Quetzalcoatlus and Other Toothless Terrors The azhdarchoids

may be the last branch on our tree, but they are most certainly not the least, because among their number they include the largest flying creatures of all time— Quetzalcoatlus. Most members of the azhdarchoid clan have only come to light in the last two decades, and the group itself was first recognized just over 20 years ago. As in many other pterosaurs, the most distinctive features of this clan are to be found in the skull, which is depicted in Figure 4.13. The complete absence of teeth, a development that occurred quite independently of that in pteranodontians, is striking, but the most extraordinary development concerns the snout, which rises high above the level of the eye and has a huge opening for the nostril.

Early azhdarchoids such as Tapejara are best known from the Lower Cretaceous Santana and Crato Formations of Brazil.74 With its deep, rather parrot-like skull and extraordinary sail-shaped crest, Tapejara, a medium-size pterosaur represented by several skulls and skeletons, must have presented a bizarre sight as it flew through the skies. Initially found only in South America, evidence of tapejarids has also turned up in Africa. In a truly spectacular series of discoveries, several complete skeletons, representing a whole flock of these creatures, have recently been found in the Lower Cretaceous Jehol Biota of northeast China.75 A second group of early azhdarchoids, including Tupuxuara and its relatives, grew to much larger sizes, attaining wingspans of 6 meters (20 feet) or so. With a huge crest that ran the length of the skull, they must have looked just as strange as tapejarids.76

The most evolved azhdarchoids all belong to a single exclusively Upper Cretaceous group, the azhdarchids. Fossil remains of these pterosaurs, immediately identifiable from the extreme elongation of the neck (achieved as

FIGURE 4*13 Azhdarchoids, the toothless terrors of the skies, represented by the 8 inch (20 centimeter) long skull of Tapejara (above left), the 12 inch (29 centimeter) long skull of Zhejiangopterus (above right), and the skeleton of Zhejiangopterus, with a wingspan of about 10 feet (3 meters), below. (Redrawn from Peter Wellnhofer, 1991, and David Unwin and Lujunchang, 1997.)

in ctenochasmatoids by lengthening individual neck vertebrae), have been found all over the world and indicate the existence of at least five or six different kinds of azhdarchid. Some of these, such as Zhejiangopterus, shown in Figure 4.13 and recovered from volcanic ash beds that are used for building stone in eastern China, were relatively small stork-like forms with wings only 2 meters (6 feet) or so across.77 Others, most famously Quetzalcoatlus, reached huge sizes, with wingspans of 10 meters (33 feet) or more. Discovered in 1973 by Douglas Lawson while he was carrying out field work in Big Bend Park in Texas, Quetzalcoatlus is known from the remains of a single forelimb that belonged to a giant individual and several much more complete skeletons, with skulls, of individuals that were only about half this size.78

Quetzalcoatlus and its relatives from Spain, France, Jordan and Romania,79 many of which also reached giant size, existed right at the end of the Cretaceous and were, in one sense, the topmost twigs of the pterosaur tree. Thanks to a steadily increasing array of new discoveries and aided by some intensive computer-based genealogical work, we can now trace our path backward from these terminal pterosaurs, along the twigs and branches and down the main trunk, almost all the way back to the still half-hidden roots of the tree. New fossil finds and new studies will, undoubtedly, bring currently invisible parts of the tree into view and might even redirect some of the branches we have visited here, but the overall shape of the tree probably will not change that much. For now we can turn to other questions about pterosaurs— how they were constructed, grew and flew— but we will return to this tree in the last two chapters to see how answers to these questions may have both shaped its growth and brought it to an end.

Pterosaurs
0 0

Post a comment