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Rhaetian Lorraine Region

Rhaetian fossils from the Lorraine region.

Fossil shark remains

Rhaetian Sharks

 

During the Rhaetian, sharks were undergoing rapid evolutionary changes. At that time, they were generally not at the top of the marine food chain. Other marine predators such as early Ichthyosauria and Plesiosauria were larger and acted as the top predators. Sharks, however, were becoming larger and the fine structure of their enameloid was starting to change. 

At that time, hybodonts dominated shark faunas and the Neoselachii (modern level sharks) were just beginning to appear. These evolutionary changes are reflected in the enameloid microstructure of the teeth, which can be studied after treating them with different kinds of acid. The classification of some Rhaetian shark species remains problematic because of complications in the contemporary evolutionary history of the  enameloid microstructure. Usually, teeth of Neoselachian sharks have three layers of crystallites which make up the outer covering of the tooth. Hybodonts usually have only a single layer of crystallites. Explaining the scientific terms on which researchers base their conclusions is not the purpose of this website; if you are interested in more information, check the bibliography! Over the past few decades, quite a few Rhaetian sharks were seen as hybodonts, but after more detailed research they were placed in the Neoselachii whereafter some of them ended back up as hybodonts. Another difficulty researchers struggle with is the fact that the teeth of some species posses striking similarities with those of recent sharks due to convergent development of their teeth, while the enamel microstructure points towards a hybodont origin. By the end of the Cretaceous, the hybodonts became extinct; the Ptychodontidae were their last representatives. 

The shark remains recovered from the Lorraine sediments show some signs of transportation, although some of them are still pristine. They mainly consist of teeth, which are very fragile, but dermal denticles and dorsal fin spines have also been found.

Although the European Rhaetian has been the subject of many scientific research, new species are being discovered  occasionally. Therefore, the following list of genera and species might no be complete. Due to improving technology, future research might reveal different relationships among these species. Therefore, several species or genera on this website might need revision in the future.

Let's commence with an up-to-date faunal list for the Rhaetian sharks of the Lorraine region.

-Hybodontiformes:  

  • Pseudodalatias barnstonensis (The teeth of this species look like modern Neoselachii but they have a unique enameloïd microstructure which resembles that of Hybodonts as well as that of Neoselachii).
  • Vallisia coppi (Based on faunal list of Duffin et al., 1983. Not yet retrieved by authors of this website. The enameloid is said to have a highly unusual composition. Even though the teeth look like those of modern batoids, they probably represent a highly adapted hybodont.)
  • Nemacanthus monilifer (ID originally based only on fin spines, not yet positively ID'ed by authors of this website and it's probably a nomen dubium since no related teeth have ever been recovered.)

Hybodontiformes

Teeth presented in this section belong to primitive sharks.

Lissodus minimus (Agassiz, 1839)

Hybodontiformes  Zangerl, 1981

Lonchidiidae  Herman, 1977

Lissodus minimus (Agassiz, 1839)            

  

 

 

Lissodus minimus is a true hybodont shark since it contains one layer of crystallites in the enameloid. It is also one of the most succesful species of the Rhaetian, being represented by thousands of teeth. This species comes in many forms. The crowns can be rounded or practically horizontal. The surface might be completely smooth, worn by eating (or transportation?), or covered with grooves. Some examples have multiple small cusps on the crown, but these are mostly worn away. 

This is by far the most common marine species from the Rhaetian bonebeds in the Lorraine region. The teeth are very fragile and are usually found broken. The tooth shown in the first image is a complete specimen (with root). Most specimens lack the root, as seen in the second image. Therefore most people think they have found a complete tooth, but it is actually only the crown they have collected.  

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Polyacrodus cuspidatus (Agassiz, 1843)

Hybodontiformes Zangerl, 1981

Polyacrodontidae Gluckman, 1964

Polyacrodus cuspidatus (Agassiz, 1843) (Previously Polyacrodus cloacinus(Quenstedt, 1856))

 

 

Teeth of this hybodont species stand out from the other shark teeth found in these deposits because of their large size. Mostly, recovered specimens of this species are broken. Usually it is only the main cusp that is found. Only on rare occasions are complete teeth of this species recovered due to their fragile nature. The nomenclature of this species has been rather turbulent. In most written records about the Rhaetian fauna, this species is referred to as Polyacrodus cloacinus. Yet, this species is the same as Polyacrodus cuspidatus.The original description of P. cloacinus is based on worn teeth of P. cuspidatus. Therefore, the argument that differentiated between these two species (that the crown of P. cuspidatus was more ornamented) became invalid, leaving P. cuspidatus as the only valid name for this species.

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Neoselachiformes

Teeth in this section probably belong to modern sharks.

Rhomphaiodon minor (Agassiz, 1839) 

Incertae sedis → probably Synechodontiformes (Duffin & Ward, 1993)

Incertae sedis 

Rhomphaiodon minor (Agassiz, 1839) (Previously 'Hybodus' minor)

 

 

 

 

 

  

Originally described by Agassiz from a single fin spine specimen. Agassiz suggested that teeth of this architecture should be associated with the spines, and both have been considered as belonging to a hybodont. Acid treatment of the teeth revealed their 3 layered construction so this species is now placed among the Neoselachii. This means that the original fin spine probably belonged to another (hybodont) shark. The affinities of these teeth with other Neoselachians remain unsure. The composition of the 3 layers is quite different to that in other Neoselachians, making more detailed assignment within Neoselachii a difficult task. Some say it might be related to Synechodontiformes such as Synechodus, whilst others see closer resemblances with the closely related Paraorthacodus. This controversy will surely be continued.

This species is very common in the Rhaetian bonebeds of the Lorraine region. The size of the teeth varies quite a lot. The bigger specimens usually lack one or more of the lateral cusplets; whereas the smaller specimens often are pristine in quality. Seen under a microscope, these teeth are absolutely wonderful. 

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Synechodus rhaeticus (Duffin, 1982a)

Synechodontiformes (Duffin & Ward, 1993) 

Palaeospinacidae (Regan, 1906) 

Synechodus rhaeticus (Duffin, 1982a)

 

 

 

Synechodus rhaeticus (originally called Palaeospinax rhaeticus, based only on fin spines) is one of the earliest Neoselachian sharks. Even though this species has teeth with 3 different layers in the enameloid, the composition of some of those layers is somewhat chaotic and uncharacteristic for Neoselachians. This situation is typical for a number of Triassic shark remains. However, the presence of the 3 different layers is sufficient to place this species among the Neoselachii. 

The teeth of Synechodus rhaeticus were one of the least common finds at the outcrop. The size of these teeth varies from 3mm to >1cm. Some of the fin spines which have been recovered might belong to this species.

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Pseudocetorhinus pickfordi Duffin, 1998  

Incertae sedis

Incertae sedis

Pseudocetorhinus pickfordi Duffin, 1998    

 

Pseudocetorhinus pickfordi is a very interesting species. When looking at these teeth, a lot of similarities with current filter-feeding sharks such as Cetorhinus maximus can be observed. Yet again, their crystallitemicrostructure differs quite a lot from that of modern day filter-feeders. It is definitely a Neoselachian shark, but the striking similarities might be due to convergence instead of being a direct relative of modern day filter-feeders.

Teeth of these species are rare in the Rhaetian deposits. 

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Duffinselache holwellensis (Duffin, 1998)

Incertae sedis

Incertae sedis

Duffinselache holwellensis (Duffin, 1998)

 

 

 

Duffinselache holwellensis is a little known species. The species is a rather uncommon find in Rhaetian deposits. The origin of this species is currently uncertain. It was thought that these teeth represented a typical hybodont species, resulting in an early attribution to the genus Polyacrodus. However, this attribution seemed rather doubtful since microstructural examination of the enameloid has indicated that their affinities with hybodonts are not as self-evident as used to be perceived. More recent research on enameloid microstructure has shown that teeth of Duffinselache holwellensis resemble the enameloid microstructure of Neoselachian teeth. As of 2012, the species is no longer attributed to Hybodonts or to an uncertain affinity, yet a new genus has been erected for the species and it was placed among Neoselachiformes.

UPDATE: A recent literature review discarded this species as being a genuine seperate species. There seems to be speculation as to these teeth representing more lateral or even posterior teeth of the aformentioned Pseudocetorhinus pickfordi. Personally, I am still trying to figure out where the teeth of this type would fit in the dentition of Pseudocetorhinus. The rare occurence of this type of tooth doesn't match the rate of genuine Pseudocetorhinus teeth, which would suggest that for some odd reason anterior or anterolateral files would be found (a lot) more than lateral or posterior files of the same species. Due to the method of sampling required to gather teeth of this size from sandy deposits (meshes with very small sizes), there is practically no basis for collection bias to be at the source of the small amount of Duffinselache recovered, in comparison to teeth of Pseudocetorhinus. Therefore, I would like to suggest some prudence in discarding this species, in favour of it representing lateral or posterior teeth of Pseudocetorhinus. I would suggest awaiting further scientific literature debating this topic. *this section will be updated with new data soon*

Some might confuse these teeth with those of Lissodus minimus but the two forms are easily distinguished. L.minimus usually has a ribbed surface on the crown, and its crown is also higher. The teeth of D. holwellensis, are thin and almost horizontal, whereas the teeth of L. minimus are mostly bent (especially the crown).  This means that the ratio between height and length of the teeth of the two species is different. Teeth of D. holwellensis are long and thin, while teeth of L. minimus are long and high. Furthermore, Lissodus minimus tends to be found in large quantities with broken roots, whereas the roots of Duffinselache holwellensis seem to be present in every specimen found by the authors of this website.

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Problematica

Teeth in this section show problematic affinities. Future research needs to point out whether these teeth are Hybodonts or Neoselachii.

Pseudodalatias barnstonensis  (Sykes, 1971)

Incertae sedis

Pseudodalatidae Reif, 1978

Pseudodalatias barnstonensis  (Sykes, 1971)

 

 

 

 

 

 

These teeth are uncommon in Rhaetian deposits, not only in the Lorraine region but in the UK as well. They are extremely fragile and are often found in bits and pieces. Most of the teeth figured above are lower jaw teeth. The upper jaw teeth are very slim, small and thin with rudimentary side cusps. Due to their size, photographing these small teeth is a difficult task. However, good results were achieved, now some of the upper jaw teeth are also being figured. Teeth from the upper jaw are even more rare than the lower teeth due to their small size.

The enamel composition of these teeth is unique. It does not resemble that of Neoselachii, but it is also different from that of hybodonts. Therefore, the exact classification of Pseudodalatias is currently unclear. First it was thought that this species is related to the extant Dalatias licha (Bonnaterre, 1788) because of the convergence shown in the upper and lower teeth. Today it is thought that these species are not related at all and resemblances are due to ontogenetic convergence. Probably they ate similar kinds of food, therefore their teeth developed in the same way over time.

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