Palaeozoologist who gave second life
to the fourlegged fish
by Hans Bjerring
One of Erik Jarvik's colleagues once defined him as a person who can be silent in seven languages. This judgement clearly did not stem from meeting Jarvik in his laboratory or on his favourite hunting grounds, the Devonian outcrops of East Greenland. There he was anything but shy. Jarvik was one of the foremost palaeozoologists of this century. His scientific work has had a vast impact on the studies of the evolution of vertebrates, vaster, indeed, than can be related within the limits of the space allotted here.
In 1927, when Jarvik began his studies of natural history at the Uppsala University, traditional wisdom regarding the evolution of vertebrates was: the cyclostomes (jawless vertebrates) are the most primitive representatives of the group and include the ancestors of the gnathostomes (jawed vertebrates); the chondrichthyans (cartilaginous or sharklike fishes) are the most primitive gnathostomes and forerunners of the remaining gnathostomes; the lungfishes are ancestral to the urodeles (salamanders and newts) which, in turn, include the ancestors of all other tetrapods; the osteichthyans (bony fishes) are at the beginning of their history subdivided into crossopterygians (fringe-finned extinct fishes) and actinopterygians (ray-finned fishes), the latter of which constitute most of today's piscine world; the status of the placoderms (plate-skinned fossil fishes) as jawless or jawed is unknown.
Stensiö and Jarvik
Jarvik aboard ship
During his 60-odd-years stay at the Swedish Museum of Natural History (Section of Palaeozoology) Jarvik came to adopt his own view, outlined in his book 'Basic Structure and Evolution of Vertebrates' (1980, Academic Press):
(1) Cyclostomes and gnathostomes share a common ancestor; thus the cyclostomes cannot be considered more primitive than the gnathostomes, and they do not include the ancestors of the latter.The extant cyclostomes are diphyletic in origin; the Recent lampreys are closely related to the fossil cephalaspids and the Recent hagfishes to the fossil heterostracans. Consequently, the first two groups are classified as cephalaspidomorphs and the last two as pteraspidomorphs. Neither group is jawless (agnath); the former has a rasping type of jaw apparatus, the latter a grabbing type.
(2) The gnathostomes divided early into two principal groups, plagiostomes and teleostomes. The former are characterized by a subterminal mouth and, in contrast to teleostomes, lack an outer dental arcade. This rather heterogenous assemblage reached the zenith of its evolution in Devonian times and is today represented by a few holocephalians (rabbit-fishes) and lungfishes, as well as the sharks and rays. The fossil plagiostomes include the placoderms, whose origin is obscure, and the acanthodians (spiny sharks), which are closely related to sharks.
(3) The teleostomes have a terminal mouth and an outer dental arcade. They comprise the actinopterygians - the largest group of piscine vertebrates - the brachiopterygians (reedfishes), the coelacanthiforms (tufttails), the Devonian struniiforms, the urodelomorphs (porolepiform fishes and urodelans) and the osteolepipods (osteolepiform fishes and eutetrapods). Thus, tetrapods have evolved more than once.
Jarvik's view of vertebrate evolution differs much from earlier and current ones. It emerged gradually and is based on comparative anatomical studies of both living and extinct vertebrates. Many palaeoanatomical details have been procured with the use of Sollas' grinding method and wax-plate models. These ground sections and models have enabled study of the three-dimensional cephalic morphology of plagiostomes and teleostomes that became extinct in Palaeozoic and Mesozoic times. One of these serially ground fishes is the osteolepiform Eusthenopteron foordi from the Upper Devonian of Miguasha, Canada. It is today incomparably the best known fossil fish.
Jarvik with wax model of Eusthenopteron anatomy
Most vertebrate palaeontologists seem to have been unwilling to accept the conclusion that the tetrapods are diphyletic in origin. However, no one has been able so far to prove Jarvik wrong. An attempt was made in 1981 by four researchers to revive the notion that tetrapods and lungfishes are collateral relatives. Jarvik's acrid reply (in Systematic Zoology) asserted that his four cladistic critics had ignored well-known facts while themselves contributing groundless assertions, inaccurate descriptions, and sheer mistakes.
At an international symposium held 1967 in Stockholm, the Swedish entomologist Lars Brundin asked Jarvik, and got his permission, to deliver an unscheduled talk about the principles of phylogenetics and phylogenetic systematics advanced earlier by W. Hennig. This talk started what today is called cladism. But as Jarvik saw it, there is nothing new or revolutionary in Hennig's cladistic theory. Jarvik once wrote: 'Of course, when assessing relationship primitive characters must be disregarded. Only unique specialisations can be used; these, however, must be weighed with care. It is not with cladistic terms but through comparative studies of extinct and extant vertebrates that phylogenetic knowledge increases. In this way new light has been shed also on many intricate problems, such as the basic composition of the vertebrate head, the origin of the paired limbs, and the phylogeny of the ear ossicles'.
With regard to the three ear ossicles in mammals, Jarvik considered them derivatives of one and the same gill arch, not of two consecutive arches. He identified their homologues in a Devonian osteolepiform fish and argued strongly for the abandonment of the classical Reichert-Gaupp theory.
The last paper Jarvik wrote was published in 1996. It is a monograph on the anatomy of Ichthyostega, the 'fourlegged fish' from the Upper Devonian sandstone of East Greenland. This amphibious tetrapod was already much specialized and is not the progenitor of other tetrapods.
Jarvik was a legend in his own time. His career lasted 62 years. Privately, he was the kindest and most courteous of men. In assemblies he was taciturn, even shy. He died on January 11th, 1998, at the age of ninety in a nursing home in the outskirts of Stockholm.
The author (left) with Jarvik at Miguasha, Québec, the Eusthenopteron fossil locality
The author: Hans C. Bjerring is at the Section of Palaeozoology, Swedish Museum of Natural History, Stockholm, Box 50007, SE-104 05 Stockholm, Sweden.