Why Brontosaurus was huge

By Razib Khan | May 11, 2010 10:22 am










CATEGORIZED UNDER: Biology, Evolution
MORE ABOUT: dinosaurs, sauropod
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  • MW

    I’ve not read the paper – this is just based on your post.

    We have a critter which is too big for carnivores to attack, but is very slow. (The long neck argument suggests that it spends most of its time stationary.) The problem is that there is a window of extreme vulnerability when growing up: small enough to eat, too slow to run away. One countermeasure is mentioned above: try to grow through this vulnerable window as fast as possible. This isn’t a very reliable method however.

    Logically I would expect another countermeasure: parental protection. The young stick close to the parents, and when a predator comes along they hid under mum or dad. Possibly they’d be in herds (other parents hassling predators who come near their kids also helps your kids.) One might also expect some weaponry on the adults, probably on the tail. (Perhaps such a big tail doesn’t need anything else.)

    Is there evidence (fossil footprints?) for parental protection?

  • Sandgroper

    “Thus, titanosaurid (and by extension, all other) sauropods produced numerous small eggs with very precocial young that were left to fend for themselves and suffered high mortality before reaching sexual maturity in the second or third decade of their life.”

    “Limited data from trackways and bonebeds suggest that sauropod herds were composed of a much higher proportion of juvenile animals than is observed in aggregations of mammalian herbivores. Correspondingly, trophic energy represented by large herbivore species should have been available to a predator guild to a much higher degree in the sauropod ecosystem as compared to large mammal-dominated ecosystems with reproductive output of large herbivores confined to a few well-protected young.”

    “With sauropod hatchlings being so small, there must have been strong selection pressure for high juvenile growth rates because they would have shortened the time during which the young sauropods were endangered by predators.”

    But also: “Top speeds of nearly 20 km h−1 appear possible based on preliminary computer-aided engineering (CAE) modeling. Sauropods are similar in their limb design to elephants, with sturdier sauropods having similar, or even slightly greater, strength indicators to extant proboscideans. This indicates that they were comparably athletic. Since elephants can move at speeds of up to 35 km h−1, we must assume that similarly sized sauropods achieved similar speeds, while larger animals with equal strength indicators were even faster.”

    (Citations omitted for brevity.)

    So parental protection no, herd protection maybe, fully grown adults appear immune to predation, they normally moved slowly or not at all but were capable of higher speeds, they had lots of kids who were precocious and grew fast, and a lot of the kids got eaten.

  • Toadal

    The Wiley article indicates a high atmosphere oxygen content does help to explain an increased body size, but notes there is little correlation between atmospheric oxygen content and sauropod body mass.

    Body size increases gradually from the Late Triassic to the Late Jurassic, forming a plateau in the Cretaceous. The two sharp drops in body mass in the Early and Late Cretaceous are probably due to a poor terrestrial fossil record at these times. Note the lack of correlation between atmospheric composition and sauropod body mass.

    Fig. 8 from the Wiley article provides a chart that indicates the Jurassic periods average oxygen level at ~13% and the Cretaceous average at ~17%, which is significantly less than it is today and much less that the Carboniferous periods 32.5%. Therefore we are led to believe a very low atmosphere oxygen content did not detract from body size.

    However, the article contradicts the Jurassic and Cretaceous Wikipedia entries which describes the Jurassic atmospheric oxygen content at 26% and Cretaceous at 30%; percentages that could more easily support the evolution of giant lizards.

    So whom do we believe?



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