With the precious fossils laid out carefully on a sun-hat held in my hands, I took a confident stride from one boulder to the next. And slipped. My left knee cap took the full impact of my body on another boulder, about a meter down. My head, fortunately, hit the Buller River, as did the fossils. A nuclear explosion of pain burst out of the knee, and adrenaline took over. I fished the fossils out of the river, and limped my way back to the steep slope where I still needed to pull myself up through shrubs and back onto the road. Getting into bed for weeks afterwards was painful, any movement that flexed that knee. But I had those damned fossils.
I have a vague memory of a barrel of water with some living horsetails outside the Otago Univresity Botany lab door in my undergrad days. But beyond that, I was thrilled to see my first wild-living horsetails (Equisetum) in Washington State, USA, then China, then Finland. In fact, they are a common plant over much of the world in wet spots, typically with shallow standing-water. However, New Zealand and Australia are the exceptions. Barring some recently arrived weeds, both of these countries have a fossil record of horse-tails, but only up until the Cretaceous. For at least 65 million years, there has been no evidence that horsetails existed anywhere in Australasia. They are an odd kind of plant, related to ferns – just a simple rush-like stem with whorls of needle-like leaves at regular intervals.
In 1979 my mother and I were collecting plant fossils from a Miocene (Manuherikia Group) outcrop near the New Zealand village of Bannockburn. One small fossil appeared that immediately made me think “horsetail”. But then, as I knew, New Zealand didn’t have horse-tails at that time. It wasn’t much, just a length of stem with what could have been a whorl of leaves. I never forgot it, but there wasn’t much I could do with it then.
A few years later (1980s) I was systematically collecting through the Bannockburn sequence of sediments, documenting its plant fossils, as part of my PhD. At the head of one briar-rose lined gully, I dug out blocks of nearly white clay. The darker forms of criss-crossing stems were apparent, and more importantly, they had some ‘nodes’, each with a line of little bumps across them (see featured image and image below). Now here was something much more convincing as horse-tails. In the end, most of my PhD material was published in some form, but not these. I filed them away in boxes labelled ‘jointed stems’, still not confident there was enough to go on.
And then that one sunny day in the 1990s, scouting along the Buller River, in the north-west of New Zealand’s South Island. It was another Miocene fossil plant locality, and had featured in the PhD of another paleobotanist, Aline Holden. The tread on my boots was getting a bit worn, I seem to remember a couple of little skids, but wasn’t paying attention. What I found, on the surface of a huge bolder, almost in the river, were more of those jointed stems’.
Wasn’t it James Bond who said “Once is nothing, twice it’s coincidence, three times it’s enemy-action?” It was time to take these things seriously. I had collected fossil horsetails from older rocks in New Zealand. But these ones have a special, and unmistakable device on them that holds their spores – it looks like a little spoked wheel. That group went extinct and younger horsetails don’t have this feature. Was there any chance these ‘jointed stems’ could be something much more mundane, like a grass (think, ‘bamboo’) or even a she-oak (casuarina)? I wasn’t confident enough to say. Back-up required.
I sent photos to Steve McLoughlin, of the Swedish Museum of Natural History. He has lots of experience in older plant fossils, from times when horse-tails were much more common. Perhaps he was familiar enough with the actual form of those ‘joints’ to say horsetail, or not. And – he agreed they were. Steve helped flesh-out a paper on the first fossil record of horsetails existing in New Zealand (and in fact in Australasia) over the last 65 million years or so. The fossils are around 15-20 million years old, so it’s fairly likely that they had lingered on in New Zealand over that time ‘gap’. It’s just that no-one has found them as fossils yet, or recognised them. In fact it was Steve who pointed out some fossils described in 1891 from the New Zealand Cretaceous by pioneering palaeobotanist Baron Constantine von Ettingshausen. They had been identified as ‘Casuarina’ and ‘Bambusites’, but as Steve noted, these were likely horsetails – and the most recent record in New Zealand, up til now.
So they were here, but why did they go? My guess is that it wasn’t just one simple reason, like a climatic threshold that was crossed. For example, horsetails now grow in Alaska, so it’s unlikely that simple cold is an answer. More probably New Zealand underwent a series of rapid ecological and climatic changes, rainfall, soil, fire-regime, and so-on. The horsetails were one of many plant groups that were likely split into small populations which were then vulnerable to chance events.
And speaking of ‘joints’, my knees. Currently they both feel buggered. Can’t be a result of that fall, because that was only onto one of them. Logical?
Reference (click for a pdf)