Fossil remains of the large extinct Oryzomyine rodent Megalomys curazensis of uncertain age have been known from the island of Curaçao for more than four decades. They occur in a hard, red, "phosphatic oolite" exposed in fissures and flank margin caves cut into Miocene and Pleistocene limestones. This 'phosphatic oolite' has also yielded remains of the capybara Hydrochaeris and the endemic megalocnid sloth Paulocnus, but the age of none of these fossils has been determined.

The fossil bearing matrix occurs in fissures along the Middle Terrace of northern Curaçao, where it has been well exposed in the mouth of Cueba Hermanus by 19th century phosphate mining activity. Here, the matrix overlies several large stalagmites and is in turn overlain by a 7 cm thick flowstone cap. TIMS ²³⁰Th /²³⁴U dates on the upper flowstone and basal stalagmite respectively bracket the rodent deposit and securely place the fauna in the mid-Pleistocene. This new data provides the first radiometric framework for the interpretation of the multiple colonization events that define the radiation and evolution of the genus Megalomys in the Antilles.