Main Page
Welcome to the explain xkcd wiki!
We have an explanation for all 3042 xkcd comics,
and only 19
(1%) are incomplete. Help us finish them!
Latest comic
| T. Rex Evolution |
 Title text: Unfortunately, body size and bite force continue to increase. |
Explanation
|
This explanation may be incomplete or incorrect: Created by a BOT WITH NEGATIVE LIMBS - fact-check the graph's "early" claim and flesh things out a bit. Do NOT delete this tag too soon. |
The small and seemingly useless forelimbs of Tyrannosaurus rex have often been used as a source of humour in works of fiction that feature dinosaurs. Randall claims that the ancestors of T. Rex had (relatively) longer and therefore more useful forelimbs, and hypothesizes that - had non-avian dinosaurs not suffered an extinction event - this trend of "reduced limbs" would continue until present-day descendants of T. Rex were limbless creatures not unlike a giant snake.
In reality, while animals do lose usage of their limbs - such as the hind legs of a whale - the development of these vestigial limbs would not apply to other limbs. A T. rex would continue to have substantial need for its hind legs, which it used for running and chasing prey, and would have no reason to lose legs unless environmental factors favored a limbless lifestyle. This has happened multiple times in the Order Squamata, the lizards and snakes, where limbless body plans have evolved convergently over and over such as in blind worms as compared to true snakes. However these circumstances that encourage such lifestyles are not likely to happen to the large predatorial Tyrannosaurus. With that said Tyrannosaurus would likely eventually lose its arms altogether if it never went extinct.
The title text claims that as T. Rex was also larger than its ancestors, the same trend in growth would continue such that the hypothetical limbless present-day descendant would be even larger than the famously elephant-sized T. Rex. In reality animals do not linearly grow in size and a modern Tyrannosaurus would not necessarily be dramatically larger, and could easily have gotten somewhat smaller even with the same body plans and lifestyle.
This comic may be tangentially related to the fact that birds are dinosaurs that survived the KT extinction, which is a recurring theme on xkcd.
Extrapolation was previously mentioned in comic 605: Extrapolating.
Transcript
|
|
This transcript is incomplete. Please help editing it! Thanks. |
- [A graph of limbs over time, with 3 animals represented]
- [The vertical axis is labelled Limbs, from 0 to 4]
- [The horizontal axis is not labelled but represents time, in ticks of 10 million years, from 180 million years ago to 0.]
- ["Extinction" points to 65 million years ago, and "Now" points to 0.]
- [The first animal, a regular dinosaur, is in the top left: 4 limbs, 150 million years ago.]
- 4 normal limbs
- [An arrow goes from it to the second animal, a T. Rex, in the middle, just left of "extinction".]
- Barely more than 2
- [A dashed arrow with a question mark goes from it to the last animal: a leg-less dinosaur with a big mouth.]
- ???
- [Caption below the panel:]
- If T. Rex hadn't gone extinct
- (Linear extrapolation)
Is this out of date? .
New here?
Last 7 days (Top 10) |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
You can read a brief introduction about this wiki at explain xkcd. Feel free to sign up for an account and contribute to the wiki! We need explanations for comics, characters, themes and everything in between. If it is referenced in an xkcd web comic, it should be here.
- If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this Wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.
- Discussion about the wiki itself happens at the Community portal.
- You can browse the comics from List of all comics or by navigating the category tree at Category:Comics.
- There are incomplete explanations listed here. Feel free to help out by expanding them!
Rules
Don't be a jerk!
There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.
If you want to talk about a specific comic, use its discussion page.
Please only submit material directly related to (and helping everyone better understand) xkcd... and of course only submit material that can legally be posted (and freely edited). Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.
If you need assistance from an admin, post a message to the Admin requests board.
