A tick grasping a dinosaur feather inside 99 million-year-old Burmese amber. (Image: Peñalver et al., 2017)
When we look at amber we wonder at the creatures often caught up inside, changeless in their warm-coloured, luminous prison. It is the fossilised resin exuded by some plants to protect themselves, and first became abundant around 150 million years ago (mya), though the oldest animals found trapped in amber are some mites dating from 230 mya. In the science fiction film "Jurassic Park" the blood-meal of mosquitoes preserved in ancient amber is used to re-breed dinosaurs. (Insects generally are far more ancient than dinos - anything from 412-479 mya.)
Amber is still being produced today, but it takes millions of years to mutate from a sticky sap, through a hardened stage called copal, to the transparent-stone-like final condition.
The very earliest amber found so far dates from around 320 million years ago (mya) and was found in 2008 in an Illinois coal deposit. This was from the Carboniferous period (359 - 299 mya), long before the the age of dinosaurs (previously said to be 220 - 65 mya - though in 2012 another dinosaur fossil was found dating to 243 mya.)
The Illinois amber discovery is something of a mystery as modern trees and flowering plants came later, in fact many millions of years after dinosaurs first appeared. Until recently, the ancestors of flowering plants that produce seeds in protective ovaries (angiosperms) were believed to date from perhaps 160 mya. But before angiosperms there were gymnosperms (plants carrying seed without covers) such as conifers and ginkos, which started in the late Carboniferous period and so it may be one of them that produced that earliest amber.
Having said that, the emergence of flowering plants and angiosperms is being redated too: last year a scientific team produced a model of the earliest flower, from 140 mya; yet in 2013 fossil plant pollen was found from 240 mya and so angiosperms may have developed in the "Early Triassic (between 252 to 247 million years ago) or even earlier."
The Natural History Museum says that dinosaurs evolved in the Triassic (252-201 mya) when all the world's land mass was clumped together (Pangea); lived though the split in Pangea that created the North Atlantic Ocean; survived the still-mysterious mass extinctions at the end of the Triassic and became far more numerous and various in the Jurassic (201-145 mya); and saw the further splitting of landmasses in the Cretaceous period, and diversification in plants and insects (including the appearance of bees).
So we're still finding out when dinosaurs first saw (and presumably ate from) modern trees and flowering plants. Scientists used to think that dinosaurs never even got to munch grass - but thanks to analysis of fossilised dinosaur poo the origin of grass has been pushed back from 55 mya to 66 mya, and some of its cousins may be much older.
There they are, these specimens, frozen in time; yet our understanding of the past keeps changing.