What Big Eyes They Had!
A tiny news item caught my eye: “Creature liberated from oilsands” (Edmonton Journal November 4, 2000 G1). Apparently a rare marine fossil was found earlier this year near Fort McMurray. The oilsands are making quite a name for themselves as a source of fossils. Besides unfossilized remains of trees, excavators have turned up nine marine reptiles, mostly plesiosaurs, from the oilsands. One of the earlier specimens, like the recent find, was identified as an ichthyosaur.
The name ichthyosaur roughly translated means “fish-lizard.” As the name suggests, these were reptiles. This name sounds peaceful enough, but in general most of our impressions of modern reptiles are negative. Have you ever gazed into the steely eyes of a snake? They don’t seem to be overly endowed with empathy or a kindly personality do they? The same goes for turtles and other reptiles as well. A crocodile may appear to smile, but there is a distinct lack of congeniality behind that grimace. Despite this generally negative image, reptiles are an amazing group of organisms. Nevertheless, some of their most interesting representatives are extinct.
Other reptiles, which most of us have heard about, are the spectacular flying pterosaurs. Fossils of these creatures have been found worldwide in rocks of a similar level to those that contain dinosaurs. There are no “almost pterosaur” fossils. All the specimens discovered are of creatures highly specialized for flying. Not only were they able fliers, but they appeared to have good eyesight and large brains as well. These characteristics would help them catch their preferred food which was fish and insects. These organisms may have been as intelligent as the birds we see today. One specimen, called “Ptexas Pterosaur”, or Quetzalcoatlus, had a wing span close to 12 metres. Hmm… I don’t know how pleased I would be so see one of those approaching from the sky. Anyway we do not have to worry. While they are extinct, their fossils remain. In Alberta, up to a dozen pterosaur bones are found every year.
Already reptiles look more interesting. There were some really special swimming reptiles too, like plesiosaurs. Some people are convinced that the Loch Ness Monster of Scotland and “Champ,” a similar creature in Lake Champlain (bordering New York, Vermont and Quebec) and the Ogopogo of Lake Okanagan (in British Columbia) are plesiosaurs still living today. Whether extant or extinct, plesiosaurs are considered rather awkward creatures. What we do know for sure is that fossils of plesiosaurs have been found worldwide in much the same rocks as pterosaurs.
But why are we wasting time on plesiosaurs? Let’s get back to the really scary creatures, the fiercest marine reptiles of all, which were the ichthyosaurs. These specimens must indeed have been a terrifying sight. Some were as long as a bus, while others were only about 40 cm long. Whatever their size, they were all extremely well designed for a predatory lifestyle. At first glance, many ichthyosaurs looked like dolphins. Dolphins, of course, are not fish at all, but really marine mammals (like whales). Well ichthyosaurs were not fish either. They were reptiles and very unique ones at that.
The first ichthyosaur fossil was found in England by an eleven year old girl, the daughter of a widow who sold fossils in order to make a living. In 1810, Mary Anning saw bones protruding from a cliff in southern England. She and her brother chipped rock away from a 10 m long skeleton. Later this extinct marine reptile was named Ichthyosaurus. Such fossils have since been found worldwide. In England, large numbers are found in the “Oxford Clay” which stretches in a thin band southwest from coast to coast through central England. The most spectacular specimens, however, come from the Holzmaden quarry near Stuttgart in Germany. There, large numbers of dolphin-shaped ichthyosaurs are preserved in exquisite detail. In some cases a carbonaceous film in the rock indicates the actual outline of the body. That is how we know about their dorsal fin which contained no bone. Even more remarkable are the pregnant female ichthyosaurs. One particularly famous specimen contains seven young, with one apparently just leaving the birth canal. This is a dramatic example of sudden death and sudden burial in water borne sediments.
Normally geologists would conclude that the fine sediments in this quarry had slowly settled in quiet water. At that rate it would take a long time to bury anything. Nevertheless, recent work indicates that fine particles can form pelletoids which sink quickly from fast moving water currents. Indeed Dr. Christopher McGowan remarks, in his critique of the creation model: “I do not deny that certain burial sites do suggest that some sort of local catastrophe has occurred. The famous Jurassic quarries of Holzmadon, in southern Germany, come to mind, where particularly well preserved, skeletons of ichthyosaurs … are found in large numbers at some horizons, suggesting mass burial.” (In the Beginning… A Scientist Shows Why the Creationists are Wrong Macmillan p 91).
It is obvious that these ichthyosaurs are pretty fascinating. The most interesting question, however, is their origin. An article on these creatures in the December 2000 issue of Scientific American, concludes that these creatures were extremely well suited to their lifestyles. But, the author says, it is not possible to figure out if these animals started to become fish-like before they invaded the sea, or whether they invaded the sea first and then became more fish-like in response to the changing demands of their life style. In other words, why abandon a perfectly good life on the land? Or – in yet other words, which came first, the chicken or the egg?
As we ponder this issue, let’s consider the characteristics of ichthyosaurs. Like land-based reptiles, they were all air breathing. Some of them had snake-like bodies, big mouths armed with fearsome teeth, and weak paddle-like limbs. No fish has such limbs as we find in the ichthyosaurs. The back bone of these lizard-like creatures was also very unlike that of fish. The shape of the bones allowed for great flexibility of the body. This was ideal for creatures that lived in shallow marine bays. They swooped and dipped through the water to catch small fish and squid, octopi and their relatives with shells, the ammonites.
The fish-like ichthyosaurs lived far from the land, in the open sea, and the contours of their bodies reflected this watery habitat. A streamlined head merged with the body proper and the region of the gut was greatly broadened, all very fish-like in appearance. The back bone, however, was very unfish-like. In the case of these organisms, it conferred a fairly rigid posture on the body. This was ideal for a creature which needed to move efficiently through the open sea. The flippers, with a solid array of small bones, also contributed to fast, efficient motion. This predator probably undertook deep dives (perhaps to 500 m) in order to catch prey like squid and ammonites. The heavy body allowed for great reserves of oxygen in the blood so that the animal could stay underwater as long as twenty minutes.
In addition, these creatures had huge eyes. Such a characteristic is interesting because larger eyes pack in more light receivers and thus see better. We can tell which animals need acute vision by the relative size of their eyes. The horse, for example, has eyes which are 5 cm across, very large for a land animal. Calculations suggest that huge eyes enabled ichthyosaur predators to see their prey in the murky depths of the ocean. One medium sized ichthyosaur (about 9 m long), Ophthalamosaurus, had the largest eyes relative to body size of any adult vertebrate (possessing a backbone) living or extinct. In addition, a larger specimen Temnodontosaurus (with eyes measuring 26 cm across) had the largest eyes that we know about. Giant squid, with eyes at 25 cm, come close. The giant squid however are much bigger creatures and they are invertebrates (no backbone). Among large animals with backbones, the blue whale (as long as 26 m) has eyes which are 15 cm across, but this looks small compared to the massive size of the creature. It is relative size of the eye which is significant as well as absolute size — and in both categories the ichthyosaurs score highest.
So, where did the ichthyosaurs come from? It is obvious that they were wonderfully suited to their particular lifestyles. The design features include body shape, special back bones, paired limbs, and the ability to survive extended periods between breaths. Some people think that the lizard-like ichthyosaurs were a “primitive” stage which eventually developed deep sea capabilities (the dolphin-like shape). Each creature, however, was perfectly suited to its particular environment. This was not a case of slow change over long periods of time. God designed the ichthyosaurs for their particular roles in nature. They were specialized reptiles from the beginning. Now they are extinct. Whether the last representatives died during or after the Flood, we do not know. Undoubtedly they are gone. Do you suppose a few survivors might some day be found in an obscure corner of the sea? If there are living fossil coelacanths (a fish), why not plesiosaurs and ichthyosaurs? Wouldn’t it be fun to discover living specimens? If I were an octopus or squid in the oceans, I might keep a look out for those really big eyes. Then again, maybe it might be smarter to concentrate on more pressing dangers. In other words let’s just enjoy the insights that we have.
(For a picture of an ichthyosaur giving birth, and for comparisons of eye size in various organisms see Ryosuke Motani. 2000. Rulers of the Jurassic Seas. Scientific American. December issue pp. 52-59)
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