Saniwa

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Saniwa
Temporal range: Eocene
Saniwa FMNH.jpg
Skeleton of Saniwa ensidens in the Field Museum of Natural History
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus:† Saniwa
Leidy, 1870
Species
  • †S. ensidensLeidy, 1870 (type)
  • †S. orsmaelensisDollo, 1923
Synonyms

Saniwa is an extinct genus of varanid lizard that lived during the Eocene epoch. It is known from well-preserved fossils found in the Bridger and Green River Formations of Wyoming, United States. The type species S. ensidens was described in 1870 as the first fossil lizard known from North America. A second species, S.orsmaelensis, is recognised from remains found in Europe. It is a close relative of Varanus , the genus that includes monitor lizards.

Contents

Description

The skull of S. ensidens Saniwa ensidens head.jpg
The skull of S. ensidens

Saniwa measured 1.3 to 2.1 m (4.3 to 6.9 ft). [1] [2] Like other varanid lizards, Saniwa had a long, pointed snout and nostrils placed farther back in the skull than most lizards and a tail that was almost twice as long as the body. [2] Although similar in appearance to extant monitor lizards, Saniwa had many primitive traits, including teeth on its palate, a jugal bone beneath the eye that extended farther forward, and a suture between the frontal and parietal bones that was straight rather than curved. [3]

A study in 2018 by scientists from the Senckenberg Research Institute and Yale University found Saniwa had two parietal eyes, one that developed from the pineal gland and the other from the parapineal gland. The parietal eye is a light-sensitive structure present in the tuatara, most lizards, frogs, salamanders, certain bony fish, sharks and lampreys, a group of jawless fish. [4] It plays an important role in geographical orientation and regulating circadian and annual rhythms. Saniwa is the only known jawed vertebrate to have both a pineal and a parapineal eye, as the only other vertebrates that have both are the jawless lampreys. In most vertebrates, the pineal gland forms the parietal eye, however, in lepidosaurs, it is formed from the parapineal gland. This implies that Saniwa reevolved the pineal eye. [5]

History and species

In 1870, American geologist Ferdinand Vandeveer Hayden found the first fossils of Saniwa near the town of Granger, Wyoming, and gave them to paleontologist Joseph Leidy. [2] 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. [6] 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." [7] Leidy saw a close similarity between Saniwa and the living Nile monitor.

Leidy's illustrations of the humerus of S. major and the vertebrae of S. ensidens Saniwa Leidy.jpg
Leidy's illustrations of the humerus of S. major and the vertebrae of S. ensidens

Although his first description was brief, Leidy studied the genus thoroughly and provided illustrations in an 1873 paper. In this paper, Leidy called it Saniwa. He also named a second species, Saniwa [sic] major, on the basis of a broken humerus and some isolated dorsal vertebrae. [7] In 1918, Baron G. J. de Fejérváry suggested that S. major was not a species of lizard, noting that the humerus was "undoubtedly" nonreptilian. [8] 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. [2]

The vertebrae and limb bones of the holotype specimen of S. ensidens Saniwa ensidens Gilmore.jpg
The vertebrae and limb bones of the holotype specimen of S. ensidens

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. [6] 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. [9]

A fossil of Paranecrosaurus, formerly "Saniwa" feisti Paranecrosaurus feisti -img2.jpg
A fossil of Paranecrosaurus , formerly "Saniwa" feisti

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 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 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. [2] A 2022 study found S. orsmaelensis to be a distinct and valid species of Saniwa, with remains of the species also reported from France. [10] "S." feisti was named from the Eocene Messel Pit in Germany in 1983. [11] "S." feisti is no longer considered to be a species of Saniwa, but is placed in the separate genus Paranecrosaurus within the family Palaeovaranidae, which is more distantly related to Varanus than Saniwa. [3] [12]

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. [2]

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 it is more closely related to Varanus than any other varanid. Below is a cladogram from Conrad et al. (2008) that shows a sister-group relationship between Saniwa ensidens and Varanus: [3]

Varanoidea  

† Mosasaurs

†"Saniwa" feisti

Below is a cladogram from Dong et al. 2022. [13]

Varanidae

Related Research Articles

<span class="mw-page-title-main">Pineal gland</span> Endocrine gland in the brain of most vertebrates

The pineal gland is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles. The shape of the gland resembles a pine cone, which gives it its name. The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. It is one of the neuroendocrine secretory circumventricular organs in which capillaries are mostly permeable to solutes in the blood.

<span class="mw-page-title-main">Varanidae</span> Family of lizards

The Varanidae are a family of lizards in the superfamily Varanoidea and order Anguimorpha. The family, a group of carnivorous and frugivorous lizards, includes the living genus Varanus and a number of extinct genera more closely related to Varanus than to the earless monitor lizard (Lanthanotus). Varanus includes the Komodo dragon, crocodile monitor, savannah monitor, the goannas of Australia and Southeast Asia, and various other species with a similarly distinctive appearance. Their closest living relatives are the earless monitor lizard and Chinese crocodile lizard. The oldest members of the family are known from the Late Cretaceous of Mongolia.

<span class="mw-page-title-main">Monitor lizard</span> Genus of reptiles

Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recognized.

<span class="mw-page-title-main">Megalania</span> Extinct species of giant monitor lizard

Megalania is an extinct species of giant monitor lizard, part of the megafaunal assemblage that inhabited Australia during the Pleistocene. It is the largest terrestrial lizard known to have existed, but the fragmentary nature of known remains make estimates highly uncertain. Recent studies suggest that most known specimens would have reached around 2–3 m (6.6–9.8 ft) in body length excluding the tail, while some individuals would have been significantly larger, reaching sizes around 4.5–7 m (15–23 ft) in length.

<span class="mw-page-title-main">Parietal eye</span> Part of the epithalamus

A parietal eye is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production for thermoregulation. The hole that contains the eye is known as the pineal foramen or parietal foramen, because it is often enclosed by the parietal bones.

<i>Peltosaurus</i> Extinct genus of lizards

Peltosaurus is an extinct genus of anguid lizard from North America that lived from the Eocene to the Oligocene. Peltosaurus belongs to the anguid subfamily Glyptosaurinae. The type species Peltosaurus granulosus was named in 1873 by American paleontologist Edward Drinker Cope. Many additional species have been named, but most have been reassigned to different genera. For example, Peltosaurus piger, named in 1928, was reclassified as Odaxosaurus piger, and P. jepseni, named in 1942 from the Paleocene of Wyoming, but was later reclassified as Proxestops jepseni. In 1955 a new species, Peltosaurus macrodon, was named from the Eocene of California. Lizard bones from the Late Miocene of Nebraska were attributed to a new species of Peltosaurus called P. minimus in 1976, extending the fossil range of Peltosaurus and Glyptosaurinae into the Neogene. However, these bones were later referred to a genus of skinks called Eumeces, meaning that the fossil range of Peltosaurus and Glyptosaurinae does not go beyond the Paleogene.

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<span class="mw-page-title-main">Charles W. Gilmore</span> American paleontologist

Charles Whitney Gilmore was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum. Gilmore named many dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus ovatus and Thescelosaurus.

<i>Tsoabichi</i> Extinct genus of reptiles

Tsoabichi is an extinct genus of caimanine crocodylian. Fossils are known from the Green River Formation in Wyoming, and date back to the Ypresian stage of the Eocene. The genus was named and described in 2010 by paleontologist Christopher A. Brochu, with the type species being Tsoabichi greenriverensis. According to the current understanding of caiman evolutionary relationships, Tsoabichi is a basal member of Caimaninae and may have evolved after caimans dispersed into North America from northern and central South America, their main center of diversity in the Cenozoic.

<i>Telmasaurus</i> Extinct genus of lizards

Telmasaurus is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 75 million years ago. The type species Telmasaurus grangeri was named in 1943.

<i>Bahndwivici</i> Extinct genus of lizards

Bahndwivici is an extinct genus of lizard known from a nearly complete and articulated skeleton discovered in rocks of the Green River Formation of Wyoming, United States. The skeleton is very similar to that of the modern Chinese crocodile lizard, Shinisaurus.

<span class="mw-page-title-main">Shinisauria</span> Clade of lizards

Shinisauria is a clade or evolutionary grouping of anguimorph lizards that includes the living Chinese crocodile lizard Shinisaurus and several of its closest extinct relatives. Shinisauria was named in 2008 by Jack Lee Conrad as a stem-based taxon to include all anguimorphs more closely related to Shinisaurus than to Anguis fragilis, Heloderma suspectum or Varanus varius. Several recent phylogenetic analyses of lizard evolutionary relationships place Shinisauria in a basal position within the clade Platynota, which also includes monitor lizards, helodermatids, and the extinct mosasaurs. Shinisaurians were once thought to be closely related to the genus Xenosaurus, but they are now considered distant relatives within Anguimorpha. The fossil record of shinisaurians extends back to the Early Cretaceous with Dalinghosaurus, which is from the Aptian aged Yixian Formation of China. Two other extinct shinisaurians are currently known: Bahndwivici from the Eocene of Wyoming and Merkurosaurus from the Late Oligocene of Germany and the Early Miocene of the Czech Republic. An indeterminate shinisaurian is known from an isolated tail found in the Eocene aged Messel pit in Germany.

Babibasiliscus is an extinct genus of casquehead lizard that lived in what is now Wyoming during the early Eocene, approximately 48 million years ago. The genus is known from a single species, Babibasiliscus alxi, which was named by paleontologist Jack Conrad in 2015 on the basis of a fossilized skull from the Bridger Formation in the Green River Basin. The name Babibasiliscus comes from the Shoshoni word babi, meaning "older male cousin", and Basiliscus, a modern-day genus of casquehead lizards. The specimen is undeformed and nearly complete except for the tip of the snout and the top of the skull, making it unclear whether the distinctive bony crest of living corytophanids was present in prehistoric relatives like Babibasiliscus. The skull is about 42 millimetres (2 in) in length and the entire body is estimated to have been about 0.6 metres (2 ft) long. Bones on the right side of lower jaw of the specimen are thickened and fused together, suggesting that the jaw had broken and healed when the animal was alive.

Saichangurvel is an extinct genus of iguanian lizards from the Late Cretaceous of Mongolia. It is a member of a clade called Gobiguania, an exclusively Late Cretaceous group of iguanian lizards that was likely endemic to the Gobi Desert. The type species, Saichangurvel davidsoni, was named by paleontologists Jack Conrad and Mark Norell of the American Museum of Natural History in 2007. It is known from a single nearly complete and fully articulated skeleton called IGM 3/858, which was found eroding from a block of sandstone during a thunderstorm at a fossil locality called Ukhaa Tolgod. IGM 3/858 comes from the Djadochta Formation, which is between 75 and 71 million years in age. Just as it is today, the Gobi was a desert during the Cretaceous. IGM 3/858 may have died in a collapsing sand dune, the rapid burial preserving its skeleton in pristine condition.

Geiseltaliellus is an extinct genus of iguanian lizards that lived in what is now western Europe during the Eocene. It belongs to the family Corytophanidae, which includes modern casquehead lizards. Many fossils are known from Germany, France, and Belgium, with the most well preserved coming from the Messel pit lagerstätte in Messel, Germany. German paleontologist Oskar Kuhn named the genus in 1944 after the Geiseltal valley where the first specimens were found, designating the type species Geiseltaliellus longicaudus. Three new species — G. louisi, G. lamandini, and G. grisolli — were named in the 1990s and 2000s on the basis of more fragmentary remains from France and Belgium, although G. louisi has since been synonymized with G. longicaudus. In 2009 the Messel pit specimens were recognized as belonging to a species distinct from that of the G. longicaudus specimens in Geiseltalt and were collectively reclassified under a new name, G. maarius.

<span class="mw-page-title-main">Palaeovaranidae</span> Extinct reptilian clade

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<i>Paranecrosaurus</i> Extinct genus of lizards

Paranecrosaurus is an extinct genus of lizard from the Eocene Messel Pits of Germany. It contains a single species, Paranecrosaurus feisti, originally described as a species of Saniwa. It was carnivorous, as indicated by the presence of the lizard Cryptolacerta as stomatch contents. It is placed in the family Palaeovaranidae.

<i>Archaeovaranus</i> Genus of extinct lizards

Archaeovaranus is genus of varanid lizard from the early Eocene (Ypresian) Yuhuangding Formation of Hubei Province, China. The genus contains a single species, Archaeovaranus lii, known from a nearly complete skeleton. The holotype, which includes an intact skull, is associated but disarticulated. Archaeovaranus fills a gap in the varanid fossil record, as it represents a stem-varanid from the early Eocene of East Asia, and is the closest known relative of Varanus.

This is an overview of the paleofauna of the Eocene Messel Formation as explored by the Messel Pit excavations in Germany. A former quarry and now UNESCO World Heritage Site, the Messel Formation preserves what once were a series of anoxic lakes surrounded by a sub-tropical rainforest during the Middle Eocene, approximately 47 Ma.

References

  1. ↑ Pianka, Eric R.; King, Dennis; King, Ruth Allen (2004). Varanoid Lizards of the World. Indiana University Press. pp. 33 to 38. ISBN   978-0253343666.
  2. 1 2 3 4 5 6 Rieppel, O.; Grande, L. (July 2007). "The anatomy of the fossil varanid lizard Saniwa ensidens Leidy, 1870, based on a newly discovered complete skeleton". Journal of Paleontology . 81 (4): 643–665. doi:10.1666/pleo0022-3360(2007)081[0643:TAOTFV]2.0.CO;2. S2CID   130800851.
  3. 1 2 3 Conrad, J.; Rieppel, O.; Grande, L. (December 2008). "Re-assessment of varanid evolution based on new data from Saniwa ensidens Leidy, 1870 (Squamata, Reptilia)" (PDF). American Museum Novitates (3630): 1–15. doi:10.1206/596.1. hdl:2246/5939. S2CID   83550662.
  4. ↑ Dodt, Eberhard (1973). "The Parietal Eye (Pineal and Parietal Organs) of Lower Vertebrates". Visual Centers in the Brain. Handbook of Sensory Physiology. Vol. 7 / 3 / 3 B. Springer, Berlin, Heidelberg. pp. 113–140. doi:10.1007/978-3-642-65495-4_4. ISBN   9783642654978.
  5. ↑ Smith, Krister T.; Bhullar, Bhart-Anjan S.; Köhler, Gunther; Habersetzer, Jörg (2 April 2018). "The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex". Current Biology . 28 (7): 1101–1107.e2. Bibcode:2018CBio...28E1101S. doi: 10.1016/j.cub.2018.02.021 . ISSN   0960-9822. PMID   29614279.
  6. 1 2 Gilmore, C.W. (1922). "A new description of Saniwa ensidens Leidy, an extinct varanid lizard from Wyoming". Proceedings of the U.S. National Museum. 60 (23): 1–28. doi:10.5479/si.00963801.60-2418.1. S2CID   22291809.
  7. 1 2 Leidy, J. (1873). Contributions to the extinct vertebrate fauna of the Western Territories. Report of the United States Geological Survey of the Territories. Vol. 1. United States Government Printing Office. p. 358.
  8. ↑ Fejérváry, G.J. de (1918). "Contributions to a monography on the fossil Varanidae and Megalanidae" (PDF). Annales Historico-Naturales Musei Nationalis Hungarici. 16: 341–467. Archived from the original (PDF) on 26 March 2012.
  9. ↑ Caldwell, M.W. (March 2003). "Holotype snout elements of Saniwa ensidens reassigned to cf. Restes sp. indet. (Xenosauridae)". Journal of Paleontology . 77 (2): 393–396. doi:10.1666/0022-3360(2003)077<0393:HSEOSE>2.0.CO;2. S2CID   129541157.
  10. ↑ Augé, Marc Louis; Annelise FOLIE, undefined; Smith, Richard; PhéLizon, Alain; Paul GIGASE†, undefined; Smith, Thierry (2022-08-02). "Revision of the oldest varanid, Saniwa orsmaelensis Dollo, 1923, from the earliest Eocene of northwest Europe". Comptes Rendus Palevol. 21 (25): 511–529. doi: 10.5852/cr-palevol2022v21a25 . ISSN   1777-571X.
  11. ↑ Stritzke, R. (1983). "Saniwa feisti n. sp., ein Varanide (Lacertilia, Reptilia) aus dem Mittel-Eozän von Messel bei Darmstadt" (PDF). Senckenbergiana Lethaea. 64 (5–6): 497–508.
  12. ↑ Smith, Krister T.; Habersetzer, Jörg (2021). "The anatomy, phylogenetic relationships, and autecology of the carnivorous lizard "Saniwa" feisti Stritzke, 1983 from the Eocene of Messel, Germany". Comptes Rendus Palevol (in French). 20 (23): 441–506. doi: 10.5852/cr-palevol2021v20a23 . S2CID   236259655.
  13. ↑ Dong L, Wang YQ, Zhao Q, Vasilyan D, Wang Y, Evans SE (March 2022). "A new stem-varanid lizard (Reptilia, Squamata) from the early Eocene of China". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 377 (1847): 20210041. doi:10.1098/rstb.2021.0041. PMC   8819366 . PMID   35125002.
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