The Tonian (from Greek tonas, "stretch") is the first geologic period in the Neoproterozoic Era and lasted from 1000 Mya to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry.
Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya.
The first large radiation of acritarchs occurred during the Tonian. The first Metazoans (Animals) are found in the late Tonian some 800 MYA. A notable example of this is the poriferan-like species Otavia antiqua.