Myriad differences exist between the respective biotas of Spec and Home-Earth, but the first glaring distinction to impress itself upon a visitor would be the dinosaurs. Spec's dinosaurs are wildly diverse, with species ranging from hummingbirds to gihugrongos and sabre-tyrants. Descriptions of the dinosaurs of Spec take up the bulk of this series.

Dinosaurs evolved during the Middle or Early Triassic, between 230 and 250 million years ago, as part of a larger radiation of archosaurs. These "ruling reptiles" are today represented by dinosaurs and crocodilians; both born very soon after the Permian extinction had wiped out virtually all fossilizable life on Earth. There were a few million years of confusion, but by the end of the Triassic, dinosaurs had emerged over other archosaurs, the mammals and their relatives as the dominant terrestrial vertebrates. Dinosaurs quickly diversified, and today they occupy a wide range of forms – comparable to the home world mammals

Dinosaurs are split into two principal groupings, the Saurischia (including among others sauropods and theropods, which in turn include birds) and the somewhat less diverse, but still successful Ornithischia (including ceratopsians, ornithopods, and ankylosaurs). Saurischians are the more plesiomorphic of these two clades (most similar to the common dinosaur ancestor), and usually retain superficially lizard-like hips, with the pubis (one of the three bones in the hips) pointing down or slightly forward, although many saurischians (including most maniraptors, such as birds) have hips that are swept back. The ornithischians also evolved swept-back hips, probably as an adaptation to accommodate larger, plant-digesting guts. Over the eons, both groups have experimented with carnivory, omnivory, and herbivory, but it is still safe to say that many saurischians are predators while many ornithischians eat plants.

Today, Saurischia is the more widespread and diverse of the two branches of Dinosauria. The sauropods, an ancient group of huge, long-necked saurischian plant-eaters, are still present in the warm parts of the Old World, although they are much reduced, and the abelisauroid predators roam the same areas in pretty high diversity. Most modern saurischians, however, are coelurosaurs, two-legged and feathered. Apart from a few basal representatives like the Australian cedunasaurs, the tyrannosaurs, and the archaeoplumes, all living coelurosaurs are birdlike maniraptors. Maniraptors have proved wildly successful in the world of Spec, running the gamut from lumbering segnosaur over fearsome drak to soaring bird.

The most successful maniraptoran clade, the birds, has strayed so far from its ancestors that Linnaean taxonomy took it out of Dinosauria and given it a class of its own, on par with mammals, "reptiles", and amphibians. However, now that Linnaean taxonomy has largely been abandoned, birds' obvious descent unambiguously places them within the dinosaurian group Maniraptora. In the Specworld, this relationship is easier to see than in our home timeline, with many of the intermediate forms surviving to the present day. In fact, it is so easy that we have found ourselves unable to define "bird" – see the introduction on the Maniraptora page. Birds are far more diverse in Spec than on Home-Earth, including many taxa found only in Spec. A number of ancient bird lineages, such as Enantiornithes and the toothed Ichthyornithidae, survive to the present day, and are joined by many familiar avian groups (ducks, penguins, and others), as well as number of odd groups like bunglebirds and carpos. However, they too have suffered some causalites. The troodontids are now a shadow of their former glory while ornithomimids have vanished forever.

The other dinosaurian group, Ornithischia, is not as widespread as Saurischia, but still quite successful. Most basal ornithischians have gone extinct, and though a few ankylosaur lineages still survive in Australasia and in the Americas as well. All of the remainder are either ceratopsians such as †Triceratops or ornithopods such as †Iguanodon. Ceratopsia suffered heavy losses in the early Tertiary and is today represented only by the cenoceratopsians and dinoceratopsians, two groups which ranges in size from one pig to two elephants,and in geography ranges from Africa, southern Asia to South America, with a few species in North America respectively. Far more common than the ceratopians, however, are the ornithopods, which live on every continent but Antarctica.

Ornithopoda is split into two great clades, the iguanodontians and the antarctornithopods. The divergence between these two occurred far back in the Mesozoic, with both groups evolving from small, bipedal herbivores. Iguanodontians quickly spread across the world and evolved into a wide range of forms, both small (†Dryosaurus, †Gasparinisaura) and huge (†Edmontosaurus, †Muttaburrasaurus). These creatures continue to thrive to the present day, as, among others, hmungos thundering across North America, saurolopes sweeping through the plains of Africa, and dendrosaurs swinging about the trees of Australia. Somewhat less successful, but still widespread and diverse, are the antarctornithopods. These creatures evolved from generalized basal ornithopods like †Leaellynasaura of the Early Cretaceous of Australia, and today they are still mostly restricted to the Southern Hemisphere. In Australia, especially, antarctornithopods are dominant, both in the herbivore niches (Euclasauria) and the predator guilds (Rhynchoraptoria), it should be noted that the only competition that the carnivorous ornithopods face is a flightless group of pterosaurs. The generalized viriosaurs of the Americas are also antarctornithopods, having split from their Australian cousins some time in the very early Cenozoic and walked to South America from Australia via Antarctica. Together, the two ornithopod groups occupy most of the herbivore niches of Spec.

In recent years, back in 2013, a new group small ornithopods was recently identified by our researchers: Laurasiaornithopoda. This group consists of four different clades. Struithodactylids which fulfill the role small browsers, which rely on lightning fast speed in order to escape predators. Laticanatids which are strange semi aquatic ornithopods that can be found in various warmer waters. Vanguards which are small, but heavliy armored brutes which mirror the ancient armored behemoths of the past. Finally, Eurolophia, a strange group of ornithopods which originated during the Oligocene epoch in Europe, which have now been reduced down to a hand full of surviviors.

In the 230 or more million years of their evolution, dinosaurs have conquered the land, the air, and the sea. They live on every continent as well on nearly every island of any size (as birds). In their species count, in their diversity of form, and in their sheer biomass, the dinosaurs of Spec are the unquestioned rulers of the Earth.

~Daniel Bensen and David Marjanović

[This is to make up for the lack of a phylogenic table at [1] based on genetic relations. Please modify, but don't delete. (based on [2])]

                     |           ,=ABELISAUROIDEA
        ,=Saurischia=|           |
        |            |           |               ,=CEDUNASAURIA
        |            |           |               |
        |            `=Theropoda=|               | ,=TYRANNOSAUROIDEA
        |                        `=Coelurosauria=| |
        |                                        `=| ,=ARCHEOPLUMIA
        |                                          `=|
        |                                            `=MANIRAPTORA
        |                                                   ,=VIRIOSAURIA
        |                ,=Marginocephalia=CENOCERATOPSIA & DINOCERATOPSIA   |
        |              ,=|                                  |   ,=EUCLASAURIA
        |              | |              |=EUROLOPHIA                   | ,=|
        |              | |             ,=Antarctornithopoda=| | `=RHYNCHORAPTORIA
        |              | |             |                    | |
        |              | |             |                    | | ,=VANGUARDIDAE
        |              | |             |                    | ,=|
        |              | |             |                    `=| `=LATICANATIDAE
        |              | |             |                      |
        |              | `=Ornithopoda=|                      |               ,=Struthiodactlyoidea 
        |              |               |                      `LAURASIAORNITHOPODA=Macrodactylia=|
        `=Ornithischia=|               |                                      `=Hippodactyloidea
                       |               |  
                       |               |                  ,=PSEUDOSAUROPODA
                       |               |                ,=|
                       |               |                | `=NEODYROSAURIA
                       |                 `=Iguanadontia=|
                       |                                `=HADROSAURIA