Talk:Schinderhannes bartelsi

Absurd locomotion

"The organism clearly swam, propelling itself with the 'flippers' attached to its head, and using its wing-like lobes on the 11th segment to steer."

No similarly-shaped animal, of any order, swims in this absurd way. Sharks; bony fishes; dolphins and whales; pinnipeds; extinct reptiles; crustaceans: all include creatures with similar body plans, and they ALL swim with their tails, and steer with flippers, not the other way around. The only creatures that swim (very uneconomically) with their flippers are sea turtles and boxfishes, and for a very simple reason: their body is rigid and cannot undulate. The anomalocarid body was articulated, and freely undulated. Thus the method of locomotion described is completely unrealistic. The only reason I have not corrected it in the body in the article is because the absurdity is apparently supported by a citation from an article I cannot access. Possibly the source is wrong; opinions, anyone? Freederick (talk) 12:39, 9 September 2011 (UTC)

What about copepods? They swim through rhythmic beating of their massive antennae, and they seem to be doing very well as a group. Plus, it does not appear that S. bartelsi's body was as flexible as earlier anomalocaridids.--Mr Fink (talk) 12:44, 9 September 2011 (UTC)

Copepods are tiny (two orders of magnitude smaller than S.b.), which opens up a whole new can of worms; to make it short, at these scales and Reynolds numbers fluid viscosity takes on an overwhelming importance, requiring entirely different mechanisms of swimming. You will note that the copepod antennae are not fin-shaped or streamlined at all, and that they generate viscous drag rather than lift. Functionally, they are closer to cilia than to flippers.

As for S.b., I am making an educated judgement based on the conformation shown in the picture. It appears to me that S.b. evolved convergently with these other swimmers I mentioned (sharks, dolphins, etc.) taking on the same overall shape. It stands to reason that it would swim the same way, since it is function that drives convergent evolution. The elongated rather than boxy body; the long lunate rather than fan-shaped flippers (or whatever they are anatomically); the streamlined shape of a fast, efficient swimmer; all these point to the mode of locomotion I mentioned. There is also the natural evolutionary track from long undulating forms (the early anomalocarids) propelled by eel-like whole body action, to shorter, streamlined forms that undulate their tail only and use a tailfin for more efficient propulsion; as you see, the fact that the front part of S.b.'s body was less flexible than its undulating ancestors' fits very well with this line of development. This evolutionary track is also a beaten path, having been traversed independently by a number of unrelated lineages. Some of them (sharks, tuna, ichthyosaurs) are or were side-to-side undulators; others (dolphins, crustaceans, and apparently S.b.) have a horizontal fluke moving up-and-down.

Having said all this, I must concede that while I am a fluid mechanics specialist, my biological knowledge is limited; and that I have no source, other than this obvious (and third-rate) OR to back my claims. This is why I refrained from actually editing the article. I must necessarily yield to published sources, my personal reservations to their accuracy notwithstanding. Rather than mailing me the entire text as you mentioned, I would be happy if you were kind enough to paste the relevant fragments on locomotion below. Freederick (talk) 03:03, 12 September 2011 (UTC)

A second highly differentiated appendage (A2)

is interpreted as belonging to the head (Fig. 1, A and B). It is a wide, triangular, flaplike structure with a broad proximal area (Fig. 1F). The ridgelike appearance of the margins represents thickening, and they preserve evidence of short spines. The trunk consists of 12 segments (Fig. 1B). The first 10 bear a pair of homogeneous biramous appendages. The endopods are flat and made up of at least three wide podomeres (fig. S1F). The proximal two podomeres are short and similar in length; the third is twice as long and terminates in several elongations. The exopod consists of an unsegmented axis bearing numerous flaps (fig. S1, D and E). The appendages correspond in position to the tergites. The last two segments of the trunk lack biramous appendages. Segment 11 bears a pair of lateral flukelike limbs with thickened outer and posterior margins; they partially overlap segment 12 (Fig. 1, A and B). A concentration of apatite along the axis of the trunk may reflect the position of the gut. The anus is located at the posterior margin of the last trunk segment, indicated by a circle of pyrite. The trunk terminates in a long unsegmented spine with a median keel. The spiny great appendage suggests that Schinderhannes was a predator [for example, (2)]. The large eyes imply a substantial visual capability. The flukes at the rear of the trunk indicate that swimming was the main mode of locomotion. Thrust was presumably generated by the large postoral appendage (A2), which may have functioned as a paddle or “wing,” as was deduced for the lobes in the trunk of Anomalocaris (11). Lift was also generated by

the tail flukes.

So, to summarize, thrust was generated from the flapping of the 2nd "great appendage, and lift was created by the flukes near the base of the keeled tail.--Mr Fink (talk) 04:18, 12 September 2011 (UTC)

"Lift" is by definition a force transverse to the direction of motion of the airfoil. For rigid-wing aircraft, it serves to support the weight; but for fish and the like, lift generated by an undulating fluke is the propulsive force. In general I am not impressed with the article you quoted. While the anatomical analysis is impressive and clearly impeccable, the authors seem less certain when moving outside of their area of expertise: "thrust was presumably generated by...". Still, for encyclopedic articles a published source takes precedence over my professional misgivings. I am removing the "dubious" flag against my better judgment; I am still convinced the authors got it wrong. Freederick (talk) 09:53, 14 September 2011 (UTC)