[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[dinosaur] FW: Dinosaur nest ecology and predation during Late Cretaceous

 Hm...this seems like a new version of the old 'mammals ate all the dinosaur eggs!' scenario. I find this reasoning very dubious as it is based on a number of assumptions that might well prove wrong and seem very shaky to me at best.

- That dinosaurs would not be able to protect their nests against small nest robbers.

- That birds, mammals and snakes simultaneously evolved into more capable nest-robbers.

- There actually being more large(r) potential egg predators during the later Cretaceous. This is, AFAIK, not clear from the fossil record. psittacosaurivore *Repenomamus* would be a prime suspect here, but it was Lower Cretaceous. What's more, the fossil record for smaller creatures is probably too spotty for any such claims to be on solid ground.

- The assumption that a multitude of small nest-robbers would be new for the later Cretaceous. Given that there would have been massive numbers of eggs during the entire Mesozoic it seems extremely unlikely to me that this major resource would have gone largely untapped throughout this vast time frame.

- The authors state that grasslands would be ideal areas to conceal large nests. Really? Modern day large egg-layers are not restricted to grasslands nor are they neccessarily the most succesful here. Also, it would seem unlikely that nesting colonies of large dinosaurs would be all that covered in vegetation anyway given that we are looking at numerous nests with often attending large to huge parents. Any concealing vegetation would probably end up eaten or trampled. What use is concealing vegetation for avoiding small nest robbers anyway?

- Not an assumption, but the whole argument seems to ignore the fact that dinosaurs in general appear to have been K-strategists to some extent; large numbers of offspring to offset serious losses. Nest failure was probably a feature and not a bug so we are definitely not looking at the loss of numerous eggs being something new to the later Cretaceous.

All in all, I call 'untestable', 'unverifiable' and 'far too many assumptions' on this one. I find the authors' claim of originality unwarranted too. While they may have dressed up the argument a bit, I repeat that this is the old 'mammals ate all their eggs!' re-packaged.

Brian Lauret

Van: dinosaur-l-request@usc.edu <dinosaur-l-request@usc.edu> namens Ben Creisler <bcreisler@gmail.com>
Verzonden: maandag 9 januari 2017 18:53
Aan: dinosaur-l@usc.edu
Onderwerp: [dinosaur] Dinosaur nest ecology and predation during Late Cretaceous

Ben Creisler

A new paper:

John Bois & Stephen J. Mullin (2017)
Dinosaur nest ecology and predation during the Late Cretaceous: was there a relationship between Upper Cretaceous extinction and nesting behavior?
Historical Biology (advance online publication)

Many hypotheses have been advanced to explain the K/Pg extinctions, yet none closely examines the likely interactions between dinosaurs and contemporary taxa within their communities. The diversity of predators of dinosaur nests and hatchlings increased toward the end of the Cretaceous. In addition to large snakes having been found fossilized in the act of foraging in dinosaur nests, mammals and birds had also evolved new forms potentially capable of exploiting this resource. The constraints on mammal size and niche diversity lessened prior to the K/Pg boundary. Using comparisons of predator/prey size ratios between extant species and known fossils, we demonstrate that mammalian and avian clades had members large enough to prey on dinosaur eggs and hatchlings. We argue that the reproductive strategy of obligatory nest defense was likely practiced by most non-avian dinosaur species. This strategy was highly susceptible to the increasing numbers of mammalian, avian, and reptilian predators, which rendered this strategy obsolete. Continued selection against large oviparous species in the Cenozoic has limited this life-history strategy to habitats that provide concealment – primarily grasslands, a habitat that did not exist until the Miocene. We urge the evaluation of multiple, perhaps synergistic, hypotheses when considering extinction events of this magnitude.