WASHINGTON — When the British naturalist George Shaw received a weird specimen from Australia in 1799 — one with a mole’s fur, a duck’s bill, and spurs on its rear legs — he did what any skeptical scientist would do: He looked for the stitching and glue that would unveil it to be a hoax.

“It was impossible not to entertain some distant doubts as to the genuine nature of the animal,” Shaw wrote of the seemingly built-by-committee creature, which he eventually named “platypus.”

Now, more than 200 years later, a team of scientists has determined the platypus’s entire genetic code. And right down to its DNA, it turns out, the platypus continues to strain credulity, bearing genetic modules that are in turn mammalian, reptilian, and avian.

There are genes for egg laying — evidence of the animals’ reptilian roots. Genes for making milk, which the platypus does in mammalian style despite not having nipples. Genes for making snake venom, which the animal stores in its legs. And there are five times more sex-determining chromosomes than scientists know what to do with.