The fossil record of monotremes is relatively sparse. Although biochemical and anatomical evidence suggests that monotremes diverged from the mammalian lineage before the marsupials and placental mammals arose, only a handful of monotreme fossils are known from before the Miocene epoch. The few Mesozoic fossils that do exist, such as that of Steropodon, seem to indicate that the monotremes first evolved in Australia, during the Late Jurassic or Early Cretaceous. They subsequently spread to both South America and Antarctica, which were still united with Australia at that time, but may not have survived on either continent for long.^[1]

Fossil speciesEdit

Excepting Ornithorhynchus anatinus, all the animals listed in this section are only known from fossils.

• Family Kollikodontidae
  • Genus Kollikodon
    • Species Kollikodon ritchiei. Ancient monotreme, 100-105 million years old.
• Family Ornithorhynchidae
  • Genus Ornithorhynchus. Oldest Ornithorhynchus specimen 9 million years old.
    • Species Ornithorhynchus anatinus (Platypus). Oldest specimen 10,000 years old.
  • Genus Obdurodon. Includes a number of Miocene (5-24 million years ago) Platypuses.
    • Species Obdurodon dicksoni (Riversleigh Platypus)
    • Species Obdurodon insignis
    • Species Monotrematum sudamericanum. 61 million years old. (Originally placed in separate genus, now thought an Obdurodon)
• Family Tachyglossidae
  • Genus Zaglossus. Upper Pleistocene (.1-1.8 million years ago).
    • Species Zaglossus hacketti
    • Species Zaglossus robustus
  • Genus Megalibgwilia
    • Megalibgwiilia ramsayi Late Pleistocene
    • Megalibgwiilia robusta Miocene
• Family Steropodontidae. May be part of Ornithorhynchidae; closely related to modern platypus.
  • Genus Steropodon
    • Species Steropodon galmani.
  • Genus Teinolophos
    • Species Teinolophos trusleri. 123 million years old — oldest monotreme specimen.

ReferencesEdit