TetrapodA tetrapod (; from Ancient Greek (tetra)'four' and (poús)'foot') is any vertebrateanimal of the cladeTetrapoda (). The main diagnostic and defining trait (synapomorphy) of tetrapods is having four limbs, connected to the shoulder- and pelvic girdles, for which the group is named. As a clade, Tetrapoda is defined such that it includes every organism which descended from four-limbed ancestors, including those which have lost some or all of these limbs, e.g. snakes.
VertebrateSubphylum of chordatesVertebrates (), also called craniates, are animals with a vertebral column and a cranium. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylumVertebrata ( ) with some 65,000 species, by far the largest ranked grouping in the phylumChordata. The vertebrates include mammals, birds, amphibians, and various classes of fishes and reptiles.
PlacodermPlacoderms (from Ancient Greek πλάξ [plax, plakos] 'plate' and δέρμα [derma] 'skin') are vertebrateanimals of the classPlacodermi, an extinct group of prehistoric fish known from Paleozoicfossils during the Silurian and the Devonianperiods. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates (hence the name), and the rest of the body was scaled or naked depending on the species.
CladeIn biology, a clade () (from Ancient Greekκλάδος (kládos)'branch'), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population, or a species (extinct or extant).
CladisticsCladistics ( ; from Ancient Greekkládos 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived characteristics (synapomorphies) that are not present in more distant groups and ancestors.
ChondrichthyesChondrichthyes (; from Ancient Greek (khóndros)'cartilage' and (ikhthús)'fish') is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquaticvertebrates with paired fins, paired nares, placoid scales, and conus arteriosus in the heart.
AcanthodiiAcanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes). They are currently considered to represent a paraphyleticgrade of various fish lineages basal to extantChondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans (bony fish) and chondrichthyans (cartilaginous fish).
AnimalBiological kingdomAnimals are multicellular, eukaryoticorganisms belonging to the biologicalkingdomAnimalia (). Animals consume organic material, breathe oxygen, have muscle cells, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. With few exceptions, animals are able to move. Animals form a clade, meaning that they arose from a single common ancestor.
EndoskeletonAn endoskeleton (from Ancient Greek ἔνδον (éndon), meaning "inside", and σκελετός (skeletós), meaning "skeleton") is a structural frame (skeleton) — usually composed of mineralized tissue — on the inside of an animal, overlaid by soft tissues. Endoskeletons serve as structural support against gravity and mechanical loads, and provide anchoring attachment sites for skeletal muscles to transmit force and allow movements and locomotion.
CartilageCartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and the bronchial tubes, and the intervertebral discs.
BiodiversityVariety and variability of life formsAn example of the biodiversity of fungi in a forest in North Saskatchewan (in this photo, there are also leaf lichens and mosses).Biodiversity is the variability of life on Earth. It can be measured on various levels, for example, genetic variability, species diversity, ecosystem diversity, and phylogenetic diversity.
Ancient GreekAncient Greek (Ἑλληνική, Hellēnikḗ [hellɛːnikɛ̌ː]) includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (c. 1400 – c. 1200 BC), Dark Ages (c. 1200 – c. 800 BC), the Archaic or Homeric period (c. 800 – c. 500 BC), and the Classical period (c. 500 – c. 300 BC).
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