Bite marks in Jurassic and Cretaceous ammonites: what did it?
Ammonites are amongst a number of the greatest fossils to gather. They are comparatively straightforward to seek out, for instance, within the Lower Jurassic Posidonia Shale in Germany and the Jurassic sediments of Dorset within the south of England. The bigger, nicely-preserved ones will all the time be wanted and, if of sufficiently top quality, might even be displayed in museum exhibitions. However, whereas these properly-preserved, full ammonites are perfect for figuring out species, they typically don’t say a lot concerning the life historical past and, extra particularly, the dying of the ammonite itself. On the opposite hand, learning the sub-deadly or deadly injury to the fossil shell definitely does.
This article is a few comparatively newly found sort of chew mark. It is discovered on Jurassic and Cretaceous ammonites, may need occurred worldwide, is straightforward to recognise and can also be pretty widespread.
Ventral injury
When I was searching by means of the ammonite collections of a number of Dutch museums (together with, Naturalis and Oertijdmuseum De Groene Poort) and the Geologisch-Paläontologisch Institut der Universität Münster in Germany, it turned obvious to me that there have been many specimens with injury to the outer whorl, on the again aspect of an ammonite (the ventral aspect) in its dwelling place. This injury was not solely seen on the ventral aspect, however may be seen on each lateral sides, if preservation permitted.
When seen from the lateral aspect, the injury has totally different shapes, together with triangular, sub-round, rectangular and irregular. These look like associated to the diploma of ornamentation of the ammonite shell – the stronger the ribs, the extra rectangular the injury turns into laterally.
Ventral injury to ammonites can’t be present in each assortment, as based mostly on my research of about 35,000 ammonites unfold over many such collections. However, Cretaceous and Jurassic collections do show this type of injury (Figs. P and A). I discovered it in Maastrichtian ammonites from the Netherlands and Belgium, notably within the species, Hoploscaphites constrictus. I additionally found that the Lower Cretaceous of southeast Spain (Miravetes Formation), in a set I examined, yielded many ammonites with ventral injury, for instance, within the genera, Barremites and Pseudothurmannia. In complete, 17.M% of the ammonites in that assortment have been ventrally broken. In addition, I discovered comparable injury in Lower Cretaceous ammonites from Colombia, South America.
Cretaceous ammonites from southeast France additionally confirmed ventral injury – 17.N% of the gathering I checked out. I additionally discovered comparable ventral injury in Upper Jurassic ammonites from southwest Germany (Plettenberg and Geisingen) and located the identical injury in Middle Jurassic, Indonesian, Irianites moermanni, and Middle Jurassic ammonites from Pamproux, France. Lower Jurassic collections from Dotternhausen, which have two-dimensionally preserved ammonites, are not any totally different. As talked about by Taverne (2000), the genera, Dactylioceras, Hildoceras and Harpoceras, present plentiful ventral injury. Later on, our group found that Lytoceras specimens additionally exhibit this type of injury. The proportion of ventral injury in ammonites in some layers of the Posidonia Shale in Dotternhausen is sort of excessive, with as much as 50% of specimens displaying proof of such accidents. Lower Jurassic ammonites additionally exhibit ventral injury, notably in specimens of Dactylioceras from Dorset studied primarily by Natascha Waljaard, in addition to some Pliensbachian ammonites from Germany (Fig. A).
The place of the ventral injury is remarkably uniform throughout collections. The place of this injury was measured by two strategies, that are defined in Fig. B. The higher majority of the injury may be discovered at about one hundred eighty° from the aperture. Additional evaluation of the massive collections of the Lower Cretaceous of Spain and Lower Jurassic of southwest Germany clearly exhibits that the majority injury is situated on the finish of the dwelling chamber, near the final septum. Apparently, this was a favorite place to interrupt.
The Triassic yielded combined outcomes. Rather obscure, sub-round injury was present in Triassic ammonites from Spitsbergen (Fig. 3F). However, the ceratite ammonite didn’t yield comparable ventral injury. Compared to the Mesozoic, the Palaeozoic is a totally totally different story. Browsing by way of the Palaeozoic ammonite assortment of Naturalis, it struck me that ventral injury was nearly absent in about M,four hundred specimens. To affirm this, I studied about thirteen,000 Devonian ammonites from Morocco and Australia. The conclusion was the identical – ventral injury of this type was extraordinarily uncommon. But why?
Ventral chew marks
The purpose for the distinction between Mesozoic and Palaeozoic ammonites lies in the reason for the ventral injury, which is mentioned under. Physical causes of injury to ammonite shells (reminiscent of collision whereas floating or injury whereas rolling, injury by sediment loading, and injury brought on by sediment transport and remodeling) may be excluded, as a result of they might be anticipated to point out up in comparable numbers in each Palaeozoic and Mesozoic ammonite collections. Moreover, such bodily injury is predicted to be extra random and never all the time on the similar location on the finish of the dwelling chamber. To the extent that it does seem in the identical place, these sorts of bodily processes primarily are likely to generate injury on the aperture. Implosion, one other uncommon bodily trigger of injury to the shell, causes sub-round injury to the phragmocone or shatters the shell utterly.
Damage by organic brokers consists of that inflicted by infaunal/boring organisms, brought on by the scavenging of the lifeless animal whereas it lay on the seafloor, and predation. The first and second are anticipated to supply random injury, and the second ought to often end in injury solely on one lateral aspect and fossil shell items discovered near the fossilised shell. This is just not the case with ventrally broken ammonites. However, predation within the water column may cause injury to the identical a part of the shell, trigger the bitten-off shell items to drift away and provides rise to wreck to the ventral aspect that may also be simply seen on the lateral aspect. Therefore, ventral injury should have been brought on by predation and, therefore, ought to be known as ‘ventral chew marks’.
The location of the chew means that the predator got here from behind, attacking the ammonite in its dwelling place on its blind aspect. This led to the swimming means of the ammonite being severely impaired, because the ventral muscle was (presumably) typically broken. Moreover, as soon as the shell was regionally crushed, the edible tissue was simply accessible. It additionally seems that this technique of assault was very profitable, as I have solely discovered a number of regenerated examples from such injury.
What did it?
So what sort of predator do we have to trigger these chew marks? Clearly, we require one which first turned widespread through the Early Jurassic or slightly earlier, to elucidate the large distinction within the variety of examples of ventral injury between the Jurassic/Cretaceous and Triassic/Palaeozoic. We additionally want a predator that is ready to break the shell with its beak on the similar, confined place on the finish of the dwelling chamber, and it must be agile and free-swimming.
Reptiles, akin to mosasaurs, turtles, marine crocodiles, ichthyosaurs and plesiosaurs, might be excluded, as they have been usually too giant to supply a confined chew mark. Rather, they might have utterly crushed the shell. Crustaceans can’t have been the predator both. They don’t stay within the water column and are, for instance, very uncommon within the Lower Jurassic of southwest Germany, the perfect place to seek out ventral chew marks on ammonites.
Predatory fishes, aside from giant sharks, are attainable culprits for ventral injury (though, to date, they’ve been reported primarily to assault the aperture). Such fishes are free-swimming, and have a jaw that may open to catch and break the ammonite shell. Teleost fishes are notably more likely to be accountable, as a result of they appeared within the Late Triassic and advanced from there.
Notwithstanding this, I consider that the majority ventral chew marks should have been inflicted by cephalopods, however not by ammonites or nautiloids. The latter are comparatively scarce within the Mesozoic, so they can’t have produced the huge variety of chew marks. In addition, the beaks of the previous have been principally not capable of open large sufficient, and weren’t appropriate for biting and chopping. Belemnites may need been one of many culprits, as they have been particularly ample within the Jurassic and Cretaceous. Despite the truth that that they had hooks as an alternative of suckers (which could have hampered them when grabbing ammonite shells), at the least a few of their beaks seem to have been appropriate for biting via ammonite shells.
However, I consider that the key culprits are coleoids (Fig. H), due to their comparatively sharp, triangular beaks and their suckers, which might have aided them in grabbing the ammonite shell. Today, coleoids (reminiscent of squid and octopuses) are quick-swimming, specialised predators, capable of catch and manipulate their prey and, most likely, so have been their fossil counterparts. Coleoid variety was highest after the Triassic-Jurassic boundary, when many new varieties appeared, and remained excessive till the R-T (now referred to as the R-Pg) boundary, when many teams turned extinct. Therefore, I consider that coleoid cephalopods in all probability brought on a lot of the ventral chew marks; different culprits have been predatory fishes and belemnites (Fig. S).
Fig. S. A schematic reconstruction of the reason for ventral injury: A. ammonites swimming within the water column; C, M. a cephalopod with suckers approaches the ammonite from its blind aspect; A. the cephalopod wraps its arms across the shell and positions it; and W. the cephalopod bites via the shell and removes the gentle tissue. Subsequently, the shell with the ventral injury sinks to the underside.
Research coping with predation on ammonites shells is scarce. Studies which were revealed are largely based mostly on a low variety of specimens from a restricted geographical space and/or time span. Examples of predation have included rows of round holes on Late Cretaceous ammonites attributed to mosasaurs, holes in phragmocones of Carboniferous ammonites from North America, brought on by sharks, and lateral holes on Late Cretaceous ammonites from Poland, brought on by swimming crabs. Therefore, the ventral chew mark is a vital addition to the rising proof of predation on ammonites. Given the collections studied, it’s probably that this kind of predation was a big-scale, probably worldwide phenomenon. In addition, the behaviour spans an extended interval of geological time.
My suspicion that ventral chew marks are more likely to be current in lots of extra Jurassic and Cretaceous collections everywhere in the world appears to have been confirmed by current publications. The article in Palaeogeography, Palaeoclimatology, and Palaeoecology that we revealed because of the analysis mentioned above was picked up by a staff led by Neil Landman (USA). As a end result, they featured fairly a couple of photographs of ventrally bitten specimens of their work on North American scaphites revealed in Bulletin of the American Museum of National History.
In addition, very just lately, Chris Andrew and colleagues revealed an article on ventrally broken ammonites from the Lower Jurassic of Lyme Regis (Dorset) in Proceedings of the Yorkshire Geological Society (see additionally the BBC News article at: http://news.bbc.co.uk/local/dorset/hi/people_and_places/nature/newsid_9225000/9225848.stm). They named a brand new ichnogenus and ichnospecies after this ventral chew mark. Quite probably, there are additional research on this ventral chew presently being undertaken.
About the writer
Adiël Klompmaker earned his masters diploma on the Utrecht University (the Netherlands) and is now a PhD candidate at Kent State University (Ohio, USA). He can also be editor of the webpage Earth & Climate (see http://www.kennislink.nl/aarde-en-klimaat) and could be contacted at: adielklompmaker@gmail.com.
Further studying
Klompmaker, A.A., I.A. Waljaard and J.T.B. Fraaije. 2009. Ventral chew marks in Mesozoic ammonoids. Palaeogeography, Palaeoclimatology, Palaeoecology 280: 245-257.
Taverne, I. 2000. Ammonieten als prooidier. Gea 35: N-15.
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Filed beneath: fossils Tagged: Ammonite, Ammonite Bite, Bite, Bite mark, Cretaceous, Fossil, Fossil Bite, fossils, Jurassic 
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