiny crurotarsan from the Middle Triassic. It was a suchian close to the ancestry of crocodiles, and was at one time thought to be a dinosaur, but this hypothesis has since been rejected...
and Luperosuchus
Luperosuchus
Luperosuchus is an extinct genus of crurotarsan, a group which includes crocodilians and their ancestors. It lived during the Anisian stage of the Middle Triassic, and is known from Argentina.-References:* in the Paleobiology Database...
. Another proterochampsian, which was named alongside Chanaresuchus in 1971, is Gualosuchus. It is very similar in appearance to Chanaresuchus, differing only in size and cranial proportions.
External links
- Chanaresuchus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...