Friday Headlines: 5-17-13

Friday Headlines, May 17, 2013




Ichthyosaurs were marine reptiles (not dinosaurs) that looked superficially like dolphins, the most obvious difference being that their tail fins are vertical, like all fishes, not horizontal, like all marine mammals.

Ichthyosaurus communis, Early Jurassic of England. Digital. By Nobu Tamura

A specimen of a new fossil ichthyosaur, named Malawania, was recovered from a track used by mules. The fossil preserved much of the front half of the animal, such that paleontologists could work out its relationships with other ichthyosaurs.

Malawania is Cretaceous in age. Its closest fossil relatives are from the early Jurassic, more than 66 million years earlier.

Prior to the discovery of Malawania, it was thought that each new evolutionary step in ichthyosaurs resulted in faster and more streamlined swimmers. This supported the idea of ‘gradualist‘ evolution, where species are modified in tiny steps over great spans of time.

Malawania represents evidence of ‘stasis’ in evolution, an important concept in the evolutionary process called ‘punctuated equilibrium,’ wherein species remain essentially unchanged for millions of years (stasis) then undergo rapid changes in very short intervals (punctuation).

So when you see other headlines saying that this discovery revolutionized the understanding of evolution, what is meant is that Malawania is evidence for punctuated equilibrium in the evolution of ichthyosaurs. It is not a huge change in the overall theory of evolution (unlike what some headlines seem to suggest!).



400 ppm.

You’ve probably heard that. You might not know what it means.

400 ppm means that for every million gas molecules in the atmosphere, 400 of them are carbon dioxide.

Well that doesn’t sound so bad.

The last time carbon dioxide was so high was 3-5 million years ago, well prior to the existence of modern humans.


Well, 3-5 million years ago, the world was a lot warmer than it is now, for one. The Arctic was forested, not icy. Things were different.

And this new development suggests we might be heading that way again!

Read more here.



One important question in paleontology and especially in human evolution is when, exactly, did the lineage of primates that lead to humans diverge from the lineage that leads on to modern old world monkeys.

Paleontologists and anthropologists have found many of the most important finds regarding human evolution in the East African Rift system.  This time they discovered two new species of primate in rocks approximately 25 million years old.

One of the new species, Rukwapithecus fleaglei, is recognized as a homonid (a primate on the human lineage). The other species is Nsungwepithecus gunnelli, is identified as a cercopithecid (an old world monkey). In both cases, the identifications are made based upon teeth and jaw fragments, which is common practice when dealing with fossil mammal teeth.

That these two species were found together at this locality means that as long as 25 million years ago, the lineages of men and old world monkeys were distinct. Prior to this discovery, the best localities documenting these distinct lineages were millions of years younger.

This new, older, age matches better with estimates of the splitting of the two lineages based upon DNA analysis. It’s nice when two fields of science reach generally the same conclusion!

17 thoughts on “Friday Headlines: 5-17-13

  1. Fantastic as always, Penny.

    Your first paragraph made me wonder if all marine mammals have a common ancestor, or whether convergent evolution is the accepted answer for horizontal tails. I know it isn’t your field, but if you know off-hand, I’m curious.

  2. The marine mammals like whales, dolphins, and porpoises share a common ancestor, potentially close to hippos (if I recall correctly). Manatees and dugongs share a different common ancestor from whales, though I think it also was a herbivorous mammal. The seals and walruses I think share common ancestry in carnivores.

    The horizontal flukes actually derive from the way that the vertebral column typically moves in mammals. When you watch a dog or cat run, you see its back bowing up and down (like an inchworm). In marine mammals, this continues, and having horizontal flukes is the only way that they can generate thrust from the tail. The reptiles that marine reptiles evolved from moved more like crocodiles, with the back bowing from side to side, just like fish. Thus, the vertical flukes.

  3. I remember seeing a video comparing a cheetah running with a dolphin swimming, highlighting the motion of their spines. Very cool. Manatees and dugongs have a different common ancestor, huh? Cool.

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