Wooster’s Fossils of the Week: Peanut worms from the Silurian of Illinois

Mark Wilson February 3, 2017 12:01 am

1-lecthaylus-gregarius-5-copyThis week’s fossils are a set of cool sipunculan worms from the Lockport Shale Member of the Racine Formation (Wenlockian, Silurian) of Blue Island, Illinois (which, it turns out, is not an island.). This is Lecthaylus gregarius Weller, 1925. (There is a common misspelling of the genus name as “Lecathylus”, which is how it is labeled in our collection.) They are masses of partially-carbonized bodies and external molds in a very fine-grained matrix. They are well known from this particular fossil-lagerstätte (a fossil fauna of remarkable preservation) in northern Illinois.

The Phylum Sipuncula did not often make it into the fossil record because of their entirely soft bodies, but a few are preserved way back in the Cambrian Chengjiang and Burgess Shale faunas. They show virtually no evolutionary changes in their long run to today, at least not in their outer form. They are commonly known as “peanut worms”.

2-lecthaylus-gregarius-2This is an example of the preservation modes: a black carbon film that has mostly flaked away, leaving behind a detailed external mold of the squashed peanut worms.

3-lecthaylus-gregarius-1Sipunculan bodies are divided into a main thick posterior trunk and a narrow, retractable anterior “introvert”. We’re looking here at the anterior introvert of Lecthaylus gregarius.

4-lecthaylus-gregarius-3-copyThis is the squat trunk of Lecthaylus gregarius.

5-themiste_petricola_evertedHere is the modern sipunculan Themiste petricola with introvert extended. It is the same basic plan as the Silurian Lecthaylus gregarius. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

6-themiste_petricola_invertedThe modern sipunculan Themiste petricola with its introvert retracted. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

stuart-weller-1870-1927Lecthaylus gregarius was described and named by Stuart Weller (1870-1927), an American paleontologist and geologist. He was born in the small town of Maine, New York. He earned a Bachelor’s degree in geology at Cornell University in 1894 followed by a PhD at Yale in 1901. Shortly after his Cornell degree, though, Weller traveled to the University of Chicago, where he worked his way through the ranks from a research associate to a full professor of Paleontology and Geology in 1915. He was also the director of the Walker Museum at the University of Chicago, and in 1926 he was president of the Paleontological Society. One of his sons, J. Marvin Weller (1899-1976) had a remarkably similar career as a stratigrapher and paleontologist.

References:

Kluessendorf, J. 1994. Predictability of Silurian Fossil‐Konservat‐Lagerstatten in North America. Lethaia 27: 337-344.

Roy, S.K. and Croneis, C. 1931. A Silurian worm and associated fauna. Field Museum of Natural History, Geological Series IV(7): 229-247.

Weller, S. 1925. A new type of Silurian worm. Journal of Geology 33: 540-544.

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Wooster’s Fossil of the Week: Ammonite septa from the Upper Cretaceous of South Dakota

Mark Wilson January 27, 2017 12:01 am

This week we have an ammonite from the Pierre Shale (Upper Cretaceous, Campanian-Maastrichtian) of southwestern South Dakota. It was collected on a wonderful field expedition in June 2008 with my friend Paul Taylor (The Natural History Museum, London) and my student John Sime. Ammonites are extremely common in this interval, but I like this one because it is broken in such a way to expose its complex internal walls, called septa. We are looking at a cross-section of a coiled ammonite showing an early whorl in the upper left surrounded by a later whorl. The septa are fluted at their margins as they meet the outer wall. The wiggly boundary line between a septum and the outer wall is called a suture.

Ammonite septa are remarkably complex, showing fractal patterns. Why did these animals, extinct for 66 million years, evolve such complexity in their septa? This is a hotly debated topic in paleontology. The most popular explanations include strengthening the walls of the shell to resist hydrostatic pressure at depth, buttressing the shell against the crushing pressures of biting predators, and increasing soft-tissue (mantle) surface areas for physiological advantages. Klug and Hoffman (2015) have an excellent summary of these ideas. Lemanis et al. (2016) have a fascinating mathematical study that suggests the answer in many cases complex sutures “seem to increase resistance to point loads, such as would be from predators.”

The astonishing English polymath Robert Hooke (1635-1703) took considerable interest in ammonites and their complicated septa. We have no contemporary images of him, but based on descriptions, Rita Greer painted the above portrait in 2004. Hooke’s life was as complex as the suture patterns he studied, so I leave you to other sources on him. Note in the portrait above, though, the ammonite!

These are drawings by Robert Hooke of ammonites and their suture patterns (from Kusukawa, 2013). It is a single image mirror-reversed. Beautiful.

References:

Derham W. 1726. Philosophical experiments and observations of the late eminent Dr. Robert Hooke, S.R.S. and Geom. Prof. Gresh., and other eminent virtuoso’s in his time. London: Derham.

Garcia-Ruiz, J.M., Checa, A. and Rivas, P. 1990. On the origin of ammonite sutures. Paleobiology 16: 349-354.

Klug, C. and Hoffmann, R. 2015. Ammonoid septa and sutures. In: Ammonoid Paleobiology: From anatomy to ecology (p. 45-90). Springer Netherlands.

Kusukawa, S. 2013. Drawings of fossils by Robert Hooke and Richard Waller. Notes Rec. R. Soc., 67: 123-138.

Lemanis, R., Zachow, S. and Hoffmann, R. 2016. Comparative cephalopod shell strength and the role of septum morphology on stress distribution. PeerJ 4:e2434

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Wooster’s Fossils of the Week: Revisiting a pair of hyoliths from the Middle Ordovician of Estonia

Mark Wilson January 20, 2017 12:01 am

We met these modest internal molds of the mysterious hyoliths about five years ago. With a dramatic new development in hyolith studies, they are worth seeing again.

These fossils are internal molds (the sediment that filled the shell) of of flattened cones composed of the carbonate mineral aragonite. The aragonite shells dissolved away after burial, leaving the cemented sediment behind. That’s what we see above, in their stark simplicity. (We also see wiggly indentations that are the trace fossil Arachnostega, which is what I collected them for in the first place.) They were found in the Middle Ordovician of Estonia.

Hyalites, though common throughout the Paleozoic, have been difficult to place in a taxonomic category. Because of their easily-dissolved aragonite skeletons, most fossils are like these — simple molds and casts. A few were found with some preserved internal organs, which added to the intrigue. Their flattened conical shells had a hinged lid (operculum) over the open end. Extending from each side in the space between the operculum and cone were two calcareous rods called helens (a name deliberately chosen so as not to evoke a particular function). They were rumored to be deposit-feeders, based on no real evidence, it turns out.

An excellent paper appeared earlier this month showing dramatic evidence of hyolith soft parts in the Cambrian of western Canada (Moysiuk et al., 2017). The authors reconstruct the iconic Cambrian hyolith Haplophrentis “as a semi-sessile, epibenthic suspension feeder that could use its helens to elevate its tubular body above the sea floor”. Their primary evidence is a magnificently preserved lophophore (tentacular filter-feeding apparatus) and a U-shaped digestive tract with a dorsolateral anus. These features not only give the hyoliths a life mode and feeding habit, they place them systematically among the lophophorates, a group that includes brachiopods, phoronids and bryozoans.

Haplophrentis in the Burgess Shale (Middle Cambrian) at the Walcott Quarry, Burgess Pass, British Columbia, Canada.

Reconstruction of Haplophrentis on the Cambrian sea floor. The tentacular lophophore is seen extending out underneath the operculum. Beautiful art by D. Dufault of the Royal Ontario Museum.

It’s not often we see such dramatic changes in the taxonomic placement and paleoecological habits of a large, extinct group. It is also not often that invertebrate fossils make headlines!

Reference:

Moysiuk, J., Smith, M.R. and Caron, J.B. 2017. Hyoliths are Palaeozoic lophophorates. Nature doi:10.1038/nature20804

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Wooster’s Fossils of the Week: New review paper on architectural design of trace fossils

Mark Wilson January 13, 2017 12:01 am

screen-shot-2016-12-04-at-2-59-29-pmLast year my friend Luis Buatois led a massive project to review essentially all trace fossil invertebrate ichnogenera (523!) to place them in a series architectural design categories (79). This is a new way to assess patterns of ichnodisparity (variability in morphology of trace fossils). I was proud to have a role in this work, along with Max Wisshak and Gabriela Mángano. The paper has now appeared in Earth-Science Reviews (Buatois et al., 2017).

My contributions were mostly with the bioerosion traces (along with Max), so I show Figure 65 from the paper above. Its caption: Examples of pouch borings (Category 65). A: Petroxestes pera, Ordovician, Whitewater Formation, Ohio, USA. B: Rogerella isp. in a belemnite rostrum. Jurassic, Spain. C: SEM of Rogerella isp. in an epoxy resin cast of an Echinocorys echinoid test. Upper Cretaceous, Palm Bay, Thanet, Kent, UK. D: Umbichnus inopinatus in a bivalve shell. Lower Pliocene, Huelva, Spain. Photograph courtesy of Jordi Martinell. E: SEM of Aurimorpha varia in an epoxy resin cast, including the holotype in the upper right. Middle Pennsylvanian, Desmoinesian, Boggy Formation, Buckhorn Asphalt Quarry, Oklahoma, USA.

The abstract of the paper explains the work and our ambitions for it: Ichnodisparity has been recently introduced as a concept to assess the variability of morphologic plans in biogenic structures, revealing major innovations in body plan, locomotory system and/or behavioral program. Whereas ichnodiversity is measured in terms of the number of ichnotaxa (i.e. ichnogenera or ichnospecies), ichnodisparity is evaluated based on the identification of categories of architectural design. Seventy-nine categories of architectural designs (58 for bioturbation structures and 21 for bioerosion structures), encompassing 523 ichnogenera (417 for bioturbation structures and 106 for bioerosion structures), are defined. They are restricted to invertebrate ichnotaxa, whereas vertebrate trace fossils were not included. Although the scheme is designed to be comprehensive, the proposed categories are necessarily works in progress because of the state of flux in ichnotaxonomy and the need to adjust the definitions of categories according to the scope and scale of the analysis. Although it may be said that the establishment of categories of architectural design is to a certain degree a subjective enterprise, this is not different from ichnotaxonomy because classifying trace fossils from a taxonomic perspective implies observing the morphology of the trace and interpreting it in terms of behavior. The concept of ichnodisparity is free of some of the vagaries involved in ichnotaxonomy. The fact that ichnodiversity and ichnodisparity exhibit different trajectories during the Phanerozoic underscores the importance of adding the latter to the ichnologic toolkit.
screen-shot-2016-12-04-at-3-03-44-pmFigure 80 above contrasts ichnodisparity and ichnodiversity. The five different ichnogenera illustrated in the upper portion of the diagram represent minor variations of the same architectural design. The lower portion of the diagram represents the same ichnodiversity level, but with a much higher ichnodisparity. The two hypothetical situations bear different implications regarding the extent of evolutionary innovations.

We hope that this work is long useful in paleontology, especially for projects sorting out the evolution of invertebrate communities.

Reference:

Buatois, L., Wisshak, M., Wilson, M.A. and Mángano, G. 2017. Categories of architectural designs in trace fossils: A measure of ichnodisparity. Earth-Science Reviews 164: 102-181.

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Wooster’s Fossils of the Week: Upper Ordovician brachiopods and bryozoans from paleontology class collections

Mark Wilson January 6, 2017 12:01 am

1-geopetal-tommyLast semester the Invertebrate Paleontology class at Wooster had its annual field trip into the Upper Ordovician of southern Ohio. We had a great, if a bit muddy, time collecting fossils for each student’s semester-long project preparing, identifying, and interpreting their specimens. Like all research, especially when it starts in the field, there were discoveries and surprises. I always highlight a particular specimen collecting by a student in this blog.

Above is a cross-section of a specimen found by Tommy Peterson (’19). It is the rhynchonellid brachiopod Hiscobeccus capax almost completely enveloped by an encrusting trepostome bryozoan. We’ve cut through the center of the brachiopod, revealing gray micritic sediment and clear calcite crystals. We can infer from this simple specimen that the brachiopod died and its shell remained articulated. Sediment drifted in, filling the bottom half of the shell. The bryozoan eventually sealed it all up as it used the brachiopod shell for a hard substrate on a muddy seafloor. The remaining void space was filled in by the precipitation of calcite crystals. You can see that the crystals nucleated from the outer margin of the cavity and grew inwards, a kind of calcareous geode. I’m intrigued by the irregular sediment surface and the manner in which calcite nucleated upwards from it. I suspect this sediment was itself cemented before the calcite crystals appeared.

This kind of structure is called a geopetal. It shows the “way up” at the time of crystal formation. Gravity held the pocket of sediment in the bottom of the shell, leaving the void at the top. Nice little specimen.

2-constellaria-alexisThis star-studded bryozoan found by Alexis Lanier (’20) was going to be the Fossil of the Week, but then I saw that last year I highlighted the very same species! I think the bryozoan Constellaria is cool. Read all about it and its history at the link.

3-table-of-traysHere are the completed specimen trays for half the class. (Grading this project took, as you might imagine, considerable time!). Every week in lab, after we had done the assigned work, we got out the trays and cleaned, prepared, and identified the specimens. Students learned how to use the rock saws and make acetate peels of the bryozoans and corals.

4-tray-insideInside a typical tray. We are very grateful for the many online sources to aid identification of these Cincinnatian fossils. Three in particular were most valuable: Alycia Stigall’s Digital Atlas of Ordovician Life, Steve Holland’s stratigraphic and paleontological guide to the Cincinnatian, and the spectacular Dry Dredgers website.

Ohio is a paleontological paradise!

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Wooster’s Fossils of the Week: Geological Magic Lantern Slides from the 19th Century (Part III)

Mark Wilson December 16, 2016 12:01 am

18-devonion-period[Note: Wooster’s Fossil of the Week is on holiday until January 2017.]

This is the last post illustrating the 19th Century Magic Lantern Slides recently found in Scovel Hall of Wooster’s Geology Department. Please see the December 2 post and the week before for details. To review, these slides are 4×8 inches with the image fixed on glass bolted into a thin slab of wood with metal rings. They are chromolithograph slides, each stamped “T.H. McAllister, Optician, N.Y.”. McAllister was the most prominent of many American producers of lantern slides in the late 19th century.

This last set of slides in our collection was apparently used in our old “Historical Geology” courses to evoke the geological time periods. The top image is simply labeled “Devonian“. The trees on the right appear to be towering lycopods, a kind of seedless vascular plant. They were common in the Devonian and are still around today. I can’t tell what the other plants are in the image. The rapid rise of large plants in the Middle Devonian has been called the “Devonian Explosion”. These early forests had significant effects on atmospheric composition, soil formation, erosion, and sediment transport.

[UPDATE: Please see the excellent comments by Ben Creisler. He has given us much new information and numerous links explaining the history of these images. I’ve left my amateur text in place only to record the original post! MW]

19-carboniferous-period“Carboniferous” is the title of this slide. It is dramatic, seemingly showing a Carboniferous forest dominated by ferns being torn apart by a swelling tide. Could this be a comment on the interbedding of marine and terrestrial rock units so common in the Upper Carboniferous of North America?

20-permian-periodFerns are again in the foreground of this Permian scene. I have no explanation for the mountainous seashore landscape, except that the red color of the rocks may represent the New Red Sandstone of Great Britain.

21-transition-periodThis slide is enigmatically labeled “Transition Period”. I suspect it represents the Triassic, a period just after the Permian and thus part of the transition into the Mesozoic. The shrubby plants in the foreground appear to be cycads with massive yellow cones emerging from their tops.

22-eeocen-periodThis image of the “Eocene” is the first of these period slides to depict animals (the herd of ungulates across the river and the bird in the foreground). This may mean these slides were meant to show the progression of plant life over geological time. The forests here look dominated by conifers and angiosperms.

23-miocene-periodThis is a “Miocene” image. I don’t know how I’d distinguish it from the Eocene view above.

24-drift-periodOur final slide shows what the “Drift Period”, which is clearly the Pleistocene. Not only do we have cave bears in the foreground and a herd of bison in the river, there seems to be a massive pile of ice in the left rear!

I have not discovered the artist responsible for these illustrations. If you know, please tell me in the comments!

[UPDATE: Please see excellent information and links by Ben Creisler in the comments below. Thanks, Ben!]

 

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Wooster’s Fossils of the Week: Ordovician bioerosion trace fossils

Mark Wilson December 9, 2016 12:01 am

screen-shot-2016-12-03-at-2-06-03-pmThis week’s post is a celebration of the appearance of a remarkable two-volume work on trace fossils and evolution. The editors and major authors are my friends Gabriela Mángano and Luis Buatois (University of Saskatchewan). They are extraordinary geologists, paleontologists and ichnologists (specialists on trace fossils). They led this massive effort of multiple authors and thousands of manuscript pages. Turns out they are inspiring scientific leaders as well as sharp-eyed editors.

My contribution is in the first volume within a chapter (co-authored with Gabriela, Luis, and Mary Droser of the University of California, Riverside) entitled “The Great Ordovician Biodiversification event”. We examine here the relationship between trace fossils and the critical evolution of marine communities through the Ordovician. My main responsibility was sorting out the changes in the bioeroders over the course of the period. Way back in 2001, Tim Palmer and I noticed a rise in bioerosion trace fossil diversity and abundance in the Middle and Late Ordovician. We grandly called it the “Ordovician Bioerosion Revolution”. The concept and name stuck.

The top image is Fig. 4.8 from the book. The caption: Upper Ordovician bioerosion structures. (a) Trypanites weisi (cross-sectional view) in a carbonate hardground. Katian, Grant Lake Limestone, near Washington, Kentucky, USA; (b) Trypanites weisi (bedding-plane view) in a carbonate hardground. Katian, Grant Lake Limestone, near Manchester, Ohio, USA; (c) Palaeosabella isp. in a trepostome bryozoan. Katian, Whitewater Formation, near Richmond, Indiana, USA; (d) Petroxestes pera. Katian, Whitewater Formation, Caesar Creek Lake emergency spillway, near Waynesville, Ohio, USA; (e) Ropalonaria venosa in a strophomenid brachiopod. Katian, Liberty Formation near Brookville, Indiana, USA.

screen-shot-2016-12-03-at-2-08-42-pmThe cover of the book, which is described here on the publisher’s website.

References:

Mángano, G., Buatois, L., Wilson, M.A. and Droser, M. 2016. The Great Ordovician Biodiversification event, p. 127-156. In: Mángano, G. and Buatois, L. (eds.), The trace-fossil record of major evolutionary events. Topics in Geobiology 39 (Springer).

Wilson, M..A. and Palmer, T.J. 2001. The Ordovician Bioerosion Revolution. Geological Society of America Annual Meeting, Boston, Paper No. 104-0. November 7, 2001.

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

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Wooster’s Fossils of the Week: Geological Magic Lantern Slides from the 19th Century (Part II)

Mark Wilson December 2, 2016 12:01 am

12-iguanodon-and-a-hyleosaurusThis is a continuation of last week’s post about a set of 19th century “Magic Lantern Slides” found in Scovel Hall at Wooster. These evocative scenes are taken from reconstructions of ancient life by Benjamin Waterhouse Hawkins (1807-1894). In 1855, Waterhouse Hawkins finished sculpting life-sized models of these extinct animals, along with many others, for the Crystal Palace gardens in London. Most of these extraordinary animal statues still exist.

Above is the Waterhouse Hawkins version of the Early Cretaceous dinosaurs Iguanodon (the critter on top) and Hylaeosaurus (the two on the lower level). These two genera, along with Megalosaurus, were used as the basis for the new Dinosauria erected by Sir Richard Owen in 1842, a mere dozen years before these models were created. Both of these dinosaurs were herbivorous, Iguanodon being an ornithopod and Hylaeosaurus a basal ankylosaur. They are said here to be from “the Secondary Epoch of the Earth’s history”.

13-an-iguanodon-and-a-hyleosaurus-by-benjamin-waterhouse-hawkins-1853A print version of the same scene. Modern reconstructions of these animals are dramatically different, of course. Waterhouse Hawkins was advised by Owen to make these versions as mammalian as possible. The stance and articulation of limbs is the largest change in our conception of these genera. The Iguanodon model is where a famous 1853 New Year’s Eve dinner party was held.

14-megatherium-glyptodonThis next slide is another Waterhouse Hawkins creation of a much later scene. These are reconstructions of the South American ground sloth Megatherium, which lived from the Pliocene through the Pleistocene. Aside from some unnecessary bulk, these reconstructions are not too far off from how we conceive the giant ground sloths today.

16-no-labelThis magic lantern slide from Wooster’s collection is unlabeled, and I’ve found no trace of the image online. The scene has a Mesozoic vibe, with a crinoid, ammonites (or nautiloids?), and a lurking reptile. Any identifying information would be appreciated!

17-anoplotherium-gracile-palaeotheriumAnother Waterhouse Hawkins theme, this time of Eocene ungulates. The label says they are Paleotherium (in the right foreground) and Anoplotherium gracile (on the left in the foreground). Both were originally described from the Paris region by the magnificent Georges Cuvier.

9-benjamin_waterhouse_hawkins-_photograph_by_maull__polyblankBenjamin Waterhouse Hawkins (1807-1894) was a Londoner skilled in natural history and art. His lifetime honors are a clue to his abilities: He was a Member of the Society of Arts, a Fellow of the Linnean Society, and a Fellow of the Geological Society of London. His Crystal Palace dinosaurs are his best know combination of art and science, but he produced much besides. For example, he drew figures for The Zoology of the Voyage of HMS Beagle. In 1868 he mounted a skeleton of Hadrosaurus in Philadelphia, the first dinosaur to be displayed in this way. Through his art and connections in the paleontological world, Waterhouse Hawkins brought fossils to life for millions of people in Victorian times.

 

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Wooster’s Fossils of the Week: Geological Magic Lantern Slides from the 19th Century (Part I)

Mark Wilson November 25, 2016 12:01 am

1-teleosaurus-ichthyosaurus-pentacrinites-ammonites-gryphaea“Wooster’s Fossil of the Week” is not always about actual fossils, but our topics are each paleontological. Many years ago I discovered in an old box tucked away in the attic of Scovel Hall at Wooster a set of “Magic Lantern Slides” used in geology courses. I came across them again recently and thought I would share these ancient scenes. Lantern slides were the 19th Century equivalent of PowerPoint, so generations of Wooster geology students must have sat in rapture looking at these colorful images. (At least that’s how I imagine them now viewing my PowerPoint slides!) The above imagined seashore view includes the crocodylian Teleosaurus atop the layered rocks, Ichthyosaurus immediately below, four long-necked Plesiosaurus on the left, an orange cluster of the crinoid Pentacrinus rooted inexplicably in the beach sand, and a scattering of ammonite and oyster shells.  The caption on the image says these animals lived during “the Secondary Epoch of the Earth’s history”. We would now say this is a Jurassic scene. The ichthyosaur looks the most odd to us. Not only is it crawling on the land, it lacks a dorsal fin and the characteristic bi-lobed, shark-like tail. These were later discoveries about ichthyosaurs made only after specimens were found with skin impressions.

2-ammonite-lantern-detailThis close-up shows the detail in these images. Ammonites are on the left (“6”) and the oyster Gryphaea is on the right (“7”).

3a-magic-lantern-slide-geological-585The Magic Lantern Slides are 4×8 inches with the image on glass fixed in a thin slab of wood with metal rings. These are chromolithograph slides, each stamped “T.H. McAllister, Optician, N.Y.”. McAllister was the most prominent of many American producers of lantern slides in the late 19th century.

4-megalosaurus-pterodactyleThe quadrupedal beasts in the foreground are the of the Jurassic theropod dinosaur Megalosaurus, with pterodactyls in the background. We now know Megalosaurus was bipedal, like all theropod dinosaurs.

5-megalosaurus-headAnother detail showing the fine quality of these color images on glass.

6-gigantic-lizards-and-some-pterosauria-by-benjamin-waterhouse-hawkins-1853Most readers with any background in the history of paleontology recognize these reconstructions of ancient life from the work of Benjamin Waterhouse Hawkins (1807-1894). In 1855, Waterhouse Hawkins finished sculpting life-sized models of these extinct animals, along with many others, for the Crystal Palace gardens in London. He was advised for the anatomical details by Sir Richard Owen (1804-1892), a hero of paleontology but not a fan of Darwinian evolution. He is responsible for the dinosaurs of Waterhouse Hawkins looking rather mammalian. Most of these extraordinary animal statues still exist.

9-benjamin_waterhouse_hawkins-_photograph_by_maull__polyblankBenjamin Waterhouse Hawkins (1807-1894). More reconstructions from him, along with his brief biography, in the next installment.

 

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Wooster’s Fossil of the Week: A juvenile conch from the Upper Pleistocene (Eemian) of The Bahamas

Mark Wilson November 18, 2016 12:01 am

inagua-lobatus-gigasI collected this beautiful shell from a seashore exposure of Pleistocene sediments on Great Inagua, the third largest island of The Bahamas. I was on an epic expedition to this bit of paradise with Al Curran and Brian White of Smith College in March 2006. We were pursuing evidence for a sea-level change event in the Eemian, about 125,000 years ago. This was some of the most exciting scientific work I’ve done, so this little shell brings back many memories. I found it loosely cemented into a small patch of carbonate sediments inside a hollow of an ancient coral reef. This shell and numerous other samples were basic data for a rapid rise and fall of sea level during the last interglacial interval. The project is summarized in the Thompson et al. (2011) reference below.

This is a juvenile of the common Queen Conch Lobatus gigas (Linnaeus, 1758). In its adult form with a flared aperture it is one of the most recognizable modern shells in the world. Some of you may be surprised by the generic name. I was. I knew this shell as Strombus gigas, the original name given to it by the sainted father of taxonomy Carolus Linnaeus in 1758. After several adventures in the literature, Landau et al. (2008) placed the species in the genus Lobatus Swainson 1837.

salvador-lobatus-gigas-1The species looks exactly the same today, at least in its shell. This is a similar modern Queen Conch juvenile collected from San Salvador Island in The Bahamas. Note the color patterns which are lost in the fossil.

salvador-lobatus-gigas-2This is the apertural view of the same modern shell. With time it would have grown a much thicker apertural margin to protect it from predators.

buonanni-strombus-gigas-figureThis is the earliest image known of the Queen Conch (Buonanni, 1684). For a long time the type specimen (the specimen of record defining the taxon) of Strombus gigas (the older Linnaeus name) was missing. In 1941 this figure — the figure itself — was designated a neotype (a replacement type) of the species. (First time I’ve heard of that move.) The original type specimen, though, was found in Sweden in 1953, so there is an actual shell in the collections and no need for this neotype.

bonanno-coverThat first figure of Lobatus gigas was drawn by Filippo Bonanni (1638-1723), a remarkable Italian Jesuit scholar. It is found in the book above, which is the first known guide to seashells for collectors. (Note the “SUPERIORUM PERMISSU”, meaning he published with the permission of his Jesuit superiors.) Bonanni was one of the first to suggest fossils had at least some organic origins, speculating that they were either organism remains or “products of natural powers.”

References:

Buonanni, F. 1684. Recreatio mentis, et oculi in observatione animalium testaceorum curiosis naturae inspectoribus italico sermone primum proposita. p. Philippo Bonanno . Nunc denuo ab eodem latine oblata, centum additis testaceorum iconibus, circaquae varia problemata proponuntur. Ex typographia Varesij, Romae, xvi + 270 + [10] pp., 139 pls.

Landau, B.M., Kronenberg G.C. and Herbert, G.S. 2008. A large new species of Lobatus (Gastropoda: Strombidae) from the Neogene of the Dominican Republic, with notes on the genus. The Veliger 50: 31–38.

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas corals. Nature Geoscience 4: 684–687.

White, B.H., Curran, H.A. and Wilson, M.A. 2001. A sea-level lowstand (Devil’s Point Event) recorded in Bahamian reefs: comparison with other Last Interglacial climate proxies; In: Greenstein, B.J. and Carney, C., (editors), Proceedings of the 10th Symposium on the Geology of the Bahamas: Bahamian Field Station, San Salvador Island, p. 109-128.

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