amniota

allyouneedisbiology.wordpress.com
Reptiles and mammals: same origin, different stories
Did mammals evolve from reptiles? The truth is they didn’t. Reptiles and mammals both have independent evolutionary histories that separated soon after the apparition of the so-called amniotic egg,...

Though all snakes have the same stripped-down, streamlined form, their hunting and killing techniques vary enormously. Some twine through the vegetation following the scent of birds’ nests, frogs’ eggs, or sleeping lizards. Others probe burrows on the forest floor, lurk next to flowers waiting to ambush hummingbirds, or dangle from branches pretending to be vines. Scent and vision are their most important senses, but pit vipers can also “see” the warmth of prey at night by using heat-seeking pits found on the snout. With no limbs, most snakes rely on their bite to kill. The bite of a coral snake also delivers a nerve agent that paralyzes a victim’s lungs and muscles. Vipers inject their prey with a potent venom that attacks the blood. Constrictors have no need for venom- they kill by asphyxiation, coiling around prey and tightening each time the victim exhales. The green vine snake (Oxybelis fulgidus), pictured above, can separate its jaw bones so that it can swallow prey wider than its own body. Backward-pointing fangs help ratchet the meal deep into the snake’s gullet. 

Text by Thomas Marent; Photo by rajeev

Kraterokheirodon

Species: K. colberti

Etymology: “Cupped hand tooth,” after the shape of the tooth

Age and Location: Late Triassic (Norian) of Arizona

Classification: Vertebrata: Eugnathostomata: Teleostomi: Euteleostomi: Sarcopterygii: Tetrapoda: ?Amniota: incertae sedis

Another bizarre tooth taxon from Triassic North America, Kraterokheirodon is among the most enigmatic members of the Chinle fauna. Once interpreted as a cynodont, and in fact featured in Walking with Dinosaurs as such, it is now considered an indeterminate amniote because its only known specimens are so hard to interpret. Whatever this animal was, however, it was large–the teeth are a few centimeters across.

Each tooth seems to consist of a row of six cups of variable size lined up perpendicular to the jaw. No known animal has a tooth that looks very much like this, though the tooth root makes it likely to belong to an amniote. It looks most like the tooth of a traversodont cynodont, somewhat similar to Exaeretodon. However, closer examination suggests that these similarities are superficial at best, so the mystery remains unsolved. If it is not a traversodont, it might be a different type of cynodont, or an unusual reptile perhaps similar to Trilophosaurus. This animal will probably remain a mystery until a lucky fossil collector finds a jawbone that contains some of these distinctive teeth.

Sources:

Chinleana

Irmis RB., Parker WG. 2005. Unusual tetrapod teeth from the Upper Triassic Chinle Formation, Arizona, USA. Canadian Journal of Earth Sciences 42:1339–1345.

Neotheropoda

Source: http://www.sciencemag.org/news/2014/10/new-meat-eating-dinosaur-lived-wake-mass-extinction

Group: Neotheropoda

Classification: Cellular Life, Archaea, Proteoarchaeota, Eukaryota, Unikota, Opisthokonta, Holozoa, Filozoa, Metazoa, Eumetazoa, Planulozoa, Bilatera, Nephrozoa, Deuterostomia, Chordata, Craniata, Vertebrata, Gnathostomata, Eugnathostomata, Teleostomi, Euteleostomi, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiforms, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Anthracosauria, Batrachosauria, Cotylosauria, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Archelosauria, Archosauriformes, Crurotarsi, Archosauria, Avemetatarsalia, Ornithodira, Dinosauromorpha, Dinosauriformes, Dinosauria, Saurischia, Eusaurischia, Theropoda 

Definition: The group including the most recent common ancestor of Ceolophysis and modern birds, and all of that animal’s descendants 

Organisms Within: Zupaysaurus, Tachiraptor, Dilophosauridae (not examined here), Coelophysoidea (not examined here), Averostra (not examined here), & two miscellaneous genera without further placement. 

Time Range: Shown below, numbers on the left in millions of years. Though the only basal Neotheropods known are from the Triassic-Jurassic boundary, members of other groups are present much earlier than that, about 220 million years ago, implying that they must have evolved at around that time or older.  

Characteristics

Neotheropods differ from basal theropods mainly on a few skeletal points. The ilium bone in the pelvis, expanded towards the top of the animal (dorsally).  The snout is more narrow than in basal theropods, there are more vertebrae fused to the hips, there is a complete loss of the fifth digit of the foot (as shown below), and a general stiffening of the legs overall. 

By @ewilloughby

Like all early dinosaurs, Neotheropods were probably covered in a layer of primitive feathers - though some theropods groups would later lose feathers, the general line leading up to birds must have kept them, given that birds have feathers. They were bipedal, fast predators, and basal members of Neotheropoda were probably outcompeted by later animals, and even during their existence Coelophysoids were far more common. 

Source: @alphynix

Fossil Locations: It is fairly likely that Neotheropods also originated in Argentina, during that very rapid early diversification of dinosaurs in the region. This assessment is based mainly on the presence of basal theropods mainly in the region, though its possible that it also occurred in North America, where many Coelophysoids lived. Coelophysoids have also been found in Europe and Asia, and so given this widespread range of this group and its early evolution, as well as the locations of basal theropods, its reasonable to suppose that Argentina is where they started, unless evidence to the contrary comes to light.

Biogeography: Neotheropods spread throughout the globe, as described above; this was relatively easy due to Panagaea, however, most Coelophysoids congregated around North America and Europe. The two basal members of the group stayed in South America. Maps from Dr. Christopher Scotese. 

Read more about Zupaysaurus here!

Read more about Tachiraptor here! 

Posts on Coelophysoidea, Dilophosauridae, and Averostra to come soon!

Sources: 

https://en.wikipedia.org/wiki/Neotheropoda

http://palaeos.com/vertebrates/theropoda/neotheropoda.html

https://en.wikipedia.org/wiki/Zupaysaurus

https://en.wikipedia.org/wiki/Tachiraptor

Shout out goes to @chequitablr!

Miscellaneous Neotheropods not examined here that do not have further placement (links added as I do posts on them): 

Altispinax

Szechuanosaurus

Group in Depth: Herrerasauridae

Source: http://dinostavros.deviantart.com/art/Chindesaurus-colored-160477241

Group: Herrerasauridae

Classification: Cellular Life, Archaea, Proteoarchaeota, Eukaryota, Unikota, Opisthokonta, Holozoa, Filozoa, Metazoa, Eumetazoa, Planulozoa, Bilatera, Nephrozoa, Deuterostomia, Chordata, Craniata, Vertebrata, Gnathostomata, Eugnathostomata, Teleostomi, Euteleostomi, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiforms, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Anthracosauria, Batrachosauria, Cotylosauria, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Archelosauria, Archosauriformes, Crurotarsi, Archosauria, Avemetatarsalia, Ornithodira, Dinosauromorpha, Dinosauriformes, Dinosauria, Saurischia, Eusaurischia, Theropoda 

It is possible, however, that Herrersaurids are not Theropods at all, but rather basal Saurischians, or even Dinosaurs that came before Ornithischians and Saurischians split. An analysis conducted in 2009 (Nesbitt et al.) found them to be basal theropods, whereas one in 2010 (Ezcurra) found them to basal Saurischians. Only more research will be able to resolve this problem. 

Definition: The most recent common ancestor of Herrerasaurus and Staurikosaurus and all of that ancestor’s descendants 

Organisms Within: Chindesaurus, Herrerasaurus, Sanjuansaurus, Staurikosaurus. Caseosaurus is a genus often included in this group, however, recent studies have found that Caseosaurus and Chindesaurus are in fact the same species (Nesbitt, Irmis & Parker, 2007). 

Time Range (numbers on the left in millions of years): 

It is clear that Herrerasaurids did not live for a particularly long period in the Earth’s history, with a range from about 231 to 225 million years ago. It is distinctly possible that they were outcompeted by the later evolved Coelophysoids, or even non-dinosaurian archosaurs. 

Characteristics: Herrerasaurids are some of the oldest known dinosaurs, with characteristics of both more advanced and basal groups. They had only two sacral vertebrae, the lowest number amongst dinosaurs; a pubic bone rotated and folded somewhat like a tetanuran (an advanced theropod), five fingers on the hand like primitive dinosaurs but elongated middle three fingers like theropods and curved claws, and a hinged jaw like theropods. Furthermore, their skulls were rectangular and vaguely like that of Archosauriformes, much more primitive than any dinosaur, and nothing like the more narrowed skull of early theropods. 

If Herrerasaurids are theropods, it implies that Theropods, Sauropodmorphs, and Ornithischians all diverged from one another in the Middle Triassic, very soon after Dinosaurs diverged from other Archosaurs. This is corroborated by evidence of primitive Theropod trackways in Argentina. They also probably were covered in feather, like all early dinosaurs, given the evidence for feathers being an ancestral trait for Avemetatarsalia. 

Source: http://www.deviantart.com/art/The-Herrera-s-Lizard-283763826

Herrerasaurids were small, bipedal carnivores, only about four meters long and a meter tall at their largest. They had backwards curved teeth to aid in the direction of food towards their throats and had strong legs good for fast running. However, even given this, they were not common in their environments - no dinosaurs were at the time - and were not top predators. 

They did not live for any long length of time and did not have a wide geographic range, indicating that their niches were filled by later theropods. They probably ate mostly herbivorous animals that weren’t dinosaurs, given the aforementioned rarity of dinosaurs in the early late Triassic, and their prey was probably small to medium sized animals such as rhynchosaurs, aetosaurs, and therapsids, though the early ornithischian Pisanosaurus may have been on the menu despite its rarity. 

Source: http://dinostavros.deviantart.com/art/Staurikosaurus-colored-160468327

Herrerasaurids themselves were probably prey for large rauisuchids and other archosaurs, and there is evidence that Herrerasaurus was cathemeral, active throughout the day and night at short intervals. The jaw of Staurikosaurus has a sliding joint allowing for a backwards and forwards movement as well as up and down to aid in the feeding process. They were lightly built predators, rare, but important in the understanding of early dinosaurian evolution. 

Fossil Locations (colored in = country has confirmed fossils of this group, line points to approximate location; multiple lines indicate multiple fossil sites):

It is evident that Herrerasaurids originated in Argentina, soon after and in a similar place as when the original dinosaurs originated. However, they did extend their range out to Brazil and even the Southwestern United States, and there is evidence that they made it as far as Poland. 

Biogeography (All maps taken from Dr. Christopher Scotese): 

It is clear that the expansion of Herrerasaurids into non-Argentine formations occurred later in their evolutionary history. 

Read more about Chindesaurus here!

Read more about Herrerasaurus here!

Read more about Sanjuansaurus here!

Read more about Staurikosaurus here!

Sources:

https://en.wikipedia.org/wiki/Herrerasaurus

https://en.wikipedia.org/wiki/Herrerasauridae

Shout out goes to @archosaurophilia​!