Anomalocaris

[wa105@mead.anglia.ac.uk]

Mickey kindly forwarded Chris Nedin's assessment of Anomalocaris's swimming 
ability.

Adam Heman had asked:
>>I was wondering if anyone has any thoughts on how fast anomolocaris was
>>able to swim.
>>I know this is a dinosaur list server, but does anyone have any Cambrian
>>background?
[snip]
>However, both of these methods are not much use when dealing with
>_Anomalocaris_ which didn't leave footmarks or have legs, not is it similar
>to any organism alive today.

Hang on...  I remember vividly the 1996 Royal Institution Christmas 
lectures.  These are traditionally given by a scientist and popular science 
writer to an audience of children (plus those few people who want to watch 
something good on television).  If I may digress a little, Richard Dawkins 
was extremely good a few years back, better than his university lectures 
which are themselves of a high standard.  But he was unrecognisable under 
the makeup.

In 1996 the lecturer was a geologist whose name I can't recall.  But while 
talking about the Burgess Shale (he was naturally not very specific about 
the etymology of Hallucigenia) he displayed a life size model of the 
Anomalocaris we all knew and loved.  This was interesting, but the really 
exciting bit was when he added the legs.  These had apparently been 
recently discovered, and IIRC were uniramous and rather diplopod-like.  
(Millipede-like, for vert types.)

If the lecturer was not mistaken, this removes Anomalocaris from the 
shrinking list of Burgess weirdos in no modern phylum, and adds it to the 
growing list of Burgess weirdos in the Arthropoda (which, incidentally, I 
am sure is monophyletic).

I think you're in a better position than me to check this out, Chris.  My 
library is inappropriate and I'm not on any other palaeo lists.

>So we can say that _Anomalocaris_ was probably faster than trilobites (=
>modern crabs) - at least over short distances - but slower than modern
>squid, who use jet propulsion and are thus considered to be cheating
>anyway. :-)

The best modern analogue would be a cuttlefish, which can hover or swim in 
either direction by undulating its lateral fins, and feeds on benthic 
arthropods, seizing them with its grasping arms and crushing them with its 
jaws.  Anomalocaris probably had no flotation organ, however.

Anyone know how fast a cuttlefish can swim without jetting?

And as for trilobites, IMO lobsters would be more appropriate.  Crabs 
scuttle sideways, taking long strides without tripping over their long 
legs.  Trilobites weren't built for that.

                                May all your shrimps be strange ones,

                                                                        Bill