This exquisitely preserved 160-million-year-old specimen of Maiopatagium furculiferum shows how early gliding evolved.Credit: Zhe-Xi Luo/UChicago
The way mammals chew and ingest their food is unique; instead of swallowing stuff whole like snakes and alligators, they chew and swallow it in small parcels.Animals evolved a wide variety of teeth for biting and grinding food to make that possible.
In contrast, mammals are nourished through suckling from the mammary glands of their mothers as their babies.This incredible biological innovation inspired our entire group, says Luo.The ability to suck and swallow, as well as the muscles that support them, enables us to consume milk.It is this apparatus that also creates the throat voice.
As recently as July, Luo published a paper showing that a close relative of true mammals, the vole-sized docodont, had preserved parts of its hyoid bones.
The analysis of both ear and throat bones was only possible due to advances in microCT scanning techniques, Krause says, similar to the hatchling study.In addition, the technique has revealed information about the olfactory abilities and brains of early mammals.The new revelations are "breathing life into a group of early mammals in ways that had previously been impossible and almost inconceivable", he says.
It has been proposed that a lot of the features we think of as defining mammals - complex teeth, excellent senses, lactation, small litter size - evolved much earlier and much more rapidly than true mammals.As time goes on, it becomes clear that everything came from evolutionary experimentation very quickly," Luo says.He states that when mammals began to roam in the Mesozoic, "the lineage had already acquired its modern features and adaptions".
It is still debated by the experts about how early mammal groups are related, and which are true mammals.Hoffman says this causes uncertainty about how certain traits evolved.
Meng and Luo disagree about the haramiyids, which they have each developed independently.Meng believes this early group belongs with true mammals, whereas Luo believes it's a side branch.The oldest Haramiyids are from 208 million years ago in the Triassic.Since mammals are true mammals, they are at least that old; if not, then the oldest known mammal is 178 million years old, well into the Jurassic.
Such questions can be answered and new surprises can be uncovered by finding more fossils.They are both studying exciting fossils, but haven't published any findings about them yet, and tens of specimens are piled up in the offices of their Chinese colleagues.
A paleontologist has many things on his wish list.Luo is trying to figure out the rate of growth of fossils.In contrast to reptiles, mammals grow in bursts in their youth and then plateau as they get older.To witness this, he would love to see a series of fossils, from babies to adults.He considers that one of the most important features of mammals that contribute to our biology.
.Meng dreams of finding a pregnant mammal.In his mind it is always a possibility that he will find a mammal inside of which there is a very delicate skeleton, which could either be a hatching egg or a more curious fetus.
.Brusatte believes we are in an exciting, nearly manic phase of receiving a great deal of new evidence, which will take time to synthesize.