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Condylarth
Condylarthra is an informal group – previously considered an Order (biology), order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Artiodactyla, being composed thus of several unrelated lineages. Taxonomic history Condylarthra always was a problematic group. When first described by , Phenacodontidae was the type and only family therein. , however, raised Condylarthra to an order and included a wide range of diverse placentals with generalized dentitions and postcranial skeletons. More recent researchers (i.e. post-WW2) have been more restrictive; either including only a limited number of taxa, or proposing that the term should be abandoned altogether. Due to their primitive characteristics condylarths ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ungulates
Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to be a polyphyletic and thereby invalid clade based on molecular data. As a result, true ungulates had since been reclassified to the newer clade Euungulata in 2001 within the clade Laurasiatheria while Paenungulata has been reclassified to a distant clade Afrotheria. Living ungulates are divided into two orders: Perissodactyla including equines, rhinoceroses, and tapirs; and Artiodactyla including cattle, antelope, pigs, giraffes, camels, sheep, deer, and hippopotamuses, among others. Cetaceans such as whales, dolphins, and porpoises are also classified as artiodactyls, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving. Two other orders o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenacodontidae
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the “wastebasket taxon” Condylarthra, which may instead represent early-stage perissodactyls. They lived from the late early Paleocene to early middle Eocene (about 60–50 million years ago) and their fossil remains have been found in North America and Europe. The only unequivocal Asian phenacodontid is '' Lophocion asiaticus''. Description These animals had a variety of body sizes, and could be as small as domestic cats ('' Tetraclaenodon'' and '' Ectocion'') and as large as sheep ('' Phenacodus''). The skull of phenacodontids is long and narrow, and equipped with a small braincase. The skeleton of phenacodontids show several primitive characteristics (the long and heavy tail for example) but also a number of advanced, Perissodactyla-like adaptations: Their long legs, for example, had five fingers, but the first finger showed a clear reduction, and in some forms (like ''Phenacod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perissodactyla
Perissodactyla (, ), or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They typically have reduced the weight-bearing toes to three or one of the five original toes, though tapirs retain four toes on their front feet. The nonweight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, artiodactyls (even-toed ungulates) bear most of their weight equally on four or two (an even number) of the five toes: their third and fourth toes. Another difference between the two is that perissodactyls digest plant cellulose in their intestines, rather than in one or more stomach chambers as artiodactyls, with the exception of Suina, do. The order was considerably more diverse in the past, with notable extinct groups including the brontotheres, palaeotheres, chalicotheres, and the paracer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Litopterna
Litopterna (from "smooth heel") is an extinction, extinct order of South American native ungulates that lived from the Paleocene to the Pleistocene-Holocene around 62.5 million to 12,000 years ago (or possibly as late as 3,500 years ago), and were also present in Antarctica during the Eocene. They represent the second most diverse group of South American ungulates after Notoungulata. It is divided into nine families, with Proterotheriidae and Macraucheniidae being the most diverse and last surviving families. Diversity The body forms of many litopterns, notably in the limb and skull structure, are broadly similar to those of living ungulates, unlike other South American native ungulate groups, which are often strongly divergent from living ungulates. Paleocene and Eocene litopterns generally had small body masses, with ''Protolipterna'' (Protolipternidae) estimated to have had a body mass of , though the Eocene Sparnotheriodontidae, sparnotheriodontids were considerably large ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Notoungulata
Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resembling animals as disparate as rabbits and rhinoceroses. Notoungulata are the largest group of South American native ungulates, with over 150 genera in 14 families having been described, divided into two major subgroupings, Typotheria and Toxodontia. Notoungulates first diversified during the Eocene. Their diversity declined from the late Neogene onwards, with only the large Toxodontidae, toxodontids persisting until the end of the Pleistocene (with ''Mixotoxodon'' expanding into Central America and southern North America), perishing as part of the Late Pleistocene extinctions, Late Pleistocene megafauna extinctions along with most other large mammals across the Americas. Collagen sequence analysis suggests that notoungulates are closely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ectocion Ralstonensis
''Ectocion'' (sometimes ''Ectocyon'') is an extinct genus of placental mammals of the family Phenacodontidae. The genus was earlier classified as ''Gidleyina'' (Simpson 1935) and ''Prosthecion'' (Patterson and West 1973). Retrieved May 2013. It reached 6 to 12 kg and was similar in size and morphology to ''Copecion''. Both these herbivorous ungulates likely occupied similar ecological niches. Paleocene specimens of these hoofed, ground-dwelling herbivores have been found in Canada (Alberta, Saskatchewan) and the United States (Colorado, Montana, North Dakota, and Wyoming). Eocene specimens have been found in Mexico and the United States (Colorado, Mississippi, Wyoming). One of the dramatic effects of the Paleocene–Eocene Thermal Maximum The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mastoid Foramen
The mastoid foramen is a hole in the posterior border of the temporal bone. It transmits an emissary vein between the sigmoid sinus and the suboccipital venous plexus, and a small branch of the occipital artery, the posterior meningeal artery to the dura mater. Structure The mastoid foramen is a hole in the posterior border of the temporal bone of the skull. The opening of the mastoid foramen is an average of 18 mm from the asterion, and around 34 mm from the external auditory meatus. It is typically very narrow. This may be around 2 mm. Variation The position and size of this foramen are very variable. It is not always present. Sometimes, it is duplicated on one side or both sides. Sometimes, it is situated in the occipital bone, or in the suture between the temporal bone and the occipital bone. Function The mastoid foramen transmits: * an emissary vein between the sigmoid sinus and the suboccipital venous plexus or the posterior auricular vein. * a small branch of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrapotheria
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, ."The uruguaytheriine Astrapotheriidae from the rich middle Miocene Honda Group of the upper Magdalena River valley in Colombia (...) are the youngest securely dated remains of that order in South America." Astrapotheres were large, rhinoceros-like animals and have been called one of the most bizarre orders of mammals with an enigmatic evolutionary history. The taxonomy of this order is not clear, but it may belong to Meridiungulata (along with Notoungulata, Litopterna, Pyrotheria and Xenungulata). In turn, Meridungulata is believed to belong to the extant superorder Laurasiatheria. Some scientists have regarded the astrapotheres (and sometimes the Meridiungulata as a whole) as members of the clade Atlantogenata. However, collagen and mitochondrial DNA sequence data analysed in 2015 places at least the notoungulates and litopterns firmly w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stapedial Branch Of Posterior Auricular Artery
In human anatomy, the stapedial branch of posterior auricular artery, or stapedial artery for short, is a small artery supplying the stapedius muscle in the inner ear. Structure In humans In humans, the stapedial artery is normally present in the fetus where it connects what is to become the external and internal carotid arteries. Part of the carotid artery system, it originates from the dorsal branch of aortic arch. Its superior supraorbital branch becomes the middle meningeal artery, while its infraorbital and mandibular branches fuses with the external carotid artery and later become the internal maxillary artery. Its trunk atrophies and is replaced by branches from the external carotid artery. In rare cases, the embryonic structure is still present after birth in which case it is referred to as a persistent stapedial artery (PSA). While the prevalence of this anomaly is unknown, it has been estimated to be present in 1 of 5,000 people. In other mammals Structures homol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Petrosal Bone
The petrous part of the temporal bone is pyramid-shaped and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three angles, and houses in its interior the components of the inner ear. The petrous portion is among the most basal elements of the skull and forms part of the endocranium. Petrous comes from the Latin word ''petrosus'', meaning "stone-like, hard". It is one of the densest bones in the body. In other mammals, it is a separate bone, the petrosal bone. The petrous bone is important for studies of ancient DNA from skeletal remains, as it tends to contain extremely well-preserved DNA. Base The base is fused with the internal surfaces of the squamous, tympanic, and mastoid parts. Apex The apex, which is rough and uneven, is received into the angular interval between the posterior border of the great wing of the sphenoid bone and the basilar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arctocyon DB
''Arctocyon'' (from Greek ''arktos'' and ''kyôn'', "bear/dog-like") is an extinct genus of large placental mammals, part of the possibly polyphyletic family Arctocyonidae. The type species is ''A. primaevus'', though up to five other species may be known. Fossils of ''Arctocyon'' have been found in Europe and North America. ''Arctocyon'' was originally named as a subgenus of the bear-dog ''Amphicyon'', though was subsequently found to belong to a genus and family of its own. The relationship between arctocyonids and other placentals is unclear, with early classification efforts placing them as carnivores or creodonts, and later ones classifying them under Condylarthra, a wastebasket taxon for various early ungulates. More recent phylogenetic analyses suggest that arctocyonids are an artificial assemblage of several distantly-related placental lineages, and ''Arctocyon'' may be closely related to '' Loxolophus'' (another arctocyonid) and to pantodonts. ''Arctocyon'' was among the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Auditory Bulla
The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic bone), which in some mammals stays separate through life. Evolutionarily, a portion of it is derived from the angular bone of the reptilian lower jaw. Surfaces Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony ear canal. Medially, it presents a narrow furrow, the ''tympanic sulcus'', for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland. Borders Its lateral border is free and rough, and gives attachment to the cartilaginous part of the ear canal. Internally, the tympanic pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
