Pelycosaur ( )
is an older term for
basal
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
or primitive Late
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
synapsids, excluding the
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
, but this is now thought to be incorrect, and seen as outdated.
Because it excludes the advanced synapsid group
Therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
a, the term is
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
and contrary to modern formal naming practice.
Thus the name ''pelycosaurs'', similar to the term ''mammal-like reptiles'', had fallen out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature.
The terms stem mammals, protomammals, and basal or primitive synapsids are used where needed, instead.
Etymology
The term ''pelycosaur'' has been fairly well abandoned by paleontologists because it no longer matches the features that distinguish a clade.
The modern word was created from Greek meaning 'wooden bowl' or 'axe' and meaning 'lizard'. The intended etymology presents a problem, since ''pelycosaur'' as created basically means 'basin lizard', but there is a ambiguity between several original Greek words in that is 'wooden bowl' and is 'basin', whereas is 'ax' (like 'double-edged ax').
Pelycosauria is a
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
taxon because it excludes the
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s. For that reason, the term is sometimes avoided by proponents of a strict cladistic approach.
Eupelycosauria
Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308million years ago during the Early Pennsylvanian epoch, with the fo ...
is used to designate the clade that includes most pelycosaurs, along with the Therapsida and Mammalia. In contrast to "pelycosaurs", Eupelycosauria is a proper
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
group.
Caseasauria
Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small inse ...
is a pelycosaur side-branch, or clade, that did not leave any descendants.
Evolutionary history
The pelycosaurs appear to have been a group of synapsids that have direct ancestral links with the
mammals, having differentiated teeth and a developing hard palate. The pelycosaurs appeared during the
Late
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
and reached their apex in the
early part of the Permian, remaining the dominant land animals for some 40 million years. A few continued into the
Capitanian, but they experienced a sharp decline in diversity in the late
Kungurian.
They were succeeded by the
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s.
Description
Some species were quite large, growing to a length of or more, although most species were much smaller. Well-known pelycosaurs include the
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
''
Dimetrodon
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontid ...
'', ''
Sphenacodon
''Sphenacodon'' (meaning "wedge point tooth") is an extinct genus of synapsid that lived from about 300 to about 280 million years ago (Ma) during the Late Carboniferous and Early Permian periods. Like the closely related '' Dimetrodon'', ''Sphen ...
'', ''
Edaphosaurus'', and ''
Ophiacodon
''Ophiacodon'' (meaning "snake tooth") is an extinct genus of synapsid belonging to the family Ophiacodontidae that lived from the Late Carboniferous to the Early Permian in North America and Europe. The genus was named along with its type spec ...
''.
Pelycosaur fossils have been found mainly in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
and
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, although some small, late-surviving forms are known from
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
and
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
.
Unlike
lepidosauria
The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species, m ...
n reptiles, pelycosaurs lacked reptilian epidermal
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
. Fossil evidence from some
varanopids
Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an ''Archaeothyris''-like synapsid in the Late Carbonifero ...
shows that parts of the skin were covered in rows of
osteoderm
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...
s, presumably overlain by horny
scutes.
[ The belly was covered in rectangular scutes, looking like those present in ]crocodile
Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
s. Parts of the skin ''not'' covered in scutes might have had naked, glandular skin like that found in some mammals. Dermal scutes are also found in a diverse number of extant mammals with conservative body types, such as in the tails of some rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...
s, sengis, moonrat
The moonrat (''Echinosorex gymnura'') is a southeast Asian species of mammal in the family Erinaceidae (hedgehogs and gymnures). It is the only species in the genus ''Echinosorex''. The moonrat is a fairly small, primarily carnivorous animal whi ...
s, the opossum
Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered North ...
s and other marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
s, and as regular dermal armour with underlying bone in the armadillo
Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, along wi ...
.
At least two pelycosaur clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s independently evolved a tall sail
A sail is a tensile structure—which is made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may ...
, consisting of elongated vertebral spines: the edaphosaurids and the sphenacodontids. In life, this would have been covered by skin, and likely functioned as a thermoregulatory
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
device or as a mating display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
.
Taxonomy
In phylogenetic nomenclature, "Pelycosauria" is not used formally, since it does not constitute a group of ''all'' organisms descended from some common ancestor (a clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
), because the group specifically excludes the therapsids which are descended from pelycosaurs. Instead, it represents a paraphyletic "grade" of basal synapsids leading up to the clade Therapsida.
In 1940, the group was reviewed in detail, and every species known at the time described, with many illustrated, in an important monograph by Alfred Sherwood Romer and Llewellyn Price
Llewellyn Ivor Price (October 9, 1905 – June 9, 1980) was one of the first Brazilian paleontologists. His work contributed not only to the development of Brazilian but also to global paleontology. He collected '' Staurikosaurus'', the first ...
.
In traditional classification, the order Pelycosauria is paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
in that the therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s (the "higher" synapsids) have emerged from them. That means Pelycosauria is a grouping of animals that does not contain all descendants of its common ancestor, as is often required by phylogenetic nomenclature
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...
. In evolutionary taxonomy
Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of Phylogenetics, phylogenetic relationship (shared descent), progenitor-de ...
, Therapsida is a separated order from Pelycosauria, and mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s (having evolved from therapsids) are separated from both as their own class. This use has not been recommended by a majority of systematists since the 1990s, but several paleontologists nevertheless continue using this word.
The following classification was presented by Benton in 2004.
* Order Pelycosauria *
** Family Eothyrididae
Eothyrididae is an extinct family of very primitive, insectivorous synapsids. Only three genera are known, ''Eothyris'', '' Vaughnictis'' and '' Oedaleops'', all from the early Permian of North America. Their main distinguishing feature is the l ...
** Family Caseidae
Caseidae are an extinct family of basal synapsids that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the south-central part of the United States (Texas, Oklaho ...
** Family Varanopidae
Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an ''Archaeothyris''-like synapsid in the Late Carbonifer ...
** Family Ophiacodontidae
** Family Edaphosauridae
** Family Sphenacodontidae
* Order Therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
a
See also
* Evolution of mammals
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked l ...
* List of pelycosaurs
This list of pelycosaurs is an attempt to create a comprehensive listing of all genera that have ever been included in the synapsida excluding therapsida and purely vernacular terms. The list includes all commonly accepted genera, but also genera t ...
* Vertebrate paleontology
Notes
References
*
External links
*
*
{{Taxonbar, from=Q319520
Synapsids
Paraphyletic groups