The first pterosaur fossil showing complete wings

The first fossil showing the extent of the wing membranes of a pterosaur was found back in 1873.

Ferris Jabr has posted a picture: pterosaur wings.

Placoderms evolved penetrative sex

Placoderms are an extinct class of armoured fishes containing several orders. Placoderm comes from Greek words for “plate” and “skin.” They are jawed fishes, but so ancient that they precede both sharks & rays and bony fishes: some elements of the skeleton are cartilaginous while others are bony and there are bony elements in their skin armour. Yes, bones and teeth are derived from skin tissue. They appeared in the fossil record about 420 Ma in the Early Silurian and by 400 Ma in the Devonian all major placoderm orders were present. (See “Australia: The Land Where Time Began: Placoderms“.}

402px-Dunkleosteus_terrelli_2 (From Wikipedia)

Before placoderms, all fertilization of eggs by sperm occurred outside the body, as females released eggs and males released sperm into the water. They might hover near each other, but if sperm found egg it was partly by chance. Female fishes release their eggs through a cloaca, an opening for both eggs and bodily wastes. As the fish that were closest had the most success, eventually males began to position themselves at the cloaca. One group of placoderms, the ptyctodontids, have these external claspers to hold the female, as do sharks. The pelvic fin perhaps developed a tube shape to funnel the male’s sperm into the female’s cloaca. Some modern fish mate in this way. What is known is that some placoderms gave birth to live young, which means that that at the very least, eggs were fertilized while still in the female. In short, these early fishes invented internal fertilization.

Two prehistoric fish swimming

Rhamphodopsis threiplandi, a placoderm with claspers (from Wikipedia)

There are two pathways after internal fertilization. One is ovivipary, where eggs are retained and hatch inside the mother, who then expels the young. Some sharks still do that. In fact, in some sharks the first young to hatch eat the other eggs to nourish themselves until birth. Females may develop areas of nourishing skin that the young can scrape off. The other main path is for the young & the female to cooperatively grow a placenta, which attaches to the her and extracts nourishment from her blood. (Placentas could  not have happened without a retrovirus inserting itself into the genome, but that’s another topic.)

At first, scientists thought that young placoderms inside larger fossils could have been evidence of predation; but at last a tiny fossil placoderm was found with a tiny umbilical cord, still attached to the mother.

Pterosaurs over the Sahara

I know I’m mixing up times and environments. Here’s the real news: A fossil pterosaur has been found in the Sahara desert. It has a wingspan of about five metres. The fossil comprises most of the bones of one wing and a number of long, slender teeth, which indicate a fish-catching habit.

 

Date of first walker pushed back 30 million years

A tiny trackway discovered in sedimentary rock has pushed back the date of the first organism capable of walking to 585 million years ago. This proof is 30 million years older than previously known evidence.It took two years to precisely date the trackway by radiometric dating of igneous rock that intruded into the sedimentary rock. The fossil was found in Uruguay.

The organism was about the size of a grain of rice. A trackway like this shows that it had front and back ends and was bilaterally symmetrical, with limbs that could move it forward. We could call it First Explorer.

See also Study resets date of earliest animal life by 30 million years.

Transitional fossils: halfway flat fish

National Geographic’s 2009 roundup of transitional fossils included a fish that is evolving to lie concealed on the ocean floor. Modern flatfish are born symmetrical, with eyes an other side of their head, but as they age one eye moves around to the other side so that the fish can watch for danger with both eyes while lying flat on the sea floor.  The lack of “halfway” forms has been used to argue against evolution. Now, one has been found. This one appears to have one eye just over the midline. I wait for anti-evolutionists to acknowledge that the theory of evolution has been confirmed once again: Amphistium, transitional fossil, a half-way flat fish.

fossil fish

Amphistium, a transitional fossil in flatfish evolution

Even older fossils at 3.4 billion years

fossil bacteria

Fossil bacteria from 3.4 billion years ago are the world’s oldest fossils.

The microfossils were found in a remote part of Western Australia called Strelley Pool. They are very well preserved between the quartz sand grains of the oldest beach or shoreline known on Earth, in some of the oldest sedimentary rocks that can be found anywhere.

They are from a billion years before plants generated our oxygen atmosphere.

The fossils are very clearly preserved showing precise cell-like structures all of a similar size. They look like well known but much newer microfossils from 2 billion years ago, and are not odd or strained in shape.

The fossils suggest biological-like behaviour. The cells are clustered in groups, are only present in appropriate habitats and are found attached to sand grains.

And crucially, they show biological metabolisms. The chemical make-up of the tiny fossilised structures is right, and crystals of pyrite (fool’s gold) associated with the microfossils are very likely to be by-products of the sulphur metabolism of these ancient cells and bacteria.

UPDATE:  Jerry Coyne has more details, and more photos, about these fossils. (They may be primitive single-celled organisms rather than bacteria.)  Newly found: the world’s oldest fossils . Larry Moran explains the biochemistry that tells us these bacteria digested sulphur in The Oldest Cells.

Adventures in Science

orange book cover with picture of Galapagos TortoiseSean B. Carroll’s book Remarkable Creatures is about major discoveries in evolution. He glides over a few details, but it’s very readable. I’d like to see each chapter done as a book about the Exciting History of Science for young people. I’m learning things I never knew: that Charles Doolittle Walcott, in addition to discovering the Burgess shale with its Cambrian Explosion fauna:

  • surveyed 25,000 vertical feet of geological strata over two seasons,
  • was one of the first 20 employees of the U.S. Geological service
  • found the first Precambrian fossils
  • consulted in the passing of the Antiquities Act to protect significant sites (e.g. Grand Canyon) and the founding of the National Park Service,
  • drafted the bill that created the national forest reserves
  • secured a museum building to house the National Museum, later the Smithsonian
  • was a science adviser to several U.S. presidents
  • raised the money from private donors to have 12,000 specimens from Roosevelt’s African expedition preserved and shipped back to the U.S.
  • discovered hundreds of thousands of fossils during summer field expeditions with his family
  • brought the Wright brothers official recognition for their work
  • and helped to found the National Advisory Committee for Aeronautics, which became NASA
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