Meet Ida! a.k.a. Darwinius masillae. Ida is a 47 million year old fossil primate that was discovered in the Eocene fossil beds in Messel Germany. Ida was 24 cm. (~10 in.) from head to tail, meaning that--by some estimates--she probably weighed a little over a pound. In the picture below you can see the whole skeleton. It is fairly rare to find complete Eocene mammal skeletons--particularly primates. You can read online research paper about Ida here.
And Ida is just wonderful! On the downside, her skull was crushed, but on the upside, you can actually see where her fur was! (click on picture to embiggenize) Kewl!!!
You might have noticed that Ida kind of looks like a lemur. But there are morphological traits there that put her into the Cercamoniinae, from which modern anthropoids (monkeys and apes) evolved. In other words, we have ourselves a complete transitional primate fossil. This is super exciting!
Another thing we know abot Ida is that she was a juvenile. How do we know that, you ask? Check out her teeth!
You can clearly see that she has a mix of fully developed and developing teeth. For example, the M1 molars above are developed and in place but the M2 molars are still moving and the M3 molars probably haven't broken through the gums yet. We can compare this pattern to the dental development of similarly sized modern primates to estimate that Ida was about 80% of the way to full maturity when she died. And as I said before, there's much more in the paper.
Yay for science!
Franzen, J., Gingerich, P., Habersetzer, J., Hurum, J., von Koenigswald, W., & Smith, B. (2009). Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005723