Livestock. All this data is very unreliable, especially for animals living in the wild, but some rough estimates were made, and we know that there are probably 30 times more mammals kept as livestock than wild land mammals, and 2 times more birds kept as livestock than wild birds. Also, there are as many cats and dogs as animals in the wild.
These “quantities” are actually a total mass of carbon, which according to the Source make roughly 15% of total body mass. So, there might be lots of chicken, but they don’t weight as much as cows. The same with little wild animals – there might be more rats than cows.
Also, some types of animals were not taken into account, for example, reptiles, arthropods, sea mammals. I decided to concentrate on mammals and birds living above the ground. I’d include reptiles, but there are no reliable estimations about them.
What: Mass of carbon inside mammals and birds.
When: Data were taken from a study published in 2018, which used data from FAO. So, I guess it’s not very old.
Where: Land and above.
Source: Bar-On, Yinon M et al. “The biomass distribution on Earth.” Proceedings of the National Academy of Sciences of the United States of America vol. 115,25 (2018).
Also, https://www.worldatlas.com used to estimate the mass of cats and dogs which were not included in the paper above.