These spine-wolves were a species of wolf that inhabited a forest found on the planet of Serenno. Dooku, a Serennian, was left as a baby in that very forest by his father, Gora. Gora then got in touch with the Jedi High Council to request that they remove his son, leading a Jedi seeker to bring Dooku to the Jedi Temple. In 90 BBY, Dooku, by then a Jedi Initiate, shared with fellow Initiate Sifo-Dyas his discovery of the dangerous spine-wolves living in that particular forest. Dooku also pondered that, had his father not abandoned him, he might have achieved far greater things than becoming a Jedi.
Later, Dooku recounted this same event to his sister, Jenza, via a holo-letter. Circa 23 BBY, Dooku presented his newly-recruited Sith assassin, Asajj Ventress, with a holographic data disk that contained the details of his conversation with Sifo-Dyas concerning the forest and its spine-wolves. After they listened to the disk together, he provided her with several more holo-letters to aid Ventress's investigation to find Jenza.
The initial mention of spine-wolves occurred during a flashback scene within the audio drama titled Dooku: Jedi Lost, which was penned by Cavan Scott and released on April 30, 2019. The spelling of the term "spine-wolves" was officially confirmed through the audio drama's script release on October 1 of that same year.