In 1985, a new species of supposed protochordate origin was described. It was dubbed "one of the most remarkable and bizarre organisms ever discovered", and not without good reason. The animal had one giant lobe protruding ventrally from it's head. It contained a huge "capsule", which was interpreted as part of the digestive system, specifically the foregut. It also had a well-muscled tail with a segmented rod forming its base. In contrary of being identified as a protochordate, it supposedly possessed a singular compound eye. It was named Ainiktozoon, meaning "ridling or enigmatic animal" (Ritchie 1985).
Obviously, there was something wrong with this interpretation. The combination compound eyes and a notocord seems odd and completely contradicts basic chordate anatomy. Because all other aspects of its anatomy were so obscure, it was decided that it is "advisable to use noncommittal names for the various parts", and it is quite clear to see why. The holotype is one giant mess, with the faint impressions of internal organs overlapping each other. Therefore, it is very hard to identify certain organs both within and without the organism.
Then, in 1997, it turned out that Ainiktozoon was in fact an arthropod, what a surprise. The Birk Knowes fossil site had provided the researchers with a more complete specimen, which made revision of the species possible. Much of its newly discovered anatomy matched that of thylacocephalans and as such, Van der Brugghen et al. identified it as a thylacocephalan. It had a pair of raptorial appendages and a supposedly bivalved carapace, both being key traits of thylacocephalans. However, its anatomy was still unusual, even compared to its relatives. This is mainly due to the abdomen greatly extending from the posterior end of the carapace. The abdomen would usually be almost fully or fully covered.
After two descriptions, you'd probably think we finally unravelled all of Ainiktozoon's secrets. But this is certainly not the case. The preservation of the "new" specimen is much better than the holotype, but it is still not ideal. Especially the front end of the animal is quite distorted.
To get a better understanding of the animal, we should look at the way of preservation first. Van Brugghen et al. clearly states that the most specimens of Ainiktozoon are laterally preserved, including their own. However, after examining the specimen myself, it seems like they were already mistaken in this respect.
Upon further inspection of the abdomen, one can notice that the the cuticles seem te be preserved dorsally rather than laterally. This means that the entire animal is probably fully preserved dorsally.
The posterior margin of Ainiktozoon loganese. Even though faint, the ridge of the cuticle is visible. This indicates that the animal was actually preserved dorsally, not laterally. Abbreviations: ce: cuticle edge, ltm: longitudal trunk muscles, lm: limb muscles. Figure modified from Van der Brugghen et al. (1997).
Another weird aspect of Ainiktozoon is its seemingly enormous carapace. Unfortunately, the preservation is... pretty damn bad. Inside it is a complete mess and the anterior part is completely distorted. Nonetheless, we can once again clearly see that the carapace is preserved in dorsal view.
The carapace of Ainiktozoon. The only major difference from the original interpretation is the compound eye, which to me seems to be located right next to the raptorial appendages, rather than slightly above them. The red line represents the axis of symmetry. Abbreviations: ls: left side of carapace, rs: right side of carapace, lsm: longitudal trunk muscles, ra: raptorial appendages, ce: compound eye. Figure modified from Van der Brugghen et al. (1997).
All things considered, Ainiktozoon loganese probably looked something like this (note: this is a very simplistic image and it is subject to change):
Ainiktozoon has once again proven that it is not what it seems like. Still, much of its anatomy remains unclear and, sadly, we probably won't ever get new discoveries again that might provide us with new insight.
"Why is that?" I hear you asking. Well, the fossil site mentioned before, Birk Knowes, which provided us with new specimens, has been permanently closed down. The reason for its taboo comes solely from mismanagement and scandals, but if you want to read more about that I'd suggest you read the Birk Knowes Affairs page, a website fully dedicated to this issue.
I'd like to finish this article with a quote from The Blog That Time Forgot. It really sums up AIniktozoon's situation quite well.
"Zoon?"
"Aye, Zoon?"
"Ye ever wonder juist whit we are? Ah mean, leukit us. Wur bizarre. Are we hings that shouldna be?"
"Aye Zoon, aye time. Dinnae fash yersel aboot it."
References
Obviously, there was something wrong with this interpretation. The combination compound eyes and a notocord seems odd and completely contradicts basic chordate anatomy. Because all other aspects of its anatomy were so obscure, it was decided that it is "advisable to use noncommittal names for the various parts", and it is quite clear to see why. The holotype is one giant mess, with the faint impressions of internal organs overlapping each other. Therefore, it is very hard to identify certain organs both within and without the organism.
Then, in 1997, it turned out that Ainiktozoon was in fact an arthropod, what a surprise. The Birk Knowes fossil site had provided the researchers with a more complete specimen, which made revision of the species possible. Much of its newly discovered anatomy matched that of thylacocephalans and as such, Van der Brugghen et al. identified it as a thylacocephalan. It had a pair of raptorial appendages and a supposedly bivalved carapace, both being key traits of thylacocephalans. However, its anatomy was still unusual, even compared to its relatives. This is mainly due to the abdomen greatly extending from the posterior end of the carapace. The abdomen would usually be almost fully or fully covered.
After two descriptions, you'd probably think we finally unravelled all of Ainiktozoon's secrets. But this is certainly not the case. The preservation of the "new" specimen is much better than the holotype, but it is still not ideal. Especially the front end of the animal is quite distorted.
To get a better understanding of the animal, we should look at the way of preservation first. Van Brugghen et al. clearly states that the most specimens of Ainiktozoon are laterally preserved, including their own. However, after examining the specimen myself, it seems like they were already mistaken in this respect.
Upon further inspection of the abdomen, one can notice that the the cuticles seem te be preserved dorsally rather than laterally. This means that the entire animal is probably fully preserved dorsally.
The posterior margin of Ainiktozoon loganese. Even though faint, the ridge of the cuticle is visible. This indicates that the animal was actually preserved dorsally, not laterally. Abbreviations: ce: cuticle edge, ltm: longitudal trunk muscles, lm: limb muscles. Figure modified from Van der Brugghen et al. (1997).
Another weird aspect of Ainiktozoon is its seemingly enormous carapace. Unfortunately, the preservation is... pretty damn bad. Inside it is a complete mess and the anterior part is completely distorted. Nonetheless, we can once again clearly see that the carapace is preserved in dorsal view.
The carapace of Ainiktozoon. The only major difference from the original interpretation is the compound eye, which to me seems to be located right next to the raptorial appendages, rather than slightly above them. The red line represents the axis of symmetry. Abbreviations: ls: left side of carapace, rs: right side of carapace, lsm: longitudal trunk muscles, ra: raptorial appendages, ce: compound eye. Figure modified from Van der Brugghen et al. (1997).All things considered, Ainiktozoon loganese probably looked something like this (note: this is a very simplistic image and it is subject to change):
It is now less of an awkward balloon creature and more of a nimble mantis shrimp. The many paddle-shaped limbs would've provided it of good mobility, especially since the drag has been decreased because of its much lower profile compared to the tall carapace it is usually reconstructed with.
Ainiktozoon has once again proven that it is not what it seems like. Still, much of its anatomy remains unclear and, sadly, we probably won't ever get new discoveries again that might provide us with new insight.
"Why is that?" I hear you asking. Well, the fossil site mentioned before, Birk Knowes, which provided us with new specimens, has been permanently closed down. The reason for its taboo comes solely from mismanagement and scandals, but if you want to read more about that I'd suggest you read the Birk Knowes Affairs page, a website fully dedicated to this issue.
I'd like to finish this article with a quote from The Blog That Time Forgot. It really sums up AIniktozoon's situation quite well.
"Zoon?"
"Aye, Zoon?"
"Ye ever wonder juist whit we are? Ah mean, leukit us. Wur bizarre. Are we hings that shouldna be?"
"Aye Zoon, aye time. Dinnae fash yersel aboot it."
References
- Ritchie, A., (1985) Ainiktozoon loganese, a new protochordate? from the Silurian of Scotland.
- Van der Brugghen, W., Schram, F. R., Martill, D. M., (1997) The fossil Ainiktozoon is an arthropod.
- Taranaich, (11-19-2017) PrehiScotInktoberFest Day 19: Ainiktozoon loganens*
*yes, I am aware of that typo, but since that is the title of the blog post I suppose I'll just leave it like that.
NB: My observations and conclusion are to be taken with a grain of salt. I have not studied the specimens mentioned in person and there is only so much a computer can do. Please take this into consideration, I ain't no Peters.
I completely agree with you here and have actually come to the same conclusions! I was in the very room when Wim van den Brugghen presented the fossils to professor Frederick Schram, who was my Master's thesis mentor during that period. Having seen its fossil remains with my very own eyes, I’m not really fond of many of the reconstructions that you can find out there that retain the strange body angle of its chordate interpretation. It's obvious that the animal was heavily crushed during fossilization and that it probably was much more compact with most of its body tucked underneath a sleek carapace much like other thylacocephalans.
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