Why did T Rex have such tiny arms?

It's easy to assume that every trait - including stubby arms on a terrifying predator - must be beneficial, but the forces of evolution don't really work like that.

Thanks to the University of Minnesota for sponsoring this video! http://twin-cities.umn.edu/

Thanks also to our supporters on https://www.patreon.com/MinuteEarth
___________________________________________

FYI: We try to leave jargon out of our videos, but if you want to learn more about this topic, here are some keywords to get your googling started:
Evolutionary Mechanisms: Forces that change the frequency of genes in populations.
Natural Selection: The process whereby traits that make animals more likely to survive and reproduce take hold in a population.
Vestigiality: The process by which a genetically-determined structure loses some or all of its functionality.
Genetic Drift: A change in the frequency of an allele due to random sampling.

___________________________________________

Credits (and Twitter handles):
Script Writer: David Goldenberg (@dgoldenberg)
Script Editor: Kate Yoshida (@KateYoshida)
Video Illustrator: Qingyang Chen (@QCVisual)
Video Director: Emily Elert (@eelert)
Video Narrator: Kate Yoshida (@KateYoshida)
With Contributions From: Henry Reich, Alex Reich, Ever Salazar, Peter Reich
Music by: Nathaniel Schroeder: http://www.soundcloud.com/drschroeder

_________________________________________

Like our videos?
Subscribe to MinuteEarth on YouTube: http://goo.gl/EpIDGd
Support us on Patreon: https://goo.gl/ZVgLQZ

Also, say hello on:
Facebook: http://goo.gl/FpAvo6
Twitter: http://goo.gl/Y1aWVC

And find us on itunes: https://goo.gl/sfwS6n
___________________________________________

If you liked this week’s video, we think you might also like:
The BrainScoop on Sue the T. Rex: https://www.youtube.com/watch?v=HHhI4eqYGdk

___________________________________________

References:

Switek, B. (2013). Paleontology: The Truth about the T. Rex 502 (424-426). Retrieved from: http://www.nature.com/news/pal....aeontology-the-truth

E. Snively, A. P. Russell, G. L. Powell, J. M. Theodor & M.J.Ryan (2014). The role of the neck in the feeding behaviour of the Tyrannosauridae: inference based on kinematics and muscle function of extant avians. Journal of Zoology 292 (290-303). Retrieved from: http://onlinelibrary.wiley.com..../doi/10.1111/jzo.121

Middleton, K., and Gatesy, S. (2000) Theropod forelimb design and evolution. Zoological Journal of the Linnean Society 128 (149-187). Retrieved from: http://onlinelibrary.wiley.com..../doi/10.1111/j.1096-

Lynch, M., Ackerman, M., Gout, J., Long, H., Sung, W., Thomas, W., and Foster, P. (2016). Genetic drift, selection and the evolution of the mutation rate. Nature Reviews: Genetics 17 (704-715). Retrieved from: http://www.nature.com/nrg/jour....nal/v17/n11/full/nrg