Saniwa
Encyclopedia
Saniwa is an extinct genus
of monitor lizard
that lived during the Eocene
epoch around 48 million years ago. Well-preserved fossils have been found in the Bridger and Green River Formation
s of Wyoming, and there is evidence that Saniwa also lived in Europe. The type species
S. ensidens was named in 1870 as the first fossil lizard known from North America. Several other species have since been added, but their validity is uncertain. It is a close relative of Varanus, the genus that includes most living monitor lizards.
, a jugal
bone beneath the eye that extends farther forward, and a suture between the frontal
and parietal bone
s that is straight rather than curved or wavy.
found the first fossils of Saniwa near the town of Granger, Wyoming
, and gave them to paleontologist Joseph Leidy
. Later that year, Leidy described the type species Saniwa ensidens on the basis of these fossils. Saniwa was the first extinct lizard to be named from North America. The first remains of S. ensidens were preserved as black bones in marl
that was part of the Bridger Formation. Hayden suggested the name Saniwa to Leidy because it was "used by one of the Indian tribes of the Upper Missouri for a rock-lizard." Leidy saw a close similarity between Saniwa and the living Nile monitor
.
Although his first description was brief, Leidy studied the genus thoroughly and provided illustrations in an 1873 paper. In this paper, Leidy called it Saniva. He also named a second species, Saniva [sic] major, on the basis of a broken humerus
and some isolated dorsal vertebrae. In 1918, Baron G. J. de Fejérváry suggested that S. major was not a species of lizard, noting that the humerus was "undoubtably" nonreptilian. Leidy even pointed out similarities between the bone and those of birds in 1873.
Soon after Leidy named Saniwa, American paleontologist Othniel Charles Marsh
erected the genus Thinosaurus in 1872 for several species of extinct lizards in the western United States. He never published a full description of these lizards, and Thinosaurus was later considered a junior synonym of Saniwa. The species T. leptodus was synonymized with S. ensidens, but all other species have remained distinct, including T. agilis, T. crassa, T. grandis, and T. paucidens.
In the 1920s, much of the holotype specimen of S. ensidens was prepared by removing marl from around the bones. This revealed many new features of Saniwa, including the underside of the skull and parts of the vertebrae. American paleontologist Charles W. Gilmore
restudied the holotype and described new features in 1922. He described many of these features from a fragment of the snout and lower jaw. Although this fossil was well preserved, it was not found in the same block of marl as other parts of the specimen. This fossil was reexamined in 2003 and was found to belong to a xenosaurid
lizard, not Saniwa.
Fossils from many other parts of the world have been assigned to Saniwa, although all are fragmentary. In 1899, Argentine paleontologist Florentino Ameghino
named another species of Saniwa, S. australis, from lower Miocene
rocks in Argentina. It is now considered a nomen dubium
, or dubious name, because the material cannot be assigned with confidence to Saniwa. S. orsmaelensis was described from Belgium
in 1923, but because its naming was informal, it was designated a nomen nudum
, or naked name. S. orsmaelensis was later suggested to be either synonymous with S. ensidens or a different, indeterminate species of Saniwa. Unlike the Argentine fossils, the Belgian remains represent a definite occurrence of Saniwa outside North America. S. feisti was named from the Eocene Messel Pit
in Germany in 1983. S. feisti is no longer considered to be a species of Saniwa, but a more primitive member of the family Varanidae
.
A complete and articulated skeleton of S. ensidens was described from the Green River Formation of Wyoming in 2007. It preserves soft tissues like scales, cartilage between bones and in the sternum
, and even the trachea
. The individual is thought to have been a juvenile.
from Conrad et al. (2008) that shows a sister-group relationship between Saniwa ensidens and Varanus:
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 monitor lizard
Monitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...
that lived during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
epoch around 48 million years ago. Well-preserved fossils have been found in the Bridger and Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
s of Wyoming, and there is evidence that Saniwa also lived in Europe. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
S. ensidens was named in 1870 as the first fossil lizard known from North America. Several other species have since been added, but their validity is uncertain. It is a close relative of Varanus, the genus that includes most living monitor lizards.
Description
Saniwa grew to around 1.3 metres (4.3 ft) in length. Like other monitor lizards, Saniwa has a long pointed snout and nostrils that are placed farther back in the skull than most lizards. The tail is almost twice as long as the rest of the body. Although similar in appearance to living monitor lizards, Saniwa has several primitive traits, including teeth on its palatePalate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
, a jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
bone beneath the eye that extends farther forward, and a suture between the frontal
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
and parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
s that is straight rather than curved or wavy.
History and species
In 1870, American geologist Ferdinand Vandeveer HaydenFerdinand Vandeveer Hayden
Dr. Ferdinand Vandeveer Hayden was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union Army during the Civil War.-Early life:Ferdinand Hayden was born in Westfield, Massachusetts...
found the first fossils of Saniwa near the town of Granger, Wyoming
Granger, Wyoming
Granger is a town in Sweetwater County, Wyoming, United States. The population was 146 at the 2000 census.-Geography:Granger is located at ....
, and gave them to paleontologist Joseph Leidy
Joseph Leidy
Joseph Leidy was an American paleontologist.Leidy was professor of anatomy at the University of Pennsylvania, and later was a professor of natural history at Swarthmore College. His book Extinct Fauna of Dakota and Nebraska contained many species not previously described and many previously...
. Later that year, Leidy described the type species Saniwa ensidens on the basis of these fossils. Saniwa was the first extinct lizard to be named from North America. The first remains of S. ensidens were preserved as black bones in marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
that was part of the Bridger Formation. Hayden suggested the name Saniwa to Leidy because it was "used by one of the Indian tribes of the Upper Missouri for a rock-lizard." Leidy saw a close similarity between Saniwa and the living Nile monitor
Nile monitor
The Nile Monitor, Water Leguaan, or River Leguaan is a large member of the monitor lizard family ....
.
Although his first description was brief, Leidy studied the genus thoroughly and provided illustrations in an 1873 paper. In this paper, Leidy called it Saniva. He also named a second species, Saniva [sic] major, on the basis of a broken humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and some isolated dorsal vertebrae. In 1918, Baron G. J. de Fejérváry suggested that S. major was not a species of lizard, noting that the humerus was "undoubtably" nonreptilian. Leidy even pointed out similarities between the bone and those of birds in 1873.
Soon after Leidy named Saniwa, American paleontologist Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
erected the genus Thinosaurus in 1872 for several species of extinct lizards in the western United States. He never published a full description of these lizards, and Thinosaurus was later considered a junior synonym of Saniwa. The species T. leptodus was synonymized with S. ensidens, but all other species have remained distinct, including T. agilis, T. crassa, T. grandis, and T. paucidens.
In the 1920s, much of the holotype specimen of S. ensidens was prepared by removing marl from around the bones. This revealed many new features of Saniwa, including the underside of the skull and parts of the vertebrae. American paleontologist Charles W. Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
restudied the holotype and described new features in 1922. He described many of these features from a fragment of the snout and lower jaw. Although this fossil was well preserved, it was not found in the same block of marl as other parts of the specimen. This fossil was reexamined in 2003 and was found to belong to a xenosaurid
Xenosauridae
The Xenosauridae is a family of lizards native to Central America and China. Also known as knob-scaled lizards, they have rounded, bumpy scales and osteoderms. Most species prefer moist or semi-aquatic habitats, although they are widespread within their native regions, with some even inhabiting...
lizard, not Saniwa.
Florentino Ameghino
Florentino Ameghino was an Argentine naturalist, paleontologist, anthropologist and zoologist.Born in Luján, son of Italian immigrants, Ameghino was a self-taught naturalist, and focused his study on the lands of the southern Pampas...
named another species of Saniwa, S. australis, from lower Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
rocks in Argentina. It is now considered a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, or dubious name, because the material cannot be assigned with confidence to Saniwa. S. orsmaelensis was described from Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
in 1923, but because its naming was informal, it was designated a nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
, or naked name. S. orsmaelensis was later suggested to be either synonymous with S. ensidens or a different, indeterminate species of Saniwa. Unlike the Argentine fossils, the Belgian remains represent a definite occurrence of Saniwa outside North America. S. feisti was named from the Eocene Messel Pit
Messel pit
The Messel Pit is a disused quarry near the village of Messel, about southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its abundance of fossils, it has significant geological and scientific importance...
in Germany in 1983. S. feisti is no longer considered to be a species of Saniwa, but a more primitive member of the family Varanidae
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
.
A complete and articulated skeleton of S. ensidens was described from the Green River Formation of Wyoming in 2007. It preserves soft tissues like scales, cartilage between bones and in the sternum
Sternum
The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...
, and even the trachea
Trachea
Trachea may refer to:* Vertebrate trachea, or windpipe, in terrestrial vertebrates, such as birds and mammals* Invertebrate trachea, in terrestrial invertebrates, such as insects and crustaceans* Vessel elements in plants...
. The individual is thought to have been a juvenile.
Classification
Since its first description, Saniwa has been recognized as a close relative of living monitor lizards in the genus Varanus. It is a member of the family Varanidae. Saniwa ensidens is often placed as the sister taxon of Varanus in phylogenetic analyses, meaning that it is more closely related to Varanus than any other varanid. Below is a cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
from Conrad et al. (2008) that shows a sister-group relationship between Saniwa ensidens and Varanus: