Wooster’s Fossils of the Week: dinosaur gastroliths (Jurassic of Utah, USA)

June 10th, 2012

These rounded stones are labeled in our collections as gastroliths (literally “stomach stones”) from Starr Springs near Hanksville, Wayne County, Utah. I’m featuring them this week in honor of our Utah Project team working right now in the baking Black Rock Desert near Fillmore, Utah.

From their reported location, these stones are likely out of the Summerville Formation (Middle-Upper Jurassic) and, in another plausible supposition, probably from some sort of dinosaur. Sometimes we just have to trust the labels on our specimens, at least for educational purposes!

My friend Tony Martin recently wrote an excellent blog post on gastroliths, so I won’t repeat his insights here. The general wisdom is that these stones were consumed by herbivorous dinosaurs to aid in their digestion. They would have lodged them in the equivalent of a gizzard and used them to grind their food, much like modern birds. (And yes, dinosaurs were birds themselves.) Gastroliths usually have a resistant lithology to be useful as grinders. The gastroliths above are chert, one of the hardest rock types.

Identifying gastroliths correctly is a bit of a challenge if you don’t find them inside a dinosaur skeleton. The most common indicators are that they are very smooth, are in a location where they were unlikely to have been transported inorganically, and are of a lithology unlike the surrounding rock (“exotics” as geologists like to call them). Still, even with all these criteria met, we must be a tad suspicious if we didn’t find them associated with dinosaur bones. I would never, for example, buy a gastrolith in a rock shop. Without context, it could be just a stream-worn stone. I’m trusting the label on ours that we have the real deal!


Stokes, W.L. 1987. Dinosaur gastroliths revisited. Journal of Paleontology 61: 1242-1246.

Wings, O. 2007. A review of gastrolith function with implications for fossil vertebrates and a revised classification. Acta Palaeontologica Polonica 52: 1-16.

Wooster’s Fossils of the Week: A calcareous sponge with a crinoid holdfast (Matmor Formation, Middle Jurassic, Israel)

April 8th, 2012

The Class Calcarea of the Phylum Porifera is a group of sponges characterized by spicular skeletons made of calcium carbonate (calcite in this case). The spicules (small elements of the skeleton) are often fused together, causing the sponges to look a bit like corals or bryozoans. They are among the most common fossils in the Matmor Formation (Middle Jurassic, Callovian) of southern Israel. Melissa Torma and I collected this particular fossil on our expedition last month. It is another indication that the Matmor Formation was deposited in very shallow waters.
This is the underside of the Matmor calcareous sponge. (I wish we had a name for it, but the taxonomy is in considerable flux right now.) You can see the way it grew radially around an encrusting center. In the lower right a circular oyster attachment is visible.
A close view of the top surface of the calcareous sponge showing radiating canals called astrorhizae. They were used to channel water currents for the sponge’s filter-feeding system.
This crinoid holdfast (the base of an attaching stem) locked onto the calcareous sponge after its death. We can tell this because it is bound to the spicular skeleton itself, which was only exposed after the sponge’s soft tissues rotted away. It is not possible to identify the crinoid, but it is likely in the genus Apiocrinites.
The Class Calcarea was named by James Scott Bowerbank in 1864. Bowerbank (1797-1877) was an English naturalist born in London. He helped run a distillery with his brother, making enough money to support his diverse interests in natural history. He collected many fossils in his life, specializing in the London Clay (Eocene). His various publications gained him membership in the Royal Society in 1842. His greatest work was probably a four-volume set titled “A Monograph of the British Spongidae”. (You can read at least part of this work online.) He was well known as a strong supporter of young scientists, opening his home and collections (and use of his valuable microscopes) to all those seriously interested in natural history. I like to think he would have been happy as a liberal arts geology professor!

Wooster’s Fossil of the Week: A curving scleractinian coral (Middle Jurassic of Israel)

March 18th, 2012

Since Melissa Torma and I recently returned from our expedition to southern Israel (see immediately previous posts), I thought our weekly fossil highlight should be one of our specimens collected from the Middle Jurassic Matmor Formation of Makhtesh Gadol.

This is a colonial scleractinian coral, a group that first appeared in the Triassic. It was originally made of aragonite and is now recrystallized to calcite. The exterior is well preserved, but the interior is coarsely crystalline. You can just make out faint outlines of the individual corallites that make up the colony.

The distinctive feature of this specimen is that it shows different growth directions. Apparently it was disturbed on the seafloor as it grew, so it periodically had to change its direction to keep growing upwards towards the sunlight. It needed the light because it had photosynthetic symbionts in its tissues.

This coral is one of many indications of the shallow paleoenvironment we’ve proposed for the Matmor Formation. It is also encrusted by a variety of sclerobionts, so it is a bit of a community all on its own.


A field day cut short by angry camels and a threat of rain … but at least the dust is gone!

March 15th, 2012

MITZPE RAMON, ISRAEL–Compare the image above to the one taken in the same place two days ago. Much better! Our only dust today was a local product from the unending winds. The Saharan dust is gone. We paid for this clarity, however, with a dramatic drop in temperature. It was 8°C (46°F) when we started work this morning. This is typical for spring fieldwork in the northern Negev. The weather is less predictable, and the temperatures can swing wildly from day to day. The summers are very predictable: sunny, hot, dry, and not a breeze. I don’t take my hat’s chinstrap in the summers, but in the spring it is tied firmly all day.

Our goal today was to travel as far south as we could along the strike of the Matmor Formation, sampling “subunit 51″ when we could. Melissa and I walked into the makhtesh about five kilometers. This was not a long distance, but in the summer we just couldn’t carry enough water to pull it off without a four-wheel drive vehicle.

We walked south from the Negev Minerals mine, where we park, along an old pipeline road until we reached Wadi Hatira (shown above). This is the wadi that drains the makhtesh through its single opening in the northeast. It is the greenest zone in the structure because it has the most soil moisture. There were some beautiful flowers along its banks, photos of which I’ll post later. From the wadi we climb up to the old British road and continue south into the Matmor Hills.

Melissa is standing above at the base of Subunit 51 of the Matmor Formation (Middle Jurassic). This is typical of its exposure in the central part of the makhtesh where there is higher relief in the Matmor Hills. The unit is difficult to follow because of an abundance of small faults cutting perpendicular to strike. Its marly nature means it is often covered with debris from the units above. The northern outcrops have lower relief, which in our case means we have more gentle slopes to search for fossils.

Around noon we ran into a camel herd wandering around our outcrops. (The most active of the beasts is shown above.) They had calves with them and were immediately disturbed by our appearance. They started to make angry camel noises. We did not want a run in with riled-up camels, nor did we want to give their Bedouin herdsmen any reason to think we were harassing them. Since the camels weren’t going anywhere, we reluctantly turned around and headed back.

To aid our decision to retreat, the skies looked very threatening (see above). Rain? Who would have thought? We could smell rain and see what looked like rain to the northeast. We did not want to be in a big rock bowl if it really did pour, so we hastened back to the car. It didn’t actually rain on us, but it may have in the makhtesh after we left.

We got a minimum amount of work done today, though, so it was not a loss. Now we’re back in our warm rooms listening to the wind continue to howl outside.

Wooster Geologists in Paleontological Heaven

March 14th, 2012

MITZPE RAMON, ISRAEL–The above is an untouched view of an eroding marl of the Matmor Formation (Middle Jurassic) in Makhtesh Gadol. I simply placed a one shekel coin in the scene for scale. This is why we love this place — the fossils are just rolling out of the outcrops (once you know where to look). Our ultimate goal is to describe the communities in this particular unit, and you can see that we have rich material to work with. You can try to identify the fossils you see here. I’ll give the answers below!

Melissa walking across the northern end of Makhtesh Gadol through the middle part of the Matmor Formation. You can see in the distance that dust (and the wind that brought it) is still an issue.

Ready for the answers to the fossil quiz above? 1 = scleractinian coral; 2 = Apiocrinites (crinoid) calyx base; 3 = Apiocrinites calyx plate; 4 = terebratulid brachiopod; 5 = Apiocrinites stem fragment; 6 = echinoid spine; 7 = oyster; 8 = Apiocrinites calyx plate; 9 = another kind of oyster.

In a close-up yet another type of brachiopod is visible. The red circle shows a thecideide brachiopod (no doubt Moorellina negevensis) attached to a crinoid column.

Cool, eh? And this is just a taste of what we saw today. Heaven indeed.

Another dusty day of fieldwork in the makhtesh

March 13th, 2012

MITZPE RAMON, ISRAEL–It was a little warmer today in Makhtesh Gadol, but the sun was still obscured by the dust blown across the southern Mediterranean from the Sahara Desert. I may have an innate tolerance for dust from my childhood in the Mojave Desert, but this particular dust triggers a kind of hay fever for me. Maybe it is because Saharan dust is rumored to have a significant fraction of insect parts!

The top image is from the Mt. Avnon overview of Makhtesh Gadol (looking south along the west wall). The road below was built by the British in the early 1940s in an attempt to find and exploit oil from the makhtesh structure. The road is very well built and has survived with relatively little repair beyond paving it. It is astonishingly narrow, though, especially when you meet large mining trucks and tour buses on it. The trip down the most challenging portion was immortalized in a 2011 movie by filmaker Will Cary. Note the blue skies that summer.

Melissa and I located a series of outcrops in the Matmor Formation (Middle Jurassic) exposing “subunit 51″, which has a diverse crinoid-brachiopod community preserved in it. This assemblage has a very patchy distribution, so we want to see as many exposures of it we can to make certain we’ve collected a representaive fossil fauna. Ordinarily our outcrops of this marly subunit look like the one above. The yellow-brown color is distinctive, so it is relatively easy to find throughout the area. There is no hope, though, of seeing sedimentary and paleontological structures in such a loose sediment — it simply erodes too quickly.

We found one site, though, where subunit 51 is preserved in a cliff (above), which prevented it from disintegrating in the usual manner. From Melissa’s hat on down is the top portion of this critical marl. We could see no structures in the featureless marl itself, but on the base of the limestone above there are infillings of a trace fossil known as Thalassinoides. These were probably created by burrowing crustaceans (likely shrimp) that dug down into the very top of our subunit 51 mud.

Our favorite fossil find of the day is this little rhynchonellid brachiopod shown below (likely Burmirhynchia) with a round hole in its dorsal valve. It is tempting to say this is a predatory borehole — the work of a carnivore of some kind — but we can’t tell for certain. It is not beveled on its periphery, so we can’t distinguish it from just a hole punched after death through the vicissitudes of burial, preservation or exposure. Still, it is fun to think of it as a fossil predatory interaction.


A dusty but successful start on field work in southern Israel

March 12th, 2012

MITZPE RAMON, ISRAEL–Melissa Torma, our friend Yoav Avni (Geological Survey of Israel), and I just ended a productive first day in the field. The two of them are shown above in classic paleontological poses. They are collecting fossils from Subunit 51 of the Matmor Formation (Middle Jurassic) in Hamakhtesh Hagadol in the northern Negev. We found excellent crinoid stems and calyx plates, brachiopods, corals, sponges, echinoid spines, serpulid worms, clams, and oysters.The day was very windy but seasonably cool.

You might be wondering why the sky in the above photograph is not the usual bright blue for this region? It is because the air is filled with dust blown off the Sahara Desert to the eastern Mediterranean countries (see NASA image below from 2011). This is a common occurrence here in the spring when a storm system is on its way. In the course of a year, every square kilometer in Israel receives 30-60 tons of this dust. The storm will bring rain to northern Israel tomorrow and Wednesday, but it is very unlikely to break the drought here in the southern dessert.

Shown below is a curious fossil Yoav found at our new site in the Matmor Formation we’ve called (creatively) “halfway”. It is a crinoid stem with a pair of skeletal galls, each with several holes. It appears some organisms infected the living crinoid, which then responded by growing skeletal tissue around the offending critters. Eventually the walled-in organisms drilled their way out, leaving the holes. This is what it looks like, anyway. Feel free to speculate!

I’ve placed a slightly different view of the fossil below to show that these are not encrusters but rather echinoderm skeletal material.

We had a great day despite the pervasive dust and wind gusts. It feels so good to get back to a desert again.

Wooster Geologists in southern Israel for Spring Break fieldwork

March 11th, 2012

It’s a low-light, iPad photo, but at least it shows Wooster geology junior Melissa Torma enjoying a fine meal in the Hotel Ramon of Mitzpe Ramon, deep in the Negev of Israel. We arrived here this afternoon after a 22-hour journey from Ohio. The hardest part for me was enduring the 10.5-hour flight and then making a quick transition to driving through heavy Tel Aviv traffic on our southern journey. It all went well, though, and we are safely in our rooms getting ready for our first day of fieldwork tomorrow.

Melissa and I are here to measure sections and collect specimens for her Senior Independent Study project involving the description and paleoecological analysis of a Jurassic brachiopod-crinoid community in the Matmor Formation of Hamakhtesh Hagadol. I’ve collected these crinoids before here, and now Bill Ausich of Ohio State University and I are describing them as a new species of Apiocrinites. Melissa and I want to find more specimens (we hope more complete specimens) of this crinoid and place them in the context of the entire marine community they inhabited. Our partner in this effort is again our friend Yoav Avni of the Geological Survey of Israel.

When we left the USA yesterday there was a series of violent actions between terrorists in Gaza and the Israel Defense Forces. You may hear about rockets from Gaza striking southern Israel, but they are far from us. We see no evidence of the fighting here. We are very safe in the vastness of the Negev Highlands.

Wooster’s Fossil of the Week: An ichthyosaur vertebra (Middle-Late Jurassic of Wyoming)

March 11th, 2012

It’s only half a bone, but the above is one of my favorite fossils. This is a vertebra of an ichthyosaur, identifiable by its figure-8 cross-section. It is from the Sundance Formation (Middle-Late Jurassic) of Natrona County, Wyoming … and is the first ichthyosaur bone I found. There is not a lot to go on with a single bone fragment like this, but luckily for me only one ichthyosaur has been found in the Sundance: Ophthalmosaurus natans (Marsh, 1879). (“Ophthalmosaurus” is sometimes spelled “Opthalmosaurus” in the literature, and the inconsistency maddens me.)

Finding the ichthyosaur bones on June 23, 2008. Image courtesy of my friend Paul D. Taylor at the Natural History Museum.
Ophthalmosaurus reconstruction (along with some nice ammonites) from Wikipedia. Image Creator: Dmitry Bogdanov.

Ichthyosaurs were magnificent animals that were contemporaries of the dinosaurs. Ichthyosaur means “fish-lizard”, but they were neither fish nor lizards but a unique type of marine reptile. Their streamlined bodies are excellent examples of convergent evolution with the unrelated dolphins and sharks.

Ophthalmosaurus is best known for its very large eyes, up to 10 cm in diameter, with protective bones called sclerotic rings. They probably used these eyes to see in deep, murky waters, or they hunted prey at night.
This view of vertebrae cut in half is from the first paper to describe ichthyosaurs: Home (1814). You can see the distinctive figure-8 shape, known professionally as “cupped vertebrae”. The ichthyosaur specimen Home presented was found by the famous Mary Anning and her brother Joseph. Home thought the animal was some kind of odd fish. Home and the Annings had much more than just these vertebrae, but I like the symmetry of their big discovery and my little one.
Sir Everard Home, 1st Baronet FRS, 1756-1832, was a British physician fascinated by anatomy. Besides the ichthyosaur, he is also known for the earliest anatomical work on the platypus.


Home, E. 1814. Some account of the fossil remains of an animal more nearly allied to fishes than any of the other classes of animals. Philosophical Transactions of the Royal Society of London 104: 571–577.

Huene, F. von. 1922. Die Ichthyosaurier des Lias und ihre Zusammenhage: Berlin (Gebr. Bonrntraeger), 114pp.

Maisch, M.W. 2010. Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity 3: 151–214.

Marsh, O.C. 1879. A new order of extinct reptiles (Sauranodontia), from the Jurassic Formation of the Rocky Mountains. American Journal of Science, 3rd series, 17: 85-86.

O’Keefe, F.R., Street, H.P., Cavigelli, J.P., Socha, J.J. and O’Keefe, R.D. 2009. A plesiosaur containing an ichthyosaur embryo as stomach contents from the Sundance Formation of the Bighorn Basin, Wyoming. Journal of Vertebrate Paleontology 29: 1306–1310.

Wooster’s Fossils of the Week: Belemnites (Jurassic of Wyoming)

November 20th, 2011

This week’s fossils are among the most recognizable. They certainly are popular in my paleontology courses because no one has ever misidentified one. Belemnites (from the Greek belemnon, meaning javelin or dart) were squid-like cephalopods that lived in the Jurassic and Cretaceous Periods. You would never guess their original appearance from the fossils above. These are guards or rostra, internal hard parts that look nothing like the external animal. They are often found in large accumulations called “belemnite battlefields” (Doyle and MacDonald, 1993).
The above image shows a remarkable fossil belemnite in the State Museum of Natural History, Stuttgart, Germany (courtesy of User Rai’ke on Wikimedia). It shows their squidy form and ten equal-sized arms studded with little hooks for holding prey. They probably ate small fish and invertebrates.
The guard or rostrum is solid calcite at its distal end with a phragmocone (chambered shell) at the other. This phragmocone is only rarely preserved. The rostrum above is from the Zohar Formation (Jurassic) of the Golan in northern Israel near Neve Atif.

Belemnites have played an important role recently in sorting out Mesozoic climate change. Their solid calcitic rostra are ideal for examining stable isotopes that fluctuated with water temperature. Dera et al. (2011) showed that the Jurassic had significant climate variations based on the isotopes in belemnite fossils.

Belemnites have a long history in folklore. The English called them “thunderbolts” because they thought they were formed by lightning strikes. The Scottish knew them as “botstones” that cured horses of various ailments. The Swedish thought they were “gnome candles”. The Chinese called them “sword stones”. Much more prosaically, the belemnite is the state fossil of Delaware.
An engraving of belemnite rostra by Captain Thomas Brown (1889).


Brown, Captain T. 1889. An atlas of fossil conchology of Great Britain and Ireland. With descriptions of all the species. Swan Sonnenschein & Co.

Dera, G., Brigaud, B., Monna, F., Laffont, R., Pucéat, E., Deconinck, J-F., Pellenard, P., Joachimski, M.M., and Durlet, C. 2011. Climatic ups and downs in a disturbed Jurassic world. Geology 39: 215–218.

Doyle, P. and MacDonald, D.I.M. 1993. Belemnite battlefields. Lethaia 26: 65-80.

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