Sauropsid
A request that this article title be changed to Sauropsida is under discussion. Please do not move this article until the discussion is closed. |
Sauropsids | |
---|---|
Clockwise from top left: captorhinid eureptile)
| |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Superclass: | Tetrapoda |
Clade: | Reptiliomorpha |
Clade: | Amniota |
Clade: | Sauropsida , 1956
Watson |
Subclades | |
|
Sauropsida (
The base of Sauropsida forks into two main groups of "reptiles": Eureptilia ("true reptiles") and Parareptilia ("next to reptiles"). Eureptilia encompasses all living reptiles (including birds), as well as various extinct groups. Parareptilia is typically considered to be an entirely extinct group, though a few hypotheses for the origin of turtles have suggested that they belong to the parareptiles. The clades Recumbirostra and Varanopidae, traditionally thought to be lepospondyls and synapsids respectively, may also be basal sauropsids. The term "Sauropsida" originated in 1864 with Thomas Henry Huxley,[2] who grouped birds with reptiles based on fossil evidence.
History of classification
Huxley and the fossil gaps
The term Sauropsida ("lizard faces") has a long history, and hails back to
Sauropsids redefined (Goodrich, 1916)
By the early 20th century, the fossils of
Detailing the reptile family tree
In 1956,
This classification supplemented, but was never as popular as, the classification of the reptiles (according to
Cladistic definitions
The class Reptilia has been known to be an
Some taxonomists, such as Benton (2004), have co-opted the term to fit into traditional rank-based classifications, making Sauropsida and Synapsida class-level taxa to replace the traditional Class Reptilia, while Modesto and Anderson (2004), using the PhyloCode standard, have suggested replacing the name Sauropsida with their redefinition of Reptilia, arguing that the latter is by far better known and should have priority.[10]
Cladistic definitions of Sauropsida include:
- Sauropsida as the total group of reptiles: "Reptiles plus all other amniotes more closely related to them than they are to mammals" (Gauthier, 1994).[1]This is a branch-based total group definition. Gauthier (1994) considered turtles to be descended from parareptiles, thus defining Reptilia as a more restricted crown group encompassing diapsids and parareptiles (apart from mesosaurs, which he considered to be the most basal branch of sauropsids).
- Sauropsida as a total group, synonymous with Reptilia sensu lato: "The most inclusive clade containing Lacerta agilis and Crocodylus niloticus, but not Homo sapiens" (Modesto & Anderson, 2004).[10]This total group definition leaves the question of turtle ancestry unresolved.
- Sauropsida as a total group, synonymous with Reptilia sensu lato: "The most inclusive clade containing
- Sauropsida as a broad node-based group: "The last common ancestor of mesosaurs, testudines and diapsids, and all its descendants" (Laurin & Reisz, 1995).[11]Though formulated differently, this grouping was similar in scope and intention to the definition provided by Gauthier (1994).
Evolutionary history
Sauropsids evolved from basal amniotes approximately 320 million years ago, in the Carboniferous Period of the Paleozoic Era. In the Mesozoic Era (from about 250 million years ago to about 66 million years ago), sauropsids were the largest animals on land, in the water, and in the air. The Mesozoic is sometimes called the Age of Reptiles. In the Cretaceous–Paleogene extinction event, the large-bodied sauropsids died out in the global extinction event at the end of the Mesozoic era. With the exception of a few species of birds, the entire dinosaur lineage became extinct; in the following era, the Cenozoic, the remaining birds diversified so extensively that, today, nearly one out of every three species of land vertebrate is a bird species.
Phylogeny
The cladogram presented here illustrates the "family tree" of sauropsids, and follows a simplified version of the relationships found by M.S. Lee, in 2013.[12] All genetic studies have supported the hypothesis that turtles (formerly categorized together with ancient anapsids) are diapsid reptiles, despite lacking any skull openings behind their eye sockets; some studies have even placed turtles among the archosaurs,[12][13][14][15][16][17] though a few have recovered turtles as lepidosauromorphs instead.[18] The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results.[12]
Amniota |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Laurin & Piñeiro (2017) and Modesto (2019) proposed an alternate phylogeny of basal sauropsids. In this tree, parareptiles include turtles and are closely related to non-araeoscelidian diapsids. The family Varanopidae, otherwise included in Synapsida, is considered by Modesto a sauropsid group.[19][20]
| |||||||||||||
In recent studies, the "
Structure difference with synapsids
The last common ancestor of synapsids and Sauropsida lived at around 320mya during Carboniferous, known as Reptiliomorpha.
Thermal and secretion
The early synapsids inherited abundant glands on their skins from their amphibian ancestors. Those glands evolved into sweat glands in synapsids, which granted them the ability to maintain constant body temperature but made them unable to save water from evaporation. Moreover, the way synapsids discharge nitrogenous waste is through urea, which is toxic and must be dissolved in water to be secreted. Unfortunately, the upcoming Permian and Triassic periods were arid periods. As a result, only a small percent of early synapsids survived in the land from South Africa to Antarctica in today's geography. Unlike synapsids, sauropsids do not have those glands on the skin; their way of nitrogenous waste emission is through uric acid which does not require water and can be excreted with feces. As a result, sauropsids were able to expand to all environments and reach their pinnacle. Even today, most vertebrates that live in arid environments are sauropsids, snakes and desert lizards for example.
Brain structure
Different from how synapsids have their cortex in six different layers of neurons which is called neocortex, the cerebrum of Sauropsida has a completely different structure. For the corresponding structure of the cerebrum in the classic view, the neocortex of synapsids is homology with only the Archicortex of the avian brain. However, in the modern view appeared since the 1960s, behavioral studies suggested that avian neostriatum and hyperstriatum can receive signals of vision, hearing, and body sensations, which means they act just like the neocortex. Comparing an avian brain to that to a mammal, nuclear-to-layered hypothesis proposed by Karten (1969), suggested that the cells which form layers in synapsids' neocortex, gather individually by type and form several nuclei. For synapsids, when one new function is adapted in evolution it will be assigned to a separate area of cortex, so for each function, synapsids will have to develop a separate area of cortex, and damage to that specific cortex may cause disability.[23] However, for Sauropsida functions are disassembled and assigned to all nuclei. In this case, brain function is highly flexible for Sauropsida, even with a small brain, many Sauropsida can still have a relatively high intelligence compared to mammals, for example, birds in the family Corvidae. So, it is possible that some non-avian dinosaurs, like Tyrannosaurus, which had tiny brains compared to their enormous body size, were more intelligent than previously thought.[24]
References
- ^ a b Gauthier J.A. (1994): The diversification of the amniotes. In: D.R. Prothero and R.M. Schoch (ed.) Major Features of Vertebrate Evolution: 129–159. Knoxville, Tennessee: The Paleontological Society.
- ^ a b Huxley, Thomas Henry (1864). "The Structure and Classification of the Mammalia". Medical Times and Gazette. Huxley Archives. Retrieved 2023-03-16.
- ^ Huxley, Thomas Henry (1877). "Lectures on Evolution". Collected Essays IV. Retrieved 2023-03-16.
{{cite book}}
:|website=
ignored (help) - ^ .
- .
- ^ Romer, A.S. (1933). Vertebrate Paleontology. University of Chicago Press., 3rd ed., 1966.
- ^ Gauthier, .A., Kluge, A.G & Rowe, T. (1988). The early evolution of the Amniota. Pages 103–155 in Michael J. Benton (ed.): The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Syst. Ass. Spec. Vol. 35A. Clarendon Press, Oxford.
- ^ Laurin, Michel; Gauthier, Jacques (January 1996). "Amniota. Mammals, reptiles (turtles, lizards, Sphenodon, crocodiles, birds) and their extinct relatives". Tree of Life Web Project. Archived from the original on 10 April 2006. Retrieved 2023-03-16.
{{cite web}}
: CS1 maint: unfit URL (link) - ^ Pearse, A.S. (ed, 1947): Zoological Names: a List of Phyla, Classes, and Orders. Prepared for Section F, American Association for the Advancement of Science. Second edition. Durham, North Carolina, U.S.A., pp. 1-22
- ^ PMID 15545258.
- .
- ^ S2CID 2106400.
- PMID 10508547.
- PMID 9826682.
- PMID 15625185.
- PMID 17719245.
- S2CID 12116018.
- PMID 21775315.
- ISSN 2296-6463.
- S2CID 209672518. Retrieved 29 December 2020.
- S2CID 2478132.
- ISSN 0024-4082.
- ^ Karten, H. J. in Comparative and Evolutionary Aspects of the Vertebrate Central Nervous System (ed. Pertras, J.) 164–179 (1969).
- doi:10.1038/nrn1606.