Growth and development

Until recently, we knew next to nothing about sauropod nesting, and indeed, as recently as the early 1990s, it was proposed that sauropods gave birth to live young.

In 1997, however, a sauropod nesting ground was discovered in Patagonia. This site, known as Auca Mahuevo ("Auca more eggs"), consists of a massive nesting ground covering more than a square kilometer and littered with tens of thousands of large, unhatched eggs. Upon further investigation, four layers of eggs were uncovered and, in each layer, the eggs were organized into clusters of 15-34 linearly paired eggs, thought to represent individual nests or clutches. Most spectacularly, a high proportion of these eggs contained embryonic skeletons, some with impressions of embryonic skin (Figure 8.18)!

The geographical extent of the nesting horizons reaffirmed gregarious behavior in sau-ropods. Clearly several enormous colonies were preserved, to which mothers would regularly return. Because there is no fossil evidence of adults preserved at Auca Mahuevo, the females likely left the site after laying their eggs, although it is possible that they may have communally guarded the whole nesting area from its periphery. If so, the eggs may also have been covered by mounds of vegetation to keep them at optimal temperature and humidity.

Since the find at Auca Mahuevo, eggs have been associated with particular sauropods in the Upper Cretaceous of southern France, Mongolia, and India, where, in 2007, a second, massive sauropod nesting ground was also uncovered. Does any of this suggest that sauro-pods were r-strategists (see Chapter 7)?

Beyond these bonanzas, what do we know about the general aspects of sauropod reproduction, growth, and life histories? Sex in these animals assuredly involved coupling between a tripodal male and a quadrupedal female; however, beyond this most elemental of positions all else remains speculative. For example, was the trenchant thumb claw used in this aspect of sauropod behavior as well?

Once hatched, sauropodomorphs apparently grew at very high rates. New studies of the microscopic structure of sauropod bone indicates rapid and continuous rates in both pro-sauropods and sauropods. Rather than imagining animals taking about 60 years to reach sexual maturity and having a longevity of perhaps 200-300 years, estimates are that it took about 20 years or less for a sauropod (and probably for a prosauropod as well) to become sexually mature. Similarly, lifespans for these animals were probably on the order of not much more than 100 years.

Figure 8.18. Titanosaurian remains from the Auca Mahuevo locality of Patagonia, Argentina. (a) Titanosaur skull (fossil); (b) reconstructed skull;

(c) titanosaur skin (fossil) impressions;

(d) reconstructed egg/embryo; and

(e) schematic field of nests.

Figure 8.18. Titanosaurian remains from the Auca Mahuevo locality of Patagonia, Argentina. (a) Titanosaur skull (fossil); (b) reconstructed skull;

(c) titanosaur skin (fossil) impressions;

(d) reconstructed egg/embryo; and

(e) schematic field of nests.

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