What is "megaoryzomys"

Megaoryzomys curioi, also known as the Galápagos giant rat, is an extinct species of sigmodontine rodent, known only from Santa Cruz Island in the Galápagos Islands. It likely met its demise when European settlers introduced invasive species to the island. It is the only species in the genus Megaoryzomys. Its relationships are currently unclear; it has been placed in both Oryzomyini and Thomasomyini in the past.