Feature WITH Early like this -sized Liaoconodon hui coexisted with GALLERY feathered dinosaurs like Sinotyrannus in the temperate ecosystems of the in what is now OF TALENTS in northern China. Many archetypal mammalian features evolved in a short burst early in mammal , including innovations in HALLMARKS movement, development and diet. SKY GLIDERS A raft of extraordinary fossil nds is revealing Several modern mammals glide details of how mammals evolved from on wings of stretched , but reptilian forebears more than 178 million years the exquisitely preserved furry membranes of -era ago. Discoveries in the past two decades show Maiopatagium furculiferum revealed that early mammals were a diverse bunch, that this ability evolved early, by with sophisticated skills such as gliding and 160 million years ago. -sized Maiopatagium probably feasted on burrowing that researchers thought evolved fruit, but other gliders from the same only later. Many of the features that dene period had teeth more suited to . -covered skin membrane mammals – like suckling , exceptional stretches between front and and small sizes – had already hind limbs appeared by the time true mammals were roaming the land, rivers and skies.

By John Pickrell Illustration by Davide Bonadonna SUCKLING AND All mammals nourish their young with Design by Wes Fernandes milk, and to do this, the juveniles require a special in their to suckle and swallow. Microdocodon gracilis from the Jurassic has a form of ~200 mya this that resembles that of modern mammals and is the earliest mammal known to have suckled milk.


Liaoconodon 120 mya Hyoid can bone bend and bow to allow muscles to Malleus Mobile move make down the hyoid Ossified cartilage Ectotympanic JAW BECOMES GREAT AND SMALL more Mammals have three Early mammals came in a wide flexible – the malleus, incus and ectotympanic assortment of shapes and sizes, Hyoid Modern bone (yellow) – responsible for their from the -sized bones mammal fine hearing. In and the (pictured right) and -like Mobile ancestors of mammals, these bones ; to Liaoconodon (main joints formed part of the jaw and helped to picture), about the size of a rat; process food. When researchers and tiny -like Microdocodon Microdocodon reported Liaoconodon hui in 2011 (main (pictured right). (Jurassic 165 mya) Mammals picture), they realized it represented a transitional state: a piece of hardened ( 250 mya) Mammaliaforms Ear bones separated cartilage in the jaw (orange) supported from jaw bone some of the bones and the .

Maiopatagium Liaoconodon Domestic DEBATABLE furculiferum hui Triassic Jurassic Cretaceous DYNASTY 250 Million years ago 200 Microdocodon 150 Repenomamus 100 gracilis robustus Researchers disagree about the shape of the mammal tree, which species fall in or out Haramiyids of it, and even where the tree begins. One view suggests that the earliest true mammals are Docodonts DINNER 178 million years old; another argues that the Species like Repenomamus robustus (, ) oldest mammal dates from 208 million years ago. from the challenge Many recent fossil finds represent long-extinct Eutriconodonts the typical stereotype of early groups that branched oŒ before the tree gave mammals as diminutive - rise to the three groups of modern mammals. ‘True’ mammals* Multituberculates fluŒballs. This creature was the size of a badger and a specimen found in Metatherians (includes ) Liaoconodon hui and evolution of the ear bones (J. Meng et al. 472, 181–185; 2011). Maiopatagium 2005 had the bones of a baby furculiferum and gliding mammals (Q.-J. Meng et al. Nature 548, 291–296; 2017). Microdocodon gracilis dinosaur – a beaked, bipedal hyoid bone and suckling (C. F. Zhou et al. Science 365, 276–279; 2005). Repenomamus robustus (Y. Hu et al. Nature 433, 149–152; 2005). Timeline adapted from Z.-X. Luo Nature 450, 1011–1019; 2008. – in its . *Researchers do not know the exact timing of when lineages split from each other Eutherians (includes placentals)

Nature | Vol 574 | 24 October 2019 Nature | Vol 574 | 24 October 2019