What IS Ainiktozoon?

[Steeman, Fedor]

Hello all,

Well, if you'd ask me: Ainiktozoon is definitely not a chordate of the kind
that Ritchie proposed. More likely than anything else, it really is a
thylacocephalan. I have worked with Thylacocephalans during my Master's for
Fred Schram. I have also studied some of the specimens of Ainiktozoon that
van der Brugghen showed Schram and helped make sense of these. Admittingly,
Ainiktozoon is a very strange thylacocephalan, but it exhibits most of the
basic features of thylacocephalans, save the characteristic arched 3 pairs
of forelimbs. 

Basically, Ritchie has turned the creature the wrong side round. the
"ventral lobe" of Ritchies reconstruction appears to be a thin-shelled
dorsal carapace with thickened edges. I have seen a specimen where this
so-called "lobe" was shifted more towards the tail and actually enclosing it
much like we see in a crustacean. I recommend reading the article in Nature
by van der Brugghen et al. (1997).  

Before we start jumping to reconstructions of freak creatures we should keep
in mind Occam's Razor and first try to make sense of it on the basis of
known groups. Compound eyes like Ainiktozoon has them are known only in
arthropods as far as I know (but correct me if I am wrong). 

Yours sincerely, 

Fedor Steeman

van der Brugghen, W, F.R. Schram, & D.M. Martill. 1997. The fossil
Ainiktozoon is an arthropod. Nature 385:589-590. 

-----Original Message-----
From: Bjørn, Per de Place 
Sent: 7. maj 2002 08:57
To: Steeman, Fedor
Subject: RE: [TAXACOM] What IS Ainiktozoon?


http://usobi.org/archives/cgi-bin/wa.exe?SUBED1=taxacom&A=1

/per

-----Original Message-----
From: Steeman, Fedor 
Sent: 7. maj 2002 08:54
To: Bjørn, Per de Place
Subject: RE: [TAXACOM] What IS Ainiktozoon?

Hej Per, 

Kan du fortælle mig om og hvordan jeg kan tilmelde mig denne mailingliste?
Ken har ignoreret min henvendelse indtil nu. Ainiktozoon er helt bestemt
ikke en chordat, medmindre man bruger meget fantasi. Tværtimod viser den de
fleste karaktere typiske af Thylacocephala...

Mvh, 

Fedor


-----Original Message-----
From: Bjørn, Per de Place 
Sent: 3. maj 2002 22:24
To: Steeman, Fedor
Subject: FW: [TAXACOM] What IS Ainiktozoon?




-----Original Message-----
From: Ken Kinman [mailto:kinman at HOTMAIL.COM] 
Sent: 3. maj 2002 17:23
To: TAXACOM at USOBI.ORG
Subject: [TAXACOM] What IS Ainiktozoon?


Dear All,
     First off, Alex Ritchie assures me that the "weird fossil" is indeed
just an inorganic concretion---either a septarian nodule or a "thunder egg".
  Darn it, how disappointing reality can be, but I guess it's time to move
on to "real" fossils.
     I was surprised to learn that Ritchie does NOT accept the recent
re-interpretation of Ainiktozoon as a thylacocephalan crustacean, if it is
an arthropod at all.  In his 1985 paper on Ainiktozoon (Alcheringa,
9:117-142), he argues that it could very well be a highly specialized
protochordate related to urochordates (tunicates).  I preliminarily
classified it as such in my 1994 classification, but also noted that it
could be a hemichordate or an even more primitive deuterostome.
     I would be interested to hear if others have any opinions on the
affinities of Ainiktozoon, as an arthropod, a deuterostome, or something
else.  Quite frankly, it would not surprise me if it turned out to be
related to molluscs.  Afterall, arthropods aren't the only animals which
have evolved compound eyes (they also occur in some bivalves and sabellid
tubeworms).
     So I guess the classification of Ainiktozoon remains an open question.
Trouble is that very few people pay much attention to it, even those who are
fascinated by problematica.
         --- Cheers, Ken Kinman


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