Jurassic garden

What would our gardens have looked like in the time of the dinosaurs? TIM ENTWISLE takes us on a flight of floral fancy

Imagine how our gardens might have looked in the time of the dinosaurs

Imagine

you’re living in the time of the dinosaurs. You’ve purchased a home on a new block in southern Gondwana, and it’s time to spruce up the backyard with a garden. What do you plant?

Well, you could start with the tree ferns championed by AB Bishop in the September 2019 issue of the magazine. You also have a palette of pine and other conifers, ginkgo, cycad, clubmoss and horsetail to choose from. Those same plants are eaten by your local herbivore, a rather large dinosaur. It’s a diet rich in greens but not many other colours.

Of course, this is a flight of fancy. Humans didn’t share the earth with dinosaurs, and if they had, finding food and fending off creatures 10 times bigger than today’s African elephants would have been a higher priority than gardening.

But stick with me while we dig a little deeper into the Jurassic and other ancient floras, which, for gardeners, gives us another perspective on the plants that we love to grow today. And it’s fun – as are the dinosaurs that grazed and munched their way across the earth for some 180 million years.

f loral explosion

Although dinosaurs dominated the Jurassic period, they also hung around long enough to experience the so-called ‘explosion’ of flowering plants that began 105 million years ago in the Cretaceous period that followed. Over the next 40 million years, flowering plants went from a small fraction of the earth’s flora to almost all of it.

The dinosaurs saw the first flowers bloom. While these new plants would have added variety and colour to their diet, it has been suggested that alkaloids in the plants made them toxic to dinosaurs. This may have contributed, alongside asteroids, volcanoes and climate change, to the demise of the dinosaurs.

The first flowers were only 1cm across, with a cluster of white tepals surrounding groups of male and female parts. The tepals – floral parts that could be considered either petals or sepals – were in whorls of three, with three or four whorls per flower. Picture something like a mix of current-day bay laurel, magnolia and buttercup.

As flowering plants diversified, displacing the conifers and ferns, flowers evolved to have fewer petal-like parts, and adopted specific colours and shapes to attract insects and other pollinators. Most flowers today have separate whorls of petals and

sepals, often in fives. But in the early years, they were small and white, with crowded floral parts. They were heavily outnumbered in the forest by cones and spore clusters.

So, there was a limited choice of plants. And how about the terroir? During the Jurassic period, Australia was still part of Gondwana (although the break-up of the supercontinent had begun) and was situated a little south of where Tasmania is today. The world climate was generally warm, and there were no polar ice caps.

planting an idea

For your Jurassic garden, imagine a climate something like today’s wet tropics (depending on where you live, you might have to build an imaginary glasshouse first). Your soil is rich and friable, with plenty of decomposing bacteria, fungi and other microorganisms, and plants grow fast with all that warmth, water and nutrients.

Now you can start planting in your mind. Begin with a cycad or two, such as the local burrawang (Macrozamia communis), standing proud in a carpet of ferns. The cycad brings with it a plant-like organism – cyanobacterium – in its coralloid roots near the soil’s surface, to help it access nitrogen. Cyanobacteria (blue-green algae) have been on earth for 2.7 billion years of the planet’s 4.6-billion-year existence.

In a spare corner in your mind, also create an Archaean garden from that geological eon of 4–2.5 billion years ago. This consists solely of mounds built by cyanobacteria, like the stromatolites you see at Shark Bay in Western Australia. Alternatively, create a more modern, Devonian garden from 419–359 million years ago, with columnar fungi up to 6m tall dwarfing the ferns and cycads, until they are overshadowed during the latter part of this geological period by the first trees. Encourage the mosses, which today have been on earth for about 400 million years. The earliest of these plants shared dry earth with a few worms and millipedes when backboned animals were all aquatic.

Back to your Jurassic garden, where many of the ferns look like those we grow today, particularly coral fern, royal fern and the Queensland sun fern. Clubmoss, or tassel fern, is all over the place.

There’s also horsetail (Equisetum spp.), which looks a bit like a sedge or, when clothed in whorls of thin green stems, a young pine. Early in its evolution, it got to 30m tall, but by the Jurassic period it’s more like the ones we see today, a few metres tall at most. Best to leave horsetail in your imaginary garden, though, as it has been declared a weed across Australia.

The trees in your garden will have to be conifers, plus a ginkgo or two. I’d suggest a Wollemi pine – for patriotic reasons, and in honour of its relative in the Dillwynites genus from the mid-Cretaceous period. And that’s probably it for your Jurassic garden.

If all that seems too hard, you could simply create a bird-attracting garden with lots of coloured flowers. Birds are dinosaur descendants – the ones that made it through the last mass extinction – after all.