In phylogenetics , the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade , a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants.
32-623: † Antarctoboenus ?† Parvulivenator ?† Stintonornis † Masillaraptoridae Falconidae The order Falconiformes ( / f æ l ˈ k ɒ n ɪ ˌ f ɔːr m iː z / ) is represented by the extant family Falconidae (falcons and caracaras) and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families Cathartidae (New World vultures and condors) , Sagittariidae (secretarybird) , Pandionidae (ospreys) , Accipitridae (hawks) were classified in Falconiformes. A variety of comparative genome analyses published since 2008, however, found that falcons are part of
64-601: A clade of birds called Australaves , which also includes seriemas , parrots and passerines . Within Australaves falcons are more closely related to the parrot-passerine clade than they are to the seriemas. The hawks , vultures and owls are placed in the clade Afroaves . The cladogram of the Telluraves shown below is based on the study by Josefin Stiller and collaborators published in 2024. The species numbers are taken from
96-432: A stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all
128-423: Is given the designation "crown-", to separate it from the group as commonly defined. Both birds and mammals are traditionally defined by their traits, and contain fossil members that lived before the last common ancestors of the living groups or, like the mammal Haldanodon , were not descended from that ancestor although they lived later. Crown-Aves and Crown-Mammalia therefore differ slightly in content from
160-618: Is no consensus phylogeny. Stem arthropods constitute a group that has seen attention in connection with the Burgess Shale fauna. Several of the finds , including the enigmatic Opabinia and Anomalocaris have some, though not all, features associated with arthropods , and are thus considered stem arthropods. The sorting of the Burgess Shale fauna into various stem groups finally enabled phylogenetic sorting of this enigmatic assemblage and also allowed for identifying velvet worms as
192-434: Is not necessary for a species to have living descendants in order for it to be included in the crown group. Extinct side branches on the family tree that are descended from the most recent common ancestor of living members will still be part of a crown group. For example, if we consider the crown-birds (i.e. all extant birds and the rest of the family tree back to their most recent common ancestor), extinct side branches like
224-508: Is poorly documented. The only stem-falcons that have mostly complete remains are Masillaraptor parvunguis and Danielsraptor phorusrhacoides , while the other taxa Stintonornis mitchelli and Parvulivenator watteli are known from fragmentary remains. Mayr (2009) noted the similarity of Masillaraptor to the seriemas. One study from Wang et al. (2012) using 30 nuclear loci from 28 taxa found Falconidae and Cariamidae being sister taxa to each other. This has, however, not been supported by
256-461: Is the crown group and all organisms more closely related to it than to any other extant organisms. In a tree analogy, it is the crown group and all branches back to (but not including) the split with the closest branch to have living members. The Pan-Aves thus contain the living birds and all (fossil) organisms more closely related to birds than to crocodilians (their closest living relatives). The phylogenetic lineage leading back from Neornithes to
288-453: Is thought by some to make the Cambrian explosion easier to understand without invoking unusual evolutionary mechanisms; however, application of the stem group concept does nothing to ameliorate the difficulties that phylogenetic telescoping poses to evolutionary theorists attempting to understand both macroevolutionary change and the abrupt character of the Cambrian explosion . Overemphasis on
320-642: The London Clay of England, and Masillaraptor , from Messel Pit in Germany. Masillaraptorids had long legs, which may indicate that they had a terrestrial lifestyle, foraging on the ground similar to modern caracaras . They had large pygostyles , suggesting that they would have likely had long tail feathers. This, in addition to their long ulnae , suggest that they were capable of well-developed flight. Their beaks are similar to those of extinct phorusrhacids and extant caracaras. The cladogram below displays
352-405: The dinosaurs and the pterosaurs . The last common ancestor of birds and crocodilians—the first crown group archosaur—was neither bird nor crocodilian and possessed none of the features unique to either. As the bird stem group evolved, distinctive bird features such as feathers and hollow bones appeared. Finally, at the base of the crown group, all traits common to extant birds were present. Under
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#1732844229468384-531: The dodo or great auk are still descended from the most recent common ancestor of all living birds , so fall within the bird crown group. One very simplified cladogram for birds is shown below: † Archaeopteryx other extinct groups Neornithes (modern birds, some extinct like the dodo) In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of
416-466: The last common ancestor of the crown group and their closest living relatives. It follows from the definition that all members of a stem group are extinct. The "stem group" is the most used and most important of the concepts linked to crown groups, as it offers a means to reify and name paraphyletic assemblages of fossils that otherwise do not fit into systematics based on living organisms. While often attributed to Jefferies (1979), Willmann (2003) traced
448-426: The lungfish , our nearest relatives among the fishes. In addition to a series of lobe-finned fishes , they also include some of the early labyrinthodonts . Exactly what labyrinthodonts are in the stem group tetrapods rather than the corresponding crown group is uncertain, as the phylogeny of early tetrapods is not well understood. This example shows that crown and stem group definitions are of limited value when there
480-493: The phylogenetic position of Masillaraptoridae within the Falconiformes: Caracara plancus (crested caracara) [REDACTED] Masillaraptor parvunguis [REDACTED] Danielsraptor phorusrhacoides † Dynamopterus spp. Cariama cristata (red-legged seriema) [REDACTED] Llallawavis scagliai [REDACTED] Patagornis marshi [REDACTED] Stem-group The concept
512-521: The Crocodilia branch. Basal branch names such as Avemetatarsalia are usually more obscure. However, not so advantageous are the facts that "Pan-Aves" and "Aves" are not the same group, the circumscription of the concept of "Pan-Aves" (synonymous with Avemetatarsalia) is only evident by examination of the above tree, and calling both groups "birds" is ambiguous. Stem mammals are those in the lineage leading to living mammals, together with side branches, from
544-1160: The December 2023 version of the list maintained by Frank Gill , Pamela C. Rasmussen and David Donsker on behalf of the International Ornithological Committee (IOC). This list includes the Cathartiformes (New World vultures) in the order Accipitriformes. Strigiformes (owls – 254 species) Cathartiformes (New World vultures – 7 species) Accipitriformes ( hawks , osprey and secretarybird – 258 species) Coliiformes (mouse birds – 6 species) Leptosomiformes (cuckoo roller – 1 species) Trogoniformes (trogons and quetzals – 46 species) Bucerotiformes ( hornbills and relatives – 77 species) Coraciiformes ( kingfishers and relatives – 186 species) Piciformes ( woodpeckers and relatives – 448 species) Cariamiformes (seriemas – 2 species) Falconiformes (falcons – 65 species) Psittaciformes (parrots – 408 species) Passeriformes (passerines – 6,719 species) The fossil record of Falconiformes sensu stricto
576-457: The clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the Neornithes clade, being descended from an earlier ancestor. An alternative definition does not require any members of a crown group to be extant, only to have resulted from a "major cladogenesis event". The first definition forms the basis of this article. Often, the crown group
608-514: The closest living relatives of arthropods. Stem priapulids are other early Cambrian to middle Cambrian faunas, appearing in Chengjiang to Burgess Shale. The genus Ottoia has more or less the same build as modern priapulids , but phylogenetic analysis indicates that it falls outside the crown group, making it a stem priapulid. The name plesion has a long history in biological systematics, and plesion group has acquired several meanings over
640-457: The common definition of Aves and Mammalia. This has caused some confusion in the literature. The cladistic idea of strictly using the topology of the phylogenetic tree to define groups necessitates other definitions than crown groups to adequately define commonly discussed fossil groups. Thus, a host of prefixes have been defined to describe various branches of the phylogenetic tree relative to extant organisms. A pan-group or total group
672-483: The diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group. Such fossils have been of particular importance in considering the origins of the tetrapods , mammals , and animals . The application of the stem group concept also influenced the interpretation of the organisms of the Burgess shale . Their classification in stem groups to extant phyla, rather than in phyla of their own,
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#1732844229468704-509: The divergence of the lineage from the Sauropsida to the last common ancestor of the living mammals. This group includes the synapsids as well as mammaliaforms like the morganucodonts and the docodonts ; the latter groups have traditionally and anatomically been considered mammals even though they fall outside the crown group mammals. Stem tetrapods are the animals belonging to the lineage leading to tetrapods from their divergence from
736-505: The extinct moa ) The crown group here is Neornithes , all modern bird lineages back to their last common ancestor. The closest living relatives of birds are crocodilians . If we follow the phylogenetic lineage leading to Neornithes to the left, the line itself and all side branches belong to the stem birds until the lineage merges with that of the crocodilians. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , stem group birds include
768-432: The full bifurcating phylogeny. Stem birds perhaps constitute the most cited example of a stem group, as the phylogeny of this group is fairly well known. The following cladogram, based on Benton (2005), illustrates the concept: Crocodilia Pterosauria Hadrosauridae Stegosauria Sauropoda Tyrannosauridae Archaeopteryx Neognathae (including the extinct dodo ) Paleognathae (including
800-484: The latest major neoavian phylogenetic studies. A 2022 study recovers massilaraptorids as true falcons. This Falconiformes article is a stub . You can help Misplaced Pages by expanding it . Masillaraptoridae Masillaraptoridae is an extinct family of stem-group falconiform birds from the Eocene of Europe. They are noted for their relatively long legs. Two genera have been named: Danielsraptor , from
832-464: The narrower one. Often, an (extinct) grouping is identified as belonging together. Later, it may be realized other (extant) groupings actually emerged within such grouping, rendering them a stem grouping. Cladistically , the new groups should then be added to the group, as paraphyletic groupings are not natural. In any case, stem groupings with living descendants should not be viewed as a cohesive group, but their tree should be further resolved to reveal
864-474: The origin of the stem group concept to Austrian systematist Othenio Abel (1914), and it was discussed and diagrammed in English as early as 1933 by A. S. Romer . Alternatively, the term "stem group" is sometimes used in a wider sense to cover any members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon or Anteosaurus are stem mammals in the wider sense but not in
896-493: The phylogenetic split from the remaining amniotes (the Sauropsida ). Pan-Mammalia is thus an alternative name for Synapsida . A stem group is a paraphyletic assemblage composed of the members of a pan-group or total group, above, minus the crown group itself (and therefore minus all living members of the pan-group). This leaves primitive relatives of the crown groups , back along the phylogenetic line to (but not including)
928-438: The point where it merges with the crocodilian lineage, along with all side branches, constitutes pan-birds. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , therefore, pan-group birds would include all dinosaurs and pterosaurs as well as an assortment of non-crocodilian animals like Marasuchus . Pan-Mammalia consists of all mammals and their fossil ancestors back to
960-597: The widely used total-group perspective, the Crocodylomorpha would become synonymous with the Crocodilia, and the Avemetatarsalia would become synonymous with the birds, and the above tree could be summarized as Crocodilia Birds An advantage of this approach is that declaring Theropoda to be birds (or Pan-aves ) is more specific than declaring it to be a member of the Archosauria, which would not exclude it from
992-487: The years. One use is as "nearby group" (plesion means close to in Greek ), i.e. sister group to a given taxon , whether that group is a crown group or not. The term may also mean a group, possibly paraphyletic , defined by primitive traits (i.e. symplesiomorphies ). It is generally taken to mean a side branch splitting off earlier on the phylogenetic tree than the group in question. Placing fossils in their right order in
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1024-430: Was developed by Willi Hennig , the formulator of phylogenetic systematics , as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen . It
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