Unique red-headed monitor lizard found

At over a metre long and with a bright red head, you might think the Torch monitor lizard would be quite distinctive. In fact, nobody knew such a lizard existed, until a group of American and Finnish scientists stumbled upon it last year. Their discovery has only just been reported in the journal Zootaxa.

The Torch monitor - hide and seek champion. Image: Valter Weijola

The Torch monitor, or Varanus obor, is named for its most distinctive feature, its bright red or orange face. In fact, it is the only monitor lizard known to have evolved distinctive red pigmentation.  It lives mainly in coastal palm swamps and, like many monitor lizards, feeds on small animals and carrion.

The lizard is only found on the island of Sanana. Sanana is part of the Moluccan archipelago, nestled to the west of New Guinea in Indonesia, where the lack of predatory mammals has allowed large lizards like the Torch monitor and the closely-related Komodo dragon to reach the top of the food chain. But why haven’t mammals colonised the islands and supplanted the reptilian predators?

It’s all down to sea level: animals colonised the many small islands in the area during periods of low sea level such as ice ages, when sea levels were more than 120 metres lower than today as the water was locked up in polar ice caps. However, the entire region is sliced in half by a deep sea trench running from the Indian to Pacific Ocean, which never dried up. It prevented mammals from the Asian mainland from reaching the southern and eastern islands and Australia, and allowed monitor lizards to diversify and dominate terrestrial ecosystems.

Known as the ‘Wallace Line’ the sudden change in animal species was first described by Alfred Russell Wallace, who most famously worked out the details of evolution at the same time as Charles Darwin made his discoveries.

Paper Reference: Weijola, V., and Sweet, S. (2010). A new melanistic species of monitor lizard (Reptilia: Squamata: Varanidae) from Sanana Island, Indonesia. Zootaxa. 2434, pp 17–32.

Dinosaur for dinner

Earlier this week, scientists announced the discovery of an extraordinary fossil. It contained the body of snake caught in the act of devouring newly-hatched sauropods! Dominant terrestrial predator they may have been, but the dinosaurs didn’t have it all their own way. Here, I take a look at a few of the beasts that could terrify even those terrible lizards!

Slithering hunter

Caught in the act - Sanajah devours a titanosaur. Image: Wilson et al/PLOS Biology

The early snake Sanajeh indicus could never have tackled an adult titanosaur: sauropods such as the titanosaurs were some of the largest animals ever to walk the earth. Fully grown titanosaurs could reach 25 metres long and weigh more than 38 tonnes and were almost completely immune to predators: but when young they were just as vulnerable as any other small animal.

Sanajeh took full advantage of this, hunting amongst the titanosaur nest fields littering the landscape of India 67.5 million years ago. Sanajeh wasn’t huge – around 3.5 metres long – and couldn’t expand its mouth to swallow large prey, unlike modern snakes. It did manage to devour 0.5 metre long baby sauropods, however, and one unlucky snake was frozen in time as both it and its prey were engulfed by a landslide. The fossil not only tells us about the hazards facing newly-hatched dinosaurs, it also gives us an insight into the evolution of snakes, with their amazing expandable skulls.

Amphibian Ambush

You may want to show a bit more respect to the frogs in your garden pond. Small and slimy they may be, but their ancestors were willing to go up against the toughest of them. Lurking in the late Cretaceous undergrowth of Madagascar, Beelzebufo ampinga was waiting for small dinosaurs to put a foot wrong…

Beelzebufo was a 40-centimetre-long ambush predator. It sat, perfectly camouflaged, waiting for its prey to come along before striking with its immensely powerful jaws. Sadly, there’s no direct evidence that it dined on small dinosaurs, but its size, and the location it inhabited, do suggest dinosaur was part of this primitive frogs’ diet.

Feisty Furball

Psittacosaurus - a tasty snack for a rodent? Image: bumblesweet/Flickr

The Cretaceous period wasn’t just the age of the reptiles. One small furry group – the mammals – was making its presence felt in smaller ways, even managing occasionally to drag down one of the mighty reptiles that ruled the land. A few years ago, Chinese and American scientists unearthed Repenomamus giganticus, a giant fossil rodent from 139 million years ago. Incredibly they found the remains of a young ceratopsian dinosaur in the rodent’s stomach.

Repenomamus had sharp, pointed teeth, which hint at its carnivorous habits, and weighed around 13kg. This may be small compared to today’s mammals but it was a giant amongst the mammals alive at the same time. This obviously gave it the muscle, and courage, required to hunt juvenile Psittacosaurus, a distant relative of the more-famous Triceratops armed with a fearsome hooked beak.

Paper References:

Wilson J., Mohabey D., Peters S., Head J., (2010) Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India. PLoS Biology 8(3): e1000322. doi:10.1371/journal.pbio.1000322

Hu Y, Meng J, Wang Y, Li C (2005) Large Mesozoic mammals fed on young dinosaurs. Nature 433: 149–152.

Evans, S., Jones, M., and Krause, D., (2005) A giant frog with South American affinities from the Late Cretaceous of Madagascar. PNAS 105:2951-2956; doi:10.1073/pnas.0707599105

Fantastic Fish Fossils Found

Researchers have found several new species of gigantic extinct fish that fed solely on the tiniest of food-sources – plankton. The fossil fish fill a gaping hole in the fossil record: before now, large plankton-eating fish were missing from a 100million year chunk of prehistory.

A modern Basking Shark - such a big mouth for such tiny prey. Image: Wikimedia

Long before the evolution of filter-feeding whales and sharks the seas were home to nine-metre long fish, such as the newly-discovered Bonnerichthys, which took advantage of the same food source. Until recently, researchers believed the group to which these fish belonged, the pachycormids, went extinct around 172million years ago, in the Jurassic period.

The new discoveries, which included fossils from the USA, UK and Japan, show that the pachycormids actually went extinct at the same time as the dinosaurs, 65 million years ago. Only once they were gone was there an opportunity for modern ‘planktivorous’ groups, like baleen whales and basking sharks (Cetorhinus maximus), to evolve.

Plankton – the collection of microscopic marine creatures found in every sea and ocean around the world – today supports gigantic marine animals such as the blue whale (Balaenoptera musculus). These animals use comb-like structures called baleen plates to filter the tiny plants, animals and bacteria out of seawater.

The hole in the fossil record was a complete mystery. Plankton is so abundant, and supports such large animals today that researchers expected something to eat it. Bonnerichthys and friends are, it seems, just the massive fish required to plug such a massive hole.

Paper Reference: Friedman et al. 100-Million-Year Dynasty of Giant Planktivorous Bony Fishes in the Mesozoic Seas. (2010). Science, 327 (5968), p990-993 DOI: 10.1126/science.1184743

When less really could be more

Where do new species come from? Natural variability between the individuals in a population can gradually lead to the formation of a new species, particularly if a group becomes geographically isolated. But what happens if a population of animals loses some of that natural variability? It turns out that this too can lead to rapid evolution and the formation of new species.

A male from an all-orange population - unchallenged mating rights! Image: Ammon Corl/UC Santa Cruz

Male side-blotched lizards (Uta stansburiana) usually come in one of three colour ‘morphs’, which also correspond to their favoured mating strategy. Sometimes, however, one or two of the colour ‘morphs’ disappear from a population altogether: this leads to very quick evolutionary changes in the body size and other physical features of that population. Ultimately, these changes can lead to the population becoming an entirely new species.

The American researchers who conducted the study think this counter-intuitive result is down to the sudden change. Each of the three males is adapted to successfully compete with one of the others (leading to the biological equivalent of rock-paper-scissors) and when one is lost, the others have to re-adapt to the change in their surroundings – leading to a burst of evolutionary activity.

DNA analysis showed that the original population of side-blotched lizards contained all three colour morphs. Each morph is good at getting access to girls in one way: orange males are strong, and fight for and defend a large harem of females; blues are smaller and can only defend one female; yellows are sneaky – they look similar to females so can infiltrate the harem of an orange male, but cannot fool the blues. In some places the population switches between the three male strategies in turn, but in others the yellows, and sometimes blues, mysteriously disappear altogether.

The environment you live in consists of more than just the physical features of the landscape, or the predators and prey that share the local area. The influence of other members of your species can be an important evolutionary driving force – some scientists think it was the pressure of social living that led to the development of our large human brains. In the case of the side-blotched lizards, a change in their environment (the loss of a competitor for mates) leads to different selective pressures – and possibly even a whole new evolutionary path.

Paper Reference:    Corl, A., Davis, A.R., Kuchta, S.R., & Sinervo, B. (2010). Selective loss of polymorphic mating types is associated with rapid phenotypic evolution during morphic speciation. PNAS, published online before print February 16, 2010. doi:10.1073/pnas.0909480107

‘Soup? Not for me!’

Life on Earth may have begun not in the primordial soup, but amongst the rocks around hydrothermal vents, according to British and German scientists. Microscopic cracks around a certain type of hydrothermal vent in the ocean share certain chemical features with our cells, making them a perfect place for life to arise.

Yeast cells. From basic chemistry to beer, life has come a long way... Image: Masur/Wikimedia

But how can a hydrothermal vent create life? The answer relies on some clever chemistry: hydrothermal vents (which spew out warm, mineral-rich water from deep within the Earth’s crust) establish a gradient of positively-changed hydrogen ions, or protons, in the microscopic cracks in the surrounding rocks, which are lined with naturally-occurring organic membranes.

The earliest forms of life exploited this chemical imbalance to generate power. As the hydrogen ions try to even out the gradient by diffusing from areas with lots of ions to areas with fewer ions they pass across the organic membranes, where simple proteins could use the energy from the hydrogen to power a simple chemical reaction. This in turn produced even more energy in the form of a molecule called ATP, which our cells still rely on today as a source of power.

The problem with the primordial soup theory is that there is nothing to create and sustain the proton gradient, which the scientists argue is a vital prerequisite for early life. Without the natural proton gradient at the hydrothermal vents, early life couldn’t have generated enough energy to get started.

The final leap these early cells took was to set up their own proton gradients by using some of their energy to ferry hydrogen ions across the cell membrane. Once they evolved to this stage, the cells were free to colonise the oceans and ultimately the entire world, giving rise to every living thing we see today.

It’s an extraordinary hypothesis that rivals an idea that has existed for eighty-one years – the primordial soup idea was put forward by a researcher called J.B.S. Haldane in 1929 – and it will need extraordinary evidence to support it, which the scientists don’t have, yet.

Paper reference: Lane, N., Allen, J.F., & Martin, W. How did LUCA make a living? Chemiosmosis in the origin of life. Bioessays. Published Online: Jan 27 2010 DOI 10.1002/bies.200900131