Guthrie defined Eaves to include only the modern bird groups, Thatcher group. This was done by excluding most groups known only from fossils, and assigning them, instead, to the in part to avoid the uncertainties about the ligament of Archaeopteryx’s in relation to animals traditionally thought of as tethered dinosaurs. Guthrie identified four conflicting ways of defining the term “Eaves”, which is a problem because the same biological name is being used four different ways.
Guthrie proposed a solution, number 4 below, which is to reserve the term Eaves only for the crown group, the last common ancestor of all living birds and all of its descendants. He assigned other names to the other groups. Crocodiles Birds Turtles izard (including Snakes) The birds’ phylogeny relationships to major living reptile groups. 1 . Eaves an mean those advanced orchards with feathers (alternately Philosophical) 2. Eaves can mean those that fly (alternately Available) 3. Eaves can mean all reptiles closer to birds than to crocodiles (alternately Familiarities [=Panes]) 4.
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Eaves can mean the last common ancestor of all the currently living birds and all of its descendants (a “crown group”). (ultraconservatives) Under the fourth definition Archaeopteryx’s is an villa, and not a member of Eaves. Gatherers proposals have been adopted by many researchers in the field of paleontology and bird evolution, though the exact definitions applied have been inconsistent. Available, initially proposed to replace the traditional fossil content of Eaves, is often used synonymously with the vernacular term “bird” by these researchers. L] Most researchers define Available as branch-based Claude, though definitions vary. Many authors have used a definition similar to “all therefore closer to birds than Available is also occasionally defined as an phonograph-based Claude (that is, one based on physical characteristics). Jacques Guthrie, who named Available in 1986, re- defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.