Eritherium: mammals exploded rapidly

A recent paper published in PNAS details the earliest member of the elephant family yet found, dating from just 60 million years agO (just five million years after the dinosaur extinction event).

The eritherium would have weighed only about 5kg, with no significant tusks. But it was identified as the earliest (most primitive) member of the Proboscidea order, of which the (three similar species of) elephant is the only survivor.

The specimen was found in Morocco; the author suggests it is indicative of a rapid evolution of a variety of placental mammals (in particular paenungulates), due to favourable ecosystem development in Africa.

To look at the implications, it pays to take some perspective. It was a dinosaur world (the mesozoic era) for about 180 million years, until meteor impact(s) 65 million years ago cleared the decks of all larger animals (and much else). The first true mammals emerged early in the mesozoic; placental mammals (as opposed to egg-layers or marsupials) emerged about 120 mya, but under the domination of dinosaurs remained largely nocturnal and shrew-sized.

According to the study's author Emmanuel Gheerbrant, the discovery "supports an explosive radiation of placental mammals" in the five million years immediately after dinosaur extinction. This is not entirely new, but reinforces what had already been hypothesised.

Of course, all this simply demonstrates the part environment plays in the evolutionary radiation of different species. In their time, dinosaurs effectively shaped the environment for other species. Meteor impact then remodelled the global environment, and mammals no longer needed to compete for resources with - or evade - (non-avian) dinosaurs.

Humans in turn evolved from the primate lineage only over the past four million years. According to Tudge (p492 - 512), the evolution of brain size (and gracility) was in response to environmental factors such as cooling temperatures and scarcity of resources, and the heavier, less brainy hominid species died out.

So we have 180 million years of dinosaur dominance, followed by a real explosion of mammal species in the next 5 million years. Most recently, homonids evolving over 4 million years; brain size grew rapidly from 3 mya to 1 mya; modern H sapiens sapiens first appearing just 100,000 years ago. Evolutionary change and radiation can be slow when environmental factors mitigate against it, and rapid in favourable conditions. (Yet in the case of the emergence of humans, challenges may have propelled evolution rather than holding it back.)


References
Gheerbrant, E (2009): Paleocene emergence of elephant relatives and the rapid radiation of African ungulates, PNAS 30 June 2009 - abstract here
Tudge, C (2000): The Variety of Life. Oxford University Press, Oxford.
Wikipedia on Placental mammals

Pirates have a "Golden Age"

Speaking of pirates, today my son got a pirate book and model ship for his 7th birthday (thanks, sis).

It's one of the many kids' themes that just seems to knock around eternally*. Dinosaurs seem to be particularly overdone, but there I can weave into the kids' interest some meaningful narrative around evolution. Pirates, fairies, unicorns,... less useful but mostly harmless as kiddie themes, and our children have a good grip on the line between fact and fiction.

Anyway, the book characterises a "Golden Age of Piracy", from 1690 to 1730. It also distinguishes pirates from privateers, those who were granted licence by their country's rulers to attack ships from nations they were at war with.

In depicting a mythologised era, such books are fostering interest in themes that are harmless when seen from a distance. Yet in this case, we are now noticing that these narratives are not so far removed, and we are not fully innoculated from the effects.

Of course, piracy has never entirely disappeared from the earth - for example, it has long existed around the shipping lanes separating southeast Asian mainland from the archipelagoes (such as the Strait of Malacca). And of course, the Gulf of Aden has currency for the Somali pirates operating there.

Not so far removed. Australia is now considering a request to provide naval resources to patrol the seas around Somalia. And my son has a friend whose father is in the navy, which could bring the issue very close to home indeed.

"Golden Age" pirates in the West Indies sometimes found berth in the more lawless ports where they were less likely to be hounded by authorities. Those ports have their mirror in modern-day Somalia, and however freewheelin' it may sound, they are today places that few can feel safe.

It's a minor point perhaps: my beef is with the sanitisation, the stripping of meaning then in particular the romanticisation of something that is not romantic at core, which still has the potential - however latent - to render the trivialisation hypocritical.



* Is piracy as kiddytheme traceable to Stevenson's Treasure Island?

Britain: a dinosaur melting pot?

News yesterday of a study that shows Britain to be home to one of the most diverse set of dinosaurs in the world.

It was a review study, which found 108 different species of dinosaurs had been discovered in Britain. Of course, It's not as if such a variety was intermingling all at once. The Mesozoic era (the dinosaur heyday) spanned 180 million years - although the article posits a 135 million year span for those dinosaurs identified in the review.

The originating article stresses that Britain was a final land bridge before North America finally separated from Europe (and Asia) - according to the article, that split happened at about the end of the Mesozoic (and the dinosaur) era.

Yet, as is pointed out, Britain has the longest history of research and exploration. Given global discoveries to date can only be scratching the surface of the extant fossil record, I imagine this contributes an amount of bias to the outcome of the study. However, that's not to deny the significance of a (relatively narrow) land bridge in the mixing of what could by then have been two rather distinct populations.


The work was published by the Geological Society of London, by academics at the University of Portsmouth. Of note, one of the authors is Darren Naish, who writes the always-interesting Tetrapod Zoology blog.