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We began the week with our first Mystery Monday for paleoaerie.org with the picture of an interesting Arkansas fossil. Today, Forum Friday will become Fossil Friday as well as we identify the fossil. Did you guess what it was? See if you were right below the picture.
Congratulations go to Allie Valtakis, who correctly identified it as a nautiloid cephalopod. This particular one is Rayonnoceras solidiforme. It has traditionally been placed within the Order Actinocerida, although some workers have placed them into the Order Pseudorthocerida, which is known for their resemblance to the more commonly recognized orthocerid cephalopods.
What are cephalopods, much less nautiloid cephalopods, you ask? Cephalopods are the group of molluscs that include squids, octopuses, and cuttlefish. There are three major groups: Coleoidia, which includes almost all the modern cephalopods; Ammonoidea, which includes almost all the extinct ones and are known for their complexly sutured shells; and the Nautiloidea, which are mostly extinct, the only living form is the Nautilus. The ammonoids and the nautiloids both formed shells. What differs between them is how they made them. Some of those in Coleoidia also form shells, but they have been greatly reduced and internalized, such as in squids, or lost altogether, such as octopuses. For those with external shells, they have the problem that shells don’t get bigger once the mineral is laid down, so they quickly grow out of their shells. They solve this by adding mineral to the front of the opening in an ever-increasing funnel, periodically walling off the back of the living chamber (leaving a small opening for the siphuncle that goes all the way through the shell, creating a series of gradually increasing sections.
The ammonoids are well known in the fossil record, particularly the subgroup called ammonites, having a diverse array of straight, curved, and coiled shells. What makes them unique from the nautiloids is the sutures between sections are wavy, sometimes showing astoundingly complicated patterns. The nautiloids, on the other hand, sport very simple, smooth curves. It is this group in which Rayonnoceras belongs.
Rayonnoceras lived about 325 million years ago in the Mississipian Period, although nautiloids as a group have been around since the Cambrian Period over 500 million years ago. What makes this particular species so interesting to Arkansans is that the largest nautiloid cephalopod ever found (update: largest pseudorthocerid nautiloid, not largest nautiloid) was discovered near Fayetteville, AR. It was 2.4 m (8 feet) and found in a rock unit named, appropriately enough, the Fayetteville Shale, a unit of dark gray to black shale and limestone, indicative of a warm, shallow marine environment without a lot of sediment input, much like many areas within the Bahamas today.
To recap what we’ve covered over on the Facebook page, we recommended a book discussing misunderstandings in human evolution and another in how evolution affects our health. We saw a hominid fossil hand bone that helped to show how we differed from australopithecines and genetics work that showed us how we didn’t differ from Neanderthals.
We read about genetics work that informed us how flowering plants evolved by doubling their own genes and stealing genomes from other plants. We learned about a “second code” within DNA and why the hype was bigger than the story, but may help us rethink our DNA analogies.
We saw how birds defend themselves against cheaters and learned the first lizards and snakes may have given live birth. We also got some information on how teaching and testing will need to change under the Next Generation Science Standards.
On a final note, this will be the last post this year on paleoaerie.org. Enjoy the holidays and join us in January, when we will be embarking on discussion of the Ordovician rocks and fossils in Arkansas. Over the spring, we plan on discussing several vertebrate fossils found in the state. There are several books and online resource reviews coming up as well. We will be adding to our Scientists in the Classroom and adding several new resources to the links pages. As always, we will be posting a plethora of current news items on Facebook, so stay tuned! In the meantime, tell us what you liked, didn’t like, want to see more of, and any questions you may have.
It may seem that the earth is pretty stable. You can always count on the mountains being there when you look for them. But the Earth is a dynamic place. Volcanoes, floods, landslides, and earthquakes all change the landscape in ways we can see quickly. What we don’t typically see is that if we expand these processes over long periods of time, those same processes alter the landscape far beyond our experiences. The surface of the Earth is covered in a crust broken up into numerous plates, which are constantly shifting and moving. The plates only move between 2.5 – 15 cm/year (the previous link contains information on how this is measured and provides activities for teachers for use in the classroom), but add this up over millions of years and the Earth looks quite different. Add into this mountain-building and erosion wearing down the mountains and you get radically different geographies for the planet.
So what did the Earth look like in the past? There are two excellent sources providing maps of the planet through time. The first is the PALEOMAP Project, by Dr. Christopher Scotese. On this website, you will find maps ranging from 650 million years ago to the modern day and even into the future. There are 3D animated globes and interactive maps. He includes a methods section for how the maps wer put together and a list of references and publications. There is also a climate history section providing brief descriptions of the climate at various points in time. For teachers, there are several educational resources available, some of which are free, but others are available for a fee. There is even an app for the iPhone/iPad. It is not available yet for either android or Windows, but that has been admirably taken care of by the Howard Hughes Medical Institute with their Earthviewer app and they have done a wonderful job. the app is fully interactive, allowing easy scrolling through time and full rotation of the globe. You can also track atmospheric oxygen and carbon dioxide, day length, important fossils, biological and geological events, and major meteor impacts. The app even provides a bibliography of their source material. In addition to the maps from Dr. Scotese, the app extends the timeline back to 4.5 billion years (although this extension is obviously not nearly as detailed as the Scotese maps due to the greatly extended time and the greatly decreased amount of available data). All in all, a great app, also reviewed by the NSTA.
The second site that will be of interest is the Library of Paleogeography run by Dr. Ron Blakely. These maps cover approximately the same time frame as those provided by Dr. Scotese and are not animated. However, Dr. Blakely provides maps in different projections and provides regional coverage beyond that of global maps. So if you are specifically interested in paleogeographic maps of North America and Europe, this is an excellent resource.
A third site also provides paleogeographic maps which are very useful. In this case, the maps are secondary to the main purpose of mapping fossil locations. The Paleobiology Database contains records of fossil locations that have been published in the primary literature. One can perform a search by organism or group, country, rock unit or type, time interval, paleoenvironment, or publication. The results from the search are mapped onto global maps based on the PALEMAP Project.
All of these sources are available to the public and are used by professional researchers. Therefore, one can safely assume they represent accurate assessments of current, generally accepted thoughts on our Earth through time. You may notice that maps from Scotese and Blakely may not completely agree on all aspects. This is because it is very hard to piece together all the evidence and trace the movements of the continents backwards through time. Often, the data is incomplete and they have to make judgment calls based on the available evidence. Not everyone makes the same choices. This is true even for maps of current geography and is even more so for paleogeography. As we get more data and better techniques, those disagreements become fewer and fewer, but there is still much work to be done, so these maps can and will most likely be refined in the future to reflect new research.