Enige bijzondere kaakloze vissen (Agnatha) uit het Onder-Siluur van Lanarkshire (Schotland)
Grondboor & Hamer , Volume 59 - Issue 2 p. 24- 28
Two unusually preserved specimens of the enigmatic agnathan Lasanius problematicus are described. One specimen seems to have a curious tail. However, the 'tail' is another undescribed creature with probably the orbits showing as two darker spots in the rock. The lighter coloured line through this ?agnathan could be an indication of the notochord. The fossils are embedded in such a particular way that they seem to be associated (images 2a and 2b). The second Lasanius split in two due to decomposing gasses and mortis regis. The left and right side of the body are visible, just like a kipper (image 3), but this one is about 430 Ma old! Undisturbed specimens of the thelodont Lanarkia horrida are extremely rare. Images 4a and 4b show an intact specimen (in part- and counterpart) with indications preserved of the orbits and part of the finweb between the caudal fins. The conservation of the caudal fins on image 5a, a Lanarkia lanceolata, is even better. They demonstrate a finweb with many scale covered finrays. This fish also shows an arch shaped object in the snout. This could be the rostral cartilage situated between the nasal capsules. Images 6 and 7 are other examples of this yet unnoticed object in thelodonts. Märss and Ritchie (1998) have described paired pelvic fins in Shielia taiti. Images 9a and 9b (also a S. taiti) probably verify another example of paired structures, which stand apart from the body outline and could be interpreted as remains of the pelvic fins. Also visible are a clear oval shaped oral aperture; ?nasal capules; position of the orbits; pectoral fins; possible remains of the dorsal fin and a caudal finweb without finrays which seems to be characteristic for S. taiti, according to Märss and Ritchie.
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