New light is thrown on turtle evolution

Turtles have a bountiful fossil record filled with well-preserved specimens and dating back to around 200 million years ago: a biologist’s dream. Surprisingly, it hasn’t been given much attention.

A study by Joyce et al. published in BMC Evolutionary Biology in October describes a new fossil from China and revisits how modern day turtles came to be distributed around the world.

The fossil turtle Sichuanchelys palatodentata is peculiar in that it retains the ancestral character of teeth on the palate, although the authors doubt this was useful to the species. This species was found to be part of a now-extinct lineage of turtles which is now starting to come to light.

The seven specimens described were unearthed in Northwest China and date from around 160 million years ago, a time when the landscape was dominated by dinosaurs. They include a skull, shell, as well as bones of the legs and arms of the turtles.

Classifying fossils like that of Sichuanchelys p. allows scientists to reconstruct the geographical history of living groups, which tells us why species are where they are today.

Today, turtles occupy a variety of environments: land, freshwater and saltwater. The ability to tolerate saltwater seems to have evolved multiple times independently, and allows turtles to disperse freely across oceans. This makes it difficult to retrace their evolution.

There are two main groups of turtles: the hidden necked and side necked turtles. The former predominantly occupy the southern hemisphere, while the latter are found in the northern. So how did this come to be?

The old hypothesis was that the two groups diverged on the same landmass and each found themselves better adapted in one hemisphere, while the other went locally extinct.

However, by ignoring the saltwater turtles in their analysis, Joyce et al. saw a different pattern emerge. It turns out to be more likely that the two groups were separated during the break-up of Pangaea, and then evolved in isolation from one another. Furthermore, southern hemisphere deserts could have local barriers to freshwater turtles, driving the diversification of the group.

This study reinforced the presence of now-extinct turtle lineages, ignored in the past. It also cats a new light on extinction, diversification and distribution of the modern turtles. In our current biodiversity crisis, a understanding of these topics is more relevant than ever.

Image: Fossil of Sichuanchelys palatodentata shell dorsal and ventral view.

Article: A toothed turtle from the Late Jurassic of China and the global biogeographic history of turtles. Joyce et al. 2016 (DOI 10.1186/s12862-016-0762-5)

Alien Australian possums could be helpful, not harmful to recovering ecosystems in New Zealand

Horror stories of an alien species taking over and annihilating diversity in a native ecosystem have become pervasive in ecological news. This happens as our world continues to become more and more interconnected: species are moved around by humans- be it intentional or not. There are the rabbit, cane toad and camel  population sizes exploding in Australia. There are the well established parrot populations of Europe. Countless “weeds” that have pervaded native ecosystems and are thought to cause trouble.

But it could be that alien species aren’t all the bad guys we make them out to be.

This was recently shown a long term experiment on succession after landslides in New Zealand. Ecological succession is what happens when an ecosystem is deeply disturbed and recolonized by a series of plants species, one after the other. Usually mosses, grasses and sedges,”weedy” species that grow fast in poor conditions, are the first to arrive. They are followed by shrubs, then trees until a full, diverse, forest is recovered. Australian opossums introduced to New Zealand in the 1800’s were thought to hurt this process by eating native plants.

Since the possums were introduced by humans to New Zealand, they have grazed on plants that weren’t grazed on before. To see if this was disruptive, a team of researchers set out on an 11-year long experiment, taking advantage of large landslides that destroyed all vegetation in an area of the Western South island in 2002.

The scientists cleverly created plots and introduced the same vegetation in all of them, the only difference being that some of them were caged off: possum proof. They expected to the possum proof areas to  re-vegetate faster, since there would be no inappropriate grazing. However, they were surprised to see the opposite result.

Areas munched on by possums contain more of a “high quality” shrubby plant species: one that can harness nitrogen in the air to use it, also making it available to fellow plants. More plants growing also means more carbon in the ground: more biomass created and stored. Bacteria species are also more abundant and diverse in plots visited by possums. But why? It seems that the possums are grazing on grassy species, freeing up ecological space for the later species in succession. This speeds up the process, aiding in recovery and overall benefitting diversity in the system.

Careful analysis only will allow us to determine whether specific alien species are harmful to ecosystems or not. In a world where we have pervasively modified which species are present where, we should tread carefully in trying to control them. They might actually be reinforcing our efforts to restore the quality of our environment.

Let me know what you think in the comments!


For more on this topic I recommend a great book: The New Wild by Fred Pearce

Article: Bellingham et al. 2016 Journal of Ecology.