Progress on the Fossil Xanthoidea Macleay, 1838 (Decapoda, Brachyura)
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Contributions to Zoology, 72 (2-3) 181-186 (2003) SPB Academic Publishing bv, The Hague Progress on the fossil Xanthoidea MacLeay, 1838 (Decapoda, Brachyura) Carrie+E. Schweitzer Kent State Stark Department of Geology, University, Campus, 6000 Frank Ave. NW, Canton, Ohio 44720, USA Keywords: : Decapoda, Brachyura, Xanthoidea, Xanthidae, proxy characters Abstract notable recent works by neontologists do provide dorsal information carapace (Ng, 1998; Davie, 2002) Identification and utilization of characters in extant fa- proxy and are thus quite useful to the paleontologist as is has milies been accomplished with success for fossil members the work on the sternum, abdomen, and pereiopods of the Calappidae, Hepatidae, Necrocarcinidae, Matutidae, and by Guinot (1968a, b, 1978, 1979) and others. Hexapodidae. The fossil and extant Raninidaehave been revised Because many xanthoid families are using primarily hard-part morphology preserved in the fossil superficially record and similar in of dorsal although formal designation of “proxy characters” has amazingly terms carapace not occurred. Hard-part characters can be used to differentiate also morphology, it can be very difficult to place fossil among members of the Atelecyclidae and the Cheiragonidae. xanthoids within a family. In addition, the dorsal the method of Thus, using proxy characters is demonstrably carapace morphology of members of subfamilies suitable for like the Xanthoidea. application to a difficult group within the same family are often extremely diver- in gent, as the Goneplacidae, Panopeidae, and Pi- Introduction lumnidae (Davie, 2002; Karasawa & Kato, in press). Thus, the framing of a family-level diagnosis for Fossil Xanthoidea have traditionally been referred these xanthoid families based upon features of the to the 1838 dorsal is Xanthidae MacLeay, senso lato, and carapace nearly impossible. occasionally arrayed within the various xanthid The application of the work of Guinot (1968a, subfamilies (Rathbun, 1930; Glaessner, 1969). Over b, 1978, 1979) on the sternal, abdominal, and first the past four decades, biologists have separated the pereiopod morphology of brachyurans has been of in extant Xanthoidea into several families. At the time great assistance family placement of fossil xan- of this writing, twelve extant families are widely thoids. For example, members of the Carpiliidae & & have been in the fossil record based recognised (Martin Davis, 2001; Ng Liao, 2002; recognized upon in Schweitzer, press), and an additional two ex- the merus of the major cheliped being fused to the tinct families are known (Schweitzer, in press) basis-ischium and the direct articulation ofthe merus (Table 1). Extant xanthoids are diagnosed based and coxa (Guinot, 1968a, b). Differences in the features of the of fusion of male abdominal somites upon eyes, antennae, mouthparts, degree has gonopores, gonopods, and the degree of fusion of been quite useful in placing fossils into the Hexapo- the articles of the first pereiopods, the abdomen, didae and Goneplacidae and promises to be useful and the sternum (Guinot, 1979; Davie, 2002). Most for the Panopeidae and Pilumnidae as well (Schweit- of these features rarely, if ever, fossilize. Thus, zer & Feldmann, 2001; Davie, 2002; Karasawa & are forced Kato, in Paleontologists to rely primarily upon press). features of the dorsal In Even articles of the carapace. some serendipi- though pereiopods and ele- tous cases, the entire cheliped, sternum, and abdo- ments of the sternum and abdomenare useful, they men much are preserved and can be used as well. Some are less commonly preserved than the dorsal Downloaded from Brill.com10/04/2021 08:41:18AM via free access 182 - C.E. Schweitzer Progress on thefossil Xanthoidea In often carapace. addition, they are incompletely not designate proxy characters. Hard-part charac- such Thus, features, as whether ters can also be used to differentiate preserved. important among mem- in the eighth sternite is visible dorsal view or not, bers of the Atelecyclidae Ortmann, 1893 and the be may not observable. The latter feature is im- Cheiragonidae Ortmann, 1893 (Schweitzer & Salva, portant for classifying goneplacids and pilumnids 2000). Thus, the method is demonstrably suitable Karasawa & in (Davie, 2002; Kato, press). Conse- for application to a difficult group like the Xan- quently, it is important to try to identify a suite of thoidea. characters of the primarily dorsal carapace, but of including some features the chclipeds, sternum, and abdomen, that are diagnostic for a particular Examples family. These suites of dorsal carapace characters called characters are proxy (Schweitzer & Feldmann, The Carpiliidae are clearly recognizable if the el- 2000; Schweitzer, in The term char- press). ‘proxy ements of the first pereiopods are preserved; even acter’ is used because these characters track with if the they are not, smooth, vaulted carapace; long, the that soft-part morphology neontologists typi- convex anterolateral margins; lobate front; narrow use. These characters be found in cally proxy may posterior margin; posterolateral to posterior mar- both and fossil members extant of a taxon, but they gin angle of 25-30 degrees; and fused male abdo- are seldom if noted ever by neontologists when minal somites 3-5 are diagnostic for the family are described. in decapods (Schweitzer, press). Although there are certainly Definition, choice, and use of proxy characters other smooth, xanthoid decapods in the fossil record, is relatively straightforward. Members of extant of this entire suite characters is diagnostic only for defined decapod families, as by biologists based the Carpiliidae and not for other smooth xanthoids. lar- upon soft-part morphology, serology, genetics, Fossil Pseudoziidae are not easily distinguished and are examined either in from vae, sperm, museum carpiliids; however, several features can be collections or from illustrations in biological lit- used to differentiate the two families. Pseudoziids erature. Then, distinctive features of the dorsal have smooth carapaces; short anterolateral margins; be identified that characterize carapace can most a posterolateral to posterior margin angle of 40-45 or all members of the In group. many cases, sev- degrees; a broad posterior margin; an incompletely eral characters must be used as a suite. together fused merus and basis-ischium, and no fusion of Often there is not one dorsal char- single carapace abdominal somites (Schweitzer, in press). that identifies members of if there acter a family; MembersofVia’s (1959) subfamily Zanthopsinae classification of the Xanthoideawould be was, not (= Xanthopsinae) have often been placed within so difficult! The of characters that have types proven the Carpiliidae (Schweitzer, 2000); however, they to be useful thus far are various length/width ra- are morphologically distinct. The merus is not fused tios; the shape, length, and ornament of the front to the and the basis-ischium, merus does not ar- and anterolateral margins; the angle of the poste- ticulate with the directly coxa; thus, they are easily rolateral to the the rela- If margin posterior margin; excluded from the Carpiliidae. the chelipeds are tive size of the and ornament carapace regions; shape not preserved, zanthopsines may be recognized of the orbits; and the of maximum width because have position they a relatively smooth carapace that of the carapace. is not separated into distinctive regions; shallow identification and utilization of characters proxy grooves; a tightly convex anterolateral margin; a in extant families has been with suc- male accomplished quadri-lobed front; and fused abdominal so- cess for fossil members of the mites Calappidae, Hepa- (Schweitzer, in press). They form a distinc- tidae, Necrocarcinidae, Matutidae, and tive Hexapodidae group united by these morphological features. (Schweitzer & Feldmann, 2000, 2001). Tucker Several fossil genera cannot be accommodated (1998) revised the fossil and extant Raninidae de known by any family; a new family has been erected Haan, 1839, using primarily hard-part morphology to contain them (Schweitzer, in press). Palaeo- preservable in the fossil record although she did xanthopsis Beurlen, 1958, Verrucoides Vega et al., Downloaded from Brill.com10/04/2021 08:41:18AM via free access Contributions to Zoology, 72 (2-3) - 2003 183 and two all characterized to take into account these mor- 2001, new genera are by vastly divergent exhibiting a broad carapace; extremely deep, V- phologies. the and branchial Within those families that have dorsal shaped grooves separating gastric divergent nodes the members with each regions; large on carapaceregions; a long carapace morphologies, usually anterolateral 4 5 distinctive within the margin with or pronounced spines; morphology are placed same and a last anterolateralspine that is especially long subfamily of the family. Thus, at least for the Gone- directed These and it and laterally or posterolaterally. placidae, Panopeidae, Pilumnidae, appears features are quite distinct from any other known that proxy characters will need to be developed at xanthoid; thus, a new family has been erected to the subfamily, not family, level. Each subfamily would then have contain these genera (Schweitzer, in press). to be considered when working the Members of the Hexapodidae are recognized by with these families. This greatly complicates their that is widest a as the number of subfamilies rectangular carapace distally; work, recognized bi-lobed rostrum that extends