# Use and Modify

The length of an organism is typically strongly correlated with its body mass. This is useful because it allows us to estimate the mass of an organism even if we only know its length. This relationship generally takes the form:

Mass = a * Lengthb

Where the parameters `a` and `b` vary among groups. This allometric approach is regularly used to estimate the mass of dinosaurs since we cannot weigh something that is only preserved as bones.

The following function estimates the mass of an organism in kg based on its length in meters for a particular set of parameter values, those for Theropoda (where `a` has been estimated as `0.73` and `b` has been estimated as `3.63`; Seebacher 2001).

``````get_mass_from_length_theropoda <- function(length){
mass <- 0.73 * length ** 3.63
return(mass)
}
``````
1. Add a comment to this function so that you know what it does.
2. Use this function to print out the mass of a Spinosaurus that is 16 m long based on its reassembled skeleton. Spinosaurus is a predator that is bigger, and therefore, by definition, cooler, than that stupid Tyrannosaurus that everyone likes so much.
3. Create a new version of this function called `get_mass_from_length()` that estimates the mass of an organism in kg based on its length in meters by taking length, a, and b as parameters. To be clear we want to pass the function all 3 values that it needs to estimate a mass as parameters. This makes it much easier to reuse for all of the non-theropod species. Use this new function to estimate the mass of a Sauropoda (`a = 214.44`, `b = 1.46`) that is 26 m long.
[click here for output]