Enlarge (credit: CHOKSAWATDIKORN / SCIENCE PHOTO LIBRARY)

The hydra is a Lovecraftian-looking microorganism with a mouth surrounded by tentacles on one end, an elongated body, and a foot on the other end. It has no brain or centralized nervous system. Despite the lack of either of those things, it can still feel hunger and fullness. How can these creatures know when they are hungry and realize when they have had enough?

While they lack brains, hydra do have a nervous system. Researchers from Kiel University in Germany found they have an endodermal (in the digestive tract) and ectodermal (in the outermost layer of the animal) neuronal population, both of which help them react to food stimuli. Ectodermal neurons control physiological functions such as moving toward food, while endodermal neurons are associated with feeding behavior such as opening the mouth—which also vomits out anything indigestible.

Even such a limited nervous system is capable of some surprisingly complex functions. Hydras might even give us some insights into how appetite evolved and what the early evolutionary stages of a central nervous system were like.

Enlarge / The echidna, an egg-laying mammal, doesn't develop teeth. (credit: Yvonne Van der Horst)

Outliers among mammals, monotremes lay eggs instead of giving birth to live young. Only two types of monotremes, the platypus and echidna, still exist, but more monotreme species were around about 100 million years ago. Some of them might possibly be even weirder than their descendants.

Monotreme fossils found in refuse from the opal mines of Lightning Ridge, Australia, have now revealed the opalized jawbones of three previously unknown species that lived during the Cenomanian age of the early Cretaceous. Unlike modern monotremes, these species had teeth. They also include a creature that appears to have been a mashup of a platypus and echidna—an “echidnapus.”

Fossil fragments of three known species from the same era were also found, meaning that at least six monotreme species coexisted in what is now Lightning Ridge. According to the researchers who unearthed these new species, the creatures may have once been as common in Australia as marsupials are today.

Enlarge / Later theropods had multiple adaptations to varied temperatures. (credit: SCIEPRO/SCIENCE PHOTO LIBRARY)

Dinosaurs were once assumed to have been ectothermic, or cold-blooded, an idea that makes sense given that they were reptiles. While scientists had previously discovered evidence of dinosaur species that were warm-blooded, though what could have triggered this adaptation remained unknown. A team of researchers now think that dinosaurs that already had some cold tolerance evolved endothermy, or warm-bloodedness, to adapt when they migrated to regions with cooler temperatures. They also think they’ve found a possible reason for the trek.

Using the Mesozoic fossil record, evolutionary trees, climate models, and geography, plus factoring in a drastic climate change event that caused global warming, the team found that theropods (predators and bird ancestors such as velociraptor and T. rex) and ornithischians (such as triceratops and stegosaurus) must have made their way to colder regions during the Early Jurassic. Lower temperatures are thought to have selected for species that were partly adapted to endothermy.

“The early invasion of cool niches… [suggests] an early attainment of homeothermic (possibly endothermic) physiology in [certain species], enabling them to colonize and persist in even extreme latitudes since the Early Jurassic,” the researchers said in a study recently published in Current Biology.