'data.frame':   5731 obs. of  8 variables:
 $ continent: chr  "AF" "AF" "AF" "AF" ...
 $ status   : chr  "extant" "extant" "extant" "extant" ...
 $ order    : chr  "Artiodactyla" "Artiodactyla" "Artiodactyla" "Artiodactyla" ...
 $ family   : chr  "Bovidae" "Bovidae" "Bovidae" "Bovidae" ...
 $ genus    : chr  "Addax" "Aepyceros" "Alcelaphus" "Ammodorcas" ...
 $ species  : chr  "nasomaculatus" "melampus" "buselaphus" "clarkei" ...
 $ mass     : num  70000 52500 171002 28050 48000 ...
 $ reference: chr  "60" "63, 70" "63, 70" "60" ...