"and also the carcass shall they halve": whence they ruled: An ox worth a hundred which gored an ox worth a hundred, or an ox worth two hundred which gored an ox worth two hundred — he (the owner of the dead ox) takes half (of the value of the living ox.) An ox worth a hundred which gored an ox worth two hundred — he takes (the value of) all of it. An ox worth two hundred which gored an ox worth a hundred — he takes a quarter of it.
Also the Carcass Shall They Halve, the Mekhilta Derives Practical
Mekhilta Tractate Nezikin 12:5