CHAPTER 3 



Fossils 



The oldest fossil sea urchin is probably Bothriocidaris ^ from the Ordo- 

 vician of Russia (Esthonia). This fossil was accepted as the ancestor 

 of the Echinoidea until Mortensen (1928, 1930), the eminent Danish 

 authority, considered it a cystoid and not an echinoid. Mortensen's 

 views were opposed by equally good authorities, Hawkins (1929, 193 1), 

 Jackson (1929), and H. L. Clark (1932, 1946), but Mortensen in his 

 comprehensive monograph of 1 928-1 951 (1935, M H, p. 15) still 

 holds to his own view. However, Jackson (191 2, p. 208) has said: "The 

 most primitive type of Echini, I believe emphatically, is Bothriocidaris.'' 



Though rare in the Ordovician, and few in the Silurian and Devo- 

 nian, fossil sea urchins are abundant in all periods after the Devonian, 

 and have been excellent material for the palaeontologist. There are 

 about 6,000 fossil species (Grasse, 1948, p. 162; Clark, 1946, p. 277). 



Fossils of sea urchins were scattered over northern Europe during 

 the glacial period, and these have played a part in folklore. They were 

 regarded as thunder stones, fallen from heaven with the thunder, and 

 thus supposed to protect against thunder. They were also used in 

 prehistoric times as amulets (Mortensen, 1927a, p. 9). 



Fossil spines of some large sea urchins are known as Jewstones or 

 Lapides Judaici. These were especially well known in Syria and Pale- 

 stine, where they were used in medicine as a diuretic (Sir John Hill, 

 1 751; Oxford Dictionary). They have been found also, together with 

 the tests filled with chalk in the Chalk Pits of Kent. These "chalk-eggs" 

 were used to cure digestive troubles and were therefore saved by the 

 workmen (Sir Hans Sloane, 1725). 



Fossil sea urchins are used by oil companies to determine the age 

 of the beds at certain depths. This is especially true of the Cretaceous 

 of Texas. 



The family of Arbaciidae is known from the Tertiary to Recent 

 (Jackson, 19 12, p. 209) and there are many fossil genera in the family 

 (Mortensen, 1935, M H, p. 548). Fossil tests and spines of Arbacia 



' The statement by Jackson (191 2, p. 244) that Aldrovandi figured Bothriocidaris in 

 1606 is apparently a mistake (Mortensen, 1913a, 1928; Jackson, 1929). 



