Sunday, September 20, 2015

Fossil yucca? plant

One of the rarest fossils I have collected from the Pico Formation south of Newhall, southern California is what I believe is a small base (trunk) of a yucca plant. It is from the upper part of this formation and is of late Pliocene age (about 3 million years old). 

The Pico Formation in this area was deposited in a marine-delta environment, and, as I mentioned in one of my earlier posts (8/15/2014), fossil pine cones can be found (rarely) in these beds. The pine cones were derived from pine trees that grew in the adjacent, ancient San Gabriel Mountains east of the delta. Some of the pine cones eventually floated down a braided river (full of coarse debris consisting of pebbles and cobbles) and were deposited in fine-grained sandstone near an ancient shoreline, and mixed with shallow-marine fossils (e.g., seashells and shark teeth). It seems likely that presumed yucca remains could have also floated into this marine-environment setting.

When I first saw the presumed yucca fossil, I thought it was a pine cone. Upon closer inspection, however, I realized the yucca? fossil is not like the pine cones from this formation. As I walked back to my car, I came across a modern yucca plant (see photo and comments below). I was immediately struck by the fact that the vertical-striations on some of the woody part of the trunk of both the modern and presumed fossil yucca are very similar. If you have knowledge of the bases of fossil yucca plants, please let me know if you think my identification is correct or not.

Late Pliocene yucca? base (trunk), height 12 cm (4.75 in.), width 7 cm (3 in.), from the upper Pico Formation near Newhall, California. The white fossil sticking out along the upper left side is a shallow-marine clam. Notice the cross-section of the high-spired, shallow-marine gastropod shell
of Turritella cooperi near the bottom. 

Modern-day base (trunk) and a few green leaves of a yucca [probably Hesperoyucca whipplei] height 24 cm (9.5 in.), width 15 cm (5 in.), from near Newhall, California. The non-green, hard, woody trunk is 14 cm height. Hesperoyucca whipplei is one of the most common yuccas of the chaparral and coastal-sage scrub plant communities living below 4000 feet in elevation in southern California. The leaves of this yucca are stiff and dagger like.

Monday, September 7, 2015

Dinosaur gastroliths

Gastroliths are literally “stomach stones.” It has long been postulated that they were swallowed voluntarily by giant sauropods (herbivorous dinosaurs) for the purpose of aiding digestion by grinding food material. 

Gastroliths look just like highly polished river gravel, and this fact has helped convince some paleontologists that gastroliths are nothing more than sedimentary gravel and never used by dinosaurs to aid their digestion process. It would follow, therefore, that if you believe you have found "stomach stones," it would strengthen your hypothesis if you could show that they came from inside of a dinosaur skeleton in the stomach area.

Many years ago, a reputable vertebrate paleontologist gave me a stomach stone (see the red stone shown below), which he said that he had collected from the stomach area of a large sauropod of Late Jurassic age in the San Rafael Swell area of Utah.

A gastrolith 9 cm long (= a small cobble) from Utah. The rock, which is heavy, is an iron-bearing (reddish) quartzite.

The other picture (shown below) is of two other gastroliths, also from Utah. These specimens were part of a private collection that was sold.

Two gastroliths (small one is 1.8 cm long = large pebble; large one is 3.8 cm long = very large pebble) from Utah. The rock type, which is lightweight, is a hard but highly polished detrital sedimentary rock (probably coarse-grained sandstone).