The Origin of Dinosaurs as told by The Smithsonian, Wiki, etc.

Many of the biggest dino museums in the world
have produced their version of the origin of dinosaurs. Here’s what they have to say online:

Smithsonian – National Museum of Natural History
“The earliest dinosaurs were probably carnivorous, bipedal animals less than two meters long and weighing about 10 kilograms. From these small beginnings evolved thousands of different dinosaurs species.”

“Dinosaurs evolved within a single lineage of archosaurs 232-234 Ma (million years ago) in the Ladinian age, the latter part of the middle Triassic. Dinosauria  is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus.

“The process leading up to the Dinosauromorpha and the first true dinosaurs can be followed through fossils of the early Archosaurs such as the Proterosuchidae, Erythrosuchidae and Euparkeria which have fossils dating back to 250 Ma, through mid-Triassic archosaurs such as Ticinosuchus 232-236 Ma. Crocodiles are also descendants of mid-Triassic archosaurs.

“Dinosaurs can be defined as the last common ancestor of birds (Saurischia) and Triceratops (Ornithischia) and all the descendants of that ancestor. With that definition, the pterosaurs* and several species of archosaurs narrowly miss out on being classified as dinosaurs. Archosaur genera that also narrowly miss out on being classified as dinosaurs include Schleromochlus 220-225 Ma, Lagerpeton* 230-232 Ma and Marasuchus* 230-232 Ma.

“The first known dinosaurs were bipedal predators that were 1-2 metres (3.3-6.5 ft) long. Spondylosoma may or may not be a dinosaur; the fossils (all postcranial) are tentatively dated at 235-242 Ma.

“The earliest confirmed dinosaur fossils include saurischian (‘lizard-hipped’) dinosaurs Nyasasaurus 243 Ma, Saturnalia 225-232 Ma, Herrerasaurus 220-230 Ma, Staurikosaurus possibly 225-230 Ma, Eoraptor 220-230 Ma and Alwalkeria 220-230 Ma. Saturnalia may be a basal saurischian or a prosauropod. The others are basal saurischians.”

* these are false nestings according to the tree topology of the large reptile tree.

University of Bristol
“Those archosaurs most closely related to the dinosaurs are forms such as Marasuchus. The detailed evolutionary relationships are still debated, but by the late Triassic, several early theropods are known, as the dinosaurs rapidly diversified. These dinosaurs, such as Eoraptor, Coelophysis and Herrerasaurus were all carnivores, and, despite their diversity, were quite rare at this time.”

Natural History Museum of Los Angeles County
“The ancestry of dinosaurs can be traced back some 230 million years ago to the Late Triassic. All dinosaurs belong to a group of reptiles called archosaurs-a group that also includes crocodiles and a variety of Mesozoic reptiles (pterodactyls and others) that are often misinterpreted as dinosaurs. The anatomical characteristics of both the earliest known dinosaurs and their archosaurian relatives suggest that the common ancestor of all dinosaurs was a small bipedal predator, which had forelimbs shorter than hind limbs. This ancestor was probably similar to the 235-million-year-old Lagosuchus from Argentina, pictured below.

“From the most primitive Triassic forms to the most advanced ones of the latest Cretaceous, all dinosaurs share defining traits that distinguish them from their closest archosaurian relatives. Among these innovations, the femur (or upper leg bone) developed a distinct head for a tied attachment into a hollow hip socket. These and other changes resulted in a hind limb that was tucked directly underneath the body, providing upright, pillar-like support of the body and also enhancing locomotive abilities. The changes that led to the erect posture of dinosaurs from the sprawling posture of their reptilian predecessors had a profound effect on the evolutionary success of these animals. These transformations may have also been coupled with the evolution of a higher metabolism (a step towards warm bloodedness) that endowed them with a greater capacity for sustained activities such as running.”

Genesis park
“The Bible states that on the fifth day of creation God created great sea monsters and flying creatures. This would have included the great swimming and flying reptiles (like the plesiosaur and pterosaur creatures mentioned at our Genesis Park website). On the sixth day God created the land animals, which would have included all of the dinosaur kinds (Genesis 1:20-25).”

Brief Lecture on the Origin of Dinosaurs – one commenter correctly noted, “This doesnt (sp) explain the actual origin of dinasaurs (sp) like the title states.”

The origin and evolution of dinosaurs Paul Sereno
Annual Review of Earth and Planetary Sciences
Vol. 25: 435-489 (Volume publication date May 1997)

“Phylogenetic studies and new fossil evidence have yielded fundamental insights into the pattern and timing of dinosaur evolution and the emergence of functionally modern birds. The dinosaurian radiation began in the Middle Triassic, significantly predating the global dominance of dinosaurs by the end of the period. The phylogenetic history of ornithischian and saurischian dinosaurs reveals evolutionary trends such as increasing body size. Adaptations to herbivory in dinosaurs were not tightly correlated with marked floral replacements. Dinosaurian biogeography during the era of continental breakup principally involved dispersal and regional extinction.”

American Museum of Natural History
Strangely, they don’t have an online account of dinosaur origins.
Meet a long list of the best known taxa preceding dinos, the advent of dinos and see their family tree here and here. More specifics here (Fig. 1).

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

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