No mammals that are marsupial or monotreme are kosher. The extant monotreme species are the platypus and four species of echidnas. They share a similar fauna which includes marsupial and monotreme mammals and ratite birds. This database has data for every known marsupial and monotreme immune gene. The platypus, a monotreme mammal, has a system of 5 pairs of XY chromosomes. Teinolophos trusleri is a prehistoric species of monotreme, or egg-laying mammal. A 61-Ma-old platypus-like monotreme fossil from Patagonia may represent an Australian immigrant. However, the five species of monotreme, the platypuses and the echidnas, lay eggs. Echidnas are the sole monotreme species in the park. The modern platypus, a monotreme, appeared. The platypus's electroreception is the most sensitive of any monotreme. "Steropodon" is the oldest monotreme (egg-lying mammal) discovered. Obdurodon tharalkooschild is an extinct species of monotreme in the genus "Obdurodon". It is the largest extant monotreme. Obdurodon dicksoni is an extinct species of ornithorhynchid monotreme discovered in Australia.