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120-615: See below Dimetrodon ( / d aɪ ˈ m iː t r ə ˌ d ɒ n / or / d aɪ ˈ m ɛ t r ə ˌ d ɒ n / ; lit.   ' two measures of teeth ' ) is an extinct genus of non- mammalian synapsid belonging to the family Sphenacodontidae that lived during the Cisuralian age of the Early Permian period , around 295–272 million years ago. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb),

240-601: A maxilla recovered in 1845 by a man named Donald McLeod, living in the British colony of Prince Edward Island . These fossils were purchased by John William Johnson, a Canadian geologist, and then described by Joseph Leidy in 1854 as the mandible of Bathygnathus borealis , a large carnivore related to Thecodontosaurus , although it was later reclassified as a species of Dimetrodon in 2015, as Dimetrodon borealis . Fossils now attributed to Dimetrodon were first studied by American paleontologist Edward Drinker Cope in

360-548: A maxilla recovered in 1845 by a man named Donald McLeod, living in the British colony of Prince Edward Island . These fossils were purchased by John William Johnson, a Canadian geologist, and then described by Joseph Leidy in 1854 as the mandible of Bathygnathus borealis , a large carnivore related to Thecodontosaurus , although it was later reclassified as a species of Dimetrodon in 2015, as Dimetrodon borealis . Fossils now attributed to Dimetrodon were first studied by American paleontologist Edward Drinker Cope in

480-487: A direct ancestor of mammals. Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally – but incorrectly – called "mammal-like reptiles", but now known as stem mammals. This groups Dimetrodon together with mammals in the clade Synapsida, while reptiles are placed in a separate clade, Sauropsida . Single openings in the skull behind each eye, known as temporal fenestrae , and other skull features distinguish Dimetrodon and true mammals from most of

600-403: A dozen species have been named since the genus was first erected in 1878. Dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the advent of dinosaurs. Although reptile-like in appearance and physiology, Dimetrodon is much more closely related to mammals than to reptiles, though it is not

720-434: A form of thermoregulation . Some recent studies argue that the sail would have been ineffective at removing heat from the body, due to large species being discovered with small sails and small species being discovered with large sails, essentially ruling out heat regulation as its main purpose. The sail was most likely used in courtship display , including threatening away rivals or showing off to potential mates. Dimetrodon

840-554: A genus which Cope named in 1882 on the basis of skulls that evidently belonged to herbivorous animals given their blunt crushing teeth. E. C. Case named the species Dimetrodon longiramus in 1907 on the basis of a scapula and elongated mandible from the Belle Plains Formation of Texas. In 1940, Romer and Price recognized that the D. longiramus material belonged to the same taxon as another specimen described by paleontologist Samuel Wendell Williston in 1916, which included

960-436: A nearly complete specimen of Dimetrodon to D. gigas . Dimetrodon gigas is now recognized as a synonym of D. grandis . Dimetrodon giganhomogenes was named by E. C. Case in 1907 and is still considered a valid species of Dimetrodon . Dimetrodon macrospondylus was first described by Cope in 1884 as Clepsydrops macrospondylus . In 1907, Case reclassified it as Dimetrodon macrospondylus . Dimetrodon platycentrus

1080-431: A nearly complete specimen of Dimetrodon to D. gigas . Dimetrodon gigas is now recognized as a synonym of D. grandis . Dimetrodon giganhomogenes was named by E. C. Case in 1907 and is still considered a valid species of Dimetrodon . Dimetrodon macrospondylus was first described by Cope in 1884 as Clepsydrops macrospondylus . In 1907, Case reclassified it as Dimetrodon macrospondylus . Dimetrodon platycentrus

1200-480: A paper called "The Theromorphous Reptilia" in which he described Dimetrodon cruciger . D. cruciger was distinguished by the small projections that extended from either side of each neural spine like the branches of a tree. In 1886, Cope moved D. cruciger to the genus Naosaurus because he considered its spines so different from those of other Dimetrodon species that the species deserved its own genus. Naosaurus would later be synonymized with Edaphosaurus ,

1320-578: A reptile in accordance with Linnean taxonomy , which ranked Reptilia as a class and Dimetrodon as a genus within that class. Mammals were assigned to a separate class, and Dimetrodon was described as a "mammal-like reptile". Paleontologists theorized that mammals evolved from this group in (what they called) a reptile-to-mammal transition. List of Dimetrodon species See below Dimetrodon ( / d aɪ ˈ m iː t r ə ˌ d ɒ n / or / d aɪ ˈ m ɛ t r ə ˌ d ɒ n / ; lit.   ' two measures of teeth ' )

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1440-420: A reptile in accordance with Linnean taxonomy , which ranked Reptilia as a class and Dimetrodon as a genus within that class. Mammals were assigned to a separate class, and Dimetrodon was described as a "mammal-like reptile". Paleontologists theorized that mammals evolved from this group in (what they called) a reptile-to-mammal transition. Temporal fenestra The supratemporal fenestra , also called

1560-514: A semi-sprawling posture between that of a mammal and a lizard and also could walk in a more upright stance with its body and the majority or all of its tail off the ground. Most Dimetrodon species ranged in length from 1.7 to 4.6 m (6 to 15 ft) and are estimated to have weighed between 28 and 250 kg (60 and 550 lb). The smallest known species D. teutonis was about 60 cm (24 in) long and weighed 14 kilograms (31 lb). The larger species of Dimetrodon were among

1680-586: A similar crest exists." In the first few decades of the 20th century, American paleontologist E. C. Case authored many studies on Dimetrodon and described several new species. He received funding from the Carnegie Institution for his study of many Dimetrodon specimens in the collections of the American Museum of Natural History and several other museums. Many of these fossils had been collected by Cope but had not been thoroughly described, as Cope

1800-465: A similar crest exists." In the first few decades of the 20th century, American paleontologist E. C. Case authored many studies on Dimetrodon and described several new species. He received funding from the Carnegie Institution for his study of many Dimetrodon specimens in the collections of the American Museum of Natural History and several other museums. Many of these fossils had been collected by Cope but had not been thoroughly described, as Cope

1920-471: A similarly elongated mandible and a long maxilla. Williston did not consider his specimen to belong to Dimetrodon but instead classified it as an ophiacodontid . Romer and Price assigned Case and Williston's specimens to a newly erected genus and species, Secodontosaurus longiramus , that was closely related to Dimetrodon . Dimetrodon is an early member of a group called synapsids , which include mammals and many of their extinct relatives, though it

2040-467: A similarly elongated mandible and a long maxilla. Williston did not consider his specimen to belong to Dimetrodon but instead classified it as an ophiacodontid . Romer and Price assigned Case and Williston's specimens to a newly erected genus and species, Secodontosaurus longiramus , that was closely related to Dimetrodon . Dimetrodon is an early member of a group called synapsids , which include mammals and many of their extinct relatives, though it

2160-453: Is an extinct genus of non- mammalian synapsid belonging to the family Sphenacodontidae that lived during the Cisuralian age of the Early Permian period , around 295–272 million years ago. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb), the most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from

2280-545: Is fairly distant. Dimetrodon also may have had large scutes on the underside of its tail and belly, as other synapsids had these. Evidence from the varanopid Ascendonanus suggests that some early synapsids may have had squamate -like scales. However, some recent studies have put varanopids as taxonomically closer to diapsid reptiles . ( it has not been proven that dimetrodon has any hair, and if any new information comes out then this article will be updated.) The earliest discovery of Dimetrodon fossils were of

2400-539: Is fairly distant. Dimetrodon also may have had large scutes on the underside of its tail and belly, as other synapsids had these. Evidence from the varanopid Ascendonanus suggests that some early synapsids may have had squamate -like scales. However, some recent studies have put varanopids as taxonomically closer to diapsid reptiles . ( it has not been proven that dimetrodon has any hair, and if any new information comes out then this article will be updated.) The earliest discovery of Dimetrodon fossils were of

2520-414: Is known as "dimetrodont" differentiation. Near the vertebra body, the spine cross section is laterally compressed into a rectangular shape and, closer to the tip, it takes on a figure-eight shape as a groove runs along either side of the spine. The figure-eight shape is thought to reinforce the spine, preventing bending and fractures. A cross section of the spine of one specimen of Dimetrodon giganhomogenes

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2640-412: Is known as "dimetrodont" differentiation. Near the vertebra body, the spine cross section is laterally compressed into a rectangular shape and, closer to the tip, it takes on a figure-eight shape as a groove runs along either side of the spine. The figure-eight shape is thought to reinforce the spine, preventing bending and fractures. A cross section of the spine of one specimen of Dimetrodon giganhomogenes

2760-402: Is known from two skeletons, one nearly complete (MCZ 1365) and another less complete but larger (MCZ 1367). D. milleri is the oldest known species of Dimetrodon . Besides its small size, D. milleri differs from other species of Dimetrodon in that its neural spines are circular rather than figure-eight shaped in cross-section. Its vertebrae are also shorter in height relative to the rest of

2880-402: Is known from two skeletons, one nearly complete (MCZ 1365) and another less complete but larger (MCZ 1367). D. milleri is the oldest known species of Dimetrodon . Besides its small size, D. milleri differs from other species of Dimetrodon in that its neural spines are circular rather than figure-eight shaped in cross-section. Its vertebrae are also shorter in height relative to the rest of

3000-422: Is much more closely related to mammals than to reptiles, though it is not a direct ancestor of mammals. Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally – but incorrectly – called "mammal-like reptiles", but now known as stem mammals. This groups Dimetrodon together with mammals in the clade Synapsida, while reptiles are placed in a separate clade, Sauropsida . Single openings in

3120-473: Is not an ancestor of any mammal (which appeared millions of years later ). It is often mistaken for a dinosaur in popular culture, despite having become extinct some 40 million years (Ma) before the first appearance of dinosaurs in the Triassic period. As a synapsid, Dimetrodon is more closely related to mammals than to dinosaurs or any living reptile. By the early 1900s most paleontologists called Dimetrodon

3240-422: Is not an ancestor of any mammal (which appeared millions of years later). It is often mistaken for a dinosaur in popular culture, despite having become extinct some 40 million years (Ma) before the first appearance of dinosaurs in the Triassic period. As a synapsid, Dimetrodon is more closely related to mammals than to dinosaurs or any living reptile. By the early 1900s most paleontologists called Dimetrodon

3360-433: Is rectangular in shape but preserves figure-eight shaped rings close to its center, indicating that the shape of spines may change as individuals age. The microscopic anatomy of each spine varies from base to tip, indicating where it was embedded in the muscles of the back and where it was exposed as part of a sail. The lower or proximal portion of the spine has a rough surface that would have served as an anchoring point for

3480-432: Is rectangular in shape but preserves figure-eight shaped rings close to its center, indicating that the shape of spines may change as individuals age. The microscopic anatomy of each spine varies from base to tip, indicating where it was embedded in the muscles of the back and where it was exposed as part of a sail. The lower or proximal portion of the spine has a rough surface that would have served as an anchoring point for

3600-506: Is similar to that of D. milleri , suggesting a close relationship. Dimetrodon specimens found in Utah and Arizona probably also belong to D. occidentalis . Dimetrodon teutonis was named in 2001 from the Thuringian Forest of Germany and was the first species of Dimetrodon to be described outside North America. It is also the smallest species of Dimetrodon . In 1878, Cope published

3720-500: Is similar to that of D. milleri , suggesting a close relationship. Dimetrodon specimens found in Utah and Arizona probably also belong to D. occidentalis . Dimetrodon teutonis was named in 2001 from the Thuringian Forest of Germany and was the first species of Dimetrodon to be described outside North America. It is also the smallest species of Dimetrodon . In 1878, Cope published a paper called "The Theromorphous Reptilia" in which he described Dimetrodon cruciger . D. cruciger

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3840-445: Is tall and compressed laterally , or side-to-side. The eye sockets are positioned high and far back in the skull. Behind each eye socket is a single hole called an infratemporal fenestra . An additional hole in the skull, the supratemporal fenestra , can be seen when viewed from above. The back of the skull (the occiput ) is oriented at a slight upward angle, a feature that it shares with all other early synapsids . The upper margin of

3960-454: Is ventrally bordered by a zygomatic arch composed of the jugal and squamosal bones. This single temporal fenestra is homologous to the infratemporal fenestra, as displayed most clearly by early synapsids. In later synapsids, the cynodonts , the orbit fused with the fenestral opening after the latter had started expanding within the therapsids . Most mammals have this merged configuration. Later, primates re-evolved an orbit separated from

4080-462: The temporal fossa . This separation was achieved by the evolution of a postorbital bar , with haplorhines (dry-nosed primates) later evolving a postorbital septum . Physiological speculation associates temporal fenestrae with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae, but two more advanced lines did:

4200-408: The D. rectiformis specimen he described. Cope commented on the purpose of the sail in 1886, writing, "The utility is difficult to imagine. Unless the animal had aquatic habits, and swam on its back, the crest or fin must have been in the way of active movements... The limbs are not long enough nor the claws acute enough to demonstrate arboreal habits, as in the existing genus Basilicus , where

4320-407: The D. rectiformis specimen he described. Cope commented on the purpose of the sail in 1886, writing, "The utility is difficult to imagine. Unless the animal had aquatic habits, and swam on its back, the crest or fin must have been in the way of active movements... The limbs are not long enough nor the claws acute enough to demonstrate arboreal habits, as in the existing genus Basilicus , where

4440-532: The Red Beds of Texas and Oklahoma . More recently, its fossils have also been found in Germany and over a dozen species have been named since the genus was first erected in 1878. Dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the advent of dinosaurs. Although reptile-like in appearance and physiology, Dimetrodon

4560-570: The University of Chicago 's Walker Museum (most of the Walker fossil collection is now housed in the Field Museum of Natural History ). Sternberg sent some of his own specimens to German paleontologist Ferdinand Broili at Munich University , although Broili was not as prolific as Cope in describing specimens. Cope's rival Othniel Charles Marsh also collected some bones of Dimetrodon , which he sent to

4680-415: The University of Chicago 's Walker Museum (most of the Walker fossil collection is now housed in the Field Museum of Natural History ). Sternberg sent some of his own specimens to German paleontologist Ferdinand Broili at Munich University , although Broili was not as prolific as Cope in describing specimens. Cope's rival Othniel Charles Marsh also collected some bones of Dimetrodon , which he sent to

4800-425: The epaxial muscles of the back and also has a network of connective tissues called Sharpey's fibers that indicate it was embedded within the body. Higher up on the distal (outer) portion of the spine, the bone surface is smoother. The periosteum , a layer of tissue surrounding the bone, is covered in small grooves that presumably supported the blood vessels that vascularized the sail. The large groove that runs

4920-424: The epaxial muscles of the back and also has a network of connective tissues called Sharpey's fibers that indicate it was embedded within the body. Higher up on the distal (outer) portion of the spine, the bone surface is smoother. The periosteum , a layer of tissue surrounding the bone, is covered in small grooves that presumably supported the blood vessels that vascularized the sail. The large groove that runs

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5040-423: The synapsids (stem-mammals and mammals) and the diapsids (most reptiles and later birds). There are four types of amniote skull, classified by the number and location of their temporal fenestrae. Though historically important for understanding amniote evolution, some of these configurations have little relevance to modern phylogenetic taxonomy . The four types are: This vertebrate anatomy –related article

5160-432: The upper temporal fenestra , is positioned above the other fenestra and is exposed primarily in dorsal (top) view. In some reptiles, particularly dinosaurs, the parts of the skull roof lying between the supratemporal fenestrae are thinned out by excavations from the adjacent fenestrae. These extended margins of thinned bone are called supratemporal fossae . Synapsids , including mammals , have one temporal fenestra, which

5280-470: The vertebrae . It was an obligate quadruped (it could only walk on four legs) and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States , the majority of these coming from a geological deposit called the Red Beds of Texas and Oklahoma . More recently, its fossils have also been found in Germany and over

5400-475: The 11 closest to the hip. Since these first few caudal vertebrae narrow rapidly as they progress farther from the hip, many paleontologists in the late 19th and early 20th centuries thought that Dimetrodon had a very short tail. A largely complete tail of Dimetrodon was not described until 1927. The sail of Dimetrodon is formed by elongated neural spines projecting from the vertebrae. Each spine varies in cross-sectional shape from its base to its tip in what

5520-474: The 11 closest to the hip. Since these first few caudal vertebrae narrow rapidly as they progress farther from the hip, many paleontologists in the late 19th and early 20th centuries thought that Dimetrodon had a very short tail. A largely complete tail of Dimetrodon was not described until 1927. The sail of Dimetrodon is formed by elongated neural spines projecting from the vertebrae. Each spine varies in cross-sectional shape from its base to its tip in what

5640-465: The 1870s. Cope had obtained the fossils along with those of many other Permian tetrapods from several collectors who had been exploring a group of rocks in Texas called the Red Beds . Among these collectors were Swiss naturalist Jacob Boll , Texas geologist W. F. Cummins , and amateur paleontologist Charles Hazelius Sternberg . Most of Cope's specimens went to the American Museum of Natural History or to

5760-416: The 1870s. Cope had obtained the fossils along with those of many other Permian tetrapods from several collectors who had been exploring a group of rocks in Texas called the Red Beds . Among these collectors were Swiss naturalist Jacob Boll , Texas geologist W. F. Cummins , and amateur paleontologist Charles Hazelius Sternberg . Most of Cope's specimens went to the American Museum of Natural History or to

5880-618: The Walker Museum. The first use of the name Dimetrodon came in 1878 when Cope named the species Dimetrodon incisivus , Dimetrodon rectiformis , and Dimetrodon gigas in the scientific journal Proceedings of the American Philosophical Society . The first description of a Dimetrodon fossil came a year earlier, though, when Cope named the species Clepsydrops limbatus from the Texas Red Beds. (The name Clepsydrops

6000-429: The Walker Museum. The first use of the name Dimetrodon came in 1878 when Cope named the species Dimetrodon incisivus , Dimetrodon rectiformis , and Dimetrodon gigas in the scientific journal Proceedings of the American Philosophical Society . The first description of a Dimetrodon fossil came a year earlier, though, when Cope named the species Clepsydrops limbatus from the Texas Red Beds. (The name Clepsydrops

6120-431: The articular developed into the malleus bone of the middle ear . The reflected lamina became part of a ring called the tympanic annulus that supports the ear drum in all living mammals. The tail of Dimetrodon makes up a large portion of its total body length and includes around 50 caudal vertebrae . Tails were missing or incomplete in the first described skeletons of Dimetrodon . The only caudal vertebrae known were

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6240-410: The back of the skull links Dimetrodon to mammals and distinguishes it from most of the earliest sauropsids, which either lack openings or have two openings . Features such as ridges on the inside of the nasal cavity and a ridge at the back of the lower jaw are thought to be part of an evolutionary progression from early four-limbed land-dwelling vertebrates to mammals . The skull of Dimetrodon

6360-452: The basis of skulls that evidently belonged to herbivorous animals given their blunt crushing teeth. E. C. Case named the species Dimetrodon longiramus in 1907 on the basis of a scapula and elongated mandible from the Belle Plains Formation of Texas. In 1940, Romer and Price recognized that the D. longiramus material belonged to the same taxon as another specimen described by paleontologist Samuel Wendell Williston in 1916, which included

6480-624: The crack to spread through the tooth. Unlike Albertosaurus , Dimetrodon teeth lacked adaptations that would stop cracks from forming at their serrations. The teeth of D. teutonis lack serrations, but still have sharp edges. A 2014 study shows that Dimetrodon was in an arms race against its prey. The smaller species, D. milleri , had no tooth serrations because it ate small prey. As prey grew larger, several Dimetrodon species started developing serrations on their teeth and increasing in size. For instance, D. limbatus had enamel serrations that helped it cut through flesh (which were similar to

6600-622: The crack to spread through the tooth. Unlike Albertosaurus , Dimetrodon teeth lacked adaptations that would stop cracks from forming at their serrations. The teeth of D. teutonis lack serrations, but still have sharp edges. A 2014 study shows that Dimetrodon was in an arms race against its prey. The smaller species, D. milleri , had no tooth serrations because it ate small prey. As prey grew larger, several Dimetrodon species started developing serrations on their teeth and increasing in size. For instance, D. limbatus had enamel serrations that helped it cut through flesh (which were similar to

6720-629: The decades following Romer and Price's monograph, many Dimetrodon specimens were described from localities outside Texas and Oklahoma . The first was described from the Four Corners region of Utah in 1966 and another was described from Arizona in 1969. In 1975, Olson reported Dimetrodon material from the Washington Formation of Ohio, which has been given a tentative assignment of D. cf. limbatus . A new species of Dimetrodon called D. occidentalis (meaning "western Dimetrodon ")

6840-508: The decades following Romer and Price's monograph, many Dimetrodon specimens were described from localities outside Texas and Oklahoma . The first was described from the Four Corners region of Utah in 1966 and another was described from Arizona in 1969. In 1975, Olson reported Dimetrodon material from the Washington Formation of Ohio, which has been given a tentative assignment of D. cf. limbatus . A new species of Dimetrodon called D. occidentalis (meaning "western Dimetrodon ")

6960-468: The earliest sauropsids . Dimetrodon was probably one of the apex predators of the Cisuralian ecosystems, feeding on fish and tetrapods , including reptiles and amphibians . Smaller Dimetrodon species may have had different ecological roles . The sail of Dimetrodon may have been used to stabilize its spine or to heat and cool its body as a form of thermoregulation . Some recent studies argue that

7080-430: The earliest sauropsids, which either lack openings or have two openings . Features such as ridges on the inside of the nasal cavity and a ridge at the back of the lower jaw are thought to be part of an evolutionary progression from early four-limbed land-dwelling vertebrates to mammals . The skull of Dimetrodon is tall and compressed laterally , or side-to-side. The eye sockets are positioned high and far back in

7200-438: The first time. Twenty species of Dimetrodon have been named since the genus was first described in 1878. Many have been synonymized with older named species, and some now belong to different genera. Dimetrodon limbatus was first described by Edward Drinker Cope in 1877 as Clepsydrops limbatus . (The name Clepsydrops was first coined by Cope in 1875 for sphenacodontid remains from Vermilion County, Illinois , and

7320-436: The first time. Twenty species of Dimetrodon have been named since the genus was first described in 1878. Many have been synonymized with older named species, and some now belong to different genera. Dimetrodon limbatus was first described by Edward Drinker Cope in 1877 as Clepsydrops limbatus . (The name Clepsydrops was first coined by Cope in 1875 for sphenacodontid remains from Vermilion County, Illinois , and

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7440-414: The genus Dimetrodon , making D. limbatus the type species of Dimetrodon . Remains tentatively assigned to this species are also known from Washington County, Ohio , which correspond to a relatively large individual. These remains are slightly older than others assigned to D. limbatus from the west, although potential D. limbatus remains from New Mexico may be concurrent with it. The first use of

7560-412: The genus Dimetrodon , making D. limbatus the type species of Dimetrodon . Remains tentatively assigned to this species are also known from Washington County, Ohio , which correspond to a relatively large individual. These remains are slightly older than others assigned to D. limbatus from the west, although potential D. limbatus remains from New Mexico may be concurrent with it. The first use of

7680-527: The inner surface of the nasal section of skull are ridges called nasoturbinals , which may have supported cartilage that increased the area of the olfactory epithelium , the layer of tissue that detects odors. These ridges are much smaller than those of later synapsids from the Late Permian and Triassic, whose large nasoturbinals are taken as evidence for warm-bloodedness because they may have supported mucous membranes that warmed and moistened incoming air. Thus,

7800-472: The inner surface of the nasal section of skull are ridges called nasoturbinals , which may have supported cartilage that increased the area of the olfactory epithelium , the layer of tissue that detects odors. These ridges are much smaller than those of later synapsids from the Late Permian and Triassic, whose large nasoturbinals are taken as evidence for warm-bloodedness because they may have supported mucous membranes that warmed and moistened incoming air. Thus,

7920-453: The jaw joint, while the articular developed into the malleus bone of the middle ear . The reflected lamina became part of a ring called the tympanic annulus that supports the ear drum in all living mammals. The tail of Dimetrodon makes up a large portion of its total body length and includes around 50 caudal vertebrae . Tails were missing or incomplete in the first described skeletons of Dimetrodon . The only caudal vertebrae known were

8040-503: The largest predators of the Early Permian, although the closely related Tappenosaurus , known from skeletal fragments in slightly younger rocks, may have been even larger at an estimated 5.5 metres (18 ft) long. Although some Dimetrodon species could grow very large, many juvenile specimens are known. A single large opening on either side of the back of the skull links Dimetrodon to mammals and distinguishes it from most of

8160-448: The length of the spine was once thought to be a channel for blood vessels, but since the bone does not contain vascular canals, the sail is not thought to have been as highly vascularized as once thought. Some specimens of Dimetrodon preserve deformed areas of the neural spines that appear to be healed-over fractures. The cortical bone that grew over these breaks is highly vascularized, suggesting that soft tissue must have been present on

8280-448: The length of the spine was once thought to be a channel for blood vessels, but since the bone does not contain vascular canals, the sail is not thought to have been as highly vascularized as once thought. Some specimens of Dimetrodon preserve deformed areas of the neural spines that appear to be healed-over fractures. The cortical bone that grew over these breaks is highly vascularized, suggesting that soft tissue must have been present on

8400-569: The maxilla. Large incisor teeth are also present at the tips of the upper and lower jaws, rooted in the premaxillae and dentary bones . Small teeth are present around the maxillary "step" and behind the caniniforms, becoming smaller further back in the jaw. Many teeth are widest at their midsections and narrow closer to the jaws, giving them the appearance of a teardrop. Teardrop-shaped teeth are unique to Dimetrodon and other closely related sphenacodontids , which helps to distinguish them from other early synapsids. As in many other early synapsids ,

8520-567: The maxilla. Large incisor teeth are also present at the tips of the upper and lower jaws, rooted in the premaxillae and dentary bones . Small teeth are present around the maxillary "step" and behind the caniniforms, becoming smaller further back in the jaw. Many teeth are widest at their midsections and narrow closer to the jaws, giving them the appearance of a teardrop. Teardrop-shaped teeth are unique to Dimetrodon and other closely related sphenacodontids , which helps to distinguish them from other early synapsids. As in many other early synapsids ,

8640-424: The most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae . It was an obligate quadruped (it could only walk on four legs) and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States , the majority of these coming from a geological deposit called

8760-479: The name Dimetrodon came in 1878 when Cope named the species Dimetrodon incisivus along with Dimetrodon rectiformis and Dimetrodon gigas . Dimetrodon rectiformis was named alongside Dimetrodon incisivus in Cope's 1878 paper, and was the only one of the three named species to preserve elongated neural spines. In 1907, paleontologist E. C. Case moved D. rectiformis into the species D. incisivus . D. incisivus

8880-429: The name Dimetrodon came in 1878 when Cope named the species Dimetrodon incisivus along with Dimetrodon rectiformis and Dimetrodon gigas . Dimetrodon rectiformis was named alongside Dimetrodon incisivus in Cope's 1878 paper, and was the only one of the three named species to preserve elongated neural spines. In 1907, paleontologist E. C. Case moved D. rectiformis into the species D. incisivus . D. incisivus

9000-399: The nasal cavity of Dimetrodon is transitional between those of early land vertebrates and mammals. Another transitional feature of Dimetrodon is a ridge in the back of the jaw called the reflected lamina, which is found on the articular bone, which connects to the quadrate bone of the skull to form the jaw joint. In later mammal ancestors, the articular and quadrate separated from

9120-419: The nasal cavity of Dimetrodon is transitional between those of early land vertebrates and mammals. Another transitional feature of Dimetrodon is a ridge in the back of the jaw called the reflected lamina, which is found on the articular bone, which connects to the quadrate bone of the skull to form the jaw joint. In later mammal ancestors, the articular and quadrate separated from the jaw joint, while

9240-587: The possibility that D. kempae may not fall within the genus Dimetrodon , preferring to classify it as Sphenacodontidae incertae sedis . Dimetrodon loomisi was first described by Alfred Romer in 1937 along with D. booneorum , D. kempae , and D. milleri . Remains have been found in Texas and Oklahoma. Dimetrodon milleri was described by Romer in 1937. It is one of the smallest species of Dimetrodon in North America and may be closely related to D. occidentalis , another small-bodied species. D. milleri

9360-527: The possibility that D. kempae may not fall within the genus Dimetrodon , preferring to classify it as Sphenacodontidae incertae sedis . Dimetrodon loomisi was first described by Alfred Romer in 1937 along with D. booneorum , D. kempae , and D. milleri . Remains have been found in Texas and Oklahoma. Dimetrodon milleri was described by Romer in 1937. It is one of the smallest species of Dimetrodon in North America and may be closely related to D. occidentalis , another small-bodied species. D. milleri

9480-464: The sail to supply the site with blood vessels . Layered lamellar bone makes up most of the neural spine's cross-sectional area, and contains lines of arrested growth that can be used to determine the age of each individual at death. In many specimens of D. gigashomogenes , the distal portions of spines bend sharply, indicating that the sail would have had an irregular profile in life. Their crookedness suggests that soft tissue may not have extended all

9600-462: The sail to supply the site with blood vessels . Layered lamellar bone makes up most of the neural spine's cross-sectional area, and contains lines of arrested growth that can be used to determine the age of each individual at death. In many specimens of D. gigashomogenes , the distal portions of spines bend sharply, indicating that the sail would have had an irregular profile in life. Their crookedness suggests that soft tissue may not have extended all

9720-439: The sail would have been ineffective at removing heat from the body, due to large species being discovered with small sails and small species being discovered with large sails, essentially ruling out heat regulation as its main purpose. The sail was most likely used in courtship display , including threatening away rivals or showing off to potential mates. Dimetrodon was a quadrupedal , sail-backed synapsid that most likely had

9840-495: The serrations that can be found on Secodontosaurus ). The second-largest species, D. grandis , has denticle serrations similar to those of sharks and theropod dinosaurs, making its teeth even more specialized for slicing through flesh. As Dimetrodon' s prey grew larger, the various species responded by growing to larger sizes and developing ever-sharper teeth. The thickness and mass of the teeth of Dimetrodon may also have been an adaptation for increasing dental longevity. On

9960-493: The serrations that can be found on Secodontosaurus ). The second-largest species, D. grandis , has denticle serrations similar to those of sharks and theropod dinosaurs, making its teeth even more specialized for slicing through flesh. As Dimetrodon' s prey grew larger, the various species responded by growing to larger sizes and developing ever-sharper teeth. The thickness and mass of the teeth of Dimetrodon may also have been an adaptation for increasing dental longevity. On

10080-434: The skeleton than those of other Dimetrodon species. The skull is tall and the snout is short relative to the temporal region. A short vertebrae and tall skull are also seen in the species D. booneorum , D. limbatus and D. grandis , suggesting that D. milleri may be the first of an evolutionary progression between these species. Dimetrodon angelensis was named by paleontologist Everett C. Olson in 1962. Specimens of

10200-433: The skeleton than those of other Dimetrodon species. The skull is tall and the snout is short relative to the temporal region. A short vertebrae and tall skull are also seen in the species D. booneorum , D. limbatus and D. grandis , suggesting that D. milleri may be the first of an evolutionary progression between these species. Dimetrodon angelensis was named by paleontologist Everett C. Olson in 1962. Specimens of

10320-491: The skull behind each eye, known as temporal fenestrae , and other skull features distinguish Dimetrodon and true mammals from most of the earliest sauropsids . Dimetrodon was probably one of the apex predators of the Cisuralian ecosystems, feeding on fish and tetrapods , including reptiles and amphibians . Smaller Dimetrodon species may have had different ecological roles . The sail of Dimetrodon may have been used to stabilize its spine or to heat and cool its body as

10440-601: The skull slopes downward in a convex arc to the tip of the snout. The tip of the upper jaw, formed by the premaxilla bone, is raised above the part of the jaw formed by the maxilla bone to form a maxillary "step". Within this step is a diastema , a gap in the tooth row. Its skull was more heavily built than a dinosaur's skull. The size of the teeth varies greatly along the length of the jaws, lending Dimetrodon its name, which means "two measures of tooth" in reference to sets of small and large teeth. One or two pairs of caniniforms (large, pointed, canine -like teeth) extend from

10560-419: The skull. Behind each eye socket is a single hole called an infratemporal fenestra . An additional hole in the skull, the supratemporal fenestra , can be seen when viewed from above. The back of the skull (the occiput ) is oriented at a slight upward angle, a feature that it shares with all other early synapsids . The upper margin of the skull slopes downward in a convex arc to the tip of the snout. The tip of

10680-443: The species D. grandis . In his 1878 paper on fossils from Texas, Cope named Clepsydrops gigas along with the first named species of Dimetrodon , D. limbatus , D. incisivus , and D. rectiformis . Case reclassified C. gigas as a new species of Dimetrodon in 1907. Case also described a very well preserved skull of Dimetrodon in 1904, attributing it to the species Dimetrodon gigas . In 1919, Charles W. Gilmore attributed

10800-439: The species D. grandis . In his 1878 paper on fossils from Texas, Cope named Clepsydrops gigas along with the first named species of Dimetrodon , D. limbatus , D. incisivus , and D. rectiformis . Case reclassified C. gigas as a new species of Dimetrodon in 1907. Case also described a very well preserved skull of Dimetrodon in 1904, attributing it to the species Dimetrodon gigas . In 1919, Charles W. Gilmore attributed

10920-500: The species were reported from the San Angelo Formation of Texas. It is also the largest species of Dimetrodon. Dimetrodon occidentalis was named in 1977 from New Mexico. Its name means "western Dimetrodon " because it is the only North American species of Dimetrodon known west of Texas and Oklahoma. It was named on the basis of a single skeleton belonging to a relatively small individual. The small size of D. occidentalis

11040-436: The species were reported from the San Angelo Formation of Texas. It is also the largest species of Dimetrodon. Dimetrodon occidentalis was named in 1977 from New Mexico. Its name means "western Dimetrodon " because it is the only North American species of Dimetrodon known west of Texas and Oklahoma. It was named on the basis of a single skeleton belonging to a relatively small individual. The small size of D. occidentalis

11160-401: The teeth of most Dimetrodon species are serrated at their edges. The serrations of Dimetrodon teeth were so fine that they resembled tiny cracks. The dinosaur Albertosaurus had similarly crack-like serrations, but, at the base of each serration was a round void , which would have functioned to distribute force over a larger surface area and prevent the stresses of feeding from causing

11280-399: The teeth of most Dimetrodon species are serrated at their edges. The serrations of Dimetrodon teeth were so fine that they resembled tiny cracks. The dinosaur Albertosaurus had similarly crack-like serrations, but, at the base of each serration was a round void , which would have functioned to distribute force over a larger surface area and prevent the stresses of feeding from causing

11400-524: The upper jaw, formed by the premaxilla bone, is raised above the part of the jaw formed by the maxilla bone to form a maxillary "step". Within this step is a diastema , a gap in the tooth row. Its skull was more heavily built than a dinosaur's skull. The size of the teeth varies greatly along the length of the jaws, lending Dimetrodon its name, which means "two measures of tooth" in reference to sets of small and large teeth. One or two pairs of caniniforms (large, pointed, canine -like teeth) extend from

11520-402: The way to the tips of the spines, meaning that the sail's webbing may not have been as extensive as it is commonly imagined. No fossil evidence of Dimetrodon' s skin has yet been found. Impressions of the skin of a related animal, Estemmenosuchus , indicate that it would have been smooth and well-provided with glands, but this form of skin may not have applied to Dimetrodon , as its lineage

11640-401: The way to the tips of the spines, meaning that the sail's webbing may not have been as extensive as it is commonly imagined. No fossil evidence of Dimetrodon' s skin has yet been found. Impressions of the skin of a related animal, Estemmenosuchus , indicate that it would have been smooth and well-provided with glands, but this form of skin may not have applied to Dimetrodon , as its lineage

11760-574: The western area. While this seaway probably did exist, the discovery of fossils outside Texas and Oklahoma show that its extent was limited and that it was not an effective barrier to the distribution of Dimetrodon . In 2001, a new species of Dimetrodon called D. teutonis was described from the Lower Permian Bromacker locality at the Thuringian Forest of Germany, extending the geographic range of Dimetrodon outside North America for

11880-446: The western area. While this seaway probably did exist, the discovery of fossils outside Texas and Oklahoma show that its extent was limited and that it was not an effective barrier to the distribution of Dimetrodon . In 2001, a new species of Dimetrodon called D. teutonis was described from the Lower Permian Bromacker locality at the Thuringian Forest of Germany, extending the geographic range of Dimetrodon outside North America for

12000-448: Was a quadrupedal , sail-backed synapsid that most likely had a semi-sprawling posture between that of a mammal and a lizard and also could walk in a more upright stance with its body and the majority or all of its tail off the ground. Most Dimetrodon species ranged in length from 1.7 to 4.6 m (6 to 15 ft) and are estimated to have weighed between 28 and 250 kg (60 and 550 lb). The smallest known species D. teutonis

12120-482: Was about 60 cm (24 in) long and weighed 14 kilograms (31 lb). The larger species of Dimetrodon were among the largest predators of the Early Permian, although the closely related Tappenosaurus , known from skeletal fragments in slightly younger rocks, may have been even larger at an estimated 5.5 metres (18 ft) long. Although some Dimetrodon species could grow very large, many juvenile specimens are known. A single large opening on either side of

12240-410: Was distinguished by the small projections that extended from either side of each neural spine like the branches of a tree. In 1886, Cope moved D. cruciger to the genus Naosaurus because he considered its spines so different from those of other Dimetrodon species that the species deserved its own genus. Naosaurus would later be synonymized with Edaphosaurus , a genus which Cope named in 1882 on

12360-413: Was first coined by Cope in 1875 for sphenacodontid remains from Vermilion County, Illinois , and was later employed for many sphenacontid specimens from Texas; many new species of sphenacodontids from Texas were assigned to either Clepsydrops or Dimetrodon in the late 19th and early 20th centuries.) C. limbatus was reclassified as a species of Dimetrodon in 1940, meaning that Cope's 1877 paper

12480-413: Was first coined by Cope in 1875 for sphenacodontid remains from Vermilion County, Illinois , and was later employed for many sphenacontid specimens from Texas; many new species of sphenacodontids from Texas were assigned to either Clepsydrops or Dimetrodon in the late 19th and early 20th centuries.) C. limbatus was reclassified as a species of Dimetrodon in 1940, meaning that Cope's 1877 paper

12600-423: Was first described by Alfred Romer in 1937 on the basis of remains from Texas. Dimetrodon kempae was named by Romer in 1937, in the same paper as D. booneorum , D. loomisi , and D. milleri . Dimetrodon kempae was named on the basis of a single humerus and a few vertebrae, and may therefore be a nomen dubium that cannot be distinguished as a unique species of Dimetrodon . In 1940, Romer and Price raised

12720-420: Was first described by Alfred Romer in 1937 on the basis of remains from Texas. Dimetrodon kempae was named by Romer in 1937, in the same paper as D. booneorum , D. loomisi , and D. milleri . Dimetrodon kempae was named on the basis of a single humerus and a few vertebrae, and may therefore be a nomen dubium that cannot be distinguished as a unique species of Dimetrodon . In 1940, Romer and Price raised

12840-408: Was first described by Case in his 1907 monograph. It is now considered a synonym of Dimetrodon macrospondylus . Paleontologist Alfred Romer erected the species Dimetrodon natalis in 1936, previously described as Clepsydrops natalis . D. natalis was the smallest known species of Dimetrodon at that time, and was found alongside remains of the larger-bodied D. limbatus . Dimetrodon booneorum

12960-406: Was first described by Case in his 1907 monograph. It is now considered a synonym of Dimetrodon macrospondylus . Paleontologist Alfred Romer erected the species Dimetrodon natalis in 1936, previously described as Clepsydrops natalis . D. natalis was the smallest known species of Dimetrodon at that time, and was found alongside remains of the larger-bodied D. limbatus . Dimetrodon booneorum

13080-408: Was first described by Edward Drinker Cope in 1888 as Embolophorus dollovianus . In 1903, E. C. Case published a lengthy description of E. dollovianus , which he later referred to Dimetrodon . Paleontologist E. C. Case named a new species of sail-backed synapsid, Theropleura grandis , in 1907. In 1940, Alfred Romer and Llewellyn Ivor Price reassigned Theropleura grandis to Dimetrodon , erecting

13200-406: Was first described by Edward Drinker Cope in 1888 as Embolophorus dollovianus . In 1903, E. C. Case published a lengthy description of E. dollovianus , which he later referred to Dimetrodon . Paleontologist E. C. Case named a new species of sail-backed synapsid, Theropleura grandis , in 1907. In 1940, Alfred Romer and Llewellyn Ivor Price reassigned Theropleura grandis to Dimetrodon , erecting

13320-534: Was known for erecting new species on the basis of only a few bone fragments. Beginning in the late 1920s, paleontologist Alfred Romer restudied many Dimetrodon specimens and named several new species. In 1940, Romer coauthored a large study with Llewellyn Ivor Price called "Review of the Pelycosauria" in which the species of Dimetrodon named by Cope and Case were reassessed. Most of the species names considered valid by Romer and Price are still used today. In

13440-477: Was known for erecting new species on the basis of only a few bone fragments. Beginning in the late 1920s, paleontologist Alfred Romer restudied many Dimetrodon specimens and named several new species. In 1940, Romer coauthored a large study with Llewellyn Ivor Price called "Review of the Pelycosauria" in which the species of Dimetrodon named by Cope and Case were reassessed. Most of the species names considered valid by Romer and Price are still used today. In

13560-408: Was later employed for many sphenacontid specimens from Texas; many new species of sphenacodontids from Texas were assigned to either Clepsydrops or Dimetrodon in the late nineteenth and early twentieth centuries.) Based on a specimen from the Red Beds of Texas , it was the first known sail-backed synapsid. In 1940, paleontologists Alfred Romer and Llewellyn Ivor Price reassigned C. limbatus to

13680-408: Was later employed for many sphenacontid specimens from Texas; many new species of sphenacodontids from Texas were assigned to either Clepsydrops or Dimetrodon in the late nineteenth and early twentieth centuries.) Based on a specimen from the Red Beds of Texas , it was the first known sail-backed synapsid. In 1940, paleontologists Alfred Romer and Llewellyn Ivor Price reassigned C. limbatus to

13800-484: Was later synonymous with the type species Dimetrodon limbatus , making D. rectiformis a synonym of D. limbatus . Described in 1881 on the basis of upper jaw bones, Dimetrodon semiradicatus was the last species named by Cope. In 1907, E. C. Case synonymized D. semiradicatus with D. incisivus based on similarities in the shape of the teeth and skull bones. D. incisivus' and D. semiradicatus are now considered synonyms of D. limbatus . Dimetrodon dollovianus

13920-480: Was later synonymous with the type species Dimetrodon limbatus , making D. rectiformis a synonym of D. limbatus . Described in 1881 on the basis of upper jaw bones, Dimetrodon semiradicatus was the last species named by Cope. In 1907, E. C. Case synonymized D. semiradicatus with D. incisivus based on similarities in the shape of the teeth and skull bones. D. incisivus' and D. semiradicatus are now considered synonyms of D. limbatus . Dimetrodon dollovianus

14040-412: Was named in 1977 from New Mexico. The specimens found in Utah and Arizona probably also belong to D. occidentalis . Before these discoveries, a theory existed that a midcontinental seaway separated what is now Texas and Oklahoma from more western lands during the Early Permian, isolating Dimetrodon to a small region of North America, while a smaller sphenacodontid called Sphenacodon dominated

14160-410: Was named in 1977 from New Mexico. The specimens found in Utah and Arizona probably also belong to D. occidentalis . Before these discoveries, a theory existed that a midcontinental seaway separated what is now Texas and Oklahoma from more western lands during the Early Permian, isolating Dimetrodon to a small region of North America, while a smaller sphenacodontid called Sphenacodon dominated

14280-416: Was the first record of Dimetrodon . Cope was the first to describe a sail-backed synapsid with the naming of C. natalis in his 1878 paper, although he called the sail a fin and compared it to the crests of the modern basilisk lizard ( Basilicus ). Sails were not preserved in the specimens of D. incisivus and D. gigas that Cope described in his 1878 paper, but elongated spines were present in

14400-416: Was the first record of Dimetrodon . Cope was the first to describe a sail-backed synapsid with the naming of C. natalis in his 1878 paper, although he called the sail a fin and compared it to the crests of the modern basilisk lizard ( Basilicus ). Sails were not preserved in the specimens of D. incisivus and D. gigas that Cope described in his 1878 paper, but elongated spines were present in

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