The Anapsids and Diapsids

The Amnion Image from: http://www.ucmp.Berkley.edu

Relative diversity of living vertebrates

We are here

Parareptilia (Olson 1947) An extinct group among basal amniotes Upper Pennsylvanian to Upper Triassic Do not have a temporal fenestra and have been called Anapsida (Williston 1917) when the taxon included the turtles.

Parareptilia (Olson 1947) These varied from small aquatic to large terrestrial forms Procolophon, broad and flattened burrowing animals from the upper Permian to the Triassic.  Image by Arthur Weasley, Wikipedia Scutosaurus, a pareisaur, once thought to be the group from which the turtles emerged.  Image by Arthur Weasley, Wikipedia Mesosaurus, a small aquatic animal. Image by Nobu Tamura

Diapsida (Osborn 1903) 2 temporal fenestrae Relatively long radius in most This group includes all reptiles and birds, a taxon called Sauropsida (Watson 1956)

Class Eodiapsida These are the basal diapsids and include 2 very different groups: Younginomorpha (Pennsylvanian to Lower Triassic) Ichthyosauromorpha (Mid Triassic to Mid Cretaceous) ? The relationship between the two groups that are merged here to create the Eodiapsida, a sister group to the Lepidosauromorpha and Archosauromorpha.  In general, this figure is based on Benton (2005) and shows the relationship between this group and the other higher taxa of gnathostomes. 

Class Eodiapsida Younginomorpha Lizard-like amniotes Petrolacosaurus, the earliest known diapsid. Image from: http://taggart.glg.msu.edu/isb200/carbfor.htm

Class Eodiapsida Ichthyosauromorpha Aquatic and cetacean-like Skull lost the lower fenestration Utatsusaurus of the early Triassic was one of the earliest known ichthyosaurs.  Note the elongate body, paddle-like limbs, and the small fin on the tail. Image by: © Arthur Weasley; Creative Commons Shonisaurus of the upper Triassic was the largest known ichthyosaur with a maximum length of 21 meters.  The animal was whale-like and may have been toothless as an adult.  Image by: © Arthur Weasley Platypterygius, the last known ichthyosaur, lived in the Cretaceous.  They had very large pectoral paddles, powerful tails, and streamlined bodies.  Platypterygius grew to 7 meters long and hunted in the open ocean. Image by: Dimitry Bogdanov; Creative Commons

5. Serpentes Alternate Clades CLADOGRAM OF THE LEPIDOSAUROMORPHA MAJOR CLADES OF THE LEPIDOSAUROMORPHA 1.  Sauropterygian Clade 2.  Lepidosaur Clade 3.  Sphenodont Clade 4.  Squamata Clade 5.  Serpentes Alternate Clades

The Sauropterygian Clade Placodont Plesiosaur

Sphenodonts, the Basal Lepidosaurs A living sphenodont, the Tuatara

Squamata Clade, the Lizards Five assemblages are identified Iguania Gekkota Amphisbaena Anguimorpha Scincomorpha Gecko Mosasaur Iguana Blue-Tongued Skink Glass Lizard Komodo Dragon

The Serpentes Indian Python Indian Spectacled Cobra All living snakes seem to have been derived from Iguanids, but no living Iguanids are legless.

CLADES OF THE ARCHOSAUROMORPHA 1. RHYNCHOSAURIA, THE BASAL ARCHOSAURS 2. CROCODILIANS 3. PTEROSAURS 4. DINOSAURS 5. ORNITHISCHIANS 6. SAURISCHIANS 7. SAUROPODS 8. THEROPODS 9. THE BIRDS

Rhynchosaurs, beaked archosaurs  Protorosaurus, a long-necked rhynchosaur from the upper Permian. Hyperodapedon, a strange basal Archosauromorph that was a herbivore.  Notable adaptations included a distinctive narrow beak, specialized cheek teeth, and hind claws adapted to digging. 

Crocodilians, archosaurs with rotating ankle Euparkeria, a stem Archosaur from the middle Triassic.   Photo of an American Alligator in Florida. 

Pterosaurs, the finger-winged archosaurs An illustration of Rhamphorhynchus in a dive.  A Pteranodon in flight. 

The Dinosaurian Clade longer hind legs than front legs the skeleton and musculature of the hind legs that causes them to be underneath the body rather than splayed, including the distinct offset head an ball of the femur a reduction of the digits in the manus and pes (usually to 3 or 4) an acetabulum, hip joint, that has a hole in the center a sacrum of at least 3 fused vertebrae a reduced fibula a crest that runs much of the way down the humerus for the attachment of the deltoid and pectoral muscles Weishampel et al. (1990), Soreno (1999), and Benton (2005) 

Ornithischian Clade Painting of an ornithopod hadrosaur, a member of the ornithischian dinosaurs. The animal has a bipedal stance, but it can also move about as a quadruped.  An image of Triceratops, which was an obligate quadruped.

Saurischian Clade Tyranosaurus, one of the last theropod non-avian dinosaurs Diplodocus, one of the giant sauropods had pillar-like legs, an enormous body, and long neck and tail.  As illustrated here, the animals likely walked with their tails elevated, which served as a counterbalance.  

Avian Dinosaurs Hand of Deinonichus (L) and Archaeopteryx (R) Passer domesticus, the most widespread living theropod

Major Events in the Evolution of Flying Theropods, Birds Archaeopteryx

What about turtles?

Views of Turtle Evolution Three different cladograms regarding the relationships of the living amniotes.  Cladogram A assumes that the turtles are sisters to the diapsids.  Cladogram B assumes that the turtles arose from within the diapsids.  Cladogram C assumes that the turtles arose from a basal line of amniotes. A=Anapsid; AM=Amniote; D=Diapsid; S=Synapsid.

Pleurodires (side-necked turtles) Matamata, a pleurodire or side-neck turtle from South America.

Cryptodires, S-Necked Turtles A softshell turtle, a trinochoidean cryptodire. A sea turtle, a chelonoidean cryptodire.  An Aldabra Tortoise, a testudoidean cryptodire.

Early Turtles Restoration of Odontochelys, one of the oldest turtles. Developmental and molecular evidence suggests that they evolved from within the diapsids. Are they Lepidosaurs or Archosaurs? Adapted from Lee (2013) Adapted from Schoch and Sues (2015)