sign in sign up
<<
Home , 2021 in paleontology, Barnacle, Evolutionary Fauna, Jack Sepkoski, Mesozoic, Ordovician radiation

Contributions to Zoology, 69 (4) 213-222 (2000)

SPB Academic Publishing bv, The Hague

Crustacean through the marine record

J.+John Sepkoski+Jr. (†)

Department of the Geophysical Sciences, , Chicago, IL 60637, USA

Keywords: biodiversity, marine fossil record, rates, Ostracoda, ,

Cirripedia

Abstract Introduction

2,600 ofmarine have been Approximately genera constitute an important component of recognized in the fossil record, and crustaceans constitute the the fossil record, just as they constitute a major major componentof marine diversity from the mid- part of the living both on land and in the to the Recent. Despite problems of sporadic fossil oceans. In the marine realm, approximately 16 per- preservation and/or taxonomic ambiguity, some general state-

cent of all described of fossil ments can be made about the history of crustacean biodiversity, genera are based taxonomic data bases. Ostracodes the first on global were arthropods; on land, fossil arthropods at the family major to radiate,attaining high diversity during the Ordo- level group have proportions that are even higher (Laban- vician Period with other members ofthe Paleozoic evolutionary deira and Sepkoski, 1993). Among fossil marine of extinction and fauna;rates responses to mass were a constituent is the Crustacea, also similar those of within the Paleozoic fauna. arthropods, major to groups Malacostracans and and barnacles (cirripedes), the two other crusta- including predominantly ostracodes, cirripedes,

cean with had minor malacostracans. with groups important fossil records, diversity Together minor groups, they throughout the Paleozoic . Both diversifi- groups experienced include 45 percent of described arthropod fossil cation from the mid- to Recent with lower extinction genera from marine strata, exceeded only by the rates, as characteristic members of the Modern evolutionary diverse and rapidly of the Pa- fauna. evolving leozoic Era.

In this contribution, 1 examine these numbers

for crustaceans as relate to time Contents they geologic and

therefore to and fossil evolutionary history pres-

ervation. or taxonomic of fos- Introduction 213 Diversity, richness,

sils in taxonomic databases Caveats 214 provides a variety of

214 quantitative information. The simplest is just our

Ostracode 214 knowledge of the fossil record: The numberof fossil Malacostracan preservation 214 taxa described can be compared to other measures Crustacean diversity in the fossil record 214 modern of importance, such as diversity or fossil Relative to other arthropods 214 to deduce the of knowl- of in the fossil record 215 abundance, quality our Diversity major groups Ostracodes 216 edge of the fossil record. For example,

Barnacles , 217 are the most abundant arthropods in modern ma- Malacostracans 217 but rine pelagic ecosystems, their fossil record is Comparison to diversification 219 But with minimal. even varying quality of the fossil Summary 220 statements can be made Acknowledgements 220 record, qualitative about

References 220 evolutionary history, which is the usual goal of

Addendum 221 studies of fossil diversity.

The data here based analyzed are upon a com-

of of pilation geologic ranges all marine

that I have described genera previously (e.g.,

Sepkoski, 1996, 1997). The compilation has in-

Downloaded from Brill.com10/08/2021 03:03:48AM via free access - and 214 J.J. Sepkoski Crustacean biodiversity

standard such the as zonal fossils of the volved summarizing sources, as occasionally through parts

review- Mesozoic and . crustaceans as Treatise on , and However,

have ing primary literature to increase stratigraphic reso- a whole been viewed as having a sporadic in fossil record and therefore oflimited use lution of first and last appearances and to add newly telling

taxonomic level of time. there has been limited for described fossil genera. The Thus, impetus

is between detailed search and the employed as a compromise study. the immense, idiosyncratic, and historically com- plicated taxonomic descriptions of fossil Ostracode taxonomy and the limited numbers of crustacean families described from the fossil record (therefore subject in In- The volume on ostracodes the Treatise on taxonomic lev- to small-sample variation). At the Paleontology (Benson, 1961) was a major els of both genus and family, some might object breakthrough for the understanding of the - that supra-specific taxa are arbitrary constructs and atics of these fossils. Since that publication, the not reflect How- may any evolutionary patterns. number of described ostracode genera has more and model ever, empirical (Sepkoski et ah, 1981) is difficult this world- than doubled. It to survey (Sepkoski and Kendrick, 1993) studies have indi- wide literature and compile all revisions in strati- traditional and families reflect cated that genera graphic ranges ofolder ostracode genera. Therefore, species-level patterns of diversity quite well (see data ostracodes’ ranges in any synoptic set, despite also Gaston and Williams, 1993). In fact, when large diversity among fossil crustaceans (see below), the potential preservation of animals is quite low, minimum will be largely ranges. taxa as in the case of many crustaceans, higher

reflect of may better patterns underlying species

than fossil themselves (Sepkoski diversity speices Malacostracan preservation and Kendrick, 1993).

I few caveats about the Below, present a more Many malacostracans and other crustaceans have data. I then illustrate summaries of the history of nonmineralized to weakly mineralizedexoskclctons. for the major fossil classes of marine genus diversity The result is a sporadic fossil record. The most

crustaceans and these to the history of compare abundantcrustaceans in the oceans today, the cope- the three evolutionary of the Phan- great pods, have virtually no fossil record, and marine

erozoic. that forms are inferred largely from cysts parasitic copepods produce in . Among mala-

costracans, the fossil record is somewhat better, Caveats especially with the Mesozoic of brach-

with calcified exoskeleton. Still their yurans a In attempting to interpret crustacean diversity known history, like the history of other malacos- through geologic time, it is clear that both the is sensitive the tracan groups, very to geologic quantity of taxonomic attention and the quality of - distribution of exceptional fossil deposits Lager- preservation influence patterns seen in taxonomic statten. But if these weakly sclerotized taxa appear databases. Neitherattention nor quality is ideal for then more and more frequently in Lagerstatten, we in world crustaceans, but even an imperfect major can infer that they were becoming more important evolutionary trends in diversity are potentially in the biotic environment time. and through perceptible. Below, I discuss three problems

their resolutions:

Crustacean diversity in the fossil record

Biostratigraphy

Relative to other arthropods

Crustaceans have not been used as index fossils

fossil of through most of the Phanerozoic geologic record. Of the approximately 5,800 genera ma-

Ostracodes are an exception and have been used rine arthropods currently recognized, about 2,600

Downloaded from Brill.com10/08/2021 03:03:48AM via free access Contributions to Zoology, 69 (4) - 2000 215

I. The described of all the Phanerozoic. Crustacean is the fig. genus diversity marinearthropods through genus diversity illustratedby

lower Dots indicate data “Ma” is millions of before Abbreviations for field. points. present. geologic periods are as follows:

C=; 0=; S=; D=; C=;P=; T=; J=; K=; T=.

are crustaceans. The majority of the remaining fossil tacean diversification has not been homogeneous,

the genera are trilobites, which did not survive as described below.

such the Paleozoic Era. Other groups, as extant

to have nierostomes and pycnogonids, appear never

been diverse for the the (except perhaps ). Diversity of major crustacean groups in fossil This pattern is illustrated in Fig. 1, which exhibits record

the total described diversity of marine arthropods

through the Phanerozoic with crustacean diversity Fig. 2 illustrates the Phanerozoic history of the three

field. crus- segregated into a separate As evident, major groups of fossil crustaceans: ostracodes,

taceans have been important components of ma- barnacles (cirripedes), and malacostracans. Total rine biodiversity since the Ordovician Period and diversity in this graph differs somewhat from that

compose virtually the entire fossil arthropod fauna' in Fig. 1 because two adjustments have been made

the Mesozoic and Cenozoic when to minimize biases in the fossil data. through they First, genera attain maximum observed diversity. However, crus- confined to single stratigraphic intervals havebeen

Downloaded from Brill.com10/08/2021 03:03:48AM via free access 216 Sepkoski - Crustacean biodiversity andfossils

Marine the Phanerozoic with accommodate described in the Fig. 2. crustacean genus diversity through manipulations to biases, as text.

The three fossil of indicate cumulative Abbreviations the in major groups crustaceans are by fields. arc same as Fig. I.

eliminated in to remove some effects of eluding bradoriids) as ostracodes, although there varying durations of stratigraphic intervals and.of is debate about true affinities. Still, their diversity extraordinary Lagerstiitten (e.g., the Solnhofen is minor compared to the massive numbers of true Ordovician. Kalken) (see Sepkoski, 1996). Second, extant genera ostracodes (e.g., palaeocopids) in the

been their the have counted up until youngest fossil Ostracodes were an important component of occurrence (see Sepkoski, 1997) in order to mini- Ordovician radiations and, in fact, attained their mize the “pull of the Recent” (Raup, 1979). Thus, maximum fossil diversity during the Caradocian. while Fig. 1 is purely descriptive, Fig. 2 is some- (However, this may be somewhat artifactual be- what interpretative although still based on counts cause of intense study of Ordovician ostracodes of in Baltic genera in the synoptic database. .)

Ostracodes suffered greatly at the end-Ordovi-

Ostracodes cian mass extinction (nearly 60 percent decline)

and then recovered somewhat during the mid-Pa-

Ostracodes are the major component of the crus- leozoic, like many other members of the Paleo- tacean marine fossil record, constituting nearly 75 zoic (see below). Ostracodes

of and observed decline the Late Devonian percent accepted genera dominating experienced again at crustacean diversity throughout the Phanerozoic. () mass extinction and appear to have

I have accepted all Cambrian Archaeocopida (in- undergone nearly continuous attrition through the

Downloaded from Brill.com10/08/2021 03:03:48AM via free access Contributions to Zoology, 69 (4) - 2000 217

Paleozoic Era (19 percent loss at the end-Triassic,

27 percent loss at the end-Cretaceous).

The post-Paleozoic rediversification ofostracodes

in their reflects large part heterogeneous taxonomic history. Fig. 3 provides spindle diagrams illustrat-

ing the diversity of fossil genera within orders of

the Ostracoda. All orders originated during the early

Paleozoic, and Palaeocopida and Podocopida have

always been most diverse (other than during the

Cambrian). However, the Palaeocopida disappeared

at the end of the Permian, and the post-Paleozoic

rediversification of ostracodes reflects expansion

of the Podocopida which appear to have somewhat

lowerrates of genus origination and extinction than

the palaeocopids.

Barnacles

Barnacles (i.e., cirripedes) are a minor, yet notice-

the able, component of fossil record of marine

crustaceans. Their Paleozoic record is minor even

though it extends, putatively, to the Middle Cam-

brian Burgess Shale (Collins and Rudkin, 1989).

More certain fossils are known from the late Pa-

leozoic. Diversification becomes evident in the

fossil record of the , mostly among

thoracicans, and proceeds rather steadily (except

for the end-Cretaceous mass extinction) to the late

Cenozoic.

Malacostracans

Malacostracan crustaceans have a history of post-

Paleozoic diversification like that of barnacles, but

3. the of Fig. Spindle diagrams illustrating genus diversity ma- they are also taxonomically heterogeneous like os- rine ostracode orders throughthe Phanerozoic. The three vertical tracodes. Basal malacostracans have some diver- fields are for the Paleozoic, Mesozoic, and Cenozoic Eras; in the as illustrated in 4 where Phanerozoic sity Cambrian, Fig. periods are indicated in the margins, with abbrevia- the several tions asin Fig. I. The spindle diagramsare symmetrical, showing genera are lumped into the “- total known fossil diversity. The scale is given in the lower left spida.” Most malacostracan diversity in the mid- ofthe diagram. Paleozoic is contributed by the “phyllocarids” which

persist to the Recent in low diversity. Late Paleozoic late Paleozoic. At the end of the 80 Permian, percent contain a number of Lagerstatten disparate groups of the remaining ostracode became extinct. genera of malacostracans, including early representatives of The post-Paleozoic history ostracode diversity of the Tanaidacea and , which never appear is one of not levels recovery, although perhaps to diverse in the fossil record, probably because of experienced their . The during rare preservation. post-Paleozoic suffered at some extinction genera The main component of observed post-Paleo- events but the not to same exent as during fhe zoic diversification of malacostracans is the deca-

Downloaded from Brill.com10/08/2021 03:03:48AM via free access 218 J.J. Sepkoski - Crustacean biodiversity andfossils

4. the of Fig. Spindle diagrams illustrating genus diversity ma- rine malacostracan orders the Phanerozoic. through Graphing 5. the of infra- Fig. Spindle diagrams illustrating genus diversity conventions are the same as in Fig. 3. orders of marine decapods through the Phanerozoic. Graphing

conventions are the same as in Fig. 3.

illustrated pods, as in Fig. 4. This group is reported first from the latest Devonian (Schram et ah, 1978) ingly through the Cretaceous andCenozoic outside and has few fossil the in occurrences during succeedirtg of exceptional Lagerstatten; and are implicated

Paleozoic. With the fos- the post-Permian recovery, evolutionary development of defensive mor- sils and become more molluscan genera abundant, especially phologies among many prey through the in Lagerstatten. The Solnhofen, reflected in Fig. 4 same time period (Vermeij, 1987). The Astacidea

the narrow bar at the of the Jurassic, con- and Palinura share of the by top (“”) many same tains more than that many decapod genera any previous features so their fossil histories of diversity

After the be reflective Lagerstiitte. Solnhofen, genus diversity may similarly of true diversification recorded in the fossil record continues to increase the in the number of of (despite spike genera to a late Cenozoic maximum. palinurans at the Solnhofen). On the other hand,

The late Mesozoic-Cenozoic expansion of de- the history of low diversity of the Penaeoidea

is function of almost capod diversity largely a brachyuran (“shrimps”) certainly reflects low preser-

as illustrated in 5. This is vation of this sclerotized radiation, Fig. probably weakly group.

real a (if incomplete) pattern since tend to have well-mineralized skeletons; are found increas-

Downloaded from Brill.com10/08/2021 03:03:48AM via free access - Contributions to Zoology 69 (4) 2000 219 ,

Comparison to general Phanerozoic koski, 1984, 1998) and similar habitats, at least diversification during the Paleozoic Era (Sepkoski, 1991).

Malacostracans and barnacles resemble most

Fossil Crustacea exhibit patterns of diversification members of the Modern evolutionary fauna, such and in of bivalves and and echi- heterogeneity seen many other groups as gastropods, especially

Phancrozoic marine animals. 6 illustrates the noids and . These Fig. osteichthyan are groups

of marine within the three the Paleozoic Era but with far lower history genus diversity present during great evolutionary faunas (as defined by Sepkoski, diversity than today. Ostracodes, on the other hand,

1981, 1991) separated into cumulative fields. Each are better classified within the Paleozoic evolu- evolutionary fauna is defined by taxonomic classes tionary fauna despite their dramatic recovery of of marine animals that attain their greatest diver- diversity (and abundance) during the Mesozoic and sity during one of the three phases of Phancrozoic Cenozoic Eras. Their history and taxonomic het- diversification: the Cambrian, the post-Cambrian erogeneity are not unlike those of several other

Paleozoic, and the Mesozoic-Cenozoic. Classes in major groups that are classified in the Paleozoic these evolutionary faunas share not only broad fauna, notably the anthozoan and the cepha-

histories but also similar evolutionary rates (Sep- lopods. The stony corals of the Paleozoic Era

Fig. 6. Genus diversity of the three great evolutionary faunas of the Phanerozoic marine fossil record: “Cm”=Cambrian fauna; “Pz”=Paleozoic fauna; “Md”=Modernfauna. “” indicates the diversity of the animal-like Foraminifera and Radiolaria, which can be considered components of the Modern evolutionary fauna. Abbreviations are the same as in Fig. 1.

Downloaded from Brill.com10/08/2021 03:03:48AM via free access 220 J.J. Sepkoski - Crustacean biodiversity andfossils

Table I. Rates of origination (Orig.) and extinction (Ext.) for parison to the Modem fauna. It is reflected in the that than of Phancrozoic crustaceans span more one of ostracodes genera greater volatility at mass extinctions, interval, weighted by diversity (see text). Rates stratigraphic Paleozoic again a characteristic of members of the in units of extinctions are per-genus rates originations or per fauna in general (Sepkoski, 1984). million Number of indicates actual genus per years. genera

total number of indicates numbers used in the calculations; genera all numbers in the database. (Several dozen problematical fossil

Crustacea that cannot be in these three classes are not placed Summary included in the numbers.)

Crustaceans the of fossil Orig. Ext. Number Total compose greater part

of genera number arthropod diversity from the mid-Paleozoic to the

Recent. Their history is heterogeneous, however. Ostracoda 0.025 0.021 1189 1939 Ostracodes were the most important crustacean Cirripedia 0.021 0.007 78 93 of the Ordovician radiations, but their Malacostraca 0.024 0,012 361 538 component observed diversity waned through the later Paleo-

zoic. After the end-Permian mass extinction, which

eliminated palaeocopids, podocopids and other the (rugosans and tabulates) became extinct at end surviving orders radiated to nearly Paleozoic lev- of the Permian and were replaced in the post-Pa- els of diversity. leozoic by scleractinians, which are important in Malacostracans, cirripedes, and other crustacean modern communities but do not have the classes are minor components of the Paleozoic fossil summed diversity of their Paleozoic counterparts. record. However, malacostracans and cirripedes Modern coleoid are also abundant, radiated with other members of the Modern evo- and Mesozoic ammonoids were diverse. However, lutionary fauna through the Mesozoic and Ceno- diverse biota they were not so a component of the zoic Eras. the Or- as Paleozoic , especially during These generalizations are based upon compila- dovician radiations (see Sepkoski, 1981). tions of global paleontologic data for genera and The evolutionary rates of ostracodes also dis- must be judged in terms of the quality of taxo- tinguish them from other memebers of the Crusta- nomic study and the frequency of fossils. Still, cea and unite them with the Paleozoic evolution- quantitative patterns of diversification seen in the lesser than ary fauna, although to a degree many fossil record are consistent with qualitative expec- other such articulate Classes groups, as . tations of preservability and importance to study. within the Paleozoic fauna mostly have higher rates

of origination and extinction than classes grouped

fauna 1984, 1998). into the Modern (Sepkoski, Acknowledgements Tabic lists of and extinc- I genus rates origination

tion for ostracodes, barnacles, and malacostracahs, I thank C.M, Janis for invaluable help with figures. Compilation

calculated by stratigraphic stage using the timescale and analysis of data received support from the National Aeronautics and Space Administration (NASA) under grant of Harland et al. (1990); the rates represent weighted NAGW-1693. such that with averages stages greater diversity

received arithmetically more weight than stages

with lower diversity. References

All three classes of marine crustaceans have

rates of (which essentially equal genus origination Benson RH. 1961. Arthropoda 3 (Crustacea, Ostracoda).

be can seen as surprising given the small sample The Treatise on Invertebrate Paleontology. Lawrence, Kan-

of America and of size for cirripedes). However, the distinguishing sas; Geological Society University Kansas Press. factor is that ostracodes have an order of twice the Collins D, Rudkin DM. 1981. Priscansermarinus barnetti, rate of extinction of the other two This is groups. barnacle from the Middle Cambrian a probable lepadomorph

characteristic of the turnover rates of mem- high Burgess Shale of British Columbia. J. Paleontoi 55; 1006-

bers of the Paleozoic evolutionary fauna in com- 1015.

Downloaded from Brill.com10/08/2021 03:03:48AM via free access Contributions to Zoology, 69 (4) - 2000 22!

the world’s outdated and inaccurate. This Gaston KJ, Williams PH. 1993. Mapping spe- nera to higher taxa are probably

cies. The higher taxon approach. Biodiversity Letters 1; is especially true of Cambrian forms. Moreover, exceptional

2-8. deposits such as the Solnhofen are highly biased. (2) Statistical

Harland WB, Armstrong R, Cox AV, Craig LE, Smith generalizations, such as the one that the ostracodes in general,

AG, Smith DG. 1990. A 1989. despite their post-Paleozoic diversification, show evolutionary

Cambridge: Cambridge University Press. rates similar to components ofthe Paleozoic evolutionary fauna,

Labandeira CC, Sepkoski JJ Jr. 1993. diversity in are so abstract as to be of little use in understanding the

the fossil record. Science 261: 310-315. evolutionary history of Crustacea.

Raup DM. 1979. Biases in the fossil record of species and Jack Sepkoski was quite aware of the problems posed by

and such the in genera. Bull. Carnegie Mus. Nat. Hist. 13: 85-91. preservational monographic biases, as spikes

well- Schram FR, Feldmann RM, Copeland MJ. 1978. The Late diversity that result from exceptionally well-preserved and

Devonian Palaemonidae and the earliest decapod crusta- studied faunas, and the exaggeration of Cenozoic diversity that

results from the extension of to the Recent ceans. J. Paleontol. 52: 1375-1388. stratigraphic ranges

that he several Sepkoski JJ Jr. 1981. A factor analytic description of the (see Fig. 1). It is largely for this reason began

Phanerozoic marine fossil record. Paleobiol. 7: 36-53. construct such as those in 2, years ago to diversity curves, Fig.

of Phanerozoic with omitted and with treated Scpkoski JJ Jr. 1984. A kinetic model taxo- single-interval genera extant taxa

nomic diversity III. Post-Paleozoic families and mass ex- as if they were known from their fossil occurrences only.

fields tinctions. Paleobiol. 10: 246-267. There are interesting differences between the Crustacean

Scpkoski JJ Jr. 1991. Diversity in the Phanerozoic oceans: of Fig. 1 and Fig. 2, for example the diversity peaks in the Cam-

EC, ed. The Evo- brian Shale and other and Late Jurassic a partisan review. In: Dudley Unity of (Burgess faunas)

lutionary Biology. Portland, Oregon: Dioscorides, 210- (Solnhofen ) in Fig. 1. The larger-scale pattern ofan

236. Ordovician radiation,a Paleozoic decline, and a prolongedpost-

Sepkoski JJ Jr. 1996. Patterns of Phanerozoic extinctions: Paleozoic diversification is nevertheless present in both treatments

data bases. In: Walliser OH, of thp data. one could that the post- a perspective from global Although perhaps argue

Paleozoic increase is increase in ed. Global Events and Event Stratigraphy. Berlin: Springer, diversity exaggerated by an

the of toward the 1 know of 35-52. quality preservation Recent, no

Sepkoski JJ Jr. 1997. Biodiversity: past, present, and fu- compelling reason to think that othermajor features such asthe

Paleozoic decline artifacts. ture. J. Paleontol. 71: 533-539. Ordovician radiation and the are

the fossil record, Jack was his data, Sepkoski JJ Jr. 1998. Rates of speciation in continually scrutinizing refining stratigra-

and schemes of classification. Phil. Trans. Roy. Soc. London B 353: 315-326. phic calls, weighing alternative

his data and he Sepkoski JJ Jr, Kendrick DC. 1993. Numerical experi- Clearly, he never regarded ascomplete, recognized

taxa. their of which he discusses in ments with model monophyletic and paraphyletic shortcomings, many explicitly

the I Paleobiol. 19: 168-184, paper. would nevertheless argue that the uncertain classifi-

Sepkoski JJ Jr, Bambach RK, Raup DM, Valentine JW. cation ofCambrian genera, while an important problem for those

in 1981. Phanerozoic marine diversity and the fossil record. whose main interest lies arthropod phylogeny, is a rather

minor in the of Jack’s Nature 293: 435-437. one context principal analyses and

for the trends and which he Vermeij GJ. 1987. Evolution and Escalation: An Ecological conclusions, events on focuses are

History of Life. Princeton, New Jersey: Princeton Uni- largely post-Cambrian.

far the of whether statistical of the versity Press. As as question analysis

fossil record is an endeavor worth pursuing, this is certainly

the debate the issue. I would Received: 20 June 1999 not place to Subjectively, argue

that the recognition of distinct associations of taxa that have

covarying diversity patterns and similar rates oftaxonomic turn-

over, along with the fact that these associations show some degree Addendum insofar tend be ofecological coherence asthey to more abundant

in certain environments early in their history and to shift or

Jack had been invited at the Fourth their environmental is ofthe Sepkoski an plenary speaker expand ranges later, one most sig-

InternationalCrustacean Congress, July 20-24,1998, in Amster- nificant empirical results that paleontology has produced in the

this from his talk but passed case of ostracodes dam. Jack had prepared paper away past few decades. The specific mentioned

before formal reviews ofhis on crustacean of how receiving manuscript above also provides an interesting example apparent

in the diversity, too late to be included formal congress pro- exceptions test the rule. The three evolutionary faunas, whose

ceedings. The organizers have arranged the publication here in diversity maxima succeed each other, show successively lower

and their constituent classes Contributions to Zoology. rates oftaxonomic turnover, tend

it would be the itself do well. In statistical members Although inappropriateto modify paper to so as a sense, ostracodes, as

I would or to speculate as to how Jack would have responded, ofthe Paleozoic fauna,“shouldn’t” have diversified so strikingly

like to raised reviewers. address some of the points by after the Paleozoic. However, as Jack points out, the order of

The two principal criticisms can be paraphrased as follows: ostracodes that participates in this post-Paleozoic radiation, the

of (1) The data are of uncertain quality. Some assignments ge- Podocopida, is similar to the Modem evolutionary fauna in having

Downloaded from Brill.com10/08/2021 03:03:48AM via free access 222 J.J. Sepkoski - Crustacean biodiversity andfossils

low rates of turnover. The Ostracoda therefore in the data this the relatively genus patterns two sets, study supports argument represent something ofan evolutionary microcosm, displaying that, despite their shortcomings, Sepkoski’s data accurately

finer scale similar that in the document of and extinction at a a pattern to seen more broadly many aspects diversity, origination, defined evolutionary faunas. in the fossil record.

A recent study (Adrain JM, Westrop SR. 2000. An empirical assessment of taxic . Science 289: 110-112)

data with data that have been Michael Foote compares Sepkoski’s compiled and vetted by trilobite specialists. By showing similar Dept, ofGeophysical Sciences, University ofChicago

Downloaded from Brill.com10/08/2021 03:03:48AM via free access