xkcd.WTF!?

Explanation ➲

This comic explores the seeming paradox that certain extinct prehistoric species which are popularly thought of as being "dinosaurs" are, from a strict taxonomic viewpoint, not. It also takes into account the fact that all bird species are descended from dinosaurs and thus - again, from a strict taxonomic viewpoint - are themselves dinosaurs as well (see 1211: Birds and Dinosaurs). To illustrate this, Randall provides silhouettes of

• dinosaurs
• entities that are widely thought of as dinosaurs but are not
• entities that are not widely thought of as dinosaurs but are (i.e. birds)
• and, lastly, entities that are neither dinosaurs nor thought of as dinosaurs (which is funny because it's so all-encompassing as to be practically meaningless, just like it would be if you replaced the word "dinosaurs" by any other plural noun or adjective).

Creatures that seem like dinosaurs and are dinosaurs

• Stegosaurus was a herbivorous genus of dinosaurs from the Late Jurassic period with spikes on their tails and distinctive upright plates along their backs. The function of the spikes and plates is the subject of much speculation among scientists, with the current consensus being that the spikes were used for defense and the plates used for display. First identified during the Bone Wars, illustrations of Stegosaurus have been in popular media for over 150 years.
• Triceratops, named for the three horns on its face, was a Late Cretaceous dinosaur, living during the Maastrichtian age up until the K-PG extinction event. First displayed at the 1900 Paris Exposition, Triceratops has been one of the most popularly displayed dinosaurs, due to the abundance of fossils and distinctive appearance. Its appearance in various films over time has made Triceratops one of the most distinctive dinosaurs.
• Tyrannosaurus Rex, whose name literally translates to Tyrant-Lizard King, was also a Late Cretaceous dinosaur, living during the Maastrichtian Age at the very end of the period. It was a contemporary of Triceratops and Mosasaurs, also listed in this comic. T-Rex is arguably the most well-known dinosaur, due to the recovery of intact skeletons, as well as successful marketing and pop-culture influences, such as Jurassic Park, one of Randall's favorite films.
• Diplodocus
• Velociraptor

Creatures that seem like dinosaurs, but are not

Dinosaur is a paleontology term which refers to a specific group of reptiles, based upon evolutionary lines, bone structure and living domain. However, non-experts may have difficulty distinguishing these from other extinct large reptiles/creatures and apply the term somewhat indiscriminately, hence the confusion between what is scientifically included and what is culturally assumed to be included.

The creatures listed are:

• Mosasaurs were aquatic reptiles that existed during the Cretaceous. Although mosasaurs appeared in Jurassic World, they are not closely related to dinosaurs. They actually evolved from lizards and are most closely related to either snakes or varanoids (such as the Komodo dragon).
• Plesiosaurs were another group of Mesozoic aquatic reptiles. Their place in the reptile family tree is debated, as they are not closely related to dinosaurs or any extant reptile.
• Pteranodon belonged to the group of flying reptiles known as pterosaurs. While dinosaurs and pterosaurs are both archosaurs and are more closely related to each other than other archosaurs (such as crocodilians; see title text explanation below), they diverged around 250 MYA, and are distinct enough to be entirely separate lineages.
• Dimetrodon lived in the Paleozoic, well before dinosaurs first evolved. They are synapsids, which makes them more closely related to mammals than to any living reptiles.
• Quetzalcoatlus was a genus of flying pterosaurs, like Pteranodon, that lived in the Maastrichtian Age (the end of the Cretaceous) alongside mosasaurs, T-Rex and many others. They were some of the largest flying animals in history, with wingspans up to 36 feet (11m). They were not, however, dinosaurs, as they had pterosaur ancestry.

Creatures that don't seem like dinosaurs, but are

Due to the popular depiction of dinosaurs as prehistoric large reptiles, many people don't view modern birds as dinosaurs. However, as Randall loves to remind people, dinosaurs such as T-rex are more closely related (temporally, anatomically and phylogenetically) to birds than to some other dinosaurs such as Stegosaurus, and therefore, birds are dinosaurs in their own right.

• Penguin
• Heron
• Ostrich
• Pigeon
• Falcon or Petrel (both of them qualify)

Creatures that don't seem like dinosaurs, and are not

• Squirrel: Squirrels are mammals, and dinosaurs are reptiles. Most people also think of dinosaurs as large and dangerous, while squirrels tend to be small, cute and relatively harmless (although their bites can transmit infection). Could also be made of dark matter.
• Stapler: Staplers are inanimate objects, and dinosaurs are living creatures.
• Potted plant or pineapple: Dinosaurs are animals, and plants are not.
• Human (Cueball): Humans are mammals, and dinosaurs are reptiles. In fact, the Jurassic Park series often pits the two against each other.
• Bicycle: While they tend to be more mobile than staplers, and have some relation to horses, bicycles are also not living creatures.

The title text is a further joke about taxonomy, seemingly predicated on the assumption that staplers are biological organisms (which they are not),^{[citation needed]} and can thus be sorted into taxa. Pseudosuchia is in fact the clade of archosaurs that includes crocodilians, and staplers bear a certain resemblance to the open mouth of a crocodilian. Also, "suchia" sounds a little like "suture," and in some sense staples are pseudo sutures.

The original Linnaean taxonomy did at first have a top-level classification for "mineral" taxonomy, in addition to those for animal and plant, which in its broadest sense might allow one to assign a stapler a taxonomic relationship with dinosaurs.