Home Page

Next Page


Thelodus pagei from Traquair (Roy. Soc.Edi.1899)


The thelodonts, are characterized by their complete covering of tiny scales. Isolated thelodont scales are very common and widespread in Silurian and early Devonian marine sediments but complete thelodont specimens are very rare. The best sites in the UK are in Scotland near the village of Lesmahagow . The three common forms from the Silurian of Scotland are Sheila, Loganellia and Lanarkia. Loganellia scotica is found mostly in the Llandovery Patrick Burn Formation, associated with Jamoytius, various eurypterids (Slimonia, Erettopterus), phyllocarid crustaceans (Ceratiocaris) and with the enigmatical animal, Ainiktozoon. Shielia taiti (see Marss and Ritchie 1998) occurs in the Lower Wenlockian Waterhead Group associated with Lanarkia, and the anaspids, Birkenia and Lasanius and the osteostracan, Ateleaspis.

Thelodonts in my collection (click on thumbnails to see larger images)

Loganellia scotica    Silurian(Llandovery)   Lesmahagow, Scotland

Logaellia or Logania as it used to be known, has stud-like, interlocking spines that bulge at the base and an extensive internal dermal skeleton of tiny denticles. It has small, lateral, paired fins, plus a dorsal and an anal fin. The gill openings are located ventrally to the lateral fins. The forked tail has a longer ventral lobe and as can be seen in the isolated tail below, the caudal web has rows of enlarged scales, creating a ray effect similar to that seen in heterostracan tails.

y-Thelodont.jpg (71130 bytes)   r-thelodbid.jpg (79459 bytes)   

Loganellia scotica  Silurian (Wenlockian)    Lesmahagow/Hagshaw inlier, Scotland

ss-thelod.jpg (89193 bytes) Lateral presentation showing lateral, dorsal and anal fins, eyes and many other internal features

alex-nod.jpg (273486 bytes)    alex-nod2.jpg (217000 bytes)    alex-nod3.jpg (223951 bytes)  3D Loganellia (nodule)

qq-thelodonttail.jpg (142586 bytes)   Showing the claudal fin web  'rays' comparable to the digitations of the heterostracan tail


Sheila taiti    Silurian (Wenlockian)    Lesmahagow/Hagshaw inlier, Scotland

 r-thelodsmall.jpg (155389 bytes)   thelodont.jpg (60448 bytes) 

 NOD-SHEILASCALES.jpg (84771 bytes)  Fine scale detail from nodule/fishbed material


Lanarkia sp.    SSilurian (Wenlockian)    Lesmahagow/Hagshaw inlier, Scotland

A small thelodont with triangular lateral fins, a forked tail and spine like conical scales. Three rows of enlarged scales run down the length of the body. The larger animal shown below does seem to have an anal fin?

p-lanarkia.jpg (99468 bytes)       

NOD-LANARKIA.jpg (118131 bytes)   Head in nodule showing fine spine detail

 ar4.jpg (93856 bytes)     ar5.jpg (106208 bytes)   Juvenile 1.2cm long



Thelodonts images from literature

qq-lanc-thelod1.jpg (72731 bytes)    qq-lanc-thelod2.jpg (97619 bytes) REPORT ON FOSSIL FISHES     1899      RAMSAY H. TRAQUAIR