Sunday, June 24, 2018

Regarding forams

Life started out microscopic (at least to humans) and most of it has stayed that way. Of course, many microscopic organisms have poor fossil records, due to factors like lack of hard parts and the whole "microscopic" thing (finding and studying microfossils takes special equipment and expertise that aren't used for collecting, say, brachiopods). However, a subset of microscopic organisms have very significant fossil records. We saw the ostracodes a few years ago, but there are also a number of groups of single-celled organisms that produce hard parts suitable for fossilization. Among the most important are: coccolithophores, phytoplankton which form skeletons of scale-like objects known as coccoliths, micron-scale structures that make up chalk (and which are sometimes called nannofossils because they're so darn small); diatoms, phytoplankton with cell walls made of silica; dinoflagellates, which form organic-walled cysts; radiolarians, protozoans that form body structures of silica; and the subjects of today's entry, the foraminifera, which can be described glibly as "amoebas with shells".

A living foram, the brackish-water benthic calcareous species Ammonia tepida, showing strands of pseudopodia surrounding the coiled test. What do all these terms mean? Read on! (Photo from Wikimedia Commons; unfortunately, no scale, but you'll get an idea of the size of what we're dealing with in the photos to come.)

Sunday, June 17, 2018

Your Friends The Titanosaurs, part 1: Adamantisaurus, Aegyptosaurus, and Ampelosaurus

This is the first in what I plan as a periodic ongoing series. The response from this year's two previous titanosaur posts was better than I expected, especially considering what I thought was some dry subject matter, so if people are liking the big lugs, why not have them around more often? There are certainly plenty of species, and hopefully they don't become overwhelming if they feature once a month or so, when some other topic isn't coming together. The plan is to briefly cover three species in a post, in more or less alphabetical order. For example, in this post we have Adamantisaurus mezzalirai, Aegyptosaurus baharijensis, and Ampelosaurus atacis, taking us from Brazil to Egypt to France. The third species would have been Aeolosaurus colhuehuapensis, but because there are three species of Aeolosaurus I thought it made sense to hold it back and make the next post all Aeolosaurus. The next one would have been Alamosaurus sanjuanensis, but I have other plans for it. Therefore, Ampelosaurus atacis gets the call.

Sunday, June 10, 2018

Postglacial fragments, featuring Hartman's Cave

Although eastern North America contains many things, it is not noted for its terrestrial Cenozoic sedimentary deposits. Conditions just weren't favorable for the long-term preservation of extensive terrestrial sedimentary formations. Therefore, our knowledge of terrestrial life in this region is largely confined to some transitional coastal settings and what we might call "point sources" in comparison to the great formations of the West: sedimentary deposits of caves, fissures, bogs, ponds, and so on. These in turn are strongly biased to just the Pleistocene and Holocene. We've visited a few of these sites before, around Minnesota (Hidden Falls, I-35, Kirchner Marsh, Loring Park, and in general), and in the District of Columbia, Kentucky (Mammoth Cave), and Pennsylvania (Marshalls Creek Mastodon, Port Kennedy Bone Cave). Here is another site in northeastern Pennsylvania, plus some brief commentary on sites nearby.

Sunday, June 3, 2018

Bagualosaurus agudoensis: another sauropodomorph ahead of its time

Our subject today is the newly described Bagualosaurus agudoensis from lower Upper Triassic rocks of southern Brazil. If I'd known back in March 2016 that I'd have the opportunity in a couple of years to write about another "prosauropod" that was "ahead of its time", and that it would include a partial skull justifying a terrible "head" pun, maybe I'd have come up with another title then. Oh, well; spilled milk and all that.