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Description
This is Mirusavis, a small enantiornithine bird from Early Cretaceous China. Its holotype preserves a ridiculous amount of medullary bone, which is a type of bone formed temporarily in females as a calcium reserve for producing eggshells. Other dinosaurs and modern birds are known to have medullary bone deposits in their leg bones, but Mirusavis had it everywhere, including the ribs, vertebrae, and arm bones. This indicates that Mirusavis's eggs would have been very large compared to its body size--estimated at 20%, comparable to the massive egg of the diminutive kiwi bird today. And a large egg indicates precociality, meaning Mirusavis chicks would have been born ready to run, fly, and feed themselves.

A modern example of a superprecocial bird is the Australian brush turkey. The male turkey builds a huge mound of dirt, sticks, and leaf litter that he meticulously guards and upkeeps. The female lays her eggs inside the mound, which, since it's basically a big compost pile, provides heat to incubate the clutch of eggs. Once the chicks hatch, they must dig their way out from under a huge pile of dirt, like little bird zombies.

The weird thing is that the male turkey has no idea what his mound is for. He fastidiously checks the temperature inside the mound every day, and adds more compostables if it's too cold, or digs out a vent in the middle if it's too hot. But when the female digs a large hole in the mound to lay eggs in, he tries to chase her off and fill the hole immediately. When his chicks hatch, he tries to chase them off too, since to him they're just some unknown actors messing with his beautiful mound.

Nature is very strange. Life finds a way.

Description
This is Mirusavis, a small enantiornithine bird from Early Cretaceous China. Its holotype preserves a ridiculous amount of medullary bone, which is a type of bone formed temporarily in females as a calcium reserve for producing eggshells. Other dinosaurs and modern birds are known to have medullary bone deposits in their leg bones, but Mirusavis had it everywhere, including the ribs, vertebrae, and arm bones. This indicates that Mirusavis's eggs would have been very large compared to its body size--estimated at 20%, comparable to the massive egg of the diminutive kiwi bird today. And a large egg indicates precociality, meaning Mirusavis chicks would have been born ready to run, fly, and feed themselves.

A modern example of a superprecocial bird is the Australian brush turkey. The male turkey builds a huge mound of dirt, sticks, and leaf litter that he meticulously guards and upkeeps. The female lays her eggs inside the mound, which, since it's basically a big compost pile, provides heat to incubate the clutch of eggs. Once the chicks hatch, they must dig their way out from under a huge pile of dirt, like little bird zombies.

The weird thing is that the male turkey has no idea what his mound is for. He fastidiously checks the temperature inside the mound every day, and adds more compostables if it's too cold, or digs out a vent in the middle if it's too hot. But when the female digs a large hole in the mound to lay eggs in, he tries to chase her off and fill the hole immediately. When his chicks hatch, he tries to chase them off too, since to him they're just some unknown actors messing with his beautiful mound.

Nature is very strange. Life finds a way.