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Sphenacodontoidea
Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants (including mammals). Sphenacodontoids are characterised by a number of synapomorphies concerninproportions of the bones of the skull and the teeth The sphenacodontoids evolved from earlier sphenacodonts such as ''Haptodus'' via a number of transitional stages of small, unspecialised pelycosaurs. Classification The following taxonomy follows Fröbisch ''et al.'' (2011) and Benson (2012) unless otherwise noted. Class Synapsida * Sphenacodontoidea ** Family †Sphenacodontidae ** Therapsida See also * Evolution of mammals References * Laurin, M. and Reisz, R. R., 1997Autapomorphies of the main clades of synapsids- Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphenacodonts
Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes ''Haptodus baylei'', ''Haptodus garnettensis'' and ''Sphenacodon ferox'', but not ''Edaphosaurus pogonias''". They first appear during the Late Pennsylvanian (Upper Carboniferous) epoch. From the end of the Carboniferous to the end of the Permian, most of them remained large, with only some secondarily becoming small in size. Basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammals). One might say that the sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record). Characteristics The defining characteristics include a thickening o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphenacodont
Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes ''Haptodus baylei'', ''Haptodus garnettensis'' and '' Sphenacodon ferox'', but not ''Edaphosaurus pogonias''". They first appear during the Late Pennsylvanian (Upper Carboniferous) epoch. From the end of the Carboniferous to the end of the Permian, most of them remained large, with only some secondarily becoming small in size. Basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammals). One might say that the sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record). Characteristics The defining characteristics include a thickening of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimetrodon
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontidae. The most prominent feature of ''Dimetrodon'' is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked 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 coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, its fossils have been found in Germany. 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 first appearance of dinosaurs. Reptile-li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphenacodontidae
Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian or early Roadian San Angelo Formation. However, given the notorious incompleteness of the fossil record, a recent study concluded that the Sphenacodontidae may have become extinct as recently as the early Capitanian. Primitive forms were generally small (60 cm to 1 meter), but during the later part of the early Permian these animals grew progressively larger (up to 3 meters or more), to become the top predators of their environments. Sphenacodontid fossils are so far known only from North America and Europe. Characteristics The skull is long, deep and narrow, an adaptation for strong jaw muscles. The front teeth are large and dagger-like, whereas the teeth in the sides and rear of the jaw are much smaller (hence the name of the well-kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tree Of Life Web Project
The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site has not been updated since 2011, however the pages are still accessible. The pages are linked hierarchically, in the form of the branching evolutionary tree of life, organized cladistically. Each page contains information about one particular group of organisms and is organized according to a branched tree-like form, thus showing hypothetical relationships between different groups of organisms. In 2009 the project ran into funding problems from the University of Arizona. Pages and Treehouses submitted took a considerably longer time to be approved as they were being reviewed by a small group of volunteers, and apparently, around 2011, all activities ended. History The idea of this project started in the late 1980s. David Maddison was wor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert Reisz
Robert Rafael Reisz is a Canadian paleontologist and specialist in the study of early amniote and tetrapod evolution. Research career Reisz received his B.Sc. (1969), M.Sc. (1971) and Ph.D. (1975) from McGill University as Robert L. Carroll's first doctoral graduate. After teaching as visiting lecturer at University of California, Los Angeles for a year, he accepted an appointment in the Biology Department at the University of Toronto's Mississauga Campus in 1975 where he still maintains his research lab. His research has been funded continuously by the Natural Sciences and Engineering Research Council of Canada (NSERC). He conducted field work in North America, Africa, and Europe, where he excavated fossils from the late Paleozoic and early Mesozoic eras. These excavations were frequently funded by the National Geographic Society. Reisz has broad interests in vertebrate paleontology. He has published more than 100 scientific articles on subjects as diverse as lungfish and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michel Laurin
Michel Laurin is a Canadian-born French vertebrate paleontologist whose specialities include the emergence of a land-based lifestyle among vertebrates, the evolution of body size and the origin and phylogeny of lissamphibians. He has also made important contributions to the literature on phylogenetic nomenclature. As an undergraduate, he worked in the laboratory of Robert L. Carroll and earned his Ph.D. at the University of Toronto under the direction of Robert R. Reisz; his thesis concerned the osteology of seymouriamorphs. His 1991 review of diapsid phylogeny provided the broadest review of the subject up to that date. In 1995, Laurin and Reisz coauthored a widely cited article providing evidence that the synapsids are the sister group of all other amniotes. He later worked on untangling the phylogeny of the Stegocephalia, a group with a notoriously difficult phylogeny. He later moved to France; since 1998, he has been a CNRS researcher at the Muséum National d'Histoire Naturel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution Of Mammals
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include '' Dryolestes'', more closely related to extant placentals and marsupials than to monotremes, as well as '' Ambondro'', more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since '' Juramaia'', the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period. After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds being the only surviving dinosaurs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pelycosaur
Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is now thought to be incorrect, and seen as outdated. Because it excludes the advanced synapsid group Therapsida, the term is paraphyletic and contrary to modern formal naming practice. Thus the name ''pelycosaurs'', similar to the term ''mammal-like reptiles'', had fallen out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature. The terms stem mammals, protomammals, and basal or primitive synapsids are used where needed, instead. Etymology The term ''pelycosaur'' has been fairly well abandoned by paleontologists because it no longer matches the features that distinguish a clade. The modern word was created from Greek meaning 'wooden bowl' or 'axe' and meaning 'lizar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transitional Fossils
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors. In 1859, when Charles Darwin's ''On the Origin of Species'' was first published, the fossil record was poorly known. Darwin described the perceived lack of transitional fossils as "the most obvious and gravest objection which can be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haptodus
''Haptodus'' is an extinct genus of basal sphenacodont, member of the clade that includes therapsids and hence, mammals. It was at least in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, feeding on insects and small vertebrates. Discovery and history ''Haptodus baylei'' ''Haptodus baylei'', the type species of ''Haptodus'', is known only from a single, badly preserved specimen hosted in the Muséum National d'Histoire Naturelle of Paris. It was collected at Les Télots, near Autun of France, from a terrestrial horizon dating to the Asselian stage of the Cisuralian series, about 299-296.4 million years old. The taxonomy of many pelycosaurs was revised in details by Alfred Sherwood Romer & Llewellyn Price (1940). They synonymized many genera, including ''Callibrachion'' (from Margenne near Autun, France), ''Datheosaurus'' (from Nowa Ruda of Poland), ''Palaeohatteria'' and ''Pantelosaurus'' (both from Germany), with ''Haptod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
