| Review | |
The fossil site of Miguasha was discovered in 1842 by Dr. Abraham Gesner and promptly "forgotten" until its rediscovery in 1879 by R. W. Ells of the Geological Survey of Canada. The fossil material found, especially plants and fish, became the focus for now classic word by William Dawson and J. F. Whiteaves (Lemieux chapter). Whiteaves referred to the site as the Baie des Chaleurs of Scaumenac Bay, and for the next century, the site was known as "Scaumenac Bay".
The richness of fossil fish has drawn expeditions and collectors from all over North America and Europe: the antiarch placoderm Bothriolepis and the lungfish Scaumenacia are as common and so well preserved as the site that they have been used as the representatives of their respective groups in exhibits and teaching collections all over the world. In 1978 an interpretation centre for the Escuminac Formation fossil fish was opened under the directorship of Marius Arsenault. The fossil site was declared a provincial park, the Parc de Miguasha, in 1985 and collecting is now allowed only under strict conditions. New finds are stored and curated now in the museum of the park (Musée d'Histoire naturelle de Miguasha) which has the largest collection of Escuminac fossils in the world (Parent and Cloutier chapter).
In July 1991 the Parc de Miguasha held a very successful symposium on Early Vertebrates which was also the first international meeting of IGCP 328: Palaeozoic Microvertebrates [see Arsenault & Janvier eds. 1995]. Many of the participants at that meeting along with paleontologists and geologists from Canadian, U nited States and European institutions have co-operated to contribute to this fine book on the Miguasha assemblage.
Since the early descriptions of fish and plants, the number of taxa from Miguasha has more than tripled. This new book presents the first comprehensive description of the history, geology, paleoenvironment and fossil content of the Late Devonian site of Miguasha since Ørvig's (1957) compilation of the fish assemblage and the sedimentological and paleoenvironmental interpretation given by Dineley and Williams. For the past 25 years, the paleoenvironment of the Escuminac Formation has generated a great deal of controversy. Originally interpreted as a lacustrine environment by Dineley and Williams (1968), recent evidence suggests that the Escuminac Formation was deposited in a coastal marine environment (Schultze, 1972; Schultze and Arsenault, 1985; Vézina, 1991; Schmitz et al., 1991; Hesse and Sawh, 1992; and chapters by Prichonnet et al., Chidiac, Maples, Schultze and Cloutier).
The paleogeography of Miguasha has also been a 'hot' topic. During the Late Devonian, Miguasha was under equatorial climate as given by the position of paleocontinents (Seguin chapter) and the presence of terrestrial scorpions (Jeram, this volume) and luxurious plants (Gensel and Barnett-Lawrence chapter). Despite a rich palynomorph assemblage (McGregor chapter), the megaflora shows only low diversity, an indication of distance from the coastline and/or destruction by transport. However, McGregor reports no palynomorphs suggesting marine conditions. On the other hand, acritarchs which have yet to be described, are known from the lower part of the formation (Schultze and Cloutier chapter).
The assemblage is poor in invertebrate taxa; Jeram and Martens describe three arthropod taxa, including the first North American stylonuroid eurypterid. The first trace fossils are also recorded from the Escuminac Formation; they indicate a marginal marine environment (Maples chapter).
The entire vertebrate assemblage is revised, including some of its paleoecological interactions and microinvertebrate potential (McAllister chapter). Of the 21 taxa, the agnathans are unique and include some of the last survivors of the group; Bothriolepis, the acanthodian Triazeugacanthus, Scaumenacia, and the osteolepiform Eusthenopteron are the most abundant taxa; the acanthodian Homalacanthus and actinopterygian Cheirolepis are less common; all othe taxa are rare. Most major groups of Devonian fishes are represented in Miguasha, with the exception of heterostracan agnathans, chondrichthyans and onychodontiforms. However, these last two might be expected in the microfauna when investigated further.
The volume closes with a comparison of the fish assemblage of Miguasha with some of the contemporaneous Frasnian assemblages (Schultze and Cloutier). The ichthyofauna is highly endemic at the species level (20 of 21 species are unique), whereas at the generic level it is similar to now far distant localities in Ellesmere Isand, Scotland and Russia, and at the familial level it is reminiscent of at least one locality in Australia. The authors, however, concentrated their efforts mainly on sites with macrofauna; they might well have included some of the microfaunal sites in their comparison to provide further data; the Gneudna Formation of the Carnarvon Basin of Western Austraia and some of the newer sites in the Holy Cross Mountains spring to mind. In addition in stead of using the outmoded genus "Cladodus" they might have ascertained which cladodont teeth were represented in each fauna (e.g. Stethacanthus, Symmorium, Ctenacanthus, Cladoselache, Phoebodus, etc) to give potentially clearer picture and biostratigraphic data from the chondrichthyans – the presence of phoebodont teeth for instance can allow correlation to one or two standard conodont zones.
The book is excellently produced with a stunning orange cover design featuring Eusthenopteron against the backdrop of the Miguasha cliffs. It would certainly grace any Devonian bookshelf!
| Copyright © 2012 Verlag Dr. Friedrich Pfeil |