Cracking the coelacanth code: Living version of HMNS fossil has genome sequenced

The coelacanth — a “living fossil” believed to have hardly changed over the last 300 million years — has finally had its genome sequenced by European researchers.

courtesy of wiki media
The deep-sea fish was the inspiration for the famous 1954 film Creature from the Black Lagoon and is well-represented here at HMNS, where we have three examples on display: a Devonian fossil, a Cretaceous specimen and a model like the one sequenced.

Researchers sorted through nearly 3 billion DNA bases to conclude that the coelacanth’s four fleshy fins were likely the early predecessors of limbs.

Although the coealcanth is related to early tetrapods — the first creatures to make the transition from the ocean to land — a comparison of the coelacanth genome with the DNA profiles of lungfish and other modern land-based animals led scientists to conclude that lungfish were the closer relative.

Coelacanths have been notoriously difficult to study, having been assumed extinct until an African fisherman caught the living fossil in 1938. Since then, only a few hundred specimens have been found.

Continue the investigation yourself at our Morian Hall of Paleontology, and see why this mysterious fish has kept researchers rapt for so long.

Your questions, answered: Do we know when chimaeras shifted to deep-water habitats?

Earlier this month we received a question on one of our past posts, The Ghost Sharks of the Jurassic, asking:

“Do we know when these chimaeras shifted to deep-water habitats? If predation and, in particular, the evolution and diversification of predatory species prompted their geographic transition, at what point would a sort of critical level have been reached to drive them into the deep? How many predators are too many?”

Why do “living fossils of the deep sea” so often represent lingering survivors of groups that long ago flourished in shallow water?

 
Rabbitfish

Examples: Rabbitfish (aka chimaeras), Coelacanths, Goblin Sharks, Giant Squid.

Excellent question – one that keeps evolutionary biologists awake at 2 a.m.

First thing: we never know when a clan of species invades deep water. This is why:

Sediments deposited on top of oceanic crust in deep-water – thousands of feet deep – rarely come to the surface where the layers can be seen by fossil-hunting paleontologists. Mud does form at the bottom of deep seas and fossils do form here. But such deep specimens have a low chance of being found by us.

Deep sea bottom mud is raised above sea level when continents collide and abyssal sediment is squeezed up and thrust across slabs of continental crust. There are narrow zones of such squeezed sediments – for example, in the Taconic Mountains of New York State. Here are slices of deep crust and sediment with deep-water trilobites. However, very few vertebrate and squid fossils are known from squeezed deposits.

Medium-deep sediment, up to 200 meters deep,  do form in the bottom of “epi-continental seas” like the famous  “Cretaceous Ocean of Kansas” that covered much of the central areas of North America. Such epi-continental seas  do drain away, and the bottom sediment becomes lifted hundreds or thousands of feet, so wind and water can erode valleys into the rock layers, exposing fossils. Epi-continental sea bottoms have given us 90% of our marine vertebrate and cephalopod fossils.

Coelacanth fossils are common in shallow-water and medium-deep sediments beginning in the Early Devonian, over 400 million years ago. From then on, coelacanths remain widespread and often common. Were they in deep water too? We don’t know – we don’t have enough deep sediment exposed for study.

Abruptly, coelacanths disappear from epi-continental sea deposits in the Late Cretaceous. Naturally, we thought they were extinct. But then the fish show up alive and well, hanging around at 130 meters to 700 meters.

Ditto for the Goblin Shark: common as a fossil along New Jersey in shallow sediment but now restricted to much deeper waters. Ditto for the giant squid, who left their shells in the Cretaceous epi-continental sea sediment but now prefer deeper water.

Goblin Shark

Is there a common explanation for all the survivors in deep waters?

The most popular theory is: 1) Most new types of fish and cephalopods first evolve in shallow water. 2) It takes time for evolution to modify a fish or cephalopod so the beast can survive at 200m + depths. So the early coelacanths couldn’t colonize the great depths for tens of millions of years. As more and more clans of fish evolved in shallow water, some began their adaptive descent too – but the coelacanth had a head start. Being fully adapted to great depth already may have protected the fish from predators and competitors who are behind in the degree of their transition.

There are holes in the theory. Coelacanths do have predators – they show up in shark stomachs. They must have competitors too – teleost fish with more complex jaws.

Deep Sea Refuges continue to irritate our neat little hypotheses.

WAnt more? See the past post on ghost sharks and full comment.

Quetzalcoatlas! Grand Hall Display Through Monday

Quetzalcoatlus 1.14.11
It’s MASSIVE. See a
full set of photos of the assembly of this fossil
from this morning on Flickr.

We’ve got a new visitor to the Museum’s Grand Hall – the giant Texas Pterosaur, Quetzalcoatlus!

Quetzalcoatlus northropi and its close kin can be considered as the largest animals to have ever flown – and the cast is indeed impressively massive.

This Quetzalcoatlus northropi cast was assembled today and measured to finalize the design of a Cretaceous vignette featuring three of the giant flying Texas reptiles. This recreated fossilized drama will be part of the new Paleontology wing scheduled to open in 2012.

Check out our progress on the new family wing!

According to Dr. Bakker, the plan “is to create a portrait of the giant Texas ‘dactyl defending its nest from a curious juvenile Tyrannosaurus.”

Dave Temple, our associate curator of paleontology, said, “Typically, we would uncrate the specimen, assemble, measure and pack it up over the course of an afternoon. I am glad we have the opportunity to leave it up for a few days to give the public a sneak peek at things to come.”

Be sure to visit this weekend to check it out! Tuesday morning, the Quetzalcoatlus northropi will be placed back in the crate until final installation in our new paleo hall in 2012.

Slideshow from this morning’s Quetzalcoatlus assembly:

Quetzalcoatlus Facts:

Quetzalcoatlus northropi was discovered in Big Bend National Park in 1971 by Douglas Lawson, a student of Dr. Wann Langston from the University of Texas at Austin. The species is named for the Aztec deity Quetzalcoatl, who was worshiped in the form of a feathered serpent.

Quetzalcoatlus northropi probably weighed about 200 pounds and had as large as a 36 foot wingspan. Their large, toothless beaks create a bit of a mystery, at times hypothesized to have unearthed shellfish, arthropods, carrion and opportunistic hunting, similar to modern-day storks. Likely Quetzalcoatlus ate a variety of different items. This species went extinct at the end of the Cretaceous.

Sea Rex 3D swims into IMAX!

Explore an amazing underwater universe inhabited by larger-than-life creatures that ruled the oceans millions of years ago in Sea Rex 3D – now showing in HMNS IMAX!.

Mosasaurus hoffmannii skeleton on display at the
Maastricht Natural History Museum,
The Netherlands

Guided by Georges Cuvier, considered by many to be the father of paleontology, viewers learn about predators such as the ichthyosaur, plesiosaur, and mosasaur. These ancient creatures could grow up to 50 feet and could weigh as much as 15 tons.

Learn about the Triassic, Jurassic, and Cretaceous eras and how life evolved in the deep oceans of Earth. See a mosasaur battle the Great White Shark’s ancestor and witness the mating habits of the plesiosaur.

You’re going to love the film’s time line of the history of the Earth, showing the evolution of the first single cell organisms to the mammals that evolved and began to walk on land. What I found fascinating is the amount of time each of the dinosaurs ruled the world in comparison to humans. Dinosaurs walked the earth for over 160 million years, while humans have only been around for about 200,000 years comparatively.

Evidence of giant marine predators were first discovered in a mine shaft in the Dutch city of Maastricht in 1770, when the partial skull of a Mosasaurus hoffmannii was uncovered. Sea Rex 3D takes you on a journey from the creation of earth until the meteor that killed off 95% of life 65 million years ago. Don’t miss this incredible story about our planet’s history and the monsters that ruled the sea for over 120 million years.

Can’t see the video? Click here.

Sea Rex 3D is now showing in the Wortham IMAX Theater. See show times on our Film Schedule.