Wooster’s Fossil of the Week: A large trepostome bryozoan on a nautiloid conch (Upper Ordovician of northern Kentucky)

March 17th, 2017

This massive trepostome bryozoan, a solid lump of biogenic calcite, was collected earlier this week on the latest Team Cincinnati field expedition into the treasure-filled Upper Ordovician underlying and surrounding that city. Wooster students Matt Shearer, Luke Kosowatz and I are pursuing projects related to trepostome bryozoans and bioerosion (the biological destruction of hard substrates). The above specimen combines both these worlds, and more. Note the concavity at the base of the specimen. It comes from the Bellevue Formation (Katian) exposed on Bullitsville Road near the infamous Creation Museum (C/W-152).

Underneath the bryozoan colony (its zoarium) is this conical impression. It is an external mold of a straight nautiloid conch, the shell of a common squid-like cephalopod during the Ordovician. After the death of the nautiloid its empty tubular conch rested on the seafloor. This hard surface attracted the larvae of a variety of bryozoans that spread their calcitic zoaria (colonial skeletons) across the surface. Eventually one trepostome bryozoan species gained dominance over the space and occupied it all, growing into the large colony we see today. It even wrapped around the aperture of the conch (on the left) and grew a bit into the tube. Since the nautiloid conch was made of unstable aragonite, it long ago dissolved away, leaving an impression (external mold) in the stable calcite of the bryozoan.

How do we know there were earlier generations of bryozoans on this conch? We see them exposed upside-down on the surface of the external mold. Above we see the thin, branching cyclostome bryozoan Cuffeyella in the foreground, with a sheet of an encrusting trepostome bryozoan in the background. There are several other earlier bryozoans visible on this surface, revealing an ecological succession. There may be soft-bodied organisms preserved on this surface as well. This locality yielded the first described specimens of bioimmuration in the Ordovician (see Wilson et al., 1994).

There were other large trepostome bryozoans found in this same locality. I couldn’t resist cutting one in half to see what the inside looked like.

In this close view of the cross-section through the calcitic trepostome bryozoan we see numerous round holes drilled by some sort of worm seeking protective space so it could filter-feed. (In other words, it was not preying on the bryozoan.) The most intense boring of the specimen appears to have taken place just before and after the death of the colony. We know some borings were excavated into living bryozoan skeleton because the bryozoan formed reactive tissue around the intruder. The very tiny reddish-brown dots scattered in layers are “brown bodies“, the organic remnants of bryozoan polypides in their skeletal tubes (zooecia).

It has been a pleasure to return to the extraordinary Cincinnati fossils!

References:

Taylor, P.D. 1990. Preservation of soft-bodied and other organisms by bioimmuration—a review. Palaeontology 33: 1-17.

Wilson, M.A. 1985. Disturbance and ecologic succession in an Upper Ordovician cobble-dwelling hardground fauna. Science 228: 575-577.

Wilson, M.A., Palmer, T.J. and Taylor, P.D. 1994. Earliest preservation of soft-bodied fossils by epibiont bioimmuration: Upper Ordovician of Kentucky. Lethaia 27: 269-270.

Wooster’s Fossil of the Week: Encrusting craniid brachiopods (Upper Ordovician of southeastern Indiana)

March 10th, 2017

The two irregular patches above are brachiopods known as Petrocrania scabiosa encrusting the ventral valve of yet another brachiopod (Rafinesquina). That species name “scabiosa” is evocative if not a little unpleasant — it is also the root of the English “scab”.

Petrocrania scabiosa is in a group of brachiopods we used to call “inarticulates” because their two valves are not articulated by a hinge as they are in most brachiopods. Instead they are held together by a complex set of muscles. Now we place these brachiopods in the Class Craniforma, an ancient group which originated in the Cambrian and is still alive today.

Petrocrania scabiosa was a filter-feeder like all other brachiopods, extracting nutrients from the seawater with a fleshy lophophore. The Wooster specimens are part of our large set of encrusting fossils (a type of sclerobiont) in our hard substrate collection. They have irregular shells that are circular in outline when they grew alone, and angular when they grew against each other.

Some craniid brachiopods were so thin that their shells repeated the features of the substrate underneath them, a phenomenon known as xenomorphism (“foreign-form”).

Petrocrania scabiosa brachiopods (circular) on a Rafinesquina brachiopod, along with a trepostome bryozoan that encrusted some brachiopods and grew around others. The P. scabiosa on the far left shows xenomorphic features. Specimen borrowed from the University of Cincinnati paleontology collections.

A 2007 College of Wooster paleontology field trip to the Upper Ordovician locality near Richmond, Indiana, where these specimens were found. Students are in the traditional paleontological poses.

[Originally published May 22, 2011.]

Wooster’s Fossil of the Week: Mysterious tentaculitids (Devonian of Maryland)

March 3rd, 2017

The sharp little conical fossils above are common Paleozoic fossils, especially in the Devonian. They are tentaculitids now most commonly placed in the Class Tentaculitoidea Ljashenko 1957. Tentaculitids appeared in the Ordovician and disappeared sometime around the end of the Carboniferous and beginning of the Permian. These specimens are from the Devonian of Maryland.

The systematic placement of the tentaculitids has been controversial. Their straight, narrow shells are usually ornamented by concentric rings, and many had septa (thin shelly partitions) inside the cones. The microstructure of the shells is most interesting — it looks very much like that of brachiopods and bryozoans. For this reason and several others, several of my colleagues and I believe the tentaculitids were lophophorates (animals that filter-feed with a tentacular device called a lophophore). They may thus be related to other problematic tubeworms like microconchids and cornulitids (Taylor et al., 2010).

Tentaculitids from the New Creek Limestone (Lochkovian, Early Devonian) of New Creek, West Virginia.

Knowing how the tentaculitids fit into an evolutionary scheme, though, has not helped us figure out what they did for a living. The figure below, from Cornell et al. (2003), shows these funny cones in just about every lifestyle imaginable!

References:

Cornell, S.R., Brett, C.E. and Sumrall, C.D. 2003. Paleoecology and taphonomy of an edrioasteroid-dominated hardground association from tentaculitid limestones in the Early Devonian of New York: A Paleozoic rocky peritidal community. Palaios 18: 212-224.

Taylor, P.D., Vinn, O. and Wilson, M.A. 2010. Evolution of biomineralization in ‘lophophorates’. Special Papers in Palaeontology 84: 317-333.

[Originally published May 29, 2011.]

Wooster’s Fossil of the Week: A scaphitid ammonite (Late Cretaceous of Mississippi)

February 24th, 2017

The beauty above is Discoscaphites iris (Conrad, 1858) from the Owl Creek Formation of Ripley, Mississippi. Megan Innis and I collected it during our expedition to the Cretaceous-Paleogene boundary in the southern United States last summer. It is a significant index fossil in biostratigraphy: the Discoscaphites iris Zone is the latest in the Cretaceous (the late Maastrichtian Stage). This animal lived in the final days of the Mesozoic Era just before the mass extinction 65.5 million years ago.

Discoscaphites iris is an ammonite, a type of extinct cephalopod mollusk related to the modern octopus, squid and nautilus. It had a planispirally-coiled shell with chambers divided from each other by complexly-folded walls. If you look closely near the top of the fossil above, you will see where the shell has flaked away revealing an internal mold of sediment and a peek at the folded walls inside. “Ammonite”, by the way, is a very old term for these fossils. Pliny the Elder himself used a variant of the name, which comes from the Egyptian god Amun with his occasional coiled ram’s horn headgear.

Reconstruction of an ammonite by Arthur Weasley (via Wikipedia).

Ammonite shells were made of the carbonate mineral aragonite. This is the mineral that makes many modern mollusk shells have prismatic colors, which we call nacreous. You may know it best as “mother of pearl” or as pearls themselves. Aragonite has an unstable crystal structure and so is not common in rocks older than a few million years. The original aragonite in our ammonite fossil is thus a bonus.

In an oddly topical note, Discoscaphites iris was recently found in the Upper Cretaceous of Libya, giving it a disjunct range from the US Gulf and Atlantic coasts to the Mediterranean coast of northern Africa (Machalski et al., 2009).

Reference:

Machalski, M., Jagt, J.W.M., Landman, N.H. and Uberna, J., 2009. First record of the North American scaphitid ammonite Discoscaphites iris from the upper Maastrichtian of Libya. N. Jb. Geol. Paläont. Abh. 254: 373-378.

[Originally published April 24, 2011]

Wooster’s Fossil of the Week: A stromatoporoid (Middle Devonian of central Ohio)

February 17th, 2017

Stromatoporoids are very common fossils in the Silurian and Devonian of Ohio and Indiana, especially in carbonate rocks like the Columbus Limestone (from which the above specimen was collected). Wooster geologists encountered them frequently on our Estonia expeditions in the last few years, and we worked with at least their functional equivalents in the Jurassic of Israel (Wilson et al., 2008).

For their abundance, though, stromatoporoids still are a bit mysterious. We know for sure that they were marine animals of some kind, and they formed reefs in clear, warm seas rich in calcium carbonate (DaSilva et al., 2011). Because of this tropical habit, early workers believed they were some kind of coral, but now most paleontologists believe they were sponges. Stromatoporoids appear in the Ordovician and are abundant into the Early Carboniferous. The group seems to disappear until the Mesozoic, when they again become common with the same form and life habits lasting until extinction in the Late Cretaceous (Stearn et al., 1999).

The typical stromatoporoid has a thick skeleton of calcite with horizontal laminae, vertical pillars, mounds on the upper surface called mamelons, and dendritic canals called astrorhizae shallowly inscribed on the mamelons. These astrorhizae are the key to deciphering what the stromatoproids. They are very similar to those on modern hard sponges called sclerosponges. Stromatoporoids appear to be a kind of sclerosponge with a few significant differences (like a calcitic instead of an aragonitic skeleton).

Stromatoporoid anatomy from Boardman et al. (1987).

Top surface of a stromatoporoid from the Columbus Limestone showing the mamelons.

There is considerable debate about whether the Paleozoic stromatoporoids are really ancestral to the Mesozoic versions. There may instead be some kind of evolutionary convergence between two groups of hard sponges. The arguments are usually at the microscopic level!

The stromatoporoids were originally named by Nicholson and Murie in 1878. This gives us a chance to introduce another 19th Century paleontologist whose name we often see on common fossil taxa: Henry Alleyne Nicholson (1844-1899). Nicholson was a biologist and geologist born in England and educated in Germany and Scotland. He was an accomplished writer, authoring several popular textbooks, and a spectacular artist of the natural world. Nicholson taught in many universities in Canada and Great Britain, finally ending his career as Regius Professor of Natural History at the University of Aberdeen.

Henry Alleyne Nicholson (1844-1899) from the University of Aberdeen museum website.

References:

Boardman, R.S., Cheetham, A.H. and Rowell, A.J. 1987. Fossil Invertebrates. Wiley Publishers. 728 pages.

DaSilva, A., Kershaw, S. and Boulvain, F. 2011. Stromatoporoid palaeoecology in the Frasnian (Upper Devonian) Belgian platform, and its applications in interpretation of carbonate platform environments. Palaeontology 54: 883–905.

Nicholson, H.A. and Murie, J. 1878. On the minute structure of Stromatopora and its allies. Linnean Society, Journal of Zoology 14: 187-246.

Stearn, C.W., Webby, B.D., Nestor, H. and Stock, C.W. 1999. Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontologica Polonica 44: 1-70.

Wilson, M.A., Feldman, H.R., Bowen, J.C. and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

[Originally published on October 30, 2011]

Wooster’s Fossil of the Week: A receptaculitid (Middle Ordovician of Missouri)

February 10th, 2017

This week’s fossil is a long-standing paleontological mystery. Above is a receptaculitid from the Kimmswick Limestone (Middle Ordovician) near Ozora, Missouri. I think I found it on a field trip with Frank Koucky in the distant mists of my student days at Wooster, but so many outcrops, so many fossils …

Below is a nineteenth century illustration of a typical receptaculitid fossil. They are sometimes called “sunflower corals” because they look a bit like the swirl of seeds in the center of a sunflower. They were certainly not corals, though, or probably any other kind of animal. Receptaculitids appeared in the Ordovician and went extinct in the Permian, so they were confined to the Paleozoic Era. Receptaculitids were bag-like in form with the outside made of mineralized pillars (meroms) with square or diamond-shaped heads. The fossils are usually flattened disks because they were compressed by burial. You may notice now that the fossil at the top of this post is a mold of the original with the dissolved pillars represented by open holes. (Paleontologists can argue if this is an external or internal mold.)So what were the receptaculitids? When I was a student we called them a kind of sponge, something like a successor of the Cambrian archaeocyathids. In the 1980s a convincing case was made that they were instead a kind of alga of the Dasycladales. Now the most popular answer is that they belong to that fascinating group “Problematica”, meaning we have no idea what they were! (Nitecki et al., 1999). It’s those odd meroms that are the problem — they appear in no other known group, fossil or recent.

I find it deeply comforting that we still have plenty of fossils in the Problematica. We will always have mysteries to puzzle over.
Another Wooster receptaculitid specimen, this time seen from the underside showing side-views of the meroms.
Diagram of a receptaculitid in roughly life position showing its inflated nature and pillar-like meroms. From Dawson (1880, fig. 25): a, Aperture (probably imaginary here). b, Inner wall. c, Outer wall. n, Nucleus, or primary chamber. v, Internal cavity.

Finally, this is what a typical receptaculitid looks like in the field (Ordovician of Estonia). Note that nice sunflower spiral of the merom ends.

References:

Dawson, J.W. 1880. The chain of life in geological time: A sketch of the origin and succession of animals and plants. The Religious Tract Society, 272 pages.

Nitecki, M.H., Mutvei, H. and Nitecki, D.V. 1999. Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon. Kluwer Academic/Plenum, 241 pages.

[Originally published on September 18, 2011]

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

February 3rd, 2017

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.

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

January 27th, 2017

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

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

January 20th, 2017

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

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

January 13th, 2017

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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