Wooster’s Fossil of the Week: A phyllocarid crustacean from the Middle Cambrian Burgess Shale of British Columbia, Canada

May 20th, 2016

Canadaspis perfecta Burgess Shale 585We are fortunate at Wooster to have a few fossils from the Burgess Shale (Middle Cambrian) collected near Burgess Pass, British Columbia, Canada, including this delicate phyllocarid Canadaspis perfecta (Walcott, 1912). This species is one of the oldest crustaceans, a group that includes barnacles, crabs, lobsters and shrimp. Please note from the start that I did NOT collect it. The Burgess Shale is a UNESCO World Heritage Site, so collecting there is restricted to a very small group of paleontologists who have gone through probably the most strict permitting system anywhere. I had a wonderful visit to the Burgess Shale with my friend Matthew James in 2009, and we followed all the rules. (The photo below is of the Walcott Quarry outcrop.) Our Wooster specimen was in our teaching collection when I arrived. I suspect it was collected in the 1920s or 1930s and probably purchased from a scientific supply house.

walcottquarryMarrellaSuch a dramatic setting, which is perfect for the incredible fossils that have come from this site.

Canadaspis perfecta drawing

Canadaspis perfecta has been thoroughly studied by Derek Briggs, the most prominent of the paleontologists who have studied the Burgess Shale fauna. The above reconstruction of C. perfecta is from his classic 1978 monograph on the species. He had spectacular material to work with, including specimens with limbs and antennae well represented. Our specimen is a bit shabby in comparison! Nevertheless, we can still make out abdominal segments and a bit of the head shield.

Briggs (1978, p. 440) concluded that C. perfecta likely “fed on coarse particles, possibly with the aid of currents set up by the biramous appendages”. This is a similar feeding mode to many of the trilobites who lived alongside.

References:

Briggs, D.E. 1978. The morphology, mode of life, and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 281: 439-487.

Briggs, D.E. 1992. Phylogenetic significance of the Burgess Shale crustacean Canadaspis. Acta Zoologica 73: 293-300.

Wooster’s Fossil of the Week: A Recent Sponge Boring from South Carolina

May 13th, 2016

1 Coral on bored bivalveWe’re not actually looking at fossils here, but this bivalve-coral-sponge assemblage from the very modern Myrtle Beach in South Carolina is to cool not to share. Jacob Nowell (Wooster ’18) picked it up while on Spring Break this year and donated it to the collections. This is a bit of very worn bivalve shell punctured by clionaid sponge borings and encrusted by a columnar scleractinian coral.

2 Bored bivalve hingeHow do we know the shell remnant is from a bivalve? This is what’s left of the hinge region, the thickest part of the shell. We can tell this is a heterodont bivalve, probably of the common genus Mercenaria. The shell material is calcite.

3 Coral over EntobiaThe coral is aragonitic and exquisitely preserved. It did not make the long tumbling journey the bivalve shell did. At its encrusting base you can see that it partially covers some of the sponge borings, showing that it attached after the sponge was at least partly gone. The round structures on the coral are the corallites, each of which housed a coral polyp. The corallites have radiating vertical septa inside in the classic scleractinian manner.

4 Entobia gallery 041316 585The sponge boring is the star here. This is a side view showing the interconnected galleries and tunnels excavated by a clionaid sponge like Cliona. As a trace fossil this structure would be known as Entobia. It is very common in the fossil record, especially in the Cretaceous and later.

Bronn 041616Entobia was named and described by Heinrich Georg Bronn (1800-1862), a German geologist and paleontologist. He had a doctoral degree from the University of Heidelberg, where he then taught as a professor of natural history until his death. He was a visionary scientist who had some interesting pre-Darwinian ideas about life’s history. He didn’t fully accept “Darwinism” at the end of his life, but he made the first translation of On The Origin of Species into German.

References:

Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.

Bronn, H.G. 1834-1838. Letkaea Geognostica (2 vols., Stuttgart).

Tapanila, L. 2006. Devonian Entobia borings from Nevada, with a revision of Topsentopsis. Journal of Paleontology 80: 760–767.

Taylor, P.D. and Wilson, M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.

Wilson, M.A. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.

 

Wooster’s Fossil of the Week: A craniid brachiopod from the Upper Cretaceous of The Netherlands

May 6th, 2016

1 Isocrania costata Sowerby 1823 double 2 smThese striking little brachiopods are gifts from Clive Champion, a generous Englishman with whom I occasionally exchange packets of fossils. In January I received a surprise box with lots of delicious little brachs, including the two shown above. I remember this type well from a field trip I had to the Upper Cretaceous of The Netherlands.
2 Isocrania costata Sowerby 1823 double 1 smHere we see the reverse sides of the shells at the top. These are most likely dorsal valves of Isocrania costata Sowerby, 1823, from the Lichtenberg Horizon, Upper Maastrichtian (Upper Cretaceous) of the ENCI Quarry near Maastricht, The Netherlands. It is possible they are the closely-related species Isocrania sendeni Simon, 2007, but we don’t have enough material to sort this out.
4 Surlyk 1973 fig 2 copyCraniid brachiopods usually live out their lives attached to hard substrates, as with this Ordovician example. This species of Isocrania, however, was only attached to shelly debris on the seafloor for a short time, outgrowing its substrate early and then living free in the chalky sediment. The above reconstruction image is Figure 2 from Surlyk (1973).

Christian Emig (2009) has a bit of folklore about Isocrania. In medieval Sweden these fossils were called “Brattingsborg pennies” for their size, shape and the face-like image on their interiors. Don’t see the face? Check this out from Emig (2009):
5 Ventral C craniolaris fig 6 SurlykThe “eyes” in this ventral valve are large adductor muscle scars, and the “mouth” and “nose” are a smaller set. Here is one of the “Brattingsborg pennies” legends Emig (2009) relates —

“… at the beginning of the 13th century the archbishop Anders Sunesen spent his last days on the island of Ivö, in his own castle of which the cellar was about 2 km southeast of the castle. In 1221, subjected to the terminal stages of leprosy, he spent his last days on the island. One day he was informed that warriors had stolen a large sum of money from the Brattingsborg castle. They spent that night gambling and carousing in the cellar. The archbishop cursed this money and the following morning the warriors were stunned to find that the coins had turned into stones with a laughing death’s-head on them.”

Thanks for starting us on this trip with your gift, Clive!
3 Isocrania costata Sowerby 1823 sm
References:

Emig, C. 2009. Nummulus brattenburgensis and Crania craniolaris (Brachiopoda, Craniidae). Carnets de Géologie/Notebooks on Geology, Brest, Article, 8.

Hansen, T., and Surlyk, F. 2014. Marine macrofossil communities in the uppermost Maastrichtian chalk of Stevns Klint, Denmark. Palaeogeography, Palaeoclimatology, Palaeoecology 399: 323-344.

Simon, E. 2007. A new Late Maastrichtian species of Isocrania (Brachiopoda, Craniidae) from The Netherlands and Belgium. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 77: 141-157.

Surlyk, F. 1973. Autecology and taxonomy of two Upper Cretaceous craniacean brachiopods. Bulletin of the Geological Society of Denmark 22: 219-242.

Wooster’s Fossil of the Week: A terebratulid brachiopod from the Middle Jurassic of northwestern France

April 29th, 2016

1 Cererithyris arkelli Almeras 1970 dorsal 585We have another beautiful brachiopod this week from our friend Mr. Clive Champion in England. He sent me a surprise package of fossils earlier this year. They are very much appreciated by me and my students!

The specimen above is Cererithyris arkelli Almeras, 1970, from the Bathonian (Middle Jurassic) of Ranville, Calvados, France. (Ranville, by the way, was the first village liberated in France on D-Day.) It is a terebratulid brachiopod, which we have seen before on this blog from the Miocene of Spain and the Triassic of Israel. They have the classic brachiopod form. The image above shows the dorsal valve with the posterior of the ventral valve housing the round hole for the fleshy stalk (pedicle) it had in life.
2 Cererithyris arkelli Almeras 1970 sideThis is a side view of C. arkelli. The dorsal valve is on the top; the ventral valve on the bottom. It is from this perspective that brachiopods were called “lamp shells” because they resemble Roman oil lamps.
3 Cererithyris arkelli Almeras 1970 ventralThis is the ventral view of the specimen. These brachiopods are remarkably smooth.
4 William_Joscelyn_ArkellCererithyris arkelli was named by Almeras (1970) in honor of William Joscelyn Arkell (1904–1958). Arkell was an English geologist who essentially became Dr. Jurassic during the middle part of the 20th Century. I’m shocked to see that with all his publications, awards and accomplishments, he died when he was only 54 years old.

W.J. Arkell grew up in Wiltshire, the seventh child of a wealthy father (a partner in the family-owned Arkell’s Brewery) and artist mother (Laura Jane Arkell). He enjoyed nature as a child, winning essay contests on his observations of natural history in his native county and south on the Dorset coast. Arkell was unusually tall for his age (6 feet 4.5 inches by age 17.5 years in an unusually detailed note) and was considered to have “outgrown his strength”. Nature and writing were escapes from athletic events. He also published poems.

Arkell attended New College, Oxford University, intending to become an entomologist, but Julian Huxley was his tutor and he quickly adopted geology and paleontology. Eventually he earned a PhD at Oxford in 1928, concentrating his research on Corallian (Upper Jurassic) bivalves of England. As a side project, he published work on Paleolithic human skeletons from northern Egypt.

Oxford suited Arkell, so he stayed there as a research fellow, expanding his research to the entire Jurassic System of Great Britain, then Europe, and then the world. His work became the standard for understanding Jurassic geology and paleontology for decades.

After World War II (in which he served in the Ministry of Transport), Arkell took a senior research position at Trinity College and the Sedgwick Museum, Cambridge University, continuing his work on the Jurassic. He travelled often, including long stints in the Middle East. His health was never good, though, and he had a stroke in 1956, and died after a second stroke in 1958.

During his career Arkell received the Mary Clark Thompson Medal from the National Academy of Sciences in the USA, a Fellowship in the Royal Society, the Lyell Medal from the Geological Society of London, and the Leopold von Buch medal from the German Geological Society.

References:

Almeras, Y. 1970. Les Terebratulidae du Dogger dans le Mâconnais, le Mont dʼOr lyonnais et le Jura méridional. Étude systématique et biostratigraphique. Rapports avec la paléoécologie. Documents des Laboratoires de Géologie Lyon, 39, 3 vol.: 1-690.

Arkell, W.J. 1956. Jurassic Geology of the World. New York; Edinburgh: Hafner Publishing Co; Oliver & Boyd; 806 pp.

Cox, L.R. 1958. William Joscelyn Arkell 1904-1958. Biographical Memoirs of Fellows of the Royal Society 4: 1.

Rousselle, L. and Chavanon, S. 1981. Le genre Cererithyris (Brachiopodes, Terebratulidae) dans le Bajocien supérieur et le Bathonien des Hauts-Plateaux du Maroc oriental. CR somm. Soc. Géol France, 1981: 89-92.

Wooster’s Fossil of the Week: A thoroughly encrusted rugose coral from the Upper Ordovician of southeastern Indiana

April 22nd, 2016

1 Rugosan Exterior 123015It doesn’t look like much, this long lump of gray stone. With a close view you might pick up a hint of a bryozoan or two, but mostly we see rather shabby shades of grey. One of the coolest perks of being a geologist, though, is that you get to use a saw to cut rocks in half to see what’s inside. So that’s what I did with this specimen from the Whitewater Formation (Upper Ordovician) of southeastern Indiana at a site we’ve visited often.

2 Rugosan interior 123015In this cross-section we see first a long, cone-shaped fossil made of white calcite. It is the rugose coral Grewingkia canadensis, one of the most common fossils in the upper part of the Upper Ordovician. This coral in life would have stood upright like an ice cream cone, spreading the tentacles of its polyp to catch very small swimming prey (and maybe to do a bit of symbiotic photosynthesis). The polyp sat in the cup-like cavity on the expanded end of the cone. The coral evidently died on the Ordovician seafloor and toppled over to be encrusted on one side, presumably the one that faced upwards.

3 Coral Bryo Sed BryoThis is a closer view of the cross-section showing the encrustations on the rugose coral skeleton. The image is annotated below.

4 Coral Bryo Sed Bryo annotatedThe coral skeleton in the lower right was first encrusted by a trepostome bryozoan, which you can recognize by the tubes (zooecia) extending perpendicular from the substrate. This bryozoan is thickest on the upwards-facing surface of the coral, and it thins as it wraps around and then colonizes the cryptic space beneath (but not too far). This bryozoan is covered with a layer of sediment which appears to have rapidly cemented in place (a function of Calcite Sea geochemistry). The sediment then is encrusted by a another trepostome bryozoan with long zooecia and several layers.

5 Bryo Sed 123015In this closer view of the second bryozoan you can see that its base is irregular as it grew across the rough cemented sediment surface. In the middle of this view some of the bryozoan zooecia are occupied by dark spots known as brown bodies. These are likely the remains of bryozoan polypides (main parts of the individual zooids) that were sealed into their zooecia by some disturbance. In this case the whitish bit of sediment above the cluster may represent something that settled on the colony, stopping the growth of the zooecia below, and forcing those nearby to grow around it.

6 Borings 123015Moving down the coral skeleton away from its opening we come across borings drilled down through the coral skeleton (the white mass at the bottom of the image). The conical, large boring is filled with golden crystals of the mineral dolomite, which were formed long after burial. The shape of this boring is unusual. Typical borings in these corals have straight parallel sides, but this boring is cone-shaped. We’ll see if we can find more like it to get a better idea of its shape and distribution.

This week’s fossil, then, is a demonstration of the hidden wonders sometimes found in even the dullest of grey rocks!

 

Wooster’s Fossil of the Week: An atrypid brachiopod from the Devonian of Spain

April 15th, 2016

1 Atrypid dorsal Lr Couvinian M Dev El Pical Leon SpainOur featured fossil this week is another gift from brachiopod enthusiast Clive Champion of England. This fine specimen of Atrypa sp. was collected from the Middle Devonian (Lower Couvinian) exposed at El Pical, Leon, Spain. Atrypa is the emblematic genus of the atrypid brachiopods, which were common in the Devonian around the world. They were also prominent in the Late Ordovician of the Cincinnati region, as seen here and here. We are looking at the dorsal valve in the above view.

2 Atrypid spiraliaThis particular specimen is not notable for its special beauty (it is, after all, exfoliated and a bit misshapen), but for the view it provides of an internal feature: the spiral brachidium, sometimes called the spiralia. This was a ribbon of calcite that supported the lophophore, a tentacular apparatus used in filter-feeding. We see it here because the dorsal valve eroded away, exposing the inside of the shell. Our friends at The Falls of the Ohio have another specimen showing the spiral lophophore of an atrypid.

3 Atrypid ventralThis is a view of the flat ventral valve of our atrypid brachiopod. Inside during life the spiral lophophore would have looked like two springs perpendicular to the floor of this valve.

Thank you again, Clive, for the beautiful and inspiring brachiopods!

References:

Bose, R. 2013. A geometric morphometric approach in assessing paleontological problems in atrypid taxonomy, phylogeny, evolution and ecology, p. 1-9. In: Biodiversity and Evolutionary Ecology of Extinct Organisms. Springer, Berlin and Heidelberg.
Rudwick, M.J.S. 1960. The feeding mechanisms of spire-bearing fossil brachiopods. Geological Magazine 97: 369-383.

 

Wooster’s Fossil of the Week: A crinoid stem internal mold from the Lower Carboniferous of Ohio

April 8th, 2016

crinoid internal mold 1The Biology Department at The College of Wooster is in the midst of a massive move in advance of the construction of the new Ruth Williams Hall of Life Science. The staff has been combing through old specimen collections, giving away items they don’t need for teaching or research. Among the objects are occasional fossils they gave to the Geology Department. The above specimen is one of the most curious: a combination internal and external mold of a crinoid stem from the local Lower Carboniferous rocks.

crinoid internal mold lumen copyThis is a closer view of the fossil. It is a cylindrical cavity with faint rings in a regular distribution. (These are external molds of the individual crinoid columnals.) Suspended down the axis is a segmented pillar with a stellate cross-section. (This is the internal mold of the crinoid stem lumen, a central cavity that runs down the center of the stem.) It appears that an iron-rich cement (probably siderite) filled this lumen after the death of the crinoid. The stem fragment was enveloped in a siderite concretion and the calcite stem columnals dissolved away. This leaves us with both an external mold of the stem and an internal mold of its lumen.

Carb stem 1For comparison, this is a crinoid stem fragment in its original calcite. It was found in a local Carboniferous limestone.

Carb stem 2Here are cross-sections of the same stems showing sediment-filled stellate lumens in their centers.

Wooster’s Fossils of the Week: An encrusted and bored coral (maybe) from the Upper Ordovician of southeastern Indiana (Part II)

April 1st, 2016

6 Tetradium cavernLast week we looked at a dull gray rock found in a roadcut in southeastern Indiana near the town of Liberty. It is from the Saluda Formation (Upper Ordovician), a thin unit that was likely deposited in very shallow, lagoonal waters along the Cincinnati Arch. We know that it is primarily a platter formed by the mysterious fossil Tetradium, and that it is encrusted with a trepostome bryozoan that was infested by some sort of soft-bodied encruster on its surface, forming the trace fossil Catellocaula vallata. Now we’re examining the wonders revealed by cutting this rock in half. Above we see the surprising and spectacular geode that it is, with calcite crystals surrounding a dark cavity. Let’s see what the fossils look like when polished and magnified.

7 LongitudinalCrossTetraThe orangish, irregular patch in the lower half of the section above is the crystalline calcite near the center of the rock. The sediment-filled tubes in the top half are of the Tetradium specimen. Note that the walls of the tubes are blurry and indistinct, and that they fade and disappear into the calcite crystals below. This is apparently because the skeleton of Tetradium was made of aragonite, an unstable form of calcium carbonate. It is likely that the aragonitc, tubular skeleton of Tetradium dissolved away in the center of this encrusted mass, forming the cavity that later filled with secondary calcite crystals. The remaining tubes were apparently preserved as ghostly molds by infillings of calcitic mud that didn’t dissolve.

8 TetracrossIn this section we are cutting the Tetradium tubes perpendicularly, rather than the longitudinal cuts we saw before. The cross-sections of the tubes show a four-part symmetry, which adds to the mystery of this group. (This is where the name “Tetradium” comes from.) It has been called a chaetetid sponge (as in Termier and Termier, 1980); a “calcareous filamentous florideophyte [red] alga” (Steele-Petrovich 2009a, 2009b, 2011; she renamed it Prismostylus), and most commonly a coral of some sort (as in Wendt, 1989). I now know enough about chaetetids to say that it is not in that group. Chaetetid tubes are not aragonitic, do not show tetrameral symmetry, and have diaphragms (horizontal floors). The corals of the Ordovician are decidedly calcitic, not aragonitic, and they too have internal features in their tubes not seen here. The four-part symmetry, though, is something you see in the coral’s phylum, Cnidaria, so there is that vague resemblance. The red algal affinity strongly urged by Steele-Petrovich may be our best diagnosis for the place of Tetradium.

9 BryoTetra1On top of the tubes of Tetradium is the encrusting trepostome bryozoan. Its tubes (zooecia) are made of stable calcite, so they are well preserved compared to the aragonite tubes of Tetradium below it. Note that the bryozoan is made of two layers. One colony died or went into some sort of remission, and another of the same species grew across it. The second colony could have budded somewhere from the first colony.

10 BrownBodies122915This closer view of the bryozoan section shows details of the zooecia, including the horizontal diaphragms inside. The dark spots at the tops of the zooecia are brown bodies, the remains of polypides preserved here in clear calcite cement. (We’ve seen brown bodies before in this blog.) They likely represent some sort of traumatic event in the life of this bryozoan when this part of the colony essentially shut down and was covered with sediment.

11 Gypsumflower122915Finally, there is a mineralogy story here too! Attached to the dog-tooth calcite spar in the center of this geode is this tiny gypsum flower. The gypsum crystals are white and very delicate. The dark needles among them are mysterious. Dr. Meagen Pollock and her students will subject them to x-ray diffraction in her lab later this semester. I’ll report the results here.

It is a simple tool, the rock saw. For geologists and paleontologists, it is one of our essential instruments for discovery.

References:

Hatfield, C.B. 1968. Stratigraphy and paleoecology of the Saluda Formation (Cincinnatian) in Indiana, Ohio, and Kentucky. Geological Society of America Special Papers 95: 1-30.

Li, Q., Li, Y. and Kiessling, W. 2015. The first sphinctozoan-bearing reef from an Ordovician back-arc basin. Facies 61: 1-9.

Palmer, T.J. and Wilson, M.A. 1988. Parasitism of Ordovician bryozoans and the origin of pseudoborings. Palaeontology 31: 939-949.

Steele‐Petrovich, H M. 2009a. The biological reconstruction of Tetradium Dana, 1846. Lethaia 42: 297-311.

Steele‐Petrovich, H M. 2009b. Biological affinity, phenotypic variation and palaeoecology of Tetradium Dana, 1846. Lethaia 42: 383-392.

Steele-Petrovich, H.M. 2011. Replacement name for Tetradium DANA, 1846. Journal of Paleontology 85: 802–803.

Termier, G. and Termier, H. 1980. Functional morphology and systematic position of tabulatomorphs. Acta Palaeontologica Polonica 25: 419-428.

Wendt, J. 1989. Tetradiidae — first evidence of aragonitic mineralogy in tabulate corals. Paläontologische Zeitschrift 63: 177–181.

 

Wooster’s Fossils of the Week: An encrusted and bored coral (maybe) from the Upper Ordovician of southeastern Indiana (Part I)

March 25th, 2016

1 TopEncrustedTetradiumI found this lump of a gray rock in southeastern Indiana along a highway near the town of Liberty. It is from the Saluda Formation (Upper Ordovician), a thin unit that was likely deposited in very shallow, lagoonal waters along the Cincinnati Arch. It is not especially notable in this view. I intend to show you the wonders that can be revealed in such dull rocks by simply sawing them in half. First, though, let’s have a look at the outside. Inn the view above you can see on the left side a large trepostome bryozoan with some irregular holes in it. We’ll come back to that.

2 BaseEncrustedTetradiumFlipping the rock over we find that most of it is a fibrous fossil shaped like a dinner plate with limestone matrix and encrusting bryozoans covering most of the center.

3 CloserTubesTetraA closer view of the fibrous part shows thousands of thin tubes radiating out from the center of the plate. This is the Ordovician fossil known as Tetradium. It is strange and mysterious enough that we will use the next Fossil of the Week blog post to describe it. It has been called a chaetetid sponge (as in Termier and Termier, 1980); a “calcareous filamentous florideophyte alga” (Steele-Petrovich 2009a, 2009b, 2011; she renamed it Prismostylus), and most commonly a coral of some sort (Wendt, 1989). Interesting range of options! We’ll explore later.

4 Catellocaula122915Now, back to the trepostome bryozoan visible on the top surface. There are three kinds of holes on this specimen. The smallest are the zooecia of the bryozoan itself, each of which would have hosted a zooid (a bryozoan individual). They are the background texture of the fossil. The large holes above are a bioclaustration structure that Time Palmer and I named in 1988 as Catellocaula vallata (little chain of walled  pits). It is explained thoroughly in one of the early Fossil of the Week posts. Basically they are pits formed when the bryozoan grew up and around some sort of soft-bodied colonial organism sitting on top of the surface, forming these embedment structures connected together by tunnels at their bases.

5 Trypanites122915A third kind of hole in this bryozoan is a boring cut down into its skeleton. These are the trace fossil Trypanites, formed when some kind of filter-feeding worm bored straight into the calcite zoarium (colonial skeleton) to make a protective home, as many polychaete worms do today.

Now let’s cut this stone in half —

6 Tetradium cavernInside we find a wonderful cavern of crystals — a geode! The crystals are mostly calcite, with dog-tooth spar lining the cavity and blocky spar replacing large parts of the Tetradium skeleton. There’s a story here, and it will be told in the next Fossil of the Week post!

References:

Hatfield, C.B. 1968. Stratigraphy and paleoecology of the Saluda Formation (Cincinnatian) in Indiana, Ohio, and Kentucky. Geological Society of America Special Papers 95: 1-30.

Li, Q., Li, Y. and Kiessling, W. 2015. The first sphinctozoan-bearing reef from an Ordovician back-arc basin. Facies 61: 1-9.

Palmer, T.J. and Wilson, M.A. 1988. Parasitism of Ordovician bryozoans and the origin of pseudoborings. Palaeontology 31: 939-949.

Steele‐Petrovich, H M. 2009a. The biological reconstruction of Tetradium Dana, 1846. Lethaia 42: 297-311.

Steele‐Petrovich, H M. 2009b. Biological affinity, phenotypic variation and palaeoecology of Tetradium Dana, 1846. Lethaia 42: 383-392.

Steele-Petrovich, H.M. 2011. Replacement name for Tetradium DANA, 1846. Journal of Paleontology 85: 802–803.

Termier, G. and Termier, H. 1980. Functional morphology and systematic position of tabulatomorphs. Acta Palaeontologica Polonica 25: 419-428.

Wendt, J. 1989. Tetradiidae — first evidence of aragonitic mineralogy in tabulate corals. Paläontologische Zeitschrift 63: 177–181.

Wooster’s Fossils of the Week: A Jurassic seafloor assemblage

March 18th, 2016

1 DSC_0184 copyImages from fieldwork this week. These are all fossils exposed on a single bedding plane in the Matmor Formation (Middle Jurassic, Callovian) exposed in Makhtesh Gadol. I found them many years ago while working through the stratigraphy near the top of the formation. They present a vignette of life in a shallow carbonate Jurassic sea. They are so well preserved you can almost feel the gentle waves and hear the squawks of the pterosaurs wheeling above. In the top image we have my favorite of the set: A gastropod shell in the middle surrounded by mytilid bivalves. The bivalves were no doubt attached to the gastropod by their thin byssal threads, holding them in place in the choppy waters. The preservation is remarkable. All these shells are calcitized, but retain their ornamentation. They are exposed on a bank of a wadi, and so they have been lightly etched from the matrix by sandy water during floods.

2 DSC_0180 copyJust to show the gastropod-bivalve association is not a fluke of preservation, here’s another set. On this bedding plane are four such assemblages.

3 DSC_0178 copyHere’s another gastropod, this one with heavy spines.

4 DSC_0179 copyA high-spired gastropod is on the left, with a mytilid in side-view on the right.

5 DSC_0181 copyAnother gastropod to end the set. These are just a few of the many such fossils exposed on this bedding plane of the Matmor Formation.

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