A day at the Natural History Museum in London

June 14th, 2016

1 Drawer of brachiopodsLondon, England — My first full day at The Natural History Museum in London was interesting and inspiring as always, but it did have its tedium. This drawer of Ordovician brachiopods, for example. I scanned each with my handlens in the dim lighting looking for a particular kind of encruster.

2 Drawers of brachiopodsDrawer after drawer. Saw many curious fossils, but not one example of what I was looking for. Not an uncommon experience!

3 Harry photographing 061416One of the best parts of a museum visit is meeting skilled staff. Harry Taylor is a master photographer of fossils. Paul Taylor and I took him a fossil this morning and he immediately created a superb image for our work. In my inexpert photograph above, what looks like a blast furnace behind the camera is his lighting and flash system.

4 Harry Paul photographyHarry and Paul discuss the image on screen.

5 Bryo copyHere is a small version of the final result of Harry’s artistry. The original file is 111 megabytes! This is a brachiopod (Rafinesquina ponderosa) from the Cincinnatian rocks of southern Ohio. It is encrusted with something special I’ll describe in a later post. We’ll use this high-resolution image for detailed mapping of this surface.

6 Emanuela Di Martino SEM 061416Paul and I visited our colleague Emanuela Di Martino to congratulate her on Italy’s recent win in the Euro 2016 football tournament. She is operating the Scanning Electron Microscope (SEM) Paul and I will be using in two days. I’ve sat here for many hours scanning specimens with Paul.

7 Tony Wighton cuttingPaul and I had a bryozoan we wanted to cut in half to study its interior. Tony Wighton immediately sliced it for us.

8 Tony Wighton polishingTony then gave each half a mirror finish, producing spectacular specimens that considerably enhance the value of the collections.

It was a good day at the museum. The rain stopped long enough for us to get fresh hamburgers at the nearby open market for lunch, and then we had drinks at the Victoria & Albert Museum next door. I don’t take any of this for granted!

Wooster’s Fossils of the Week: A bored Ordovician hardground from Ohio, and an introduction to a new paper on trace fossils and evolution

June 3rd, 2016

Bull Fork hdgdAbove is an image of a carbonate hardground (cemented seafloor) from the Upper Ordovician of Adams County, Ohio. It comes from the Bull Fork Formation and was recovered along State Route 136 north of Manchester, Ohio (Locality C/W-20). It is distinctive for two reasons: (1) the many external molds (impressions, more or less) of mollusk shells, including bivalves and long, narrow, straight nautiloids, and (2) its many small borings called Trypanites, a type of trace fossil we’ve seen on this blog before.
Bull Fork boringsIn this closer view we can see the shallow external molds of small bivalve shells, especially on the left side, and the many round perforations of the Trypanites borings.

The dissolved mollusk shells (from bivalves and nautiloids) were originally composed of the calcium carbonate mineral aragonite. This aragonite dissolved early on the seafloor, liberating calcium carbonate that quickly precipitated as the mineral calcite in the sediment, cementing it into a rocky seafloor (hardground) that was then bored by the animal that made Trypanites. This all happened because of the distinctive geochemistry of the ocean water at that time. High levels of carbon dioxide and a decreased Mg/Ca ratio dissolved aragonite yet enabled calcite (the more stable polymorph of calcium carbonate) to rapidly precipitate. This geochemical condition is known as a Calcite Sea, which was common in the early to middle Paleozoic, especially in the Ordovician. This is not the case in today’s marine waters in which aragonite is the primary calcium carbonate precipitate (“Aragonite Sea“). See Palmer et al. (1988) for more details on this process and the evidence for it.

I’m using this Ordovician carbonate hardground to introduce a new paper that just appeared this week in the Proceedings of the National Academy of Sciences (PNAS): “Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Ordovician Biodiversification Event“. The authors are the renowned trace fossil experts Luis Buatois and Gabriela Mángano, the ace geostatistician Ricardo Olea, and me. I’m excited about this paper because it adds to the literature new information and ideas about two major evolutionary radiations: the “explosion” of diversity in the Cambrian (which established basic body plans for most animals) and the diversification in the Ordovician (which filled in those body plans with abundant lower taxa). This is one of the few studies to look in detail at the trace fossil record of these events. Trace fossils (records of organism behavior in and on the sediment substrate) give us information about soft-bodied taxa otherwise rare in a fossil record dominated by shells, teeth and skeletons. It is also the first systematic attempt to compare the diversification of trace fossils in soft sediments and on hard substrates (like the hardground pictured above).

As for the paper itself, I hope you can read it. Here is the abstract —

Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (Series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal–substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.

Thank you to Luis Buatois for his leadership on this challenging project. I very much appreciate the way this work has placed the study of trace fossils into a critical evolutionary context.
Fig1_PNASFigure 1 from Buatois et al. (2016): “Ichnodiversity changes during the Ediacaran-Ordovician. Ichnogenera were plotted as range-through data (i.e., recording for each ichnogenus its lower and upper appearances and then extrapolating the ichnogenus presence through any intervening gap in the continuity of its record).”

References:

Buatois, L.A., Mángano, M.G., Olea, R.A. and Wilson, M.A. 2016. Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Ordovician Biodiversification Event. Proceedings of the National Academy of Sciences (in press).

Palmer, T.J., Hudson, J.D. and Wilson, M.A. 1988. Palaeoecological evidence for early aragonite dissolution in ancient calcite seas. Nature 335: 809-810.

Wilson, M.A. and Palmer, T.J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109-112.

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 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 Pseudofossils of the Week: Shatter cones from southern Ohio

March 4th, 2016

Real shatter cones 585This brief post is a correction of a previous entry. Last year I showed what I thought were shatter cones collected many years ago in Adams County, Ohio, by the late Professor Frank L. Koucky of The College of Wooster. James Chesire commented on the post and said it was more likely the specimens were cone-in-cone structures produced by burial diagenesis not bolide impacts. When he sent me the photo above of real shatter cones from the Serpent Mound impact region in southern Ohio, I knew he was correct. Shatter cones have distinctive radiating, longitudinal fractures not seen in similar conical structures in limestones. The above shatter cones are in an unknown Ordovician limestone.

Both shatter cones and cone-in-cone structures are nevertheless pseudofossils in that they are both sometimes confused with organic structures like corals and chaetetids. I shall never mix them up again! Thanks for the correction, James.

References:

Carlton, R.W., Koeberl, C., Baranoski, M.T. and Schumacher, G.A. 1998. Discovery of microscopic evidence for shock metamorphism at the Serpent Mound structure, south-central Ohio: confirmation of an origin by impact. Earth and Planetary Science Letters 162: 177-185.

Dietz, R.S. 1959. Shatter cones in cryptoexplosion structures (meteorite impact?). The Journal of Geology 67: 496-505.

Sagy, A., Fineberg, J. and Reches, Z. 2004. Shatter cones: Branched, rapid fractures formed by shock impact. Journal of Geophysical Research 109: B10209.

Shaub, B.M. 1937. The origin of cone-in-cone and its bearing on the origin of concretions and septaria. American Journal of Science 203: 331-344.

Wooster’s Fossil of the Week: A bitten brachiopod (Upper Ordovician of southeastern Indiana)

February 5th, 2016

1 Best bitten Glyptorthis insculpta (Hall, 1847)This brachiopod, identified as Glyptorthis insculpta (Hall, 1847), was shared with me by its collector, Diane from New York State. She found it in a muddy horizon of the Bull Fork Formation (Upper Ordovician) in southeastern Indiana. She immediately noted the distorted plicae (radiating ribs) on the left side of this dorsal valve, along with the invagination along the corresponding margin. (Thanks for showing this to me, Diane, and allowing me to include it in this blog.)
2 Best closer Glyptorthis insculpta (Hall, 1847)Above  is a closer view of the unusual plicae. Note that they radiate from the top center of the brachiopod, extending as the shell grew outward along its margins. Something happened, though, when the brachiopod was growing. The shell was seriously damaged by a puncturing object. The brachiopod repaired the hole by closing it up with additional shell material coming from either side. The inwardly-curved plicae show the pattern of shell regrowth.
3 Reverse of best Glyptorthis insculpta (Hall, 1847)This is a view of the same brachiopod from the other side, showing that the ventral valve was damaged in the same event, but with slightly less destruction.

So how did such damage occur on that Ordovician seafloor? Some predator likely took a bite out of the brachiopod as it lay in its living position with the valves extended upwards into the seawater. Most brachiopods do not survive such events, but this one did.

Who was the probable predator? For that we turn to the work of the late Richard Alexander (1946-2006). He did the definitive study of pre mortem damage to brachiopods in the Cincinnatian Group in 1986, concluding that the most likely predators on these brachiopods were nautiloid cephalopods. Some of this figures show nearly identical healed scars on similar orthid brachiopods.
4. Richard AlexanderRichard Alexander was an accomplished paleontologist who lost his life in a swimming accident off the coast of St. Lucia just over nine years ago. He was born in Covington, Kentucky, right across the river from Cincinnati. As is so common with children in that part of the world, he developed a passion for fossils. He attended the University of Cincinnati, majoring in geology, He then went to Indiana University, completing a PhD dissertation titled: “Autecological Studies of the Brachiopod Rafinesquina (Upper Ordovician), the Bivalve Anadara (Pliocene), and the Echinoid Dendraster (Pliocene).” (We don’t see such diverse projects very much these days.) He taught at Utah State University from 1972 to 1980, and then at Rider University in New Jersey from 1981 until his death. He served as an administrator at several levels at Rider, and was known as an excellent teacher. His research interests changed when he moved to the East Coast, becoming increasingly focused on modern mollusks. No doubt he would still be contributing to paleontology but for the randomness of a freak wave in the Caribbean.

References:

Alexander, R.R. 1981. Predation scars preserved in Chesterian brachiopods: probable culprits and evolutionary consequences for the articulates. Journal of Paleontology 55: 192-203.

Alexander, R.R. 1986. Resistance to and repair of shell breakage induced by durophages in Late Ordovician brachiopods. Journal of Paleontology 60: 273-285.

Dodd, J.R. 2008. Memorial to Richard Alexander (1946-2006). Geological Society of America Memorials 37: 5-7.

Wooster’s Fossil of the Week: A brachiopod with a heavy burden (Upper Ordovician of southeastern Indiana)

January 29th, 2016

1 Trepostome on Hebertella richmondensisYes, the above image doesn’t look much like a brachiopod, but just wait. We see a trepostome bryozoan with extended knobs and a few borings. Flip it over, though …
2 Hebertella richmondensis ventral view 585… and we see that the bryozoan almost entirely covers a brachiopod. So far, so common among Ordovician fossils. However, look closely at the margin of the brachiopod valve and how clearly it is delineated from the bryozoan. It is apparent that the bryozoan had encrusted a living brachiopod, and the brachiopod stayed alive, keeping the essential commissure (the gap between the valves) open for feeding. We are looking at the valve that was in contact with the substrate (the underside of the living brachiopod). The bryozoan occupied the upper exposed surface, growing across that valve (which is invisible to us now), past its edge, but not closing the gap with the other valve. The same bryozoan species is found on the above visible valve, but only as two thin films unconnected to the colony on the upper side.
3 Hebertella richmondensis bryo close annotatedA closer view of the brachiopod hinge shows additional evidence that the bryozoan and brachiopod were living together. The red arrow on the left points to where the fleshy pedicle (attaching stalk) of the brachiopod extended from the shell to meet the substrate. The bryozoan here curves around the now-vanished pedicle. The yellow arrow on the right shows how the bryozoan growth surface folded to accommodate the opening valves at the hinge. Pretty cool.

I can’t identify the bryozoan beyond Order Trepostomata without cutting it open. The brachiopod, though, appears to be Hebertella richmondensis Foerste, 1909. This specimen is from the Whitewater Formation (Upper Ordovician, upper Katian) exposed near Richmond, Indiana. It was collected on one of my field trips in 2003.
4 Hebertella richmondensis ventral view 585 annotatedWhat do we learn from this little assemblage? We first see a relatively uncommon example of a clear living relationship between a sclerobiont and its host. We also learn that the brachiopod could continue to open its valves for feeding despite the heavy calcitic bryozoan weighing it down. We even can see that this brachiopod was not living on a soft muddy substrate because only a small triangular-shaped area (see above) in the center was clear of encrusters; the thin bryozoan (and maybe a bit of the stromatoporid sponge Dermatostroma) had enough space between the valve and the substrate to feed and respire. None of this is surprising, but it is nice to see our models of how these organisms lived are congruent with the evidence.

References:

Alexander, R.R. and Scharpf, C.D. 1990. Epizoans on Late Ordovician brachiopods from southeastern Indiana. Historical Biology 4: 179-202.

Foerste, A.F. 1909. Preliminary notes on Cincinnati fossils. Bulletin of the Scientific Laboratory of Denison University 14: 208–232.

Walker, L.G. 1982. The brachiopod genera Hebertella, Dalmanella, and Heterorthina from the Ordovician of Kentucky. USGS Professional Paper 1066-M.

Wright, D.F. and Stigall, A.L. 2013. Phylogenetic revision of the Late Ordovician orthid brachiopod genera Plaesiomys and Hebertella from Laurentia. Journal of Paleontology 87: 1107-1128.

Wooster’s Fossils of the Week: Atrypid brachiopods attached to a trepostome bryozoan from the Upper Ordovician of southern Indiana

January 8th, 2016

Zygospira Attached 585This is a follow-up post to our entry on Christmas Day two weeks ago. Above is a trepostome bryozoan (the long porous piece) with specimens of the atrypid brachiopod Zygospira modesta clustered around it. They are positioned with their ventral valves outward because in life they were attached to this bryozoan with tiny fleshy stalks called pedicles. They were buried quickly enough that this spatial relationship was preserved. Cool. This assemblage was found in the Liberty Formation (Upper Ordovician) exposed in a roadcut in southern Indiana.
Zygospira modesta dorsal annotatedThis is a view of the dorsal side of Zygospira modesta showing the pedicle opening in the ventral valve at the apex of the shell.

References:

Copper, P. 1977. Zygospira and some related Ordovician and Silurian atrypoid brachiopods. Palaeontology 20: 295-335.

Sandy, M.R. 1996. Oldest record of peduncular attachment of brachiopods to crinoid stems, Upper Ordovician, Ohio, USA (Brachiopoda; Atrypida: Echinodermata; Crinoidea). Journal of Paleontology 70: 532-534.

Wooster’s Fossil of the Week: Tiny atrypid brachiopods from the Upper Ordovician of southern Ohio

December 25th, 2015

Zygospira modesta Waynesville 585These exquisite little brachiopods are among the most abundant fossils in the Upper Ordovician of the Cincinnati area. My Invertebrate Paleontology students collected dozens of them from the Waynesville Formation on our field trip to Caesar Creek Lake last semester. Their ubiquity, though, doesn’t make them any less precious.
Zygospira modesta dorsalThis is Zygospira modesta (Say in Hall, 1847). Above is a dorsal valve view of a single specimen. At the apex you can see a tiny round hole from which a fleshy pedicle extended to attach the brachiopod to a hard substrate.
Zygospira modesta ventralHere is the ventral valve view. Zygospira is an atrypid brachiopod, meaning that its internal support (brachidium) for the filter-feeding lophophore is looped in a characteristic way, shown below.
Hall diagram ZygospiraThe diagrams above are from Hall (1867) who named the genus Zygospira and wished to further distinguish it from other atrypid brachiopods.

The taxonomy of Zygospira modesta is a bit messy, as many early 19th Century species descriptions tended to be. It was apparently first named Producta modesta by Thomas Say (see below) but not actually published as such. James Hall described it as Atrypa modesta in 1847. Later in 1862 he named Zygospira as a new genus, making Z. modesta its type species but not indicating a type locality.
Thomas_Say_1818We met Thomas Say (1787-1834) earlier in this blog, recognizing him as the scientist who named Exogyra costata in 1820. He is shown above in an 1818 portrait. Say was a brilliant American natural historian. Among his many accomplishments in his short career, he helped found the Academy of Natural Sciences of Philadelphia in 1812, the oldest natural science research institution and museum in the New World. He is best known for his descriptive entomology in the new United States, becoming one of the country’s best known taxonomists. He was the zoologist on two famous expeditions led by Major Stephen Harriman Long. The first, in 1819-1820, was to the Great Plains and Rocky Mountains; the other (in 1823) was to the headwaters of the Mississippi. Along with his passion for insects, Say also studied mollusk shells, both recent and fossil. He was a bit of an ascetic, moving to the utopian socialist New Harmony Settlement in Indiana for the last eight years of his life. It is said his simple habits and refusal to earn money caused problems for his family. Say succumbed to what appeared to by typhoid fever when he was just 47.

References:

Copper, P. 1977. Zygospira and some related Ordovician and Silurian atrypoid brachiopods. Palaeontology 20: 295-335.

Hall, J. 1862. Observations upon a new genus of Brachiopoda. Report New York State Museum, Natural History 15: 154-155.

Hall, J. 1867. Note upon the genus Zygospira and its relations to Atrypa. Report New York State Museum, Natural History 20: 267-268.

Sandy, M.R. 1996. Oldest record of peduncular attachment of brachiopods to crinoid stems, Upper Ordovician, Ohio, USA (Brachiopoda; Atrypida: Echinodermata; Crinoidea). Journal of Paleontology 70: 532-534.

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