Wooster’s Fossil of the Week: a baculitid ammonite (Cretaceous of Wyoming)

November 13th, 2011

This is a specimen I often place on my Invertebrate Paleontology course lab tests. It is the “straight” ammonite Baculites, which is common enough, but the shell and internal walls (septa) have dissolved completely away, leaving this strangely articulated set of internal molds. This past week, though, it didn’t fool any of my students — they all identified it correctly. They must have a very good paleontology professor.

This is a view of one of the “segments” of the baculitid specimen. It shows the sediment that was pressed up against one of the septa, which then dissolved away. You can barely see branching tunnels made by worms that crawled through the mud looking for deposited organic material, forming trace fossils.

Baculites (meaning “walking stick rock”) was a magnificent ammonite. Its proximal portion was coiled as in all ammonites, but most of the shell (conch) grew straight. They moved like miniature submarines parallel to the seafloor, diving down occasionally to capture prey with their tentacles. They could grow up to two meters long and so must have been impressive predators. The above internal mold of a baculitid is weathering from the Pierre Shale in South Dakota. On the left end the complex sutures (the junctions between septa and conch) are visible; on the right is the extended body chamber.

A happy John Sime (Wooster ’09) holds a nearly complete specimen of Baculites in the collections of the Black Hills Institute of Geological Research. We were on an Independent Study trip in June 2008 to South Dakota, Wyoming and Montana.

A reconstruction of Baculites (foreground) at the Black Hills Institute of Geological Research.

The genus Baculites was named in 1799 by the famous zoologist Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck (1744-1829). In fact, Lamarck (as he is more usually known) was the first zoologist. He was a soldier as well as a scientist, and he had some of the earliest ideas about the evolution of life. I’m sure he would be proud of my students for their fossil identification skills!

Reference:

Lamarck J.-B. 1799. Prodrome d’une nouvelle classification des coquilles. Mém. Soc. Hist. nat. Paris, 74.

Wooster’s Fossil of the Week: a venerid bivalve (Upper Cretaceous of Jordan)

September 25th, 2011

This summer I joined a team describing a shell bed in the Upper Cretaceous (lower Campanian, about 80 million years old) Wadi Umm Ghudran Formation exposed northeast of Amman, Jordan (at N 32° 09.241′, E 36° 12.960′, to be exact). I hope someday to visit Jordan, so this work may be my introduction.

The fossils are diverse, including oysters, corals, gastropods and a bivalve of the Family Veneridae shown above. I was struck by how similar this fossil is to its very common modern cousin Mercenaria mercenaria (shown below).

The modern clam shell above, by the way, was one dissected by Invertebrate Paleontology students last year.

These venerid clams are infaunal, meaning they live within the sediment. Thus when east-coasters go “clamming” on a beach they are digging up clams like this from the sand at low tide. They use short tubes (siphons) like watery snorkels to suck in seawater to be filtered through their gills for suspended food particles. Since they live in the sediment their shells are usually clean of encrusters or borers while alive. After death the shells are usually cycled up to the surface and then encrusted and bored as seen below. This is an interesting feature of the Jordanian fossil shell bed — some shells are articulated and clean as the shell at the top; others are disarticulated and heavily bored. Clearly some shells were buried alive and others died long before final internment.

Venerid bivalves are heterodonts, meaning they have “different teeth”. These are not teeth for eating but rather parts of the clam’s hinge structure that hold the valves together. The shapes and sizes of these teeth are used to sort these clams into genera and species. Again, as you can see below, the teeth of the Cretaceous clam are similar to those of the modern shell, but with enough differences to make them separate genera.

The Family Veneridae is entirely marine and includes over 500 living species, many of which are delicious, I’m told. The most common clam consumed in the USA is Mercenaria mercenaria, known as the hard clam or quahog. There are 55 extinct genera in this family, which appeared first in the Early Cretaceous (Cox et al., 1969; Canapa et al., 1996).

This rather plain and common fossil will be the key to deciphering the history of our shell bed in Jordan. Sometimes the most useful fossils are the least flashy.

References:

Canapa, A., Marota, I., Rollo, F. and Olmol, E. 1996. Phylogenetic analysis of Veneridae (Bivalvia): Comparison of molecular and palaeontological data. Journal of Molecular Evolution 43: 517-522.

Cox, L.R. et al. 1969. Treatise on Invertebrate Paleontology, pt. N, Bivalvia vol. 2. The Geological Society of America, Inc. and The University of Kansas.

Mishash, b’gosh

May 29th, 2011

MITZPE RAMON, ISRAEL–Today Will and I drove south, east and north to meet Dr. Yael Edelmen-Furstenburg of the Geological Survey of Israel. She gave us a most excellent tour of the Mishash (pronounced ME-shawsh) Formation (Campanian, Upper Cretaceous) in the Wadi Ashosh region (shown above) near Zuqim and Tsofar in the Negev Desert. We talked much about the fossil fauna, particularly the trace fossils in soft and hard substrates. There could be many future Wooster Independent Study projects in this formation, especially here where it is so diverse.

As seen above, much of the Mishash Formation consists of bands of chert. The folds are syndepositional (formed at the time of deposition) as part of the Syrian Arc deformation. This makes for some very interesting local stratigraphy and depositonal patterns.

The Mishash Formation has exquisite fossil shell beds, often silicified (replaced with silica). Above you can see gastropods and bivalves.

An old Cretaceous friend, the ammonite Baculites, is used to sort out the biostratigraphy of the Mishash. They are identified by the style of ribs they have on the outside of the conch.

Like everywhere else in the Negev Desert, shade is a bonus. We always appreciate the acacia trees, even if their shade is not so complete. Will is standing here next to the Geological Survey of Israel vehicle. Shlomo, an old friend and the driver, gave us quite the off-road adventure. Many people pay for such tours!

A wall of Cretaceous ammonites

May 28th, 2011

MITZPE RAMON, ISRAEL–On our way back from Eilat this afternoon, Will and I took a short hike to see the “Ammonite Wall” on the southern outside beds of Makhtesh Ramon. It is an impressive tilted array of large ammonites in the Tamar Formation (Cenomanian). Current thoughts are that this represents a massive death assemblage. The ammonite conchs, which all seem to be of the same species, washed into an embayment and were buried. This is not uncommon as ammonite conchs probably filled with gases after death and floated great distances. They are all preserved as internal molds, with a few, such as the one below, showing their suture patterns.

Cobbling together a Late Cretaceous story

May 27th, 2011

MITZPE RAMON, ISRAEL–This morning Will and I finished our work with the Zihor/Menuha boundary cobbles. We drove to the southern side of Makhtesh Ramon (pictured above) to see the same units we examined 25 kilometers to the north in Wadi Aqrav yesterday. The scenery was spectacular — and the day so hot that the wind felt like a hair-dryer in the face.

Will standing on the very top of the Zihor Formation where it is overlain by the Menuha chalks. This picture was deliberately posed to give his parents a bit of a thrill.

The Zihor/Menuha cobbles in the southern sections. They look very much like those we studied in Wadi Aqrav. They certainly are more numerous here and easy to measure. Some have borings by bivalves (Gastrochaenolites) and worms (Trypanites). We found no encrusters here, but we did find oyster shell fragments.

A difference between these southern exposures and those to the north is that the Zihor Formation top surface here is very well exposed. We can see that it was probably lithified during the erosion that created the disconformity and the cobble lag. It is undulating and well polished. Note that it is also on the edge of oblivion.

The Zihor/Menuha boundary is very distinctive because of the erosional differences, so faults through it show up well. What kind of fault is this? (It is not a trick of perspective because the fault plane has eroded back a bit.)

This is the kind of shade we had in the field today — when we were lucky! It was 40°C by 1:00 p.m. Will is pressed up against an outcrop of the Menuha Formation, by the way, showing a sequence of carbonate nodules that may help explain the origin of the boundary cobbles.

 

The Ora Formation: A future student project?

May 27th, 2011

MITZPE RAMON, ISRAEL–I’ve always enjoyed seeing the Ora Formation, which is exposed only in Makhtesh Ramon and to the south. It is early Late Turonian in age, so it is part of the Upper Cretaceous and about 90 million years old. It has an astonishing range of depositional units, many of which Will and I saw today on our way to our localities. The Ora Formation has been very well studied by Israeli paleontologists and stratigraphers. Their work can now be expanded with more paleoecological analysis and some of the insights we’ve gained from new ideas about Calcite and Aragonite Sea alternations. Maybe another Wooster Independent Study project or two in the future?

A carbonate hardground in the Ora Formation. The holes were drilled by lithophagid bivalves, producing a trace fossil called Gastrochaenolites. These borings are very densely packed, which is more typical for the Jurassic than the Cretaceous.

A unit composed of almost entirely oyster valves in the Ora Formation. It is above what is called locally the “Vroman Bank”. The shells are like large cornflakes. We didn’t get a chance to look in detail, but I’d love to see what kind of sclerobionts are preserved on these oysters.

Will is sitting in an unusual diapiric structure in the Ora Formation. This is a dissected “mud volcano“, or at least what would have been a mud volcano but for the resistant capping rock. Soupy mud was forced out from underneath the overlying limestones forming an inverted cone in cross-section. The limestones dip into the structure because they were forced down by the accumulating mud. The criss-cross lines in the mud are planes of gypsum that intruded the sediments later. Note the blocks of limestone in the “throat” of the structure — this means the limestones were lithified during the event.

It is always a good day if there are sclerobionts in it

May 26th, 2011

MITZPE RAMON, ISRAEL–Sclerobionts are organisms that live on or in a hard substrate. Paul Taylor and I coined the term in 2002, so I use it as often as I can. Maybe someday more than six people will know what it means. A project for this year’s Israel field expedition is to revisit a locality where an extensive bed of hiatus concretions, most of them bored or encrusted by sclerobionts, is found between the Zihor and Menuha formations in the Upper Cretaceous. (This layer is pictured above.) Andrew Retzler and Micah Risacher will remember the Wadi Aqrav (Scorpion Wash) sections well from their Independent Study work last year. These hiatus concretions were formed when deep erosion produced a disconformity and a lag of cobbles. We already had a GSA presentation on this topic; now we need more information for a future paper.

Will and I hiked through Wadi Aqrav today to collect more information about these Cretaceous cobbles. We found all our previous study sections and a few more outcrops of the Zihor/Menuha formation boundary. Most important, we were able to collect more sclerobionts and other associated fossils.

One of the bored and encrusted Zihor/Menuha cobbles showing its apparent origin as a burrow-fill.

Eroded borings in the surface of one cobble. These are holes in the rock, but if you stare at them long enough they will suddenly look like bumps!

Three oysters on a cobble surface. Two grew together at the same time and one came later. Can you tell which?

Will found this nice irregular echinoid in the matrix between the cobbles. He also found a couple of shark teeth near it. A one-shekel coin, by the way, is 1.7 centimeters in diameter.

Landscape view of the Wadi Aqrav region. Beautiful desert in the Negev Highlands north of Makhtesh Ramon.

Wooster’s Fossil of the Week: A scaphitid ammonite (Late Cretaceous of Mississippi)

April 24th, 2011

The beauty above is Discoscaphites iris (Conrad, 1858) from the Owl Creek Formation of Ripley, Mississippi. Megan Innis and I collected it during our expedition to the Cretaceous-Paleogene boundary in the southern United States last summer. It is a significant index fossil in biostratigraphy: the Discoscaphites iris Zone is the latest in the Cretaceous (the late Maastrichtian Stage). This animal lived in the final days of the Mesozoic Era just before the mass extinction 65.5 million years ago.

Discoscaphites iris is an ammonite, a type of extinct cephalopod mollusk related to the modern octopus, squid and nautilus. It had a planispirally-coiled shell with chambers divided from each other by complexly-folded walls. If you look closely near the top of the fossil above, you will see where the shell has flaked away revealing an internal mold of sediment and a peek at the folded walls inside. “Ammonite”, by the way, is a very old term for these fossils. Pliny the Elder himself used a variant of the name, which comes from the Egyptian god Amun with his occasional coiled ram’s horn headgear.

Reconstruction of an ammonite by Arthur Weasley (via Wikipedia).

Ammonite shells were made of the carbonate mineral aragonite. This is the mineral that makes many modern mollusk shells have prismatic colors, which we call nacreous. You may know it best as “mother of pearl” or as pearls themselves. Aragonite has an unstable crystal structure and so is not common in rocks older than a few million years. The original aragonite in our ammonite fossil is thus a bonus.

In an oddly topical note, Discoscaphites iris was recently found in the Upper Cretaceous of Libya, giving it a disjunct range from the US Gulf and Atlantic coasts to the Mediterranean coast of northern Africa (Machalski et al., 2009).

Reference:

Machalski, M., Jagt, J.W.M., Landman, N.H. and Uberna, J., 2009. First record of the North American scaphitid ammonite Discoscaphites iris from the upper Maastrichtian of Libya. N. Jb. Geol. Paläont. Abh. 254: 373-378.

Paleoecological Reconstruction of the Menuha Formation (Upper Cretaceous, Santonian), Makhtesh Ramon Region, Southern Israel (Senior Independent Study Thesis by Andrew Retzler)

April 11th, 2011

A typical Menuha Formation outcrop south of the Makhtesh Ramon structure.

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Andrew Retzler, a senior geology major from Wooster, Ohio.  Here is a link to Andrew’s final PowerPoint presentation on this project as a movie file (which can be paused at any point). You can see earlier blog posts from his field work by clicking the Israel tag to the right. Andrew also created a Wikipedia page on the Menuha Formation.

It all began with an 11-hour flight from NYC to Tel Aviv, Israel with Dr. Wilson and fellow geology senior Micah Risacher. The airport process required for international travel of this sort was an adventure in itself. Thorough baggage checks, stern looks from security personnel, and a bombardment of questions dealing with our reasons for travelling were all offset by a seemingly endless and free movie selection on the flight! Eventually, we reached our arid destination of Mitzpe Ramon, the city that would serve as our basecamp for the next two weeks.

One of the reasons behind our trip was to scour the Menuha Formation outcrops throughout the Makhtesh Ramon region (shown above). We were hoping to collect and analyze various fossils in order to reconstruct an environment that once flourished during the Cretaceous. This process also involved taking detailed measurements and notes on each outcrop to create stratigraphic columns of each locality. This would become the basis of my thesis. Of course, none of this could have been possible without the help of our all-knowing field guide, Yoav Avni, and our shark specialist, Stuart Chubb, from the Birkbeck College of London.

Although my thesis has a strong focus on the shark and other fish teeth collected from the Menuha Formation, it also incorporates oysters, trace fossils, and several benthic/planktic foraminiferans. At least ten different species were represented in the isolated teeth: Cretalamna appendiculata, Cretoxyrhina mantelli, Squalicorax falcatus?, Squalicorax kaupi, Scapanorhynchus rapax, Scapanorhynchus raphiodon?, Carcharias samhammeri, Carcharias holmdelensis, and two other fish (Hadrodus priscus and Micropycnodon kansasensis?). Many of these fish were thought to occupy outer shallow marine realms, where the continental shelf begins transitioning into the slope. A few of the sharks are also known for being top Cretaceous predators, four or more meters in length, whose diets included plesiosaurs, mosasaurs, and ichthyodectids.

Cretalamna appendiculata tooth, a shark often considered to be an ecological generalist.

Scapanorhynchus rapax tooth. Related to the extant Goblin Shark, S. rapax had the ability to protrude its mouth in order to capture prey.

Cretoxyrhina mantelli tooth. Considered a superpredator of the Cretaceous seas, this shark could reach 5-6 meters in size.

Squalicorax kaupi tooth. The Squalicorax genus is the only group to exhibit serrated dentition, like so, in the Late Cretaceous.

Hadrodus priscus pharyngeal teeth. These teeth would have been found near the back of the throat arranged in a comb-like structure to help crush exoskeletons.

LEFT: The extended left valve of a Pycnodonte vesicularis. RIGHT: Planktic, biserial foraminiferan test (possibly Heterohelix sp.) that has been replaced by silica.

The Menuha Formation consists mainly of white and yellow/brown, glauconitic chalks that were often marly or conglomeratic. This chalk comprised a variety of phosphatic peloids, microteeth, irregular echinoid spines, and benthic/planktic foraminiferans that clearly represent a shallow marine environment.

Irregular echinoid spine recovered from the partially dissolved Menuha chalk.

Microtooth from the Menuha chalk.

Correlating the paleontology with their lithological context, a shallow marine outer continental shelf/middle continental slope environment is suggested as the paleoenvironment of the Menuha Formation. This environment would have also flourished with a variety of small to medium-sized fish, squid, and larger vertebrates (plesiosaurs and mosasaurs) in order to sustain such a shark population. Unlike the deep environment that has often been suggested, my thesis provides strong evidence towards a shallow marine environment during the early formation of the Makhtesh Ramon structure. My work also marks the first identification of the fish teeth within the Menuha Formation, beginning my contributions to the scientific world.

A Paleoenvironmental Analysis of the Zichor Formation in the Cretaceous of Southern Israel (Senior Independent Study Thesis by Micah Risacher)

April 11th, 2011

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Micah Risacher, a senior geology major from Columbus, Ohio.  Here is a link to Micah’s final PowerPoint presentation on this project as a movie file (which can be paused at any point). You can see earlier blog posts from Micah’s field work by clicking the Israel tag to the right.

In the summer of 2011 Wooster geologists Mark Wilson, Andrew Retzler, and I went to the Negev Desert in southern Israel.  We were met by a colleague from England, Stewart Chubb as well as our guide and host Yoav Avni of the Geological Survey of Israel.  The small town of Mitzpe Ramon on the edge of the Makhtesh Ramon (Figure 1) would serve as our home for the next two weeks as we explored the Ramon structure.

Figure 1. A look into the Makhtesh Ramon structure.

My research includes the Zichor Formation which can be found throughout the Makhtesh Ramon structure.  However I focused on three separate locations known as the northern, southern, and western locations.  Each location had different features exposed, the southern location (Figure 2) exposed the Zichor very well, yet it was quite hard to get at it.

Figure 2. Southern section with the Zichor section labeled.

The purpose of my I.S. was to determine the paleoenvironment of this particular formation (Zichor) using the paleontology, sedimentology, and stratigraphy seen in the field/lab.  I found many well preserved echinoids (not destroyed by churning waters), Thalassinoides trace fossils, high mud content and shell fragments in the lithology, as well as several minor regression/transgression cycles.  All of these point to a primarily shallow marine environment that would slightly deepen once or twice before shallowing again.

The echinoids (Figure 3) found were so well preserved that they could be identified down to the species level and greatly helped to correlate this assemblage with others like it around the world during that time.  This process both helps to verify my results as well as put my sites in perspective with similar ones around the world.  Hopefully, this study will go a ways into settling the current dispute as to whether or not this region was a shallow or deep sea environment during the Late Cretaceous.

Figure 3. The most prevalent echinoids Hemiaster batnensis and Rachiosoma delamarri respectively; scale bars=1cm.

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