25 July 2015

A Visit To the McWane Science Center, Part II: Southern Sea Monsters

In the previous post, we took a look at the Alabama Dinosaurs exhibit at the McWane Science Center in Birmingham, Alabama. However, as you may remember from the last post, much of Alabama was underwater during the Cretaceous Period, submerged by a shallow seaway.

Notice how much of Alabama is submerged by a shallow seaway.
[image from Sampson et al, 2010, 'New Horned Dinosaurs from Utah Provide Evidence for
Intracontinental Dinosaur Endemism'
, under CC Attribution 2.5 Generic licence]

The warm waters of this shallow sea teemed with life, and after more than 75 million years, the fossil record of these marine organisms can be found in Alabama, with a diversity and richness far surpassing the state's known collection of dinosaur fossils from this time. McWane presents a sampling of this prehistoric marine life in the sister exhibit to Alabama Dinosaurs, fetchingly entitled Sea Monsters...

WARNING: Clicking the 'read more' link below without having this open in another tab is highly dangerous. Proceed at your own risk.

The Deep Sea Fishing Rodeo is a big deal in Alabama now, but
back in the Cretaceous Period it was just ridiculous.
[photo by the author]
One of the most intimidating marine creatures of the Late Cretaceous was Xiphactinus audax, also known by the nicknames 'giant bulldog fish,' 'X-fish,' and, from a friend of mine some years back, 'the fish that ate Michael Phelps.' It was a very big animal, growing 5.2 metres (17 feet) long or more, and had a compact, powerful build that would have enabled it to reach some impressive speeds.

Xiphactinus Week: This summer on Discovery.
[photo by the author]
Xiphactinus was a ray-finned fish, a member of the largest group of bony fish that still dominate the oceans today. As you can probably tell, it was predatory and had a huge mouth studded by large, pointed teeth. These made effective tools for dispatching other sea creatures, and dispatch Xiphactinus certainly did, although sometimes at great personal expense: one famous specimen of a 4 metre (13 foot) Xiphactinus contains in its stomach another fish, called Gillicus arcuatus, that measures 1.8 metres (6 feet) long and was swallowed whole. Judging by the condition of the fossil, the Xiphactinus died shortly after gulping down such a big mouthful.

Cretaceous sea turtles, like Prionochelys, would havecome ashore to
lay their eggs in the sand, just as their modern relatives do.
[photo by the author]
Much as the terrestrial environments of the Cretaceous Period were ruled by dinosaurs, the oceans were also dominated by reptiles. Sea turtles (a very well-represented group in Alabama's fossil record) were one such group; although sea turtles persist to the present day, they were more diverse during the Cretaceous, represented by many lineages while only two groups still exist.

Somebody told me there was a hare around here talkin' smack?
[photo and disgraceful caption by the author]
One of these extinct turtles makes for a impressive mount at McWane. This is Protostega gigas, the second-largest sea turtle yet discovered. Protostega could grow 3 metres (9.8 feet) long, and was the namesake for a now-extinct family of turtles, Protostegidae. It's believe the protostegids were related to the modern leatherback sea turtle; like leatherbacks, protostegids had very reduced shells.

Skull of the mosasaur Clidastes moorevillensis. Be sure to note the smaller
rows of teeth below the eye socket -- more on that below. Sorry for the bad
glare, that's what happens when you photograph through glass in dim lighting.
[disappointing photo by the author]
The real reptilian rulers of the Cretaceous oceans were the mosasaurs. Mosasaurs are well-represented in Alabama, with many species identified in the state's rocks. Clidastes, one of the smallest mosasaurs, is the most abundant kind in Alabama; in fact, the original Clidastes fossils were found in Alabama by the legendary 19th-century palaeontologist Edward Drinker Cope.

Although dinosaurs are sometimes referred to as 'lizards,' this is completely inaccurate. However, mosasaurs really are lizards. Exactly where they fit into the lizard family tree is uncertain; they are recovered in most analyses as either being close cousins of monitors like Komodo dragons, or of snakes*.  They had long bodies with short limbs modified into flippers and (at least in some species) vertically-oriented tail flukes. They also had a business end teeming with teeth and would have been fearsome predators. Clidastes was around 3.5 metres (11.5 feet) long -- so already a bit longer than the largest extant lizards -- while the biggest species known from Alabama (and one of the largest of all mosasaurs), Tylosaurus proriger, could grow 12-14 metres (39-46 feet) long!

Even the smaller kinds like Clidastes would have been voracious predators armed with a rather nasty weapon called 'pharyngeal jaws.' Those rows of smaller teeth at the very back of the mouth in the photograph up there? They were, in life, situated near the start of the throat. Mosasaurs would have snapped up prey with their toothy jaws and manoevred it further into the mouth where it would get snagged by a second set of teeth, the pharyngeal jaws, and pulled down the throat. This is especially handy for feeding on slippery marine creatures, but would not be good news if you were to ever find yourself swimming in the Late Cretaceous ocean when a mosasaur begin to investigate your foot.

Pteranodon longiceps... and nest. Read on for more regarding that.
[photo by the author] 
Of course, not all animals in marine ecosystems live under the waves. In addition to birds, during the Cretaceous, pterosaurs would have flown over the sea. Pterosaurs, the flying reptiles related to dinosaurs (but which are not, remember, dinosaurs themselves) evolved a variety of different shapes and sizes; it was once thought that most of them were fish-eaters that flew over the sea, or at least combed beaches. Today it is known that pterosaurs occupied a wide array of ecological niches, but some were indeed animals that would have flown over the ocean hunting fish. Pteranodon was one such pterosaur, with long wings (sometimes over 6 metres [20 feet] across but usually somewhat less) well suited to riding air currents over the water.

Pteranodon babies fumble around in their nest, an unlikely scenario.
[photo by the author]
The Pteranodon mount at McWane is depicted tending to a nest with babies, but I'm not so sure that this is a good display. Pterosaur eggs and hatchlings (catchily named 'flaplings') are known, but there's no evidence of pterosaur nests. It also seems that, unlike other flying animals, pterosaur flaplings were able to take to the wing pretty much as soon as they were out of the egg. While parental care of the eggs or even the new babies isn't out of the question, building and tending a nest with little flaplings in it seems like it doesn't line up with what is known about pterosaur biology.

Another view of Pteranodon.
[photo by the author]
Overall, the McWane Center might not have the biggest fossil collection around, but it's certainly nice to take a look at palaeontology in the South, a region that is unfairly forgotten compared to other parts of the country. The exhibits balance the fossil displays and interactive points well. Overall, a visit to the dinosaurs, pterosaurs, and sea creatures at McWane comes highly recommended. 

-- M

Up next!: What Brontosaurus and Spinosaurus tell us about changing perceptions of dinosaurs.

The author on the verge of becoming fish food.
[photo by the author's mother]

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