Dimetrodon

Dimetrodon

Overview
Dimetrodon was a predatory synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...

 genus
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...

 that flourished during the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period, living between 280–265 million years ago (during the Artinskian
Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Artinskian lasted between 284.4 ± 0.7 and 275.6 ± 0.7 million years ago...

 to Capitanian
Capitanian
In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian epoch or series. The Capitanian lasted between and...

  stages).

As a synapsid it was more closely related to mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s than to true reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s such as lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

s and snakes. It is classified as a pelycosaur
Pelycosaur
The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...

. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s of Dimetrodon have been found in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. Dimetrodon had a sail on its back, which is thought to have been used for regulating body temperature, or for display.


Dimetrodon was one of the largest land animals and the apex predator of its time.
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Encyclopedia
Dimetrodon was a predatory synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...

 genus
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...

 that flourished during the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period, living between 280–265 million years ago (during the Artinskian
Artinskian
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Artinskian lasted between 284.4 ± 0.7 and 275.6 ± 0.7 million years ago...

 to Capitanian
Capitanian
In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian epoch or series. The Capitanian lasted between and...

  stages).

As a synapsid it was more closely related to mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s than to true reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s such as lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

s and snakes. It is classified as a pelycosaur
Pelycosaur
The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...

. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s of Dimetrodon have been found in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. Dimetrodon had a sail on its back, which is thought to have been used for regulating body temperature, or for display.

Description and paleobiology



Dimetrodon was one of the largest land animals and the apex predator of its time. Dimetrodon’s diet could have included freshwater sharks, amphibians, reptiles and other amniotes. The amphibian Eryops
Eryops
Eryops meaning "drawn-out face" because most of its skull was in front of its eyes is a genus of extinct, semi-aquatic amphibian found primarily in the Lower Permian-aged Admiral Formation of Archer County, Texas, but fossils are also found in New Mexico and parts of the eastern United...

and freshwater shark Xenacanthus
Xenacanthus
Xenacanthus is a genus of prehistoric sharks. The first species of the genus lived in the later Devonian period, and they survived until the end of the Triassic, 202 million years ago. Fossils of various species have been found worldwide....

were prey. Humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

es of Eryops and skulls of Xenacanthus were found to have teeth marks matching the shape of the teeth of Dimetrodon. Dimetrodon probably hunted based on sight and smell. Different types ranged in length from 90 to 400 cm (35.4 to 157.5 ) and weighing 14 to 300 kg (30.9 to 661.4 ).

The structure of the bones indicate that it was cold-blooded
Ectotherm
An ectotherm, from the Greek εκτός "outside" and θερμός "hot", refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body...

 and had low metabolism . There are few channels in the bones, which indicates limited circulation. For proper metabolism, Dimetrodon needed external heat. The growth pattern of Dimetrodon is unclear. Analysis based on the length and ossification of the thigh, the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...

 and the humerus, shows a poor correlation between the size and relative age of individuals. There was a difference in habitat between juveniles and adults in Dimetrodon. Younger animals lived mainly in habitats with plenty of shelter, such as swamps and reed-lined banks. The adults preferred the open areas of flood plains. This is the finding of fossils from the Wichita Group of Texas. The length of the upper arm and thigh, the main measure that was used to distinguish between young and adult specimens, were examined and it was determined what type of sediment the fossils occurred. A similar difference in distribution between young and adult specimens, was also found for Ophiacodon and Eryops and is also known from modern crocodiles and water turtles.

Skull



Dimetrodon has two types of teeth, shearing teeth and sharp canine teeth. Its name, in fact, means "two-measures of teeth". Dimetrodon was one of the first animals with differentiated
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...

 teeth and the teeth were suitable for killing animals then tearing them to pieces. Dimetrodon has a large skull with a temporal fenestra behind each eye orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

 on the lateral surface, a distinguishing feature of synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...

 skull. This made possible new attachment sites for jaw muscles, which could run faster and create mastication
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...

. Based on the osteology of the temporal region, the posterior part of the palate and mandible, powerful jaw muscles of Dimetrodon was found to have differentiated. Two groups of muscles have been reconstructed: the adductors
Adduction
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...

 and the pterygoideus
Lateral pterygoid muscle
The lateral pterygoid is a muscle of mastication with two heads. It lies superiorly to the medial pterygoid.-Origin and insertion:...

. The adductors were from temporal to the inside of the lower jaw and caused the closing of the jaws. The pterygoideus ran from the Pterygoid processes of the sphenoid
Pterygoid processes of the sphenoid
The pterygoid processes of the sphenoid, one on either side, descend perpendicularly from the regions where the body and great wings unite.Each process consists of a medial pterygoid plate and a lateral pterygoid plate, the upper parts of which are fused anteriorly; a vertical sulcus, the...

 and the sphenoid bone
Sphenoid bone
The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

 to the articular
Articular
The articular bone is part of the lower jaw of most tetrapods, including amphibians, sauropsids and early synapsids. In these animals it is connected to two other lower jaw bones, the suprangular and the angular...

, one of the bones in the lower jaw, and caused a backward movement of the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...

. The development of the coronoid process in Dimetrodon compared with other quadrupeds , led to an increase in the length of the moment of external muscular and thus greater bite force. The construction of the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

 and vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...

 of Dimetrodon were described by Case, but he drew no conclusions about the possible function of these organs.

In a 2001 study on the biomechanics
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...

 of the dinosaur Albertosaurus's
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...

teeth, William L. Abler observed that examined Dimetrodon teeth possessed serrations so fine they resembled a crack in the tooth. Though Albertosaurus
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...

had similar serrations, the base of each serration included a round void
Void
-In science and engineering:*Void , the empty spaces between galaxy filaments*Lack of matter, or vacuum*Void, in boiling heat transfer, formed where there is a departure from nucleate boiling, causing a critical heat flux...

 which would have functioned to distribute force over a larger surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

. These voids, termed an ampulla, would hinder the ability of the "crack" formed by the serration to propagate through the tooth. Dimetrodon was found to lack adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

s for preventing "crack" propagation.

Legs


The sturdy legs of Dimetrodon were spread beside the body. Judging from the construction of the legs Dimetrodon was a relatively fast and smoothly moving animal, especially compared to its solid build herbivorous relatives. The shape of the hip bones, the hind legs and the joints between the vertebrae can be seen.

Sail



The most striking feature of Dimetrodon has been the one meter long protrusions at the back of the spine, the spinous processes also referred to as spines. These spines have a wide base and then his long and slender with a pointed tip. It is believed that the spines were connected by a solid skin and thus formed a sail on the back.

Many suggestions have been made about the function of the sail; as camouflage among reeds while it waited for prey, for sexual display, or literally as a sail while swimming. Romer and Price first suggested that it served a mechanical function and strengthened the backbone, but Romer later realized that the sail had evolved with features strongly suggesting an early attempt at temperature regulation. The fact that these spines are present in both Dimetrodon and Edaphosaurus
Edaphosaurus
Edaphosaurus is a genus of prehistoric synapsid which lived around 303 to 265 million years ago, during the late Carboniferous to early Permian periods. The name Edaphosaurus means "ground lizard" and is derived from the Greek edaphos/εδαφος and σαυρος/sauros...

, two animals in similar geological periods, would suggest that the spines had a significant value in the survival as result of environmental factors. In a study of the relationship between body temperature and blood pressure, Rodbard analyzed the evolution of thermoregulation, which he thought was a one possible function of the sails of Dimetrodon and Edaphosaurus. The spines of Dimetrodon have grooves on the base that were presumably ingested by blood vessels and thus ensured good bloodflow through the skin of the sail. The theory is that Dimetrodon was active in the early morning when the sun rose. The sail would be pointed towards the sun and would absorb heat allowing rapid warming. This allowed Dimetrodon to hunt at a time when other animals were not sufficiently warmed up and were slow. The sail increased body surface area by 50%. According to calculations by Bramwell Fellgett, it took a 200 kg (440.9 lb) Dimetrodon approximately one and a half hours for its body temperature to go from 26 to 32 °C (78.8 to 89.6 F) A study by Haack concluded that warming was slower than previously thought and that the process probably took four hours. In order to cool its body in the hot midday sun, Dimetrodon turned its sail away from the sun, causing the heat to drain. The rapid warming using the sail give Dimetrodon an edge over larger animals, weighing over 55 kg. Smaller animals had higher body surface-to-mass ratio, making them hotter than Dimetrodon. The prey of Dimetrodon would therefore have been mostly large animals like Diadectes
Diadectes
Diadectes was a genus of large, very reptile-like amphibians that lived during the early Permian period...

, Eryops
Eryops
Eryops meaning "drawn-out face" because most of its skull was in front of its eyes is a genus of extinct, semi-aquatic amphibian found primarily in the Lower Permian-aged Admiral Formation of Archer County, Texas, but fossils are also found in New Mexico and parts of the eastern United...

and Ophiacodon
Ophiacodon
Ophiacodon was a large pelycosaur. Its fossils were found in Joggins, Nova Scotia, Canada.Ophiacodon was at least two meters in length, and the largest species were up to . It is estimated to have weighed from . The size of the various species increased during the Early Permian epoch until its...

. The changing climate during the Permian period, when the temperature increased, is a possible reason for the extinction of Dimetrodon since the sail meant no benefit over other animals and was rather a disadvantage due to its fragility.

Classification


The genus Dimetrodon was created in 1878 by the American scientist Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

 and described during the infamous Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...

 between him and 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...

. 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...

 is Dimetrodon incisivus. The genus name is derived from the Greek di ("two"), metron ("measure") and odon ("tooth"), a reference to the fact that the animal had teeth in two sizes. The species designation means "pertaining to the cutting tooth (incisor)," a reference to the size of the incisors. The holotype, bearing the name fossil is AMNH 4116.

Cope had actually previously described other species of Dimetrodon. In 1877 he named a species Clepsydrops limbatus but in 1940, Romer and Price assign this species to Dimetrodon. Cope believed in a close relationship between Clepsydrops and Dimetrodon. Nowadays it has become clear that both genera are not very closely related: Clepsydrops is now considered a member of the Ophiacodontidae
Ophiacodontidae
Ophiacodontidae were pelycosaur synapsids. They appeared in the late Carboniferous period. Archaeothyris, and Clepsydrops were among the earliest Ophiacodontids. Archaeothyris and its relatives were the members of this family. Some ophiacodonts were semi-aquatic, and few were fully aquatic, but...

. Dimetrodon was giving special place: in 1925 by Franz Nopcsa, as member of the specailly created Dimetrodontinae, but was added to the family Sphenacodontidae
Sphenacodontidae
Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...

  by Eleanor Daly in 1973.

The significance of this classification of Dimetrodon depends on the system used. In the classical Linnaeïsche system, it belongs to the genus order Pelycosauria. Since this classification, the Therapsida
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...

 and mammals traditionally been placed in the order Pelycosauria, this order is in fact paraphyletic as not all descendants belong to it. Not only the order as a whole is paraphyletic but the family within that order which contains the ancestor of the later therapsiden and mammals. Now it is the family Sphenacodontidae
Sphenacodontidae
Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...

 to which Dimetrodon belongs.
  • Class Reptiles (Reptilia)
    • Underclass Anapsida
    • Subclass Diapsida
    • Underclass Synapsida
      • Order Pelycosauria
        • Family Caseidae
          Caseidae
          The Caseidae were a widespread group of very primitive herbivorous synapsids, which appeared during the later early Permian and persisted until the late middle Permian. Although ranging in size from 1 to 5½ meters in body length, caseids were surprisingly conservative in their skeletal anatomy and...

        • Family Edaphosauridae
          Edaphosauridae
          Edaphosauridae is a family of mostly large advanced, Late Pennsylvanian to early Permian pelycosaurs.They were the earliest known herbivorous amniotes, and along with the Diadectidae the earliest known herbivorous tetrapods...

        • Family Eothyrididae
          Eothyrididae
          The Eothyrididae were a small group of very primitive, insectivorous synapsids. Only two genera are known, Eothyris and Oedaleops, both from the early Permian of North America...

        • Family Ophiacodontidae
          Ophiacodontidae
          Ophiacodontidae were pelycosaur synapsids. They appeared in the late Carboniferous period. Archaeothyris, and Clepsydrops were among the earliest Ophiacodontids. Archaeothyris and its relatives were the members of this family. Some ophiacodonts were semi-aquatic, and few were fully aquatic, but...

        • Family Sphenacodontidae
          Sphenacodontidae
          Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...

        • Family Varanopidae
          Varanopidae
          Varanopidae was a family of synapsid "pelycosaurs" that resembled monitor lizards and might have had the same lifestyle, hence their name. No known varanopids developed a sail like Dimetrodon. Their size varied from lizard-sized to dog-sized creatures. Varanopids already showed some advanced...

      • Order Therapsida
        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...



In the cladistic system, only monophyletic groups are used: that is taxa that include all the descendants. The monophyletic group that Dimetrodon belongs to also includes close relatives Ctenospondylus
Ctenospondylus
Ctenospondylus, was a pelycosaur that was about 3 meters long. It lived from Latest Carboniferous to Early Permian. Its fossils were found in the U.S. states of Ohio and Texas. It was a carnivore and preyed upon animals close to its size...

, Neosaurus
Neosaurus
Neosaurus is a little-known pelycosaur of the family Sphenacodontidae. It was related to the well known Dimetrodon, although much smaller and lived during the Early Permian. Its fossils were found in the Jura region of France....

, Secodontosaurus
Secodontosaurus
Secodontosaurus was a pelycosaur that lived in Texas during the Early Permian age. Though it had the same body style as other sphenacodontids, it had an unusually low and narrow skull. It had a long neural spines, like Dimetrodon, which Secodontosaurus was related to...

, Sphenacodon
Sphenacodon
Sphenacodon was a pelycosaur that was about in length. Sphenacodon belongs to the family Sphenacodontidae, a lineage that was related to the therapsids...

and Steppesaurus
Steppesaurus
Steppesaurus is an extinct genus of pelycosaur belonging to the Sphenacodontidae family, related to Dimetrodon and Sphenacodon....

. Within Sphenacodontidae Secodontosaurus is the closest relative of Dimetrodon. The Sphenacodontidae is classified, together with Tetraceratops
Tetraceratops
Tetraceratops insignis was a lizard-like synapsid. It lived during the Early Permian period. According to a recent, controversial report, T. insignis is the first known therapsid. Other scientists, on the other hand, say that it is a more primitive species of synapsid, possibly an unusual,...

and Therapsida (which now includes the mammals) in the clade Sphenacodontoidea
Sphenacodontoidea
Sphenacodontoidea is the name given to the clade that includes the most recent common ancestor of the Sphenacodontidae and the Therapsida and their descendants...

. The Sphenacodontoidea together with a few basal (bottom the tree upright) forms Haptodus
Haptodus
Haptodus was a small sphenacodont, a clade that includes therapsids and hence, mammals. It was at least in length. It lived from Latest Carboniferous to Early Permian, in the equatorial Pangea. It was a medium-sized predator, feeding on insects and small vertebrates. It is one of the basalmost...

 the clade Sphenacodontia
Sphenacodontia
Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants . They first appear during the Late Pennsylvanian epoch. The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front teeth; and...

.
  • Synapsida
    • Caseasauria
      Caseasauria
      The Caseasauria are one of the two main clades of early synapsids, the other being the Eupelycosauria. They are currently known only from the Permian, and include two superficially different families, the small insectivorous or carnivorous Eothyrididae, and the large herbivorous CaseidaeThese two...

      • Caseidae
        Caseidae
        The Caseidae were a widespread group of very primitive herbivorous synapsids, which appeared during the later early Permian and persisted until the late middle Permian. Although ranging in size from 1 to 5½ meters in body length, caseids were surprisingly conservative in their skeletal anatomy and...

      • Eothyrididae
        Eothyrididae
        The Eothyrididae were a small group of very primitive, insectivorous synapsids. Only two genera are known, Eothyris and Oedaleops, both from the early Permian of North America...

    • Eupelycosauria
      Eupelycosauria
      The Eupelycosauria originally referred to a suborder of 'pelycosaurs' , but has been redefined to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals...

      • Edaphosauridae
        Edaphosauridae
        Edaphosauridae is a family of mostly large advanced, Late Pennsylvanian to early Permian pelycosaurs.They were the earliest known herbivorous amniotes, and along with the Diadectidae the earliest known herbivorous tetrapods...

      • Ophiacodontidae
        Ophiacodontidae
        Ophiacodontidae were pelycosaur synapsids. They appeared in the late Carboniferous period. Archaeothyris, and Clepsydrops were among the earliest Ophiacodontids. Archaeothyris and its relatives were the members of this family. Some ophiacodonts were semi-aquatic, and few were fully aquatic, but...

      • Varanopidae
        Varanopidae
        Varanopidae was a family of synapsid "pelycosaurs" that resembled monitor lizards and might have had the same lifestyle, hence their name. No known varanopids developed a sail like Dimetrodon. Their size varied from lizard-sized to dog-sized creatures. Varanopids already showed some advanced...

      • Sphenacodontia
        Sphenacodontia
        Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants . They first appear during the Late Pennsylvanian epoch. The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front teeth; and...

        • Basic forms as Haptodus
          Haptodus
          Haptodus was a small sphenacodont, a clade that includes therapsids and hence, mammals. It was at least in length. It lived from Latest Carboniferous to Early Permian, in the equatorial Pangea. It was a medium-sized predator, feeding on insects and small vertebrates. It is one of the basalmost...

        • Sphenacodontoidea
          Sphenacodontoidea
          Sphenacodontoidea is the name given to the clade that includes the most recent common ancestor of the Sphenacodontidae and the Therapsida and their descendants...

          • Sphenacodontidae
            Sphenacodontidae
            Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...

             sensu stricto
          • Tetraceratops
            Tetraceratops
            Tetraceratops insignis was a lizard-like synapsid. It lived during the Early Permian period. According to a recent, controversial report, T. insignis is the first known therapsid. Other scientists, on the other hand, say that it is a more primitive species of synapsid, possibly an unusual,...

          • Therapsida
            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...

            • Mammalia

Species



The genus Dimetrodon currently includes several more or less recognized types:
  • D. platensis (Olson, 1962)
  • D. booneorum (Romer, 1937)
  • D. dollovianus (Cope, 1888)
  • D. fritillus (Cope, 1878)
  • D. gigas (Cope, 1878)
  • D. grandis (Case, 1907)
  • D. incisivus (Cope, 1878)
  • D. kempae (Romer, 1937)
  • D. limbatus (Cope, 1877)
  • D. loomisi (Romer, 1937)
  • D. macrospondylus (Cope, 1884)
  • D. milleri (Romer, 1937)
  • D. natalis (Cope, 1877)
  • D. occidentalis (Berman, 1977)
  • D. platycentrus (Case, 1907)
  • D. rectiformis (Cope, 1878)
  • D. semiradicatus (Cope, 1881)
  • D. teutonis (Berman et al, 2001)


Many species have been described by Edward Drinker Cope during his expeditions in 1880. Romer Alfred Sherman described a few species in the 1930s and 1940s. Most of the type specimens from the collection of which Cope based his descriptions were not released from the matrix. Reassessment after his death led to different conclusions on these specimens, including on the construction of the skull. The status of some of the species described by Cope is questionable, namely D. fritillus, D. gigas, D. incisivus, D. rectiformis and D. semiradicatus. There is a broad subdivision into species with a long skull from the Early Permian and species with a short head from the later parts of the Permian.

Relationship with modern mammals


As a synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...

, Dimetrodon was distantly related to modern mammals. Synapsids were the first tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...

s to evolve differentiated, or heterodont
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...

, teeth. While reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s barely chew their food, essentially gulping it down, synapsids like Dimetrodon developed teeth to help shear meat into smaller pieces for easier digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

. These "two-measure teeth" eventually gave rise to the various kinds of teeth present in modern mammals.

Paleoecology



Fossils are known from the United States ( Texas, Oklahoma, New Mexico , Arizona , Utah and Ohio ) and Germany, areas that the first parts of the Permian were part of the supercontinent Euramerica
Euramerica
Euramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons .300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica...

. Most fossil finds are part of lowland ecosystems, during the Permian would have been vast wetlands. In particular, the Red Beds of Texas is an area of great diversity of fossils of Dimetrodon species and other species from the Early Permian. The fossils date from 290 to 270 million years ago, which means it lived from the Cisuralian to the Guadalupian period. Dimetrodon probably developed from a Sphenacodon-like ancestor. The climate of the Late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 (Pennsylvanien) and Early Permian (Asse Lien, Sakmarien, Arti Skiing) resulted in warm, humid ecosystems in subtropical and tropical zones, consisting of vast wetland areas. In addition there were large ice sheets on the Southern Hemisphere that stretched to about 30° south. The fauna was concentrated in this period therefore in tropical and subtropical zones. Aquatic and semi-aquatic tetrapods dominated, while land predators as Dimetrodon were largely water-fed animals. The Early Permian had a drier and hotter climate where deserts began to develop. This led a climate change causing major extinction of the tetrapods, thus clearing the way for the development of therapsids
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...

. Dimetrodon was replaced as an apex predator by carnivorous therapsidens like Biarmosuchia
Biarmosuchia
Biarmosuchia, also known as Eotitanosuchia and Phthinosuchia, is an assemblage of primitive Permian therapsids that represent either a paraphyletic stem group or a very early off-shoot of the main therapsid tree....

and Dinocephalia
Dinocephalia
Dinocephalia are a clade of large early therapsids that flourished during the Middle Permian, but became extinct leaving no descendants.-Description:...

.

In popular culture


  • In many popular culture references, Dimetrodon is often erroneously regarded as a dinosaur
    Dinosaur
    Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

    , or as living alongside dinosaurs.
  • In 1907 a composite skeleton of Edaphosaurus
    Edaphosaurus
    Edaphosaurus is a genus of prehistoric synapsid which lived around 303 to 265 million years ago, during the late Carboniferous to early Permian periods. The name Edaphosaurus means "ground lizard" and is derived from the Greek edaphos/εδαφος and σαυρος/sauros...

    and Dimetrodon bones recovered from Texas went on display in the American Museum of Natural History
    American Museum of Natural History
    The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...

    . Presented by the curator
    Curator
    A curator is a manager or overseer. Traditionally, a curator or keeper of a cultural heritage institution is a content specialist responsible for an institution's collections and involved with the interpretation of heritage material...

     of vertebrate paleontology
    Vertebrate paleontology
    Vertebrate paleontology is a large subfield to paleontology seeking to discover the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord, through the study of their fossilized remains...

    , Henry Fairfield Osborn
    Henry Fairfield Osborn
    Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...

    , the composite was illustrated in the pages of Scientific American
    Scientific American
    Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...

    by scientific illustrator Charles R. Knight
    Charles R. Knight
    Charles Robert Knight was an American artist best known for his influential paintings of dinosaurs and other prehistoric animals...

     in May 1907 as Naosaurus.
  • The first film depiction of Dimetrodon was the 1959 movie Journey to the Center of the Earth
    Journey to the Center of the Earth (1959 film)
    Journey to the Center of the Earth is a 1959 adventure film adapted by Charles Brackett from the novel by Jules Verne. It stars Pat Boone, James Mason, Arlene Dahl, Peter Ronson, Diane Baker, Thayer David and Alan Napier...

    .
  • In the 1974 television
    Television
    Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

     series Land of the Lost
    Land of the Lost (1974 TV series)
    Land of the Lost is a children's television series co-created and produced by Sid and Marty Krofft. During its original run, it was broadcast on the NBC television network....

    , a very large Dimetrodon-like creature named Torchy first appeared in the Season 3 episode "Cornered". Torchy could breathe fire and would often eat coal
    Coal
    Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

     to stoke his internal furnace
    Furnace
    A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

    , and fought and defeated the show's female Allosaurus
    Allosaurus
    Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...

    , Big Alice.
  • Paleoworld
    Paleoworld
    Paleoworld was a documentary television series that was produced for The Learning Channel, and has had a total of 50 episodes. Some consider it to be the largest and most comprehensive paleontology series ever made. The series began in late September 1994 and, after 4 seasons, ended in 1997...

    , a documentary by the learning channel, featured an episode "Tale of a Sail", which depicted the evolution and the nature of Dimetrodon.
  • In the television documentary Walking With Monsters
    Walking with Monsters
    Walking with Monsters is a three-part British documentary film series about life in the Paleozoic, bringing to life extinct arthropods, fish, amphibians, synapsids, and reptiles...

    (called Before the Dinosaurs in the United States), baby Dimetrodon were shown hatching with sails, fully independent. In fact, no Dimetrodon eggs have yet been found and it is entirely possible that the sail, which would be hard to store in an egg, was either absent or not rigid upon hatching. Hatchlings were portrayed sprinting towards trees after hatching in order to escape cannibalistic adults, behaviors based on the modern Komodo Dragon
    Komodo dragon
    The Komodo dragon , also known as the Komodo monitor, is a large species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, Gili Motang and Gili Dasami. A member of the monitor lizard family , it is the largest living species of lizard, growing to a maximum length of in rare cases...

    . Dimetrodon was also shown as having an egg-laying style similar to the modern crocodile
    Crocodile
    A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

    , though no evidence regarding Dimetrodon reproduction has ever actually been found. Additionally, Dimetrodon were shown to eat ninety percent of a carcass
    Carcass
    Carcass may refer to:*Cadaver of a human, or carrion of an animal.*Carcass , a death metal/grindcore band*Carcass , a type of incendiary ammunition designed to be fired from a cannon, three ships of the Royal Navy...

    , compared to lion
    Lion
    The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...

    s which eat seventy percent, and were also shown not to ingest dung
    Dung
    Dung may refer to:* Dung, animal feces* Dung, Doubs, a commune in the Doubs department in the Franche-Comté region in eastern France* Mundungus Fletcher or "Dung", a character in the Harry Potter novels* Dung beetle...

    , to the point that they would only eat intestines after shaking out the waste inside.
  • Two male Dimetrodon are featured fighting in Dinosaur Zoo
    Dinosaur Zoo
    Dinosaur Zoo information from leading paleontologists and expose them together with current knowledge on specific species in a more accessible medium. was released on iTunes May 2011....

     released on the iPad.
  • In Peter Jackson
    Peter Jackson
    Sir Peter Robert Jackson, KNZM is a New Zealand film director, producer, actor, and screenwriter, known for his The Lord of the Rings film trilogy , adapted from the novel by J. R. R...

    's book, The World of Kong: A Natural History of Skull Island, a large, omnivorous descendant of Dimetrodon dwells in the uplands and is called Malevolusaurus perditor.

See also


  • Platyhystrix
    Platyhystrix
    Platyhystrix was a temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, Dimetrodon and Edaphosaurus...

    - an amphibian which lived at the same time as Dimetrodon and which also had a sail on its back
  • Sphenacodon
    Sphenacodon
    Sphenacodon was a pelycosaur that was about in length. Sphenacodon belongs to the family Sphenacodontidae, a lineage that was related to the therapsids...

    – a pelycosaur closely related to Dimetrodon, but without a sail
  • Arizonasaurus
    Arizonasaurus
    Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic . Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongate neural spines of the...

    - a reptile from the Triassic Period with a sail on its back
  • Spinosaurus
    Spinosaurus
    Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...

    – a carnivorous dinosaur
    Dinosaur
    Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

     with a sail on its back
  • Ouranosaurus
    Ouranosaurus
    Ouranosaurus is an unusual genus of herbivorous iguanodont dinosaur that lived during the early Cretaceous about 110 million years ago in what is now Africa. Ouranosaurus measured about seven to eight meters long...

    - a herbivorous dinosaur
    Dinosaur
    Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

     with a sail on its back
  • Evolution of mammals
    Evolution of mammals
    __FORCETOC__The evolution of mammals within the synapsid lineage was a gradual process that took approximately 70 million years, beginning in the mid-Permian. By the mid-Triassic, there were many species that looked like mammals, and the first true mammals appeared in the early Jurassic...