Ambulocetus
Reconstructions by Carl Buell
When: Eocene (~50 to 48 million years ago)
Where: Pakistan
What: Ambulocetus is fossil whale relative. This beast was about 10 feet (~3 meters) long, and not very agile in either the land or the water. It was capable of movement on land, but it would have been rather slow and lumbering, as its forelimbs were shortened compared to its fully terrestrial ancestors. In the water it would have been capable of swimming with some speed, but it would not have been able to make quick turns as it chased its prey. Therefore, it has been reconstructed as an ambush-style predator, in the same niche as the modern crocodile. It would have laid in wait in the water, with its relatively dorsal eyes and nose peeking above the sufrace, able to see and smell approaching prey. Once a prey animal got close enough, Ambulocetus would launch itself from the water and try to catch the animal in its powerful jaws, such as is shown above. I think it is some form of basal horse that is trying to avoid the snapping jaws of Ambulocetus. This ambush style strategy could have also worked with aquatic prey, such as schools of fish. Ambush predation is seen in some species of whales today, Orcas (the killer whales) have been recorded ambushing seals on ice flows.
Ambulocetus lived on the edge of the Tethys Sea (a body of water between India and Asia) in what is now Pakistan. At the time this region was one of many islands off the shore of the island continent of India, which had not yet collided with Asia (this would not happen for tens of millions of years). This warm seaway was full of mammals starting to return to the seas, including other lineages of whale relatives. In the cetacean family tree, Ambulocetus falls between Indohyus and modern whales; it was carnivorous - as all modern whales are-, and far more adapted for aquatic locomotion than Indohyus was, with shortened legs and a much more powerful tail.
Desmatosuchus
Mounted skeleton from Petrified Forest National Park, AZ.
Reconstruction by Jeff Martz.
When: Late Triassic (~225 - 200 million years ago)
Where: South Western United States, North America.
What: Desmatosuchusis an Aetosaur. This is a group of archosaurs that ranged worldwide during the Triassic.In the archosaur family tree, they are on the line leading to crocodiles, not birds, and thus are croc-line archosaur or a member of the Crurotarsi. Desmatosuchus is one of the last aetasaurs known, and is many ways is a fairly representative member of this clade. It was covered in armor plating on its back, belly, and tail. One thing that sets Desmatosuchus apart from its fellows is the two parallel rows of spikes that ran along its back on the edge of its osteoderm plating. The largest of these spikes were roughly above the shoulders and could be up to 18 inches (~45 centimeters) long. Pretty impressive on an animal that is ‘just’ 16 feet (~ 5 meters) long.
Desmatosuchus was an herbivore, so all of this armor was to try to protect it from the variety of predators that it co-existed with, such as some of the first true dinosaurs. The turned up shovel-shaped snout of Desmatosuchus coupled with its relatively weak teeth indicate this animal probably fed on softer plant material, digging though the soil to find roots and tubers. That being said, it has been proposed in the past that it was digging not for flora, but for fauna, feeding upon unearthed grubs and other insects. It is possible that Desmatosuchus had a more broad diet than has been previously assumed.
Mei
When: Early Cretaceous (~125 million years)
Where: Liaoning, China
What: Mei is a paravian dinosaur. Paraves is the clade comprised of birds and two families of non-avian dinsaurs; Troodontidae and Dromaeosauridae. As Mei is a fairly basal member of the troodontids, it is not very far removed from the common ancestor of all paravians. Its bird-like heritage can be easily seen in this extraordinary articulated fossil shown above. This specimen was found in a sleeping pose, which is very much like the resting posture of many modern birds, with the legs folded underneath the body and the head folded back and resting on the shoulder. It is this pose that gives the taxon its full name: Mei long, which translates to ‘sleeping dragon’. This animal is a sub-adult, determined via the ends of its bones not yet being fused, and would be roughly 21 inches (~53 cm) long, if it was not curled up as it is.
The find of a basal troodontid in this pose gives us far more information than just when the sleeping posture was adapted by this clade. It has been determined that modern birds commonly sleep like this to preserve their body heat, covering up the areas that are most prone to radiating heat. If Mei long and its kin were not ‘warm blooded’ than there would be no benefit to sleeping in this pose. Thus, this provides another compelling bit of evidence that the ‘warm bloodedness’ of modern birds was present in their mesozoic non-avian relatives.
Opabinia
When: Mid-Cambrian (515-500 million years ago)
Where: British Columbia, Canada.
What: Opabinia is one of the rarest forms from the Burgess Shale fossil lagerstatten. We have explored the Burgess Shale fauna before with Anomalocaris and Hallucigenia. Opabinia, unlike these other species, has not had a confusing history with various interpretations of its anatomy. This does not mean that 1.5-3 inch (4-7cm) long invertebrate is much like any modern form though! Far from it, Opabinia is unlike anything alive today. Much of its body resembled Anomalocaris, which it is possibly related to, but its head is where the most bizarre features were. It had 5 eyes and a proboscis up to 1/3rd of its length, ending in a form of gripping claw. This proboscis was flexible enough to curve around to its mouth, which was hidden on the underside of its head and directed posteriorly. It is thought Opabinia swam though the ancient seas by flexing its body, picking up soft bodied prey animals with this ‘trunk’. No traces of legs have been found in any of the ~20 or so fossil specimens.
Like most Burgess Shale taxa, the relationships of Opabinia are uncertain. It is somewhat hesitatingly placed as a stem arthropod in a lot of classifications, but this relationship is based in turn on an uncertain link with Anomalocaris. It is possible that Opabinia is far removed from all modern phyla. One of the biggest supports for this later view is its 5 eyes, a configuration never again seen in the history of life.
I might have gone a bit overboard with the images today, but this is one of my most favorite fossil forms! It is just so odd and different from anything else.
I can’t decide if this is weirdly cute or the worst thing I’ve ever seen. >:|
Proganochelys
When: Early Triassic (~210 million years ago)
Where: Germany and Thailand
What: Proganochelys is the oldest known terrestrial turtle. It shows that even in the early Mesozoic turtles already had a very modern body plan, with a fully formed shell. In fact, Proganochelys had a bit more armor than modern turtles. This is because it could not retract it limbs or head into its shell for protection. The way that this ancient turtle protected its head was a series of spikes on the top of its neck. It also had a heavily spiked tail, which ended in a club. Beyond these features, and a slightly larger shell in general, Proganochelys is remarkably simular to a modern turtle.
Proganochelys and other early Mesozoic turtles are so simular to living forms that for many years they were thought to be closely related to these extant species. Modern turtles are divided into two groups, the Cryptodira and Pleurodira. The major difference between these two forms is how the neck is retracted into the shell, with the former pulling the head straight back and the latter curving the neck into an S-shape. Recent cladistic studies now place Proganochelys and many other early Mesozoic turtles outside either of these two groupings, as stem turtles.
