Systematics in palaeontology THOMAS NEVILLE GEORGE PRESIDENT'S ANNIVERSARY ADDRESS 1969 CONTENTS Fossils in neontological categories I98 (A) Purpose and method x98 (B) Linnaean taxa . x99 (e) The biospecies . 202 (D) Morphology and evolution 205 The systematics of the lineage 205 (A) Bioserial change 205 (B) The palaeodeme in phyletic series 209 (e) Palaeodemes as facies-controlled phena 2xi Phyletic series . 2~6 (A) Rates of bioserial change 2~6 (B) Character mosaics 218 (c) Differential characters 222 Phylogenetics and systematics 224 (A) Clade and grade 224 (a) Phylogenes and cladogenes 228 (e) Phylogenetic reconstruction 23 I (D) Species and genus 235 (~) The taxonomic hierarchy 238 5 Adansonian methods 240 6 References 243 SUMMARY A 'natural' taxonomic system, inherent in evolutionary change, pulses of biased selection organisms that themselves demonstrate their pressure in expanded and restricted palaeo- 'affinity', is to be recognized perhaps only in demes, and permutations of character-expres- the biospecies. The concept of the biospecies as sion in the evolutionary plexus impose a need a comprehensive taxon is, however, only for a palaeontologically-orientated systematics notional amongst the vast majority of living under which (in evolutionary descent) could organisms, and it is not directly applicable to be subsumed the taxa of the neontological fossils. 'Natural' systems of Linnaean kind rest moment. on assumptions made a priori and are imposed Environmentally controlled morphs, bio- by the systematist. The graded time-sequence facies variants, migrating variation fields, and of the lineage and the clade introduces factors typological segregants are sources of ambiguity into a systematics that cannot well be accommo- in a distinction between phenetic and genetic dated under pre-Darwinian assumptions or be fossil grades. Trends in variants are not to be formulated by a Linnaean nomenclatural confused with trends in transients; and se- method. quential demes may (in time and space) show The fossil evidence of 'affinity' is best served trend reversals as a sign ofnongenetic (phenetic) by a system of classes defining intrinsic relation- selection. The morphospecies of the local ships that are phylogenetic. Multiple demic palaeodeme is then to be distinguished from variants, clinal bioseries, variable rates of the holomorphospecies of the lineage segment, Jl geol. Soc. vol. xz7, I97X, pp. 197-245, x9 figs. Printed in Northern Ireland. 1 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/127/3/197/4896119/gsjgs.127.3.0197.pdf by guest on 28 September 2021 T. N. George both in kind and in taxonym; and the associa- disjunction as an incipient sign of cladal tion of variant morphotypes in a unitary deme branching presents other problems in nomen- is no justification for a splitting of the deme into clature and in the definition of taxon-range. several morphospecies. Accelerated and retarded rates of bioserial Criteria of cladal disjunction are multiple. change in sub-parallel lineages further com- They may rest in one or a few 'differential' plicate systematics notably in mosaic evolution. characters, or (in a 'numerical' taxonomy) on A basic distinction between Linnaean (morpho- an Adansonian equal-weighting of 'all' char- typic) and evolutionary systematics rests in the acters. A consequence is to impose on an relevance of the question that asks whether the inferred phylogeny taxonomic incompati- class determines the characters or the charac- bilities deriving from contrasted interpreta- ters the class. tions of homology and homoeomorphy. Clinal I. Fossils in neontological categories A) PURPOSE AND METHOD TAXONOMY, the construction of an information-system, is a practical art. There can be as many kinds of taxa as there are purposes for which they are devised; and for its purpose one kind of taxon, based on whatever chosen criteria, is more acceptable than another only because it is more useful, more informative, and not because it enshrines a deeper cosmic truth. Such empiricism is generally taken for granted when emphasis is put on functional reaction rather than on static anatomy: members of a benthic community are classed as epifauna or infauna; stenothermal animals are distinguished from eurythermal; some plants are hydrophytes, some xerophytes, some halophytes. It has nevertheless been regarded as a superficial empiricism, local and tem- porary, if it penetrates no further and does not ask what biotopic elements are burrowers, what animals are heat-tolerant, what plants live in the desert; or, when it asks, does not expect a precise and definitive answer. No doubt, it may be conceded, an individual organism cannot be completely isolated from its en- vironment but has a multitude of responses to external stimulus that partly determine its nature, not least in physiological and metabolic process; but it has for centuries been the analytical practice, explicit or implicit, for its structure to be distinguished from its function, especially when as a fossil it is dead. In an abstraction of organism from context, anatomy and morphology become dominant. Identification, specificity, then presupposes a different kind of classifi- cation from the simply functional, and the 'same' kind of organism--a Kantian kind---can be both epifaunal and eurythermal, xerophytic and halophytic. In classical example, fish-like aquatic vertebrates (a class so called already circum- scribed on some taxonomic basis) then include many kinds of organisms, not only skates and plaice, sharks and salmon, but also dolphins and sea-sirens; and in a change of method by a shift of emphasis from behaviour and 'adaptive' profile to what is considered to be a more significant morphology, skates and plaice are separately distinguished and linked skates with sharks, plaice with salmon, and x98 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/127/3/197/4896119/gsjgs.127.3.0197.pdf by guest on 28 September 2021 Systematics in palaeontology dolphins and sea-sirens are separated from all 'true' fishes and linked with dogs and elephants (the nouns, the names of the organisms, the colloquial taxa, presupposing yet other taxonomic assumptions or criteria). (See Blackwelder I964.) The concentration on anatomy and morphology, formally elaborated by Lin- naeus but begun long before his day, implies or seems to imply that there are kinds of classification, expressing principles deeper than those of empirical convenience, it is the purpose of the systematist to construct. The strength of the construct, as it has been assessed in the stages through which systematics has evolved, lies in the principles the systematist invokes to justify his systematic method, notably by referring to the way in which he has not subjectively or arbitrarily imposed his system on his material but has found his material imposing its system upon him. When the method is apposite the system is then discovered; it is not invented; it is revealed as the 'systema naturae', intrinsically superior to other kinds of systems (which may be used to supplement it) by reflecting the inherent characters of the organisms classified. For over two centuries the systematist in his formal search for a 'natural system'--it has sometimes had the air of a search for the philosopher's stone--has followed many paths. The bias of his search has been overwhelmingly neontologi- cal, and in great part the systems that have emerged have been expressed in neontological format, geologically timeless. Fossils have found only an incidental place in most of them, as the dead complements of living organisms. They still continue to be forced into the frame of a Linnaean taxonomy ill devised for their reception, although it is notorious that the more they are known in their time- sequence and their facies distribution the less comfortably they fit into any neon- tological scheme. An analytical appraisal of a systematics appropriate to fossils, in a review of method and principle, is perhaps not misplaced. (B) i'.INNAEAN TAXA Linnaeus, a hundred years before Darwin, knew only a timeless biology, in which fossils occupied but a minor and incidental part. He laid down the principles of his systematics in the Aristotelian belief, a belief almost taken for granted in its I8th- century context, that his taxa, his universals, represented or should represent the 'natural' affinities and the degrees of affinity of organisms constructed to a Plan it was his task to discover and express (see Mayr x968 , p. 546). His 'natural' system, in so far as it truly reflected the 'natural' affinities of many distinct kinds and groups of organisms, was thus (so he assumed) not external, not artificial and arbitrary; and when he organized his taxa into categories of increasing rank, he regarded the hierarchical system he devised as expressing, however imperfectly, the pattern of the Plan. It is noteworthy that to him the genus was the primary taxon, the major component of the Plan: his species were sharply delineated sets in which the attributes of the genus were variously displayed: the genus determined the characters, not the characters the genus: the genus had an existence independent of the taxonomist, and was real in a Scholastic sense. (See Fig. I.) Linnaeus was a man of his time, at once a leader in his field and a channel for I99 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/127/3/197/4896119/gsjgs.127.3.0197.pdf by guest on 28 September 2021 T. N. George the currents of contemporary thought; and although he was (for his day) excep- tional in the sustained consistency of his system and of his nomenclatural notation, he formulated what had been maturing in the minds of biologists for many decades, and crystallized a method that was to persist for many decades to come. For a hundred years before 1859 his basic assumptions, his ingrained essentialist idealism, remained unchallenged, while his nomenclatural scheme, particulate and hierarchical in its set theory, rapidly permeated the corpus of taxonomics, finally to become an intrinsic element of a formal and universal biology.