We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens. Phylogenetic analysis positions Eoraptor within Sauropodomorpha, rather than among theropods, indicating it is an early member of the sauropodomorph lineage rather than closely related to later theropods such as tyrannosaurids.

Nine unambiguous synapomorphies, nonetheless, unite theropods and sauropodomorphs to the exclusion of herrerasaurids and Eoraptor. These features support the hypothesis that herrerasaurids and Eoraptor branched off before the divergence of theropods and sauropodomorphs. As a result, Eoraptor is positioned as a basal saurischian or near the base of Saurischia, outside the more derived theropod lineages that later include tyrannosauroids such as Tyrannosaurus rex.

"Eoraptor lacks the specialized features of any of the major groups of dinosaurs, and is quite similar to what would be expected for dinosaur ancestors." It has led to differing views: "This has led some to conclude that it is not part of the dinosaurs proper, but is a closely related archosaur. Others have pointed to the functionally three-fingered hand as an indication of close ties to theropod dinosaurs." The page emphasizes its basal, ancestral position rather than a close relationship to derived theropods like large carnivores.

This small therapod is one of the oldest known dinosaurs. It had sharp teeth and was probably a fast runner. Eoraptor may be as close as we'll get for some time to the ultimate ancestor of dinosaurs. Eoraptor's skull is relatively small. Some theropod skulls, such as T. rex, can be longer than 1.2 meters (4 feet)!

We report a molecular phylogeny for a nonavian dinosaur, extending our knowledge of trait evolution within nonavian dinosaurs into the macromolecular level. Despite missing sequence data, the mastodon groups with elephant and the T. rex groups with birds, consistent with predictions based on genetic and morphological data for mastodon and on morphological data for T. rex. These results match predictions made from skeletal anatomy, providing the first molecular evidence for the evolutionary relationships of a non-avian dinosaur.

Sereno et al. (1993) found Eoraptor as the basalmost theropod sister taxon to Herrerasaurus + Neotheropoda. Subsequent analyses, however, have reassessed this position, and more recent work has shifted Eoraptor to Sauropodomorpha rather than Theropoda, reflecting ongoing revision of its phylogenetic placement.

From a cladistic perspective, Eoraptor is also placed within the clade Theropoda, because of features of the jaw, hands and feet, and the presence of a furcula—a small, wedge-shaped bone of the chest present in many theropods, and later in birds. Cladistic analysis places Eoraptor at a “basal” or ancestral position within the clade, as it possessed many of the features present in later theropod species, but does not fit into the later clades. Scientists believe that Eoraptor represents a lineage that would eventually give rise to the vast majority of predatory dinosaurs, providing crucial insights into the evolution of key traits seen in later species, including later theropods like Tyrannosaurus rex, but not as a close relative of any derived theropod lineage.

T. rex peptide sequences are more similar to modern-day birds than to reptiles, according to new research, providing added evidence for a relatively close evolutionary relationship between dinosaurs and birds. These latest results, appearing in today’s issue of Science, suggest T. rex is more closely related to chickens and ostriches than to alligators and seem to confirm the long-held suspicion that dinosaurs and birds have a common ancestor. “We determined that T. rex, in fact, grouped with birds — ostriches and chickens — better than any other organism that we studied,” the senior author said.

"Theropods, like Eoraptor, were diverse, ranging from crow-sized to giants like Tyrannosaurus rex." The entry describes Eoraptor as a small predatory dinosaur within Theropoda but does not indicate a particularly close phylogenetic relationship to Tyrannosaurus rex; instead it presents them as members of the same broad group of theropods spanning a wide range of sizes and evolutionary distances.

Eoraptor lunensis is from the late Triassic of Argentina. One of the earliest known dinosaurs and a contemporary of Herrerasaurus, its already bipedal stance and short, specialized forelimbs suggest an affinity with theropod dinosaurs. Eoraptor lends support to the hypothesis that dinosaurs diverged rapidly and at small body sizes from a common ancestor, and that the main herbivorous and carnivorous lineages were already present by the Middle Carnian.

The Natural History Museum’s dino directory lists Eoraptor’s taxonomy as "Dinosauria, Saurischia, Theropoda" and describes it as "Eoraptor, a meat-eating theropod dinosaur." It presents Eoraptor as an early small theropod but does not suggest it is closely related to later large theropods such as Tyrannosaurus rex; instead, the page elsewhere notes that birds are distant relatives of T. rex, indicating the concept of broad, not close, relationships within Theropoda.

The Herrerasauridae and Eoraptor may be the earliest group of theropods, or it is quite possible that they are not even theropods at all, but rather non-dinosaurian archosaurs. This uncertainty places Eoraptor at or near the base of Theropoda if it is included, far removed from derived theropods like Tyrannosaurus rex, which belong to much later, specialized clades within Theropoda.

Over the years it has been classified as a basal theropod, a basal saurischian (“lizard-hipped” dinosaurs; the clade that includes both theropods and sauropodomorphs), and most recently, a basal sauropodomorph. Currently it is generally recognized as the latter, but its classification could change again as more research is done. Despite resembling a theropod, and indeed likely resembling the very first of all dinosaurs, Eoraptor was one of the earliest sauropodomorphs (sauropods and their earlier relatives).

Eoraptor is one of the earliest known genera of true dinosaurs. In 1995, Sereno posited that Eoraptor is the earliest-recorded theropod, and is closest to "the hypothetical dinosaurian condition than any other dinosaurian subgroup." The precise placement of Eoraptor within Dinosauria has been unstable, with opinion often varying between a basal saurischian and a basal theropod. Sereno et al. (2013) redescribed the holotype skeleton and concluded that Eoraptor was not a theropod but a basal sauropodomorph, consistent with the earlier observation made by Martinez et al. (2011). A large phylogenetic analysis of early dinosaurs by Matthew Baron, David Norman and Paul Barrett (2017) found Eoraptor to be the earliest diverging member of Theropoda, within the larger clade Ornithoscelida. Later analyses (e.g. based on Langer et al. 2017) again placed Eoraptor among early sauropodomorphs. In both alternatives, Eoraptor occupies a basal position and is not treated as a close relative of highly derived theropods such as Tyrannosaurus rex.

Eoraptor stands out not only for being one of the first dinosaurs to ever walk the Earth, but because palaeontologists cannot conclusively agree on where to place it in relation to other dinosaurs. Initially Eoraptor was classed as a theropod because of its bipedal stance and narrow build, but the sauropodomorphs (which would go on to evolve into giant quadrupedal dinosaurs like Apatosaurus and Brachiosaurus) were also bipedal with a similar body plan in their early stages of development. This is why Eoraptor has in the past been classed as a theropod by some and sauropodomorph by others, and why in 2011 it was classed again as a eusaurischian, a position that places it between these two groups. The 2013 study "Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha)" treated Eoraptor as a basal sauropodomorph.

Recent phylogenetic analysis found it to be a sauropodomorph rather than a theropod. In any case, this animal is close to the ancestry of both the sauropodomorph and theropod lineages, making it an important taxon for understanding early dinosaur evolution, but not a close relative of derived theropods such as Tyrannosaurus rex.

Eoraptor was from the saurischia, or “lizard-hipped”, order of dinosaurs and is considered to be a very primitive theropod-like species. It also belongs to the infraorder Herrerasauria which includes other early dinosaurs, like Herrerasaurus and Saltopus. Other paleontologists point out that its functional three-fingered hand indicates a connection to theropod dinosaurs. Regardless of Eoraptor’s strict classification, it still provides a good example of where and when dinosaurs began, and what they looked like in the dawn of their creation, implying a distant, ancestral position rather than a close kinship with late Cretaceous theropods such as Tyrannosaurus rex.

"For years it was often treated as an early theropod, but many later studies place it closer to the base of Sauropodomorpha instead." The page explains that Eoraptor "is considered one of the earliest and most primitive dinosaurs," and notes that its traits suggest a position near the base of major dinosaur lineages. This reassignment toward basal sauropodomorph status further distances it phylogenetically from derived theropods like Tyrannosaurus rex.

I was surprised that Eoraptor (a very early dinosaur) is classified as Sauropodomorpha (at least on Wikipedia and Smithsonian encyclopedia). My guess would have been that it is an early theropod. Other commenters point out that more recent phylogenetic analyses place Eoraptor among basal sauropodomorphs rather than within Theropoda, reflecting a shift away from its original theropod assignment.

Classification: Dinosauria, Saurischia. Eoraptor is one of the earliest known genera of true dinosaurs. It was a two legged saurischian, a medium-sized carnivore, or potentially omnivore, from approximately 231.4 million years ago (in the late Triassic period, during the Carnian age). In shape and size Eoraptor is what the typical primitive dinosaur should look like. It lacks the specialized features of many major dinosaur groups. However, its three-fingered hand suggests a closer relationship to many theropod dinosaurs. This primitive condition indicates that any relationship to later theropods such as Tyrannosaurus rex would be distant and ancestral rather than close.

That began to change in 1993 with the discovery of Eoraptor lunensis in Argentina’s Ischigualasto Formation—one of the earliest known dinosaurs, dating back about 231 million years. Scientists still debate whether Eoraptor was a primitive theropod or a more general saurischian, but either way, it marked a turning point in understanding how dinosaurs first evolved. Eoraptor lived in the Late Triassic, more than 150 million years before iconic Late Cretaceous theropods like Tyrannosaurus rex, so the two are separated by a very long span of evolutionary time.

The article describes Eoraptor as "a medium-sized carnivore" from the Late Triassic and notes that "Later dinosaurs tended to lose fingers, and by the time T. rex came along there were only two fingers on each hand." This comparison highlights that Eoraptor retains more primitive, multi-fingered hands, contrasting with the reduced, specialized hands of Tyrannosaurus rex, and implying a distant rather than close evolutionary relationship.

The entry characterizes Eoraptor as "a genus of early dinosaur that lived during the Late Triassic period" and notes that it had a slender, small body. Eoraptor is presented as among the earliest known dinosaurs, with primitive traits, while Tyrannosaurus rex is a much later, highly derived large theropod from the Late Cretaceous; the temporal and anatomical distance implies they are not close relatives despite both being theropods in some classifications.

The Eoraptor lunensis was a small theropod that lived in the Late Triassic (228 Ma) in Argentina. But Eoraptor was in fact one of the earliest sauropodomorphs, and its kind would eventually give rise to the biggest land animals of all time. In the comments, users debate whether Eoraptor should be considered a theropod or sauropodomorph, with some insisting "Eoraptors were Theropods, not Sauropods" while the post text reflects the newer interpretation as an early sauropodomorph ancestor.

Small by what we consider to be dinosaur standards, it grew to about 3 feet in length. It is generally accepted to be a theropod, but other researchers argue that it might instead be a basal sauropodomorph. In either case, it is an early, basal dinosaur far removed from the large, specialized tyrannosaurid theropods like Tyrannosaurus rex that lived much later in the Cretaceous, and is not considered a close relative of them.

Tyrannosaurus rex is a highly derived coelurosaurian theropod from the Late Cretaceous, whereas Eoraptor lunensis is an early Late Triassic dinosaur now generally regarded as a basal sauropodomorph or very basal saurischian near the divergence of theropods and sauropodomorphs. Their positions on the dinosaur family tree are therefore widely separated, with T. rex deep within Theropoda and Eoraptor near or on the sauropodomorph stem, indicating they are not close relatives among theropod dinosaurs.