Avicephala is an extinct order of bizarre diapsid reptiles that lived during the Late Permian and Triassic periods. Many species had odd specialized grasping limbs and prehensile tails, adapted to arboreal (and possibly aquatic) lifestyles. The Permian is a geologic period that extends from about 299. ... The Triassic is a geologic period that extends from about 251 to 200 Ma (million years ago). ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Parazoa Porifera (sponges) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Myxozoa (slime animals) Superphylum Deuterostomia (blastopore becomes anus) Chordata (vertebrates, etc. ... {{{subdivision_ranks}}} See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... Clades Subclass Anapsida Subclass Diapsida Infraclass Lepidosauromorpha Infraclass Archosauromorpha Sauropsids are a diverse group of mostly egg-laying vertebrate animals. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Binomial name Longisquama insignis Sharov, 1970 Longisquama (long scales) was a lizard-like reptile of the early Triassic Period 240 million years ago, which lived in what is now Turkestan. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... Orders Procolophonia (extinct) Testudines Araeoscelidia (extinct) Avicephala (extinct) Younginiformes (extinct) Sauropterygia Ichthyosauria (extinct) Placodontia (extinct) Nothosauria (extinct) Plesiosauria (extinct) Sphenodontia Squamata Prolacertiformes (extinct) Archosauria Crurotarsi Order Aetosauria Order Phytosauria Order Rauisuchia Order Crocodilia Ornithodira Pterosauria (extinct) Marasuchus (extinct) Dinosauria (extinct) Order Saurischia Order Ornithischia Reptiles are tetrapods and amniotes, animals... The Permian is a geologic period that extends from about 299. ... The Triassic is a geologic period that extends from about 251 to 200 Ma (million years ago). ...

Anatomy and Lifestyle

The name "avicephala" means "bird heads", in reference to the distinctive triangular skulls of these reptiles that mimic the shape of bird skulls. A few avicephalans, such as Hypuronector, even appear to have had pointed, toothless, bird-like beaks. This cranial similarity to birds has led a few scientists to theorize that birds descended from avicephalans like Longisquama, though a majority see the similarity simply as convergence. This similarity may also have led to the possible misidentification of the would-be "first bird", Protoavis (Renesto, 2000). Orders Many - see section below. ... It has been suggested that Morphological convergence be merged into this article or section. ... Protoavis texensis (The first bird from Texas) is regarded as an extinct species that could be the earliest fossil of a bird, pushing back avian origins into the Late Triassic. ...

Avicephalans possessed a variety of odd and distinctive characteristics in addition to their bird-like skulls. Some displayed unique dermal appendages, such as the feather-like dorsal plumes of Longisquama, and the laterally-oriented rib-like rods of Coelurosauravus, which supported membranes and may have been used to glide from branch to branch in an arboreal habitat.

Another avicephalan group, the drepanosaurids, featured a suite of bizarre, almost chameleon-like skeletal features. Above the shoulders of most species was a specialized "hump" formed from fusion of the vertebrae, possibly used for advanced muscle attachments to the neck, and allowing for quick forward-striking movement of the head (perhaps to catch insects). Many had derived hands with two fingers opposed to the remaining three, an adaptation for grasping branches. Some individuals of Megalancosaurus (possibly exclusive to either males or females) had a primate-like opposable toe on each foot, perhaps used by one sex for extra grip during mating. Most species had broad, prehensile tails, sometimes tipped with a large "claw", again to aid in climbing. These tails, tall and flat like those of newts and crocodiles, have led some researches to conclude that they were aquatic rather than arboreal. Senter (2004) dismisses this idea, while Colbert and Olsen (2001), in their description of Hypuronector, state that while other drepanosaurs were probably arboreal, Hypuronector was uniquely adapted to aquatic life. The tail of this genus was extremely deep and non-prehensile – much more fin-like than other drepanosaurs. Genera Bradypodion Calumma Chamaeleo Furcifer Brookesia Rhampholeon Chameleons (family Chamaeleonidae) are squamates that belong to one of the best-known lizard families. ... This article is about the animal called newt. ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ...

Taxonomy

Taxonomic history

The various avicephalan groups have been difficult to pin down in terms of their phylogenetic position. Some of these enigmatic reptiles, specifically the drepanosaurids and Longisquama, have been assigned by some resarches to the prolacertiformes (Renesto 1994). Senter (2004), however, found them to form a group with the coelurosauravids, for which he coined the name Avicephala, as a sister taxon to Neodiapsida (the group which includes all modern diapsids and their extinct relatives). Binomial name Longisquama insignis Sharov, 1970 Longisquama (long scales) was a lizard-like reptile of the early Triassic Period 240 million years ago, which lived in what is now Turkestan. ... Families See text Prolacertiformes (sometimes called Protorosaurs) were a bizarre order of diapsid reptiles that lived during the Permian and Triassic Periods. ... Groups Coelurosauravidae Claudiosaurus Younginiformes Ichthyopterygia Sauria: Lepidosauromorpha Archosauromorpha Neodiapsida is a clade or major branch of the reptilian family tree, that includes all Diapsids apart from some early primitive types known as Araeoscelidia. ...

Within Avicephala, Senter created the group Simiosauria ("monkey lizards") for the extremely derived tree-dwelling forms. Senter found that Hypuronector, originally described as a drepanosaurid, actually lies just outside that family, along with the primitive drepanosaur Vallesaurus. He also recovered a close relationship between the drepanosaurs Dolabrosaurus and Megalancosaurus.

Classification

Class Sauropsida Superclasses Anapsida Eurapsida Diapsida Reptilia was an old kingdom or phylum classification that has since been divided into 4 classes. ...

• Subclass Diapsida
  • Family Longisquamidae
    • Longisquama
  • Family Coelurosauravidae
    • Weigeltisaurus
    • Coelurosauravus
  • Family Drepanosauridae
    • Vallesaurus
    • Hypuronector
    • Drepanosaurus
    • Dolabrosaurus
    • Megalancosaurus

Classes Ichthyosauria Sauropterygia Lepidosauria Archosauria Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side their skulls, about 300 million years ago during the late Carboniferous period. ... Binomial name Longisquama insignis Sharov, 1970 Longisquama (long scales) was a lizard-like reptile of the early Triassic Period 240 million years ago, which lived in what is now Turkestan. ... Binomial name Longisquama insignis Sharov, 1970 Longisquama (long scales) was a lizard-like reptile of the early Triassic Period 240 million years ago, which lived in what is now Turkestan. ... This article or section does not cite its references or sources. ... Coelurosauravus was a genus of flying reptile. ...

Phylogeny

Cladogram after Senter, 2004 [1]. Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ...

 Avicephala |?- Longisquama |--Coelurosauravidae | |--Weigeltisaurus | `--Coelurosauravus `--Simiosauria |--Vallesaurus `--+--Hypuronector `--Drepanosauridae |?-Unnamed sp. (GR 1113) (Harris & Downs, 2002) |--Drepanosaurus `--+--Dolabrosaurus `--Megalancosaurus 

References

• Colbert, E. H. & Olsen, P. E. (2001). "A new and unusual aquatic reptile from the Lockatong Formation of New Jersey (Late Triassic, Newark Supergroup)." American Museum Novitates: #3334, pp. 1-24.
• Harris, J. D. & Downs, A. (2002). "A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico." Journal of Vertebrate Paleontology: Vol. 22, #1, pp. 70-75.
• Renesto, S. (1994). "Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of northern Italy." Journal of Vertebrate Paleontology: Vol. 14, #1, pp. 38-52.
• Renesto, S. (2000): Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106: 157–180. HTML abstract
• Senter, P. (2004). "Phylogeny of Drepanosauridae (Reptilia: Diapsida)." Journal of Systematic Palaeontology 2 (3): 257-268.

External links

• Monkey Lizards of the Triassic - An illustrated article on drepanosaurs from HMNH.
• Prof. Silvio Renesto—Vertebrate Paleontology at Insubria University: Research - Images and discussion of Drepanosaurus.
• Prof. Silvio Renesto—Vertebrate Paleontology at Insubria University: Research - Images and discussion of Megalancosaurus.
• Gliding Mechanism in the Late Permian Reptile Coelurosauravus (Eberhard Frey, Hans-Dieter Sues, & Wolfgang Munk) - Abstract and available full text of the article in Science.