It's time for the weekly nature identification thread! Post pictures of plants, animals, rocks, or other cool stuff that you've photographed but can't identify, and I, along with anyone else who would like to help, will try and help you identify it. I'll be making some changes to it- most notably, I'll be using the SBD proceeds from this post to give out 
Xiphactinus ("sword-ray") was an extraordinarily aggressive predatory fish alive during the late cretaceous. They grew to 20 feet in length, and were some of the most terrifying things in the ocean at the time. They're frequently found with other fish fossils in their stomach- pictured is a 13 foot long xiphactinus with a 6 foot long Gillius arcuatus in its stomach. (The xiphactinus probably died from injuries from the smaller live fish struggling inside it.) This specific fossil can be found in the Sternberg Museum in Hays, Kansas- in fact, just about every natural history museum in Kansas has them, because not only was Xiphactinus discovered in Kansas, but it remains the best place to find their fossils.
Remember: The most important information you can give along with any photo to be identified is its geographical location. This narrows down the range of possibilities more than any other info you can provide.
Plants:
Along with the photo, add where you found it, the time of year, the approximate altitude, and any interesting scents or textures not caught in the photo.
Animals:
Along with the photo, add the location you found it, the time of year, the sounds it made, any interesting behaviors, and any other features not caught well in the photo.
Rocks:
Along with the photo, add the location you found it, a description of the terrain it was found in, whether it was attached to a rock outcrop or found loose on the ground or buried in the soil, a description of its texture (especially its grain size), and a description of its weight and density. Fossils are included in this category. (Despite my greatest expertise lying here, rocks tend to be some of the hardest things to identify in a photo.)
Fungi:
I will not be identifying mushrooms and fungi for foraging purposes. Mushrooms should really only be identified for foraging purposes in person and by an expert. If another contributor wishes to identify them, that's their call, but I encourage them to be similarly cautious. I might also try to identify a few fungi that are clearly not being looked at for the purposes of eating, but that'll be a case by case decision.
