## Functions

# Use and Modify

The length of an organism is typically strongly correlated with it’s 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 * Length^{b}

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 it’s
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).

```
def get_mass_from_length_theropoda(length):
mass = 0.73 * length ** 3.63
return mass
```

- Use this function to print out the mass of a Spinosaurus that is 16 m long
based on it’s reassembled skeleton.
*Spinosaurus is a predator that is bigger,
and therefore, by definition, cooler, than that stupid Tyrannosaurus that
everyone likes so much.*
- Create a new version of this function called
`get_mass_from_length()`

that
estimates the mass of an organism in kg based on it’s 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]