 Räuberei mit Vorlieben ? Side-preferences in predation on trilobites |
Jens 
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| Räuberei mit Vorlieben ? Side-preferences in predation on trilobites |
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Hallo allerseits,
irgendwie ist es im Forum in letzter Zeit recht ruhig, freuen sich wohl schon alle auf die Trilobitentagung und packen die Sachen ;-)
Nunja, mir ist heute ein Blog aufgefallen, der in englischer Sprache über Verletzungen bei Trilobiten berichtet.
http://whyevolutionistrue.wordpress.com/...cal-trilobites/
Räubereien an Trilobiten waren und sind ja schon immer ein Steckenpferd von mir gewesen und so fand ich den Blog zu Verletzungen an Trilobiten doch recht interessant. Darin wird auf eine wichtige Arbeit von Babcock & Robison (1989), in Nature erschienen, eingegangen, worin es unterschiedliche Verhältniszahlen von sicheren und mutmasslichen Bissverletzungen an Trilobiten geht. Auch wenn die untersuchten Stückzahlen aufgrund der nicht gerade üppigen Funde nicht sehr hoch sind, scheint sich doch ein Trend abzuzeichnen, dass die rechte Seite von Trilobiten deutlich häufiger als das zu erwartende 50:50 beschädigt ist. Ein Trend der mir auch an Asaphiden im Ordovizium aufgefallen war, irgendwie haben die meisten Trilos eben auf der rechten Seite ihre Fehlstellen im Panzer.
Die Deutung der unterschiedlichen Verteilung durch mögliche Frachtsonderung (also ein taphonomischer Prozess) möchte ich nicht folgen, auch wenn es theoretisch nicht ganz abwegig ist. Aber die Beschädigungen finden sich ja auch bei ganzen Exemplaren, eben bevorzugt rechts. Und da Trilobiten schnell nach dem Tode auseinanderfallen, sind ganze Trilobiten definitiv nicht transportiert worden.
Möglicherweise zeichnet sich hier eine Preferenz der Räuber ab, gab es etwa schon im Kambrium Rechts- und Linkshänder. Ah Mist, die Räuber hatten ja noch nicht mal Hände;-)
lg,
Jens
PS: Referenzen und weitere Infos finden sich auch in einem weiteren Beitrag:
http://whyevolutionistrue.wordpress.com/...ocaris-mystery/
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11.02.2011 11:03 |
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Andries
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Hi Jens,
Statistiken sind Sachen, die ich nie mag. Ob man wirklich von einen Präferenz sprechen kann, wenn 33% links und 66% rechts gebissen wurden, schwer.
Wir wissen noch nicht einmal, ob die Verletzungen von die Gleiche Räuber verursacht wurde.
Ausserdem tue ich mich sehr schwer mit der Vorstellung, dass Fische einen links, rechts bevorzugung haben. Bei Ihnen macht es keinen wirklichen Sinn.
Ein andere Aspekt, man ist rechtshänder:
Kommt der Trilobit von recht nacht links gewandert, so beschädigt die "rechte" Hand die linke Seite.
Umgekehrt wird die rechte Flanke attackiert, wenn er von links nach rechts am Räuber vorbei zieht.
Interessant wäre hierbei die Frage, was wäre wenn der Räuber von oben käme.
Gruß Andries
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11.02.2011 12:01 |
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Jens
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Lieber Andries,
stimmt, Statistiken sind natürlich immer so eine Sache. Aber ich glaube, dass es diesen Trend tatsächlich gibt, was auch immer die Ursache ist.
Das möglicherweise der Grund auch im Verhalten des Trilobiten liegen könnte, ist durchaus plausibel. Allerdings scheinen die Laufspuren eher selten eine Seitwärtsbewegung der Trilobiten zu belegen, meist finden sich doch geradeaus verlaufende Spuren.
Wir sollten Prof. Seilacher mal befragen, der weiss sicher mehr zu berichten;-)
Aber so ein bisschen Kriminologie in der Paläontologie ist schon eine spannende Sache, leider sind wir aber momentan noch viel auf Mutmassungen angewiesen. Immerhin, fürs Kambrium und wohl auch Ordovizium können wir Fische als Täter ausschliessen, da die frühen Vertebraten meines Wissens keine ordentlichen Beisserchen entwickelt hatten.
Anomalocaris aber auch Nautiliden sind im Fokus der Ermittlungen;-)
Ich hatte auch die Idee, dass Trilobiten sich vielleich auch schräg oder in Seitenlage ins Sediment graben können. Zumindest finden sich in den schwedischen Orthocerenkalken Ptychopyge, Asaphus und Megistaspis gar nicht so selten als komplette Exemplare im 90°-Winkel zur Schichtung eingebettet. Ob es eine tatsächliche Grabpositions ist, tja das ist problematisch, man nimmt ja eher an, dass diese Trilobiten in flachen Mulden eingegraben, mit herausschauenden Augen gelebt haben. Vielleicht waren es ja auch Sedimentrutschungen, die zur Rotation eingegrabener Exemplare geführt haben, wer weiss?
lg,
Jens
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11.02.2011 12:50 |
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Andries
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Interessant ist eine Entdecken, den ich letztes Jahr im einen Magagzin gelesen hatte. Danach war das Gebiss von einem Anomalocaris so schwach ausgebildet, dass sie wohl angeblich keine Trilobiten verspeissen konnten.
Jetzt überlege ich, ob es keine Belege beim Anomalocaris gabt, die Triloresten im Magenbereich gezeigt hat.
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12.02.2011 01:33 |
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Andries
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Ein interessantes Exemplar.
Mit stellt sich sofort die Frage, wie die Verletzung erfolgen konnte.
Es sieht so aus, als wurde regelrecht was heraus gebissen.
Ein Anomalocaris würde so einen Verletzung nicht verursachen können, daher würde ich den Täter eher bei Orthocerasen oder Seeskorpionen suchen.
Es würde mich nicht verwundern, wenn es ein Orthoceras gewesen wäre, der den Trilobite gefangen hätte, ein Stück abgebissen hätte, und weil er nach nichts geschmeckt hat, wieder weggeschmissen hat.
Was meint ihr dazu?
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12.02.2011 17:41 |
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Jens
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Hi Ebonino and Andries,
I think we can avoid misunderstandings when we continue in english;-)
Anomalocaris seems to be a real predator but in the case of the injuries on trilobites, he is probably not responsible. The round mouth itself, without real teeth, seems to me not able to crush the shell in form of a W-shaped bitemark, which can frequently found on injured trilobites in the Cambrian and Ordovician as well. Also the beautiful specimen ebonino presented here, thanks for sharing.
The responsible animal for this type of injuries is unknown so far I know. In ordovician times I suggest in a talk on the last trilobite collector conference in Berlin, that cephalopods are also good candidats as trilobite-predators. No beaks of orthoceratid cephalopods are known so far, but this may be explained by a preservation bias of the not stabil organic material.
But cephalopods in cambrian times are rare and small, so probably not responsible. The question remains, who was it. Probably something big, because from Australian Lower Cambrian Emu shales Vannier & Chen 2005 reports coprolites, which contains trilobite debris - but the predator remains unknown. The fragment Vannier and Chen figured belongs probably to the Redlichia takooensis. This is not a small trilobite;-)
Direct evidence of trilobite predations is known from a unnamed arthropod close to Fuxianhuia, from the Lower Middle Cambrian Kaili Lagerstatte in China (see Zhu et al. 2009). But due to the small size of the predator, only small agnostid trilobites as Pagetia seems to be the major food source. The predator was able to crush the shells of the trilobites found in his guts, but informations about the dentition is unknown for the moment. May be, relatives of the arthropod group were able to hunt bigger prey, but this remains unknown for the moment.
greetings,
Jens
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12.02.2011 18:04 |
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Andries
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Hi Jens,
I think that cephalopods still remain a resonable predator. Although we know them as small specimen they grow 3 meter in length and longer, making them excellent predators.
Especially orthoceras are still my favorit.
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12.02.2011 19:00 |
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Jens
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Yeap, I agree, but not in the Cambrian;-) The radiation of big cephalopods started with the beginning of the Ordovician. For the moment I prefer a arthropod predator for cambrian times or there were big unknown soft tissue cephalopods in the cambrian, but that pure speculation;-)
Jens
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12.02.2011 19:33 |
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Andries
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we see there is stil a lot to dicover in the Cambrian.
It will be difficult to find a predator in the cambrian. Not only we don´t know it they have hard parts or not, at the end of the food chain, normally the dominatent predator exist of only few individuals, whereas the prey are very rich on the numbers of individuals.
Thus even if they are preserved, it still we be difficult to find one of them.
What is interesting, that we see bite marks on the carapace. Normally I would say a predator would try to turn around a trilobite and try to bite the soft parts instead of the hardened parts.
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12.02.2011 19:52 |
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Jens
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Hi Andries,
keep in mind, that we speak about unsuccessful predation, when we see complete specimens with healed injuries. The normal result of a successful predation should be only small fragments of the trilobite shell. But such fragments are not very interesting for the normal collector and I find only a paper from Pratt 1998 who investigated trilobite shell fragments and declared them as predation remains. The paper was not very popular under some trilobitologists, but he was probably right. It's difficult to separate broken shells distroyed by predators from shell fragments crushed by normal diagenetic processes and some of his figured specimens looking after normal shell hash. But some of them can't dinied because of a destruction which can't explained only by sediment compaction.
But we know, that such true predation remains exist, trilobite were a part of the food chain;-) I know that Michael Zwanzig found a rectangular shell fragment of a Calymene, the fragment has sharp edges. It's a small part of the head with the preserved eye and a part of the librigenae. The closed suture is evidence that the specimen was crushed as a living beeing and only a small fragment told us from his bad end;-) Michael discussed in his talk probable predators. The fossil was found in a erratic boulder near Berlin, known as the Greenish grey graptolithe limestone from the Silurian (Wenlock or Ludlow). This limestones are nodules from graptolithic shales - Colonus-shales and for sure sedimented in deep waters, probably around 100m water depth.
After my opinion, the side of a trilobite is the most vulnerable part, for this reason trilobites developed the enrolling to protect themself. In the cambrian the predator surely try to reach the ventral side by attacking the sides to turn around his prey. Specimens with bite marks survived a attack, the majority probably not.
There is still a lot what is worth to study;-)
all the best,
Jens
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12.02.2011 20:29 |
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ebonino
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In Cambrian, as Jens said, no cephalopods available to make injuries like the visible one are known (at today).
The oldest discovery of a cephalopod beak is dated to Carboniferous, but we know that these invertebrates are very abundant during the Ordovician (but no beak found at today).
Between the possible predators (looking at the Chengjinag biota) are arthropods like Sanctacaris and Yohoia (found also in the Burgess Shale lagersätten), Fortiforceps, Tanglangia, Parapeytoya ... and other bugs.
The problem is always the possibility to be able to crunch the mineralized skeleton by these organisms. Following some analysis of the frontal apparatus of the actual mantis shrimp appear that similar creatures are able to create the sign of predation visible in some trilobites.
May be that the predation will be caused also by bigger arthropods like anomalocaridids, just after the molt processing of the trilobite, when the exoskeleton is softer and much more vulnerable to predation.
I've little bit discussed about this theme in my book (chapter Morphological Anomalies and predation), where there is also a picture of a coprolite containing rests of trilobite (from Kaili Fm.).
Enrico
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12.02.2011 20:43 |
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Jens
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Hi Ebonino,
I think we know from the fossil record, that also early trilobites are the prey of predators and when we keep in mind that also big redlichiids are known with bite marks, we can conclude, that big hunters with effective weapons must have exist. I think it's not unpossible that we don't know all of the big ones;-) I'm not sure if all of the known cambrian lagerstatten are of that what Seilacher would call "Verschüttungs-Lagerstätten" (this means deposits where the fossil content was buried by storm or turbidids). I imagine big predators were able to avoid to be buried alive;-)
By the way, a fine book you presented last year.
A short question, I can bring some samples of attacked ordovician trilobites to Frankfurt, for the case that you are also there:)
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12.02.2011 21:04 |
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Jens
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Thats fine. Okay, so I will add some more trilobites I presented at my talk in Berlin. Unfortunately I have only a part of the interesting material here in Switzerland, but a Illaenus with 2 bite marks and preserved brown muscle attachment scars, who also indicate the early death of the big shelled specimen.
I should ask Andries if we want present this material on the exhibition or will we dicuss that seperatly, by using our loupes.
all the best and good night ;-)
Jens
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12.02.2011 22:17 |
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Andries
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Hello Jens,
you should present your trilobite at the symposium.
Although it will be not easy to get the trilobite out of the cabinet (we have to look for the key), a lot of people will like your trilobite.
You don´t see often trilobites with bite-marks and muscle scars.
Just write a little note, thus the people know, what they see.
We will have some little shield at the symposium, thus you can write it at the museum.
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12.02.2011 22:47 |
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Jens
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Thanks for the pictures. Mmh, interesting suggestion when you say that there are more injured trilobites in the Cambrian than in other times. I'm not sure if it's true. It's probably only a impression, but may be, that if's reasonable. The shell thickness increase with the time, not in all groups, but I think in most group. A thicker shell provides better protection and so it's no wonder, that in postcambrian time the majority of injured trilobites are known from groups with thin shells, which are easier to destroy.
But to get a better knowledge, we need more informations especially with a statistical background. From my own experience I can tell, that crushed shells of ordovician trilobites are not rare, but nobody recognize such remains. In the work of Nielsen about the trilobites of the scandinavian Komstad limestone he figured a lot of material, some of the specimens show clear shell damage, in a way, which I interprete as a result of durophagous predation. But I know no study about this, also Nielsen did not mentioned anything in his descriptions. I think the main problem is, that the people are not able to recognize a lethal damaged trilobite when they are deal with not articulated material. The first guess should also be, that the shells are broken mechanical, by currents or diagenetic processes. But how do we want explain thick but broken shells with a perfect preserved shell surface, showing terrasse lines, pores et cet. And to bring a taphonomical argument - buried under subtidal conditions.
I think, the majority of shell durophagy is overlooked;-)
It's the same in bivalves, I find a lot of damaged shells and some of them are clearly destroyed by predators, but in the literature there is not much published about durophagy on jurassic bivalves. But some articles about theoretical aspects, but no figured specimens;-)
greetings,
Jens
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12.02.2011 23:39 |
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Andries
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Hi Jens and Enrico,
I agree it is hard to distinguish wether the carapace was broken by predators or post mortal.
Therefor I like the trilobite number 7 wish show several injuries of rectangular shape.
This is a very intresting specimen though it is obvious that this damage isn´t done by diagenetic processes or bad preparation.
Especially the last opic is sometimes a big problem. I have seen specimens with bitemarks which I couldn´t tell wether it was done by bad preparation or if it was natural.
For Example look at number 5. Either the free cheek was prepp away or was missing wright away. Difficult to tell on this picture.
Injuries have to be obvious so it can be clearly defined.
Secondly you need a preparator who recognize the injury and prepp it free without destroying it. Especially the edge is of importance.
If it is destroyed by smoothing it with sandblasters it is of no value anymore.
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13.02.2011 10:23 |
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