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Phanerozoic-Cryptozoic and Related Transitions: New Evidence Preston E. Cloud, Jr. C. A. Nelson

Reprinted from Science, November 11, 1966, Vol. 154, No. 3750, pages 766-770 Phanerozoic-Cryptozoic and Related Transitions: New Evidence As can be seen by comparing Fig. IB with known Pteridinium to right and Abstract. The fossil Pteridinium, a distinctive component of a worldwide early left, they compare closely in their slat- metazoan (Ediacaran) assemblage, is provisionally recorded from probable early like ribbing, dimensions, and spacing Cambrian strata in eastern California. In context with other evidence, this finding of ribs. Nothing else is yet known implies a Cambrian age for the Ediacaran fauna and approximate coincidence of at this general stratigraphic level which limits between Phanerozoic-Cryptozoic, Paleozoic-Precambrian, and Cambrian- the California fossil resembles even Precambrian. faintly, and it seems likely that it is in fact a Pteridinium or closely related Recent study of markings of bio- boundary between the Paleozoic and form. This fossil was found by a Uni- logic origin in rocks near the base of Precambian eras that would take into versity of California student in the the Paleozoic in the White-Inyo Moun- consideration factors epitomized by the middle member of the Deep Spring tains of eastern California reveals simi- use of the terms Phanerozoic and Cryp- Formation (locality 6, Fig. 3B) slightly larities between one of these markings tozoic. The relatively late appearance more than 2000 feet below the lowest and the problematical genus Pteridinium of the metazoan grade of evolution occurrence of the early Cambrium tri- (1), which occurs at the base of the probably marks and is related to some lobite Fallotaspis, about 3000 feet be- Nama System in South West Africa. great episode in earth and atmospheric low a zone (locality 2, Fig. 3A) con- The Nama fauna has been correlated history that offers operationally prac- taining relatively abundant Fallotaspis with the Ediacaran fauna of South tical and philosophically satisfying and Daguinaspis (7), and 350 feet Australia (2) on the basis of their grounds for the division of geologic below a zone of trace fossils including mutual inclusion of Pteridinium and time into two major if unequal parts representatives of the arthropod sitz- also another problematical organism, (6). mark Rusophycus and crawl-track Cru- Rangea, both provisionally assigned to Under such a concept the era bound- ziana (localities 1, 3, Fig. 3A; locality 7, the Pennatulacea (3). From other fos- ary between Precambrian and Paleo- Fig. 3B). These relations are shown sils at Ediacara this correlation has zoic becomes independent of the Cam- in Fig. 2, and Fig. 3 shows the loca- been extended to strata in the Charn- brian, and one thinks of the possibility tion and local geologic relationship. wood Forest of England (4) and in of pre-Cambrian rocks of Paleozoic If the reader accepts the probable northern Russia and Siberia (5). age. Precambrian then signifies pre- presence of Pteridinium in California, Thus the elements of worldwide cor- Paleozoic, and the time may come its relation to other organisms in the relation of a very early Metazoan when this awkward term (Precambrian) same section becomes of great interest. fauna are suggested. The immediate will disappear from our language al- First let us consider the presumably problem is the relation of this fauna together. In fact, it must disappear to arthropodan sitz-mark to crawl-track to other early metazoan faunas; and resolve the absurdities inherent in try- sequence Rusophycus-Cruziana from that is quite uncertain, except for the ing to discuss the very legitimate ques- the beds 350 feet above Pteridinium. fact that the type Ediacaran fossils tion of pre-Cambrian rocks of post- Both forms are shown to be attribut- occur several hundred feet below a Precambrian age, as well as the awk- able to a single organism by certain Lower Cambrian archaeocyathid as- ward but now widely used reference semblage in a different stratigraphic to post-Precambrian in other connec- Fig. 1. (A, C) Pteridinium simplex GUrich unit. This 'bears ultimately on the ques- tions. Meanwhile we can continue to 1930, emend. Richter 1955. Kuibis Quartzite, base of Nama System, Aar, be- tion of metazoan origins and on the talk about the problem as some have tween Kuibis and Aus, southeastern South vexing question of where and how to done in terms of Phanerozoic and Cryp- West Africa. Locality P.I. 16 of State define a boundary between the major tozoic eons (perhaps eventually with Museum of South West Africa. (B) Com- divisions of geologic time known as more felicitous eon terms for still more pare Pteridinium. Close to middle of Deep Spring Formation, NEV4, NW!4, Paleozoic and Precambrian. ancient rocks with no animal life at SEV4, sec. 16, T7S, R35E, Blanco Moun- This discussion is further compli- all or without life). tain Quadrangle, California. Locality 6 cated by the historical evolution of The object that precipitates these of Fig. 3. (D) Rusophycus (upper left) and other reflections (Fig. IB) is an and Cruziana (continuous below Ruso- the term Precambrian. For many years phycus at left and also on right). Obvious- the Cambrian was considered to mark unimpressive but nevertheless distinc- ly the two names apply to the same orga- the base of the decipherable historical tive imprint which can hardly be of nism (and Rusophycus has priority), but record, and rocks older than this were nonvital origin and which compares it is convenient to use both names here. thought to represent a subordinate part among fossils known to us only with Tapeats Sandstone, Middle Cambrian, Chuar Valley, Grand Canyon, Arizona. of earth history not susceptible to Pteridinium (Fig. 1A, C), for which U.S. National Museum No. 66148. (E, G) world-wide subdivision, hence known we have ample reference material col- Arthropod (? trilobite) scratchings of only as pre-Cambrian. The use of the lected by Cloud in 1965 and also Cruziana-type from base of upper member term Precambrian as a single word loaned to him for study by P. S. Swart of Deep Spring Formation, Lower Cam- brian, center EVi, NEV4, SWV4, sec 18, with a capital P was only recently in- of the State Museum of South West T6S, R35E, Blanco Mountain Quadrangle, troduced to dignify its present treat- Africa at Windhoek. Were there any California. Locality 1 of Fig. 3. For com- ment as a major formal grouping of question about the age of the Cali- parison with Fig. ID and also with Cru- the rock succession and geologic time, fornia specimen (Fig. 2), one might ziana and other scratehings attributed to trilobites by Walcott (70, plates 37 to and not merely something that wasn't hypothesize that it was the imprint of 40). (F) Rusophycus from base of upper Cambrian. an annulately ribbed, orthoconic ceph- member of Deep Spring Formation, Lower Increasingly in recent years some alopod or sipuncle, but it occurs far Cambrian. Same locality as E and G. (All geologists and paleontologists have en- below the position in the geologic illustrations are approximately natural tertained the notion of recognizing a sequence where such fossils are known. size.)