Wooster’s Fossil of the Week: An almost planispiral gastropod from the Middle Jurassic of southern Israel

August 11th, 2013


Discohelix tunisiensis apical copyAdd this to the list of fossils that have confused me. This summer, during a Wooster expedition, Lizzie Reinthal and Steph Bosch collected the above specimen from the Matmor Formation (Middle Jurassic, Callovian) of southern Israel. I simply assumed it was an ammonite, especially because we were anxious to find ammonites to further reinforce our biostratigraphic framework (how we tell in which geological time interval our fossils belong). When I later tried to identify it by searching through the Jurassic ammonite literature, though, I could find nothing like it. I then sent a photograph to my friend Zeev Lewy, a prominent ammonite expert recently retired from the Geological Survey of Israel. His answer was a surprise: this fossil is the gastropod Discohelix tunisiensis Cox 1969.
Discohelix tunisiensis adapicalHow could this be a snail when it looks so much like a cool, multi-whorled planispiral ammonite, complete with ribs? Well, it is not planispiral, now that I look at it again. Above you see the other side of the specimen, with its slightly depressed center. Most ammonites don’t show such asymmetry. This actually is a gastropod, and it represents an ancient group (the clade Vetigastropoda — don’t get me started on the complications of gastropod systematics!) with primitive features reminiscent of Paleozoic marine snails (from a group I learned to call “archaeogastropods“). It is not as much that the snail has converged on an ammonite style of shell, it’s that the ammonites developed a similar shell much later for entirely different reasons (swimming, for example). Discohelix was likely an herbivore grazing in patchy coral reefs like we have represented in the Matmor Formation. It has become a useful index fossil for the Jurassic of the Tethyan Realm, although this is the first time I’ve found it in Israel.
Pseudotorinia (Architae-group) retiferaThe above is the marine snail Pseudotorinia (Architae-group) retifera. It used to be called Discohelix retifera, and you can see why. It may not be in the same genus, but you can see that this modern group and Discohelix are closely related. Discohelix itself is now known only from the fossil record.
DunkerDiscohelix was named as a genus in 1847 by Wilhelm Bernhard Rudolph Hadrian Dunker (1809-1885), a German natural scientist with interests in geology, paleontology and marine zoology. (I love that middle name of “Hadrian”.) Like so many 19th Century paleontologists, Dunker started with a practical training in mining engineering and then followed a passion for fossils and modern shells. He had a huge collection of materials that eventually ended up in the Museum für Naturkunde in Berlin. He traded and corresponded with many top scientists of his day, including Charles Darwin. He also published many monographs on modern and fossil molluscan taxa. In 1846, he and Hermann von Meyer established the journal Palaeontographica. This journal survives to this day in two descendants: Palaeontographica A (Paleozoology, Stratigraphy) and Palaeontographica B (Paleobotany).


Cox, L.R. 1969. Gasteropodes Jurassiques du Sud-Est Tunisien [Jurassic gastropods from SE Tunisia]. Annales de Paleontologie, Invertebres 55: 241-268.

Grundel, J. 2005. The genus Discohelix Dunker, 1847 (Gastropoda) and on the content of the Discohelicidae Schroder, 1995. Neues Jahrbuch fur Geologie und Palaontologie-Monatshefte 12: 729-748.

Tëmkin, I., Glaubrecht, M. and Köhler, F. 2009. Wilhelm Dunker, his collection, and pteriid systematics. Malacologia 51: 39-79.

Wendt, J.1968. Discohelix (Archaeogastropoda, Euomphalacea) as an index fossil in the Tethyan Jurassic. Palaeontology 11: 554-575.

Wooster’s Fossil of the Week: An irregular echinoid from the Middle Jurassic of southern Israel

August 4th, 2013

Holectypus depressus adoral 585From the view above, this fossil from the Matmor Formation (Middle Jurassic, Callovian) of southern Israel looks like your standard echinoid (a group that contains sea urchins and sand dollars), but turn it on its side (see below) and you see it is unusual. Echinoids have two large categories: those that are globular in shape (like sea urchins) are called “regular“, and those that are flattened (like sand dollars) are “irregular“. (I know, oddly value-laden terms, these.) This specimen belongs to a group that is rounded on its top portion and flattened on its bottom (oral) surface. This between-ness makes it a fun little specimen.
Holectypus depressus Side 585I could not identify this echinoid, which we collected on our Israel expedition this summer, because I could not find the most important diagnostic features. Fortunately my colleague Andrew Smith, recently retired from the Natural History Museum in London, quickly knew what it was. (This is not surprising — he’s the world’s expert on fossil echinoids. Check out his incredible Echinoid Directory.) Andrew identified this specimen as belonging to the genus Holectypus Desor, 1842, and probably the species Holectypus depressus (Leske, 1778).
Holectypus depressus apical system 585The first feature Andrew noticed was the apical disk on the very top of the test (the term for an echinoid skeleton). In the above image (where the black scale bar = 200 microns) I’ve labelled the four gonopores (where gametes exit, as you might have guessed) and the madreporite (a sieve plate at the opening of the water vascular system). This arrangement is characteristic of the genus.
Holectypus depressus oral 585Most surprising to me was Andrew’s identification of the most obvious defining feature of Holectypus, the periproct (the anal opening). I couldn’t find it, but Andrew knew where to look. In this view of the oral surface, it is the gap labeled “P”. Looks just like a place where the test is broken, right?
Callovian France HolectypusHere is the oral surface of an unbroken Holectypus specimen from the Callovian of France. The large periproct is immediately visible as the whole at the bottom. Now the broken margin of the periproct on our specimen makes sense.

Holectypus belongs to a group of irregular echinoids still around today. They are sometimes characterized as having “conservative” evolution, meaning they have not changed much over long periods. The irregular echinoids appeared earlier in the Jurassic as a modification of their regular ancestors. They became flattened and bilateral, the periproct moved out of the apical disk, their ambulacra (rows of tube feet visible as tiny holes radiating from the apical disk on the top image) pulled up away from the mouth, and their spines were reduced in size and increased in number. These were primarily adaptations for burrowing into the sediment. Holectypus has retained its inflated upper portion, has relatively large spines (some still cling to our specimen), and still is circular in outline. It was a deposit feeder but not specialized for burrowing.

We wouldn’t want to call this a “transitional fossil”, but it is a nice example of the gradient of adaptations present when there is a major outbreak of innovation as during the rise of the irregular echinoids in the Jurassic.


Kroh, A. and Smith, A.B. 2010. The phylogeny and classification of post-Palaeozoic echinoids. Journal of Systematic Palaeontology 8: 147-212.

Rose, E.P.F. and Olver, J.B.S. 1985. Slow evolution in the Holectypidae, a family of primitive irregular echinoids, p. 81-89. In: Keegan, B.F. and O’Connor, B.D.S. (eds.), Proceedings of the Fifth International Echinoderm Conference, Galway, 24-29 September, 1984.

Saucède, T., Mooi, R. and David, B. 2007. Phylogeny and origin of Jurassic irregular echinoids (Echinodermata: Echinoidea). Geological Magazine 144: 333-359.

Wooster’s Fossil of the Week: An infected crinoid from the Middle Jurassic of southern Israel

July 28th, 2013

CrinoidGalls03 copyThis weathered beauty is a stem fragment of the articulate crinoid Apiocrinites negevensis from the Matmor Formation (Middle Jurassic, Callovian) of the Negev, southern Israel. The regular divisions you see making up the stem are the columnals, which look a bit like a stack of poker chips. You can even make out the crenulations on the articulating faces of the columnals, seen as tiny zig-zags. What is unusual about this stem, of course, are the large swellings with multiple holes. These appear to be something like the galls you sometimes see in plant stems formed when a parasite is surrounded by living plant tissue.
CrinoidGalls02 copySenior Independent Studies student Lizzie Reinthal (’14) is working on these odd structures (we have dozens of examples) as part of her investigation of the taphonomy of A. negevensis in the Matmor Formation. We know that the swellings were made by the interaction of some sort of organism with the living crinoid, but we don’t yet know the timing or mechanism. It could be that the holes were drilled first into the stem and the crinoid grew the extra skeletal tissue to essentially push them away, or the swellings could have been the equivalent of galls and some sort of enclosed animal bored its way out of the structure. (And an extra point to those of you who spotted the barnacle boring! Note that it has no swelling around it and thus was likely drilled after the death of the crinoid.)

These infected crinoid stems were first described from the Matmor by Feldman and Brett (1998). They suggested they were from parasitic myzostome worms, which are usually found on crinoid arms and have a long fossil record (see Meyer and Ausich, 1983, and Hess, 2010). They could also be from some sort of embedded organism like that represented by Phosphannulus on Paleozoic crinoid stems (Welch, 1976).

Lizzie will be pursuing the mystery by careful sectioning some of these swellings and seeing if she can relate the crinoid skeletal growth patterns to either a borer or an embedded parasite. Unfortunately that means we must destroy some specimens to better understand the phenomenon, a classic dilemma paleontologists sometimes face.


Feldman, H.R. and Brett, C.E. 1998. Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution. Lethaia 31: 57–71.

Hess, H. 2010. Myzostome deformation on arms of the Early Jurassic crinoid Balanocrinus gracilis (Charlesworth). Journal of Paleontology 84: 1031-1034.

Meyer, D.L. and Ausich, W.I. 1983. Biotic interactions among recent and fossil crinoids, p. 377–427. In: Tevesz, M.J.S. and McCall, P.L., eds., Biotic interactions in recent and fossil benthic communities. Plenum Press, New York.

Welch, J.R. 1976. Phosphannulus on Paleozoic crinoid stems. Journal of Paleontology 50: 218-225.

An ancient Nabatean, Roman and Byzantine city in the northern Negev

July 12th, 2013

MamshitGuardhouseMansion071213MITZPE RAMON, ISRAEL–Our final stop of the final day: Mamshit. Above you see some of the ruins of this city east of Dimona and a short distance west of the descent into the Dead Sea Rift Valley. The highest structure is the “guardhouse” (which overlooked a reservoir) and the lower on the right is known as “the wealthy house”. All the other rocks you see are remnants of mostly homes and other dwellings.

Mamshit was established by the Nabateans as a station along the Incense Route around 50 CE. Most of the primary buildings were constructed in the Second Century after the Nabatean Kingdom became part of the Roman Empire. As a trading city it flourished until the Seventh Century when either the Persian (614 CE) or the Arab Invasion (636 CE) ended its importance and it faded away. Today we toured it for about an hour and we were the only people there.

MamshitDam071213From the Guardhouse one of the three Mamshit dams comes into view. These were the most critical structures in the settlement because they captured the winter runoff in reservoirs that could be used throughout the dry summers. The area behind this dam is now completely silted up. There was a British police post at this site in the 1930s and 1940s running a series of patrols on camels. The Brits rebuilt the dam for their own use.

MamshitWesternChurch071213This is a lavish church (the “western church” or “Church of St. Nilus”) in Mamshit. Beautiful mosaics are still preserved on the floors.

MamshitStudentsExploring071213The Wooster students are her exploring one of the grander houses built in the Second Century.

MamshitDoorways071213Steph and Lizzie are using the doorways to estimate the likely heights of the residents. Looks like they were more Lizzie size than Steph!

This was a suitable place to end the Team Israel 2013 expedition: a location where geology, archaeology, history and culture are combined in ruins still open for interpretation and study. Now we have one more night before departing early in the morning for the airport in Tel Aviv. We appreciate this opportunity for travel and research very much!

Wooster Geologists in the Dead Sea

July 12th, 2013

LizzieStephDeadSea071213MITZPE RAMON, ISRAEL–The Wooster Geologists in Israel spent their last full day in the country visiting the Dead Sea Rift Valley and an archaeological site. It feels very good to have packed our hiking boots away for the season. Above, of course, is Lizzie Reinthal and Steph Bosch floating in the hypersaline waters of the Dead Sea at an almost deserted Ein Gedi beach. The surface of the water here is at -427 meters, or about 1400 feet below sealevel, making it the lowest point on land. The water Lizzie and Steph are floating in is 8.6 times saltier than typical seawater. This means I don’t have to worry about anyone drowning here. (Swallowing the water and getting it in eyes and ears is another story!)

OscarDeadSea071213Oscar Mmari was there as well. His style was a bit more relaxed. He was no doubt pondering that the amount of bromine in these waters (at 4.2 g/kg) is the highest anywhere on Earth.

SodomSaltStudents071213On the way to Ein Gedi we stopped by the famous Mount Sodom — a mountain of salt. This is a famous salt diapir, or a salt dome that has reached the surface. The layers of salt here are vertical because of deformation caused by the upward movement of the material. The salt, mostly halite, moves up because it is less dense and more plastic than the overlying sediments.

SodomSalt071213This is a close view of the salt layers. It is very difficult to distinguish original sedimentary layers from planes developed by shear stress.

LotWifeSodomSalt071213The spot we briefly explored is underneath a jointed block of salt referred to as “Lot’s Wife”. Remember her? In Genesis she looked back at the destruction of Sodom and was turned into a pillar of salt. If this is her she was about 60 feet tall.


Last day of fieldwork for Team Israel 2013

July 11th, 2013

1_DragFoldOscar071113MITZPE RAMON, ISRAEL–We like to think that Dr. Shelley Judge would be proud of our fieldwork today. The Wooster Geologists returned to Wadi Hawarim to finish our fieldwork for Oscar Mmari’s project on synsedimentary faulting in the Mishash Formation (Campanian, Upper Cretaceous). We returned to the fault visible above just to the left of the dark outcrop of the lower Mishash. The left side is upthrown, the right downthrown, making this a very steep normal fault. the Mishash seen here is in a magnificent drag fold against the fault. The Mishash is eroded away on the upthrown block, so we could only climb to the top of the hill here and estimate the minimum displacement on the fault. The blocks are separated by at least 50 meters. The fault trace is almost exactly east-west. You can barely see Oscar in the lower right standing on the spot where the Mishash rocks fold more than 90° to become horizontal to the right. Oscar and I worked today to follow the fate of a conglomerate that is thickest at the fault where Oscar is standing (location 031 on the image at the end of this post), and then thins and becomes finer as we move away from the fault into the syncline to the south. We believe this indicates that the conglomerate came from the upthrown block and thus the fault formed while the Mishash was being deposited. (Lizzie Reinthal and Steph Bosch, in the meantime, collected more shark’s teeth for us and then explored the wadi system.)

2_HawarimPhosphorites071113This is the Mishash Formation phosphorite zone several hundred meters south of the fault (location 049 in the bottom image). It is much thicker than the section near the fault (see the top photo in this entry).

3_ThinConglomerates071113The conglomerate that is a meter thick near the fault is reduced to these two lensoidal coarse sandstones that Oscar found in this southernmost outcrop. The grain size and thickness reduces dramatically as we move away from the fault.

4_WadiHawarimSection071113This beautiful Wadi Hawarim section of the phosphorites gave us our final clues as to the relationship between the fault and the conglomerate. We also have a sealevel story here with shrimp burrows, but we’ll save that for a later post after Oscar has done some lab work.

5_Hawarim071113Here is a Google Earth view of Oscar’s collecting sites and measured sections. The fault shown in the top photo is at 031, with the photo taken from 047. The fault runs east-west, and Oscar’s sites are all to the south.


Meeting a group of excellent young Israeli geologists

July 11th, 2013

OlympiadStudents071113MITZPE RAMON, ISRAEL–Today I had the pleasure of talking with four excellent Israeli students who form their nation’s team in the upcoming 7th International Earth Science Olympiad. Their advisor and coach, Hanan Ginat (on the far right), invited me to speak to these young adults about paleontology as they study for the competition to be held in India this September. I was amazed at how hard these students are working for this event, and how much will be required of them during the Olympiad. They will have ten days of tests and practical exercises. In past events these contests have included interpreting core samples, assessing building stones, and even planning dam sites. In the written tests there are questions not only about geology and paleontology, but also oceanography, atmospheric sciences, and astronomy. Wow. Most of it in English, too.

The students had excellent questions and quickly responded to puzzles about various fossil specimens you can see scattered on the table above. It was so much fun — the time just flew by. Good luck to them in the tournament and in their future endeavors. These are very bright students who know the value of learning and persistence.

Wooster Geologists in Jerusalem

July 10th, 2013

1_JerusalemWalls071013MITZPE RAMON, ISRAEL–This is the beautiful 400-year-old Turkish wall surrounding Jerusalem. It and virtually all the buildings in Jerusalem is made of “Jerusalem Stone” (a set of Cretaceous micritic limestones, to be pedantic). When the sun rises or sets on them they turn the city into the fabled “Jerusalem of Gold”.

Team Israel 2013 made the long drive up to Jerusalem with our colleague Yoav Avni to meet with geologists at the Geological Survey of Israel, and then visit Hebrew University and the National Natural History Collections. Of course, I also gave the students a tour of the Old City with its incredible history and multi-dimensional culture.

2_YoavOffice071013Had to show an image of Yoav in his office. Typical geologist’s office, I’d say. The Geological Survey of Israel is housed in a century-old complex built as a school by Germans and then occupied by the British Army from 1918 to 1948. It is incredibly cramped so they are moving to new facilities in a few years.

3_FossilSnake071013We saw many, many fossils and modern bones at the National Natural History Museum collections on the campus of Hebrew University. The staff was very generous with their time, and their enthusiasm was inspiring. Our token image: a Cretaceous snake with tiny legs just barely visible.

4_StudentsChurchSepulchre071013Our journey through the Old City was so much fun, even though we had to move relatively quickly. We walked here from the Survey buildings through diverse neighborhoods and then down the newly-renovated Jaffa Street. Here you might be able to make out the three Wooster students in front of the Church of the Holy Sepulchre.

5_WesternWall071013We also went to the Western Wall of the Temple Mount complex, a treasured site in Judaism.

6_Dome071013We couldn’t visit the Temple Mount because it was closed, but we did get this excellent view of the Dome of the Rock, an iconic Islamic shrine.

7_ZionGate071013This is the outside of Zion Gate in the Jerusalem Old City walls. The innumerable bullet holes are a reminder of the violence this city has seen over the centuries. Most of these are from the War of Independence (1948-1949) and the Six-Day War (1967).

8_GroupGSI071013Finally, here is our last group photo: Steph Bosch, Lizzie Reinthal, Oscar Mmari, me, and Yoav Avni. Yoav is leaving for Jordan tomorrow so this is the last day he is with us. The photo was taken by my long-time friend, Israeli geologist Amihai Sneh.

What a day in such a place.

Return to the Ora Formation

July 9th, 2013

8_MudVolcano070913MITZPE RAMON, ISRAEL–The last location Wooster Geologists in Israel visited today was on the southern edge of the Makhtesh Ramon structure (N 30.58209°, E 34.89375°). Here are excellent exposures of the Ora Formation (Upper Cretaceous, Turonian). This curious feature was a challenge to the students to interpret. I also got it wrong in my explanation on the outcrop, so listen up Steph, Lizzie and Oscar! The students are standing in a portion of the outcrop that is mud with suspended blocks of limestone. This is a cross-section of a diapir, or body of sediment that has moved upwards through the rocks that cap it. This was caused by water-saturated sediment being compressed by the sediments above, forcing it upwards through cracks and crevices. What I got wrong was that the flat strata on top of the mud was present when the diapir formed. (I said it came later.) The mud never reached the surface to become a mud volcano. This is why the resistant beds below are bent downwards — the upward force of the mud flow was stopped by the capping rock, thus deflecting the edges of the units below. A complicated story — which is one of the many things that makes the Ora Formation interesting.

9_Oysters070913Also in the Ora Formation at this same site is a half-meter-thick unit composed entirely of oyster shells. Many of the oysters are encrusted with other oysters and, who knows, maybe bryozoans as well. (And no, Paul Taylor, I didn’t see any here yet!)

10_Hardground070913The Ora Formation also has a fabulous carbonate hardground, which was a cemented seafloor surface. We can tell this particular surface was hard rock on the Cretaceous seafloor because of all those little holes. These are the borings of bivalves known as Gastrochaenolites. They could only be made by grinding away at a cemented substrate.

Hardgrounds, oysters, odd diapirs … opportunities for future study! Israeli geologists have done fantastic work with this unit, so there are many collaborations possible here.

Adventures in the Triassic: Exploring the Gevanim Valley in Makhtesh Ramon, southern Israel

July 9th, 2013

2_NordmarkiteStock070913MITZPE RAMON, ISRAEL–The second visit of the day for Wooster’s Team Israel 2013 was to the Gevanim Valley on the south side of the Makhtesh Ramon structure. This is a fascinating place where Cretaceous intrusions formed an uplifted dome exposing Triassic sedimentary rocks. It is a rare place to see abundant Triassic marine fossils. Our first stop was a nordmarkite stock intruded into the Gevanim Formation (Middle Triassic, Anisian). We always dedicate this image to our own Dr. Meagen Pollock who knows what nordmarkite is without having to google it.

3_GevanimRamonalinidSite070913Our first task was to locate the Gevanim Formation and examine the many specimens of the large bivalve Ramonalina ramanensis to look for rare Triassic encrusters. Above is an outcrop of the part of the Gevanim which has large numbers of this dark-colored, shoe-shaped clam.

4_Ramonalina070913Here are two nearly complete specimens of Ramonalina ramanensis. Alas, we found not a single encruster. The rumor that there are microconchids on these shells seems to be false. Science marches on.

5_LizzieSaharonim070913Above the Gevanim Formation is the Saharonim Formation (Middle Triassic, Anisian-Ladinian). Lizzie Reinthal is here standing near the base of it exposed in the western part of the Gevanim Valley. This is a very fossiliferous limestone and marl that is extremely well exposed here.

6_CephalopodsSaharonim070913Nautiloids and ammonoids are very abundant in the Saharonim. In fact, just about every large object in this exposure of the unit is one or the other. The coin in the image above is sitting on an ammonoid (a ceratite). The other fossils are internal molds of nautiloids.

7_SaharonimBrachiopods070913Our goal today, though, was to find terebratulid bachiopods with original calcite still preserved. We found dozens, a few of which are shown above. These are mostly of the genus Coenothyris. These specimens are destined for isotopic analysis in the laboratory of Dr. Pedro Marenco at Bryn Mawr College. Mission accomplished.

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