Karl Bogislaus Reichert
Karl Bogislaus Reichert was a German anatomist and histologist. Reichert was born in East Prussia. From 1831 he studied at the University of Konigsberg, where he was a student of embryologist Karl Ernst Baer continued his education in Berlin under Friedrich Schlemm and Johannes Peter Müller. In 1836 he received his doctorate with a dissertation on the gill arches of vertebrate embryos. Afterwards, he worked as an intern at the Charité, from 1839 to 1843, served as an assistant and prosector at the University of Berlin. In 1843 he attained the chair of anatomy at the University of Dorpat, ten years succeeded Karl Theodor Ernst von Siebold as professor of physiology at the University of Breslau. In 1858 he returned to Berlin as chair of anatomy, where he succeeded his former mentor, Johannes Peter Müller. Reichert is remembered for his work in embryology, for his pioneer research in cell theory. With Ernst Gaupp, he was co-architect of the Reichert–Gaupp theory concerning the origin of mammalian ossicles of the ear.
His name is lent to the eponymous "Reichert's cartilage", described as a cartilaginous structure in the second branchial arch from which develop the temporal styloid processes, the stylohyoid ligaments, the lesser cornu of the hyoid bone. De embryonum arcubus. Berlin, 1836 – On the so-called branchial arches of embryos. Ueber die Visceralbogen der Wirbelthiere im Allgemeinen und deren Metamorphosen bei den Vögeln und Säugethieren. Archiv für Anatomie, Physiologie und wissenschaftliche Medicin: 120-222, 1837 – On the visceral arch of vertebrates in general and its metamorphosis in birds and mammals. Das Entwicklungsleben im Wirbelthierreiche. 1840, Berlin – Development of life in vertebrates. Beiträge zur Kenntniss des Zustandes der heutigen Entwicklungsgeschichte. 1843, Berlin – Contributions to the knowledge on the state of present-day developmental history. Der Bau des menschlichen Gehirns. 1859-1861, Leipzig – Construction of the human brain. Emil du Bois-Reymond OCLC WorldCat
Evolution of mammalian auditory ossicles
The evolution of mammalian auditory ossicles was an evolutionary event in which bones in the jaw of reptiles were co-opted to form part of the hearing apparatus in mammals. The event is well-documented and important as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution. In reptiles, the eardrum is connected to the inner ear via a single bone, the columella, while the upper and lower jaws contain several bones not found in mammals. Over the course of the evolution of mammals, one bone from the lower and one from the upper jaw lost their purpose in the jaw joint and were put to new use in the middle ear, connecting to the existing stapes bone and forming a chain of three bones, the ossicles, which transmit sounds more efficiently and allow more acute hearing. In mammals, these three bones are known as the malleus and stapes. Mammals and birds differ from other vertebrates by having evolved a cochlea; the evidence that the malleus and incus are homologous to the reptilian articular and quadrate was embryological, since this discovery an abundance of transitional fossils has both supported the conclusion and given a detailed history of the transition.
The evolution of the stapes was an distinct event. Following on the ideas of Étienne Geoffroy Saint-Hilaire, studies by Johann Friedrich Meckel the Younger, Carl Gustav Carus, Martin Rathke, Karl Ernst von Baer, the relationship between the reptilian jaw bones and mammalian middle-ear bones was first established on the basis of embryology and comparative anatomy by Karl Bogislaus Reichert and advanced by Ernst Gaupp and this is known as the Reichert–Gaupp theory. In the course of the development of the embryo, the incus and malleus arise from the same first pharyngeal arch as the mandible and maxilla, are served by mandibular and maxillary division of the trigeminal nerve....the discovery that the mammalian malleus and incus were homologues of visceral elements of the "reptilian" jaw articulation... ranks as one of the milestones in the history of comparative biology.... It is one of the triumphs of the long series of researches on the extinct Theromorph reptiles, begun by Owen, continued by Seeley and Watson, to have revealed the intermediate steps by which the change may have occurred from an inner quadrate to an outer squamosal articulation...
Yet the transition between the "reptilian" jaw and the "mammalian" middle ear was not bridged in the fossil record until the 1950s with the elaboration of such fossils as the now-famous Morganucodon. There are more recent studies in the genetic basis for the development of the ossicles from the embryonic arch, relating this to evolutionary history."Bapx1 known as Nkx3.2, is the vertebrate homologue of the Drosophila gene Bagpipe. A member of the NK2 class of homeobox genes...", this gene is implicated in the change from the jaw bones of non-mammals to the ossicles of mammals. Others are Dlx genes, Prx genes, Wnt genes; the earliest mammals were small animals nocturnal insectivores. This suggests a plausible evolutionary mechanism driving the change. Natural selection would account for the success of this feature. There is still one more connection with another part of biology: genetics suggests a mechanism for this transition, the kind of major change of function seen elsewhere in the world of life being studied by evolutionary developmental biology.
The mammalian middle ear contains three tiny bones known as the ossicles: malleus and stapes. The ossicles are a complex system of levers whose functions include: reducing the amplitude of the vibrations; the ossicles act as the mechanical analog of an electrical transformer, matching the mechanical impedance of vibrations in air to vibrations in the liquid of the cochlea. The net effect of this impedance matching is to increase the overall sensitivity and upper frequency limits of mammalian hearing, as compared to reptilian hearing; the details of these structures and their effects vary noticeably between different mammal species when the species are as related as humans and chimpanzees. Living mammal species can be identified by the presence in females of mammary glands which produce milk. Other features are required when classifying fossils, since mammary glands and other soft-tissue features are not visible in fossils. Paleontologists therefore use a distinguishing feature, shared by all living mammals, but is not present in any of the early Triassic therapsids: mammals use two bones for hearing that all other amniotes use for eating.
The earliest amniotes had a jaw joint composed of the quadrate. All non-mammalian amniotes use this system including lizards, crocodilians and therapsids, but mammals have a different jaw joint, composed only of the squamosal. In mammals, the quadrate and articular bones have evolved into the incus and malleus bones in the middle ear. Here is a ver
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
Sauropsida is a taxonomic clade that consists of reptiles, including birds, the extinct Parareptilia. All living sauropsids are members of the subgroup Diapsida, the Parareptilia having died out 200 million years ago; the term originated in 1864 with Thomas Henry Huxley, who grouped birds with reptiles based on fossil evidence. Sauropsids are the sister taxon to synapsids, or "mammal-like reptiles", some of which evolved into mammals; the term Sauropsida has a long history, hails back to Thomas Henry Huxley, his opinion that birds had risen from the dinosaurs. He based this chiefly on the fossils of Hesperornis and Archaeopteryx, that were starting to become known at the time. In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrate classes informally into mammals and ichthyoids, based on the gaps in physiological traits and lack of transitional fossils that seem to exist between the three groups. Early in the following year he proposed the names Ichthyopsida for the two latter.
Huxley did however include groups on the mammalian line like Dicynodon among the sauropsids. Thus, under the original definition, Sauropsida contained not only the groups associated with it today, but several groups that today are known to be in the mammalian side of the tree. By the early 20th century, the fossils of Permian synapsids from South Africa had become well known, allowing palaeontologists to trace synapsid evolution in much greater detail; the term Sauropsida was taken up by E. S. Goodrich in 1916 much like Huxley's, to include lizards and their relatives, he distinguished them from mammals and their extinct relatives, which he included in the sister group Theropsida. Goodrich's classification thus differs somewhat from Huxley's, in which the non-mammalian synapsids fell under the sauropsids. Goodrich supported this division by the nature of the hearts and blood vessels in each group, other features such as the structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, the Protosauria, which included some Paleozoic amphibians as well as early reptiles predating the sauropsid/synapsid split.
In 1956, D. M. S. Watson observed that sauropsids and synapsids diverged early in the reptilian evolutionary history, so he divided Goodrich's Protosauria between the two groups, he reinterpreted the Sauropsida and Theropsida to exclude birds and mammals making them paraphyletic, unlike Goodrich's definition. Thus his Sauropsida included Procolophonia, Millerosauria, Squamata, Crocodilia, "thecodonts", non-avian dinosaurs, pterosaurs and sauropyterygians; this classification supplemented, but was never as popular as, the classification of the reptiles into four subclasses according to the positioning of temporal fenestrae, openings in the sides of the skull behind the eyes. Since the advent of phylogenetic nomenclature, the term Reptilia has fallen out of favor with many taxonomists, who have used Sauropsida in its place to include a monophyletic group containing the traditional reptiles and the birds; the class Reptilia has been known to be an evolutionary grade rather than a clade for as long as evolution has been recognised.
Reclassifying reptiles has been among the key aims of phylogenetic nomenclature. The term Sauropsida had from the mid 20th century been used to denote all species not on the synapsid side after the synapsid/sauropsid split, a branch-based clade; this group encompasses all now-living reptiles as well as birds, as such is comparable to Goodrich's classification, the difference being that better resolution of the early amniote tree has split up most of the Goodrich's "Protosauria", though definitions of Sauropsida identical to Huxley's are forwarded. Some cladistic work has used Sauropsida more restrictively, to signify the crown group, i.e. all descendants of the last common ancestor of extant reptiles and birds. A number of phylogenetic stem and crown definitions have been published, anchored in a variety of fossil and extant organisms, thus there is no consensus of the actual definition of Sauropsida as a phylogenetic unit; some taxonomists, such as Benton, have co-opted the term to fit into traditional rank-based classifications, making Sauropsida and Synapsida class-level taxa to replace the traditional Class Reptilia, while Modesto and Anderson, using the PhyloCode standard, have suggested replacing the name Sauropsida with their redefinition of Reptilia, arguing that the latter is by far better known and should have priority.
Sauropsids evolved from basal amniotes stock 320 million years ago in the Paleozoic Era. In the Mesozoic Era, sauropsids were the largest animals on land, in the water, in the air; the Mesozoic is sometimes called the Age of Reptiles. Sixty-six million years ago, the large-bodied sauropsids died out in the global extinction event at the end of the Mesozoic era. With the exception of a few species of birds, the entire dinosaur lineage became extinct; the cladogram presented here illustrates the "family tree" of sauropsids, follows a sim
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by the postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex, namely the quadrate and pterygoid; the squamosal is bordered anteroventrally by the ventrally by the quadratojugal. In many mammals, including humans, it fuses with the periotic bone and the auditory bulla to form the temporal bone referred to as the squama temporalis. In synapsids the jaw is composed of four bony elements and referred to as a Quadro-articular jaw because the joint is between the articular and quadrate bones. In therapsids the jaw is simplified into an articulation between the dentary and the squamous part of the temporal bone, hence referred to as a dentary-squamosal jaw. In therapsids, the other two bones have moved into the ear to become the malleus and incus
Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things, it is an old science. Anatomy is inherently tied to developmental biology, comparative anatomy, evolutionary biology, phylogeny, as these are the processes by which anatomy is generated over immediate and long timescales. Anatomy and physiology, which study the structure and function of organisms and their parts, make a natural pair of related disciplines, they are studied together. Human anatomy is one of the essential basic sciences; the discipline of anatomy is divided into microscopic anatomy. Macroscopic anatomy, or gross anatomy, is the examination of an animal's body parts using unaided eyesight. Gross anatomy includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, in the study of cells.
The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have improved advancing from the examination of animals by dissection of carcasses and cadavers to 20th century medical imaging techniques including X-ray and magnetic resonance imaging. Derived from the Greek ἀνατομή anatomē "dissection", anatomy is the scientific study of the structure of organisms including their systems and tissues, it includes the appearance and position of the various parts, the materials from which they are composed, their locations and their relationships with other parts. Anatomy is quite distinct from physiology and biochemistry, which deal with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, position, blood supply and innervation of an organ such as the liver; the discipline of anatomy can be subdivided into a number of branches including gross or macroscopic anatomy and microscopic anatomy.
Gross anatomy is the study of structures large enough to be seen with the naked eye, includes superficial anatomy or surface anatomy, the study by sight of the external body features. Microscopic anatomy is the study of structures on a microscopic scale, along with histology, embryology. Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include dissection, in which a body is opened and its organs studied, endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels; the term "anatomy" is taken to refer to human anatomy. However the same structures and tissues are found throughout the rest of the animal kingdom and the term includes the anatomy of other animals.
The term zootomy is sometimes used to refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy; the kingdom Animalia contains multicellular organisms that are motile. Most animals have bodies differentiated into separate tissues and these animals are known as eumetazoans, they have an internal digestive chamber, with two openings. Metazoans do not include the sponges. Unlike plant cells, animal cells have neither chloroplasts. Vacuoles, when present, are much smaller than those in the plant cell; the body tissues are composed of numerous types of cell, including those found in muscles and skin. Each has a cell membrane formed of phospholipids, cytoplasm and a nucleus. All of the different cells of an animal are derived from the embryonic germ layers; those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic.
All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the ectoderm and endoderm. Animal tissues can be grouped into four basic types: connective, epithelial and nervous tissue. Connective tissues are fibrous and made up of cells scattered among inorganic material called the extracellular matrix. Connective tissue holds them in place; the main types are loose connective tissue, adipose tissue, fibrous connective tissue and bone. The extracellular matrix contains proteins, the chief and most abundant of, collagen. Collagen plays a major part in maintaining tissues; the matrix can be modified to form a skeleton to protect the body. An exoskeleton is a thickened, rigid cuticle, stiffened by mineralization, as in crustaceans or by the cross-linkin
An anapsid is an amniote whose skull does not have openings near the temples. Traditionally, the Anapsida are the most primitive subclass of reptiles, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic, it is however doubtful that all anapsids lack temporal fenestra as a primitive trait, that all the groups traditionally seen as anapsids lacked fenestra. While "anapsid reptiles" or "anapsida" were traditionally spoken of as if they were a monophyletic group, it has been suggested that several groups of reptiles that had anapsid skulls might be only distantly related. Scientists still debate the exact relationship between the basal reptiles that first appeared in the late Carboniferous, the various Permian reptiles that had anapsid skulls, the Testudines. However, it was suggested that the anapsid-like turtle skull is due to reversion rather than to anapsid descent; the majority of modern paleontologists believe that the Testudines are descended from diapsid reptiles that lost their temporal fenestrae.
More recent morphological phylogenetic studies with this in mind placed turtles within diapsids, some place turtles as a sister group to extant archosaurs or, more within Lepidosauromorpha. All molecular studies have upheld the placement of turtles within diapsids. However, one of the most recent molecular studies, published on 23 February 2012, suggests that turtles are lepidosauromorph diapsids, most related to the lepidosaurs. Reanalysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification and because they did not sample fossil and extant taxa broadly enough for constructing the cladogram. Testudines is suggested to have diverged from other diapsids between 200 and 279 million years ago, though the debate is far from settled. Although procolophonids managed to survive into the Triassic, most of the other reptiles with anapsid skulls, including the millerettids and pareiasaurs, became extinct in the late Permian period by the Permian-Triassic extinction event.
Despite the molecular studies, there is evidence. All known diapsids excrete uric acid as nitrogenous waste, there is no known case of a diapsid reverting to the excretion of urea when they return to semi-aquatic lifestyles. Crocodilians, for example, are still uricotelic, although they are partly ammonotelic, meaning they excrete some of their waste as ammonia. Ureotelism appears to be the ancestral condition among primitive amniotes, it is retained by mammals, which inherited ureotelism from their synapsid and therapsid ancestors. Ureotelism therefore would suggest that turtles were more anapsids than diapsids; the only known uricotelic chelonian is the desert tortoise, which evolved it as adaptation to desert habitats. Some desert mammals are uricotelic, so since all known mammals are ureotelic, uricotelic adaptation is a result of convergence among desert species. Therefore, turtles would have to be the only known case of a uricotelic reptile reverting to ureotelism. Anapsida is still sporadically recognized as a valid group, but this is not favoured by current workers.
Anapsids in the traditional meaning of the word are not a clade, but rather a paraphyletic group composed of all the early reptiles retaining the primitive skull morphology, grouped together by the absence of temporal openings. Gauthier and Rowe attempted to redefine Anapsida so it would be monophyletic, defining it as the clade containing "extant turtles and all other extinct taxa that are more related to them than they are to other reptiles"; this definition explicitly includes turtles in Anapsida. Indeed, Gauthier and Rowe themselves included only turtles and Captorhinidae in their Anapsida, while excluding the majority of anapsids in the traditional sense of the word from it. Tsuji and Müller noted that the name Anapsida implies a morphology, in fact absent in the skeletons of a number of taxa traditionally included in the group. A temporal opening in the skull roof behind each eye, similar to that present in the skulls of synapsids, has been discovered in the skulls of a number of members of Parareptilia, including lanthanosuchoids, bolosaurids, some nycteroleterids, some procolophonoids and at least some mesosaurs.
The presence of temporal openings in the skulls of these taxa makes it uncertain whether the ancestral reptiles had an anapsid-like skull as traditionally assumed or a synapsid-like skull instead. Euryapsida Introduction to Anapsida from UCMP