Homeothermy in the context of "Allen's rule"

Archaeopteryx (/ˌɑːrkiːˈɒptərɪks/ ; lit. 'ancient wing'), sometimes referred to by its German name, "Urvogel " (lit. 'Primeval Bird') is a genus of bird-like dinosaurs. The genus name derives from the Ancient Greek ἀρχαῖος (archaîos), meaning 'ancient', and πτέρυξ (ptérux), meaning 'feather, wing'. Between the late 19th century and the early 21st century, Archaeopteryx was generally accepted by palaeontologists and popular reference books as the oldest known bird (member of the group Avialae). Older potential avialans have since been identified, including Anchiornis, Xiaotingia, Aurornis, and Baminornis.

Archaeopteryx lived in the Late Jurassic around 150 million years ago, in what is now southern Germany, during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals possibly attaining the size of a raven, the largest species of Archaeopteryx could grow to about 50 cm (20 in) in length. Despite their small size, broad wings, and inferred ability to fly or glide, Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds. In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes ("killing claw"), feathers (which also suggest warm-bloodedness), and various features of the skeleton.

A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of convergent evolution. The arrangement of the members of a polyphyletic group is called a polyphyly /ˈpɒlɪˌfaɪli/. It is contrasted with monophyly and paraphyly.

For example, the biological characteristic of warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds; "warm-blooded animals" is therefore a polyphyletic grouping. Other examples of polyphyletic groups are algae, C4 photosynthetic plants, and edentates.

In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:

1. the grouping contains its own most recent common ancestor (or more precisely an ancestral population), i.e. excludes non-descendants of that common ancestor
2. the grouping contains all the descendants of that common ancestor, without exception

Monophyly is contrasted with paraphyly and polyphyly as shown in the second diagram. A paraphyletic grouping meets 1. but not 2., thus consisting of the descendants of a common ancestor, excepting one or more monophyletic subgroups. A polyphyletic grouping meets neither criterion, and instead serves to characterize convergent relationships of biological features rather than genetic relationships – for example, night-active primates, fruit trees, or aquatic insects. As such, these characteristic features of a polyphyletic grouping are not inherited from a common ancestor, but evolved independently.

In zoology, mammalogy, from Latin mamma, meaning "breast", and -logy from λόγος (lógos), meaning "study", is the study of mammals – a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous systems. The archive of the number of mammals on earth is constantly growing, but is currently set at 6,495 different mammal species including recently extinct. There are 5,416 living mammals identified on earth and roughly 1,251 have been newly discovered since 2006. The major branches of mammalogy include natural history, taxonomy and systematics, anatomy and physiology, ethology, ecology, and management and control. Mammalogists are typically involved in activities such as conducting research, managing personnel, and writing proposals.

Mammalogy branches off into other taxonomically oriented disciplines such as primatology (the study of primates), and cetology (the study of cetaceans). Like other studies, mammalogy is also a part of zoology which is also a part of biology, the study of all living things.

The salmon shark (Lamna ditropis) is a species of mackerel shark found in the northern Pacific ocean. Similar to other mackerel sharks, salmon sharks have a thunniform body type. As an apex predator, the salmon shark feeds on salmon, squid, sablefish, birds, walleye pollock, and herring. Salmon sharks get their name from their diet, which primarily consists of salmon. It is known for its ability to maintain stomach temperature (homeothermy), which is unusual among fish. This shark has not been demonstrated to maintain a constant body temperature. It is also known for an unexplained variability in the sex ratio between eastern and western populations in the northern Pacific.

Heterothermy or heterothermia (from Greek ἕτερος heteros "other" and θέρμη thermē "heat") is a physiological term for animals that vary between self-regulating their body temperature, and allowing the surrounding environment to affect it. In other words, they exhibit characteristics of both poikilothermy and homeothermy.