Midiaou Diallo
A single fossil toe is all now we have of the ‘Mitchell ornithopod,’ the nickname of the primary early Cretaceous dinosaur fossil present in Oregon in 2018. Ornithopods have been monumental herbivores akin to duck-billed dinosaurs and iguanodons, and Gregory J. Retallack, lead writer of that discovery, wished to seek out extra of its skeleton. Three years later, he returned to the location, aided by over 80 volunteers who helped excavate in additional element.
No additional ornithopod bones—certainly, no substantial dinosaur bones of any variety—have been retrieved after two weeks of digging. It was, he stated, “a failure” in that regard. What they discovered as a substitute was an entire mess, a jumble of the stays of land-based and aquatic animals. And much and many guano.
That got here from extinct flying reptiles, recognized collectively as pterosaurs, and suggests these animals could have flocked collectively on the cliffs above the coast of Oregon.
A particles discipline
A current paper printed within the journal Lethaia describes what seems to have been a mass particles stream throughout the early Cretaceous, roughly 100-113 million years in the past, carrying every part inside its path into the ocean. This particles stream explains the combo of terrestrial and marine life jumbled inside the identical stratigraphic stage of sediment—none of which might usually be discovered collectively. And because of this a wide range of vegetation and a 2.5 meter (about 8 foot) fossil log, for instance, have been preserved close to molluscs, fish bones, and shark tooth.
Extra considerably, the sediment of this particles stream contained very excessive ranges of phosphorus (ranges not seen within the shale deposits above and under it). And phosphorus is a characteristic of the guano deposits left behind by birds, which can occupy among the identical ecological niches as pterosaurs.
Different stays on the web site trace at what the pterosaurs have been consuming. Fractured shells from ammonites (historical shelled cephalopods, just like in the present day’s Nautilus) have been the most typical stays current.
Fossil ammonites are sometimes discovered intact and never crushed to small items, as they have been at this web site.
They’re maybe most acknowledged for the sort with spiral shells, discovered all through the world, together with elsewhere in Oregon. In distinction to these finds, many of the stays on this deposit have been the scale of “corn flake breakfast cereal,” based on the authors.
Retallack, professor emeritus of the College of Oregon, stated that these fragments have been a shock. “We now have collected plenty of ammonite localities and located nothing elsewhere like this,” he wrote in an e-mail to Ars.
You seem like what you eat
Whereas we nonetheless have quite a bit but to find out about pterosaurs, we are able to hypothesize about a few of their food regimen based mostly on their skulls. Dsungaripterus, for instance, is a pterosaur with a beak-like rostrum that has shell-crushing tooth behind its mouth, precisely what you’d count on to be feeding on ammonites.
There may be presently just one recognized pterosaur from Oregon, Bennettazhia oregonensis, however we don’t know what its cranium and tooth regarded like as a result of all that we’ve discovered are a humerus and a few vertebrae. So, whereas the group discovered some pterosaur tooth and a partial toothless (endentulous) mandible with grooves just like these present in Dsungaripterus, we don’t know which species these belong to.
Though a minimum of one dinosaur bone was discovered throughout the earlier dig at this web site, “no dinosaurs are recognized to be durophagous feeders,” Retallack defined, “and the one we discovered was evidently a herbivore.”
The excessive quantity of phosphorus is one other essential clue, Retallack argued. “A deposit a meter thick would take a big inhabitants of seabirds for instance. Large colonies of penguins don’t generate as a lot.” Coupled with the remnants of many pterosaur meals, this means a flock of pterosaurs could have gathered on the cliffs by the coast. It’s that meal that guidelines out historical birds because the guano producers; chicken species of the time weren’t recognized to eat mollusks.
