Introducing Oligoremora rhenana!

There’s a new fossil remora in Stuttgart  – Oligoremora! A remora from the Oligocene of . . . Baden-Württemberg. Our fossil collection definitely has a local theme. I’ve mentioned the Oligocene fossil site of Rauenberg before (it’s an important one), and this fish is from the same quarry.

OLYMPUS DIGITAL CAMERA
Oligoremora itself! The total length of this fish is approximately 10 cm.

What’s a remora? They’re actually fairly awesome. Remoras are a group of marine fishes in which the first dorsal fin has been modified into an adhesion disc that they use to attach to larger animals, such as a shark, ray, whale, or turtle. The remoras save energy by not swimming or pumping water over the gills (the fish version of breathing), and in turn keep the host clean of parasites and dead skin.

lemonshark
Shark with remoras. By: Albert Kok, CC BY-SA 3.0
2823094612_3243a49b29_o
Close-up of the adhesion disc in a living remora. By Richard Ling, CC BY-NC-ND 2.0
OLYMPUS DIGITAL CAMERA
Adhesion disc of Oligoremora, floating away from the broken up skull.

A range of potential remora hosts are known from Rauenberg, including sharks, turtles, and dugongs. While living species of remoras are quite specific in their host preferences, pinpointing Oligoremora’s host is not possible at this point. It is also possible that host preferences appeared more recently in the evolutionary history of remoras.

 The steps leading up to an adaptation as specific as the remora adhesive disc and ride-along lifestyle are bound to be interesting. Based on fossil occurrences and molecular data, it is estimated that the adhesion disc appeared at most seven million years before the widespread appearance of remoras, including Oligoremora, in European seaways in the early Oligocene. All of these early Oligocene remoras were equipped with a fully functional adhesion disc, and so the earliest evolutionary steps towards this specialized structure and lifestyle still remain poorly understood.

References

Friedman, M., Johanson, Z., Harrington, R. C., Near, T. J., & Graham, M. R. (2013). An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc. Proc. R. Soc. B 280(1766).

 Micklich, N., R. Gregorová, A. F. Bannikov, D.-S. Baciu, I. Grădianu, and G. Carnevale. 2016. Oligoremora rhenana n. g. n. sp., a new echeneid fish (Percomorpha, Echeneoidei) from the Oligocene of the Grube Unterfeld (“Frauenweiler”) clay pit. Paläontologische Zeitschrift.

 

 

Older Specimens

This summer, the Staatliches Museum für Naturkunde Stuttgart celebrates its 225th anniversary. The idea of having a museum collection with such a long history is a bit difficult to imagine – one of the oldest items in the collection, a hunting trophy of Duke Ludwig V of Wirttemberg, was collected before 1593, and at that time museums and collections were viewed very differently than they are now. The collection was a series of curiosities and art objects kept by the Duke for his personal enjoyment. 1791, the year the Stuttgart Museum recognizes as its official founding date, marks the reorganization of the ducal curiosity cabinet. Art and natural history items were treated separately, and staff scientists were appointed to care for the natural history collections.

 Fossil vertebrates have been part of the Stuttgart collection for a long time. Many of these historical specimens are exhibited in the gallery, not because they are spectacularly preserved but because they played an important role in the history of science and palaeontology. That brings us to the subject of this post, the role of Early Jurassic fossils from Baden-Württemberg in developing our understanding of ichthyosaur evolution.

Ichthyosaurs are a group of secondarily marine reptiles that lived during the Mesozoic Era. Our understanding of ichthyosaur anatomy, evolutionary history, diet, reproductive mode, and even colouration is surprisingly thorough for a group of animals that have been extinct for 95 million years.

ichthyosaurus_bw
A modern reconstruction of an ichthyosaur. Image credit: Nobu Tamura, CC BY 3.0

However, this was not always the case. Ichthyosaurs were initially thought to be somewhere between fishes and crocodiles on the ladder of life, and were often reconstructed as such.

duria_antiquior
Old-timey reconstruction featuring ichthyosaurs (1830). Duria Antiquior – a more Ancient Dorset. Henry de la Beche.

A surprising amount of information pertaining to ichthyosaur paleobiology was first deduced based on specimens in the collections of the Staatliches Museum für Naturkunde Stuttgart. Ichthyosaurs are especially well-represented in the collections thanks to quarrying of Early Jurassic marine shales in and around the village of Holzmaden, about 30 km southeast of Stuttgart. One of the first ichthyosaurs reported from this region was excavated in 1749. Although missing the head and tail, the specimen clearly shows an embryo in the birth canal of the female.

Blog
Specimen of the ichthyosaur Stenopterygius collected in 1749 from a quarry near Holzmaden.

This specimen was initially identified as a fish, most likely a ray, and subsequently ignored. However, in 1824, Georg Friedrich Jäger recognized its reptilian nature and classified it as an ichthyosaur. The live-bearing reproductive strategy of these aquatic reptiles was addressed in a subsequent publication (1842).

Further advances in ichthyosaur palaeobiology came in the late 1880s, when Bernhard Hauff devised a preparation technique that did not destroy the thin layer of preserved soft tissues surrounding many of the Holzmaden ichthyosaurs.

SMNS7800
Archival photo of the first ichthyosaur specimen with a complete soft-tissue body outline to be prepared.

This specimen led to the recognition that ichthyosaurs had a body shape more similar to that of dolphins or sharks than to crocodiles, and was fundamental in interpreting the way of life of these animals.

Unbenannt-1
Reconstruction of the ichthyosaur Stenopterygius by E. Fraas, 1892

Research on ichthyosaurs in ongoing, but this will be the subject of another post.

References

Fraas E. 1892. Ueber einen neuen Fund von Ichthyosaurus in Württemberg.Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde. 1892(2):87-90.

Jaeger, G. F. von (1824): De ichthyosauri sive proteosauri fossilis speciminibus in agro bollensi in Wirttembergia repertis. 14 S.; Stuttgart (Cotta).

Jaeger, G. F. von (1842). Amtlicher Bericht über die zwanzigste Versammlung der Gesellschaft Deutscher Naturforscher und Ärzte in Mainz im September 1842, Florian Kupferberg, Mainz, 1843, p. 117-118.

Fish Guts

Last week I attended a small conference on the theme of soft-tissue fossilization, specifically what it can tell us about conditions of preservation and biology of extinct organisms. On that note, I’m inspired to write a blog entry about fossil soft tissue preservation in what seems to be my favourite topic, Jurassic fishes.

As pointed out at the conference, it goes without saying that now-extinct organisms had skin, muscles, and so forth. The challenge, when presented with a fossil showing exceptional preservation, is to ask questions that touch on either the environmental conditions leading to such preservation or pinpoint how such structures increase our knowledge of the anatomy or biology of these extinct animals. After all, of course dinosaurs had a liver so finding a dinosaur skeleton with a fossilized liver, while kind of neat, doesn’t do much for science. On that note, today’s fossil provides information on the gastrointestinal tract.

WholeFish
Today’s fossil, a large predatory fish of the species Saurostomus esocinus, closely related to the previously discussed Pachycormus bollensis. This individual is from the Early Jurassic Posidonia Shale of Baden-Württemberg, Germany. Note the light-coloured structure in the abdominal region.

Now, to zoom in on the light-coloured structure in the above fish fossil:

spiralvalve
It’s a cololite – in other words, fossilized intestinal contents forming a negative of the shape of the inside of the intestine. The arrows indicate the coils of the spiral valve.

So fossil fish have intestines – no surprise there. What is more surprising is that Saurostomus has a spiral valve, a structure known from sharks and rays today that increases the surface area of the intestine available for nutrient absorption without increasing total length. Most bony fishes alive today belong to the teleosts, a lineage that has lost the spiral valve. However, it turns out that these intestinal structures were a fairly common feature in fossil non-teleost bony fishes, including pachycormids such as Saurostomus. A spiral valve has recently been described in some Triassic bony fishes, and the number of coils is related to body size in both these Mesozoic fishes and in living sharks.

 We can also ask why this structure is fossilized in some fishes but not in others. These intestinal contents are preserved by replacement of the original components with phosphate, the same molecules making up bones and scales. The phosphate molecules for this type of fossilization can either come from the surrounding environment, or from the intestine itself. Not surprisingly, animals that eat prey high in phosphate (in other words, prey that has bones and scales) have a higher likelihood of showing this kind of exceptional preservation of the gastrointestinal tract. However, our understanding of the fossilization process is still not good enough to make the claim in the absence of other evidence that a fossil fish with a preserved cololite had a diet, at least in part, composed of other fishes. In the case of Saurostomus, although no stomach contents have been reported for this fish its large pointy teeth make a predatory diet very likely.

References

Argyriou, T., Clauss, M., Maxwell, E.E., Furrer, H. and Sánchez-Villagra, M.R., 2016. Exceptional preservation reveals gastrointestinal anatomy and evolution in early actinopterygian fishes. Scientific reports, 6.

Dal Sasso, C. and Signore, M., 1998. Exceptional soft-tissue preservation in a theropod dinosaur from Italy. Nature, 392(6674), pp.383-387.

 

Fossil of the Year 2016

Every year, the German Palaeontological Association selects a fossil of particular interest and scientific importance for public outreach and to draw attention to Germany’s fossil resources. Their 2016 selection is Leptolepides sprattiformis, a small teleost fish from the Late Jurassic of Bavaria, Germany (approximately 150 million years old). Leptolepides is usually about 7 cm in length, and the shape of the skull and jaws suggests that it fed on plankton, as do modern baitfish such as anchovies.

IMG_5726b
In palaeontology, every species name must be associated with a specimen to which that name is permanently connected – a specimen to which palaeontologists can refer when trying to identify new material. For Leptolepides sprattiformis, this voucher (type) specimen is housed in the Stuttgart collections.

Leptolepides sprattiformis is a very common fossil from the lithographic limestones of Bavaria, and is also often found in very high abundance, with many individuals on a single bedding plane. This suggests that whole schools may have been subject to mass mortality events.

IMG_5734b
Seven individuals of Leptolepides preserved on a single surface; some slabs with up to 77 individals preserved have been recovered.

Modern baitfish form an important link in the marine food chain, consuming plankton and in turn being eaten by larger predators. It is probable that Leptolepides sprattiformis played a similar ecological role; individuals of this species are also relatively common as gastrointestinal contents of larger fishes.

6947494160_7b2bf36181_o
School of baitfish (from N, CC BY-NC-ND 2.0)

Pipefishes!

Today’s entry features a fossil fish from a genus still alive today – a Syngnathus pipefish from the early Oligocene fossil site of Rauenberg, Baden-Württemberg, Germany.

SyngnathusBlog
Only ~6 cm long! Isn’t it cute? A bit like a small stick? The black spot to the left is preserved pigments from where the eye used to be.

Although closely related to seahorses, pipefishes are straight-bodied and do not swim in an upright posture.

syngnathus_abaster_body_b
A living pipefish (Syngnathus) in an aquarium. The head is to the left. By Giacomo Radi (email to OTRS) [GFDL (http://www.gnu.org/copyleft/fdl.html)%5D, via Wikimedia Commons.
In the early Oligocene, ~32 million years ago, a narrow seaway divided Central Europe along what is now the Rhine Valley. Marine life flourished, and numerous fossil sites from Switzerland in the South to Belgium in the North document a rich diversity of animals and plants from this time period, including hummingbirds, sea cows, sea turtles, and fishes ranging in size from the tiny pipefishes to basking sharks.

CetorhinusBlog
These strange spines are fossil gill rakers, part of the filtering apparatus through which basking sharks strain plankton from the water.

Aside from its obvious charisma, this week’s fossil (and others from the same locality) represent one of the earliest appearances of Syngnathus in the fossil record, and are important for understanding the tempo and mode of evolution in pipefishes, as well as the rise of modern European coastal marine diversity.

January: Saurorhynchus

Today’s feature fossil is less than beautiful, and exemplifies why some specimens are never seen by the public. It is part of a skull of a bony fish called Saurorhynchus. Saurorhynchus was a piscivore (it ate other fish), and is well-known from the Early Jurassic of Europe and Canada. It looked a bit like a present-day needlefish, but is thought to be more closely related to sturgeons and paddlefish:

BlogNeedlefish
Atlantic needlefish. Photo from SEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC. 2010. NOAA Photo Library: fish4485. CC BY 2.0.
DSCN5531Blog
Saurorhynchus skeleton. See the resemblance to the needlefish? The white blob half-way along the length of the fish is a second small fish in the stomach.

The Saurorhynchus specimen under consideration today is considerably less complete, and more imagination is needed to visualize the fish:

96902b_PS
Skull of Saurorhynchus. The lower jaw and most of the body are missing. The part of the skull above the eye is fossilized as an impression on the rock – the bones themselves are missing. The teeth are all broken off, only the roots are left.

This fish was collected from the bed of a small creek outside the town of Göppingen in Baden-Württemberg, Germany. It is from rocks of Middle Jurassic age. Even though this fossil is, objectively speaking, pretty ugly, it is a great example of how something can be scientifically noteworthy but not worthy of exhibition. Why is it so important? Saurorhynchus was thought to have gone extinct part way through the Early Jurassic, at a time rapid global warming created inhospitable conditions in the oceans and caused many species to go extinct. This skull, from approximately 5 million years after Saurorhynchus supposedly became extinct, indicates that fishes of this kind survived these difficult environmental conditions.

References

Further details on this specimen can be found in the following publication:
Maxwell, E.E. 2015. First Middle Jurassic record of Saurichthyidae (Actinopterygii). Paläontologische Zeitschrift. doi 10.1007/s12542-015-0281-5

 

January: Pachycormus

Today’s fossil is an example of Pachycormus bollensis, a bony fish from the Early Jurassic of Baden-Württemberg, Germany (~181 million years old). Pachycormus resembled tunas in general body shape, although it belongs to an entirely extinct group of fishes and has no close living relatives. Like tunas, it was a fast swimmer, living in the open ocean. The species Pachycormus bollensis was a large fish, growing to more than a meter in length. This week’s fossil is of special interest as it has a squid preserved in the stomach. Such direct evidence of diet is rare in extinct animals, and helps us to reconstruct ancient food webs.

RestoredFish
Pachycormus bollensis, before restoration

Collections history

The fish was collected from a commercial quarry near the village of Zell unter Aichelberg in 1977. However, even after being brought to the museum, it was not spared the effects of time. Changes in temperature and humidity caused iron sulfide minerals (pyrite) in the surrounding rock to oxidize (rust) and expand, creating cracks in the fossil.

pyrite
A pyrite crystal expanding cracking the rock.

Luckily, the fossil was restored by removing the large pyrite crystals from the slab of rock and stabilizing the cracks with adhesive before any permanent damage was done (in other words, it was glued back together).

Pachycormus bollensisPS
After restoration, cracks are still visible but have been stabilized to prevent further damage.

 

Acknowledgements

Kulturstiftung der Länder, Kunst auf Lager funded the restoration of this specimen.
Restoration was carried out by C. Gasco Martin