Late Miocene calcareous nannofossil genus Catinaster: taxonomy, evolution and magnetobiochronology

A systematic study on the evolution and stratigraphic distribution of the species of Catinaster from several DSDP/ODP sites with magnetostratigraphic records is presented. The evolution of Catinaster from Discoaster is established by documentation of a transitional nannofossil species, Discoaster transitus. Two new subspecies, Catinaster coalitus extensus and Catinaster calyculus rectus are defined which appear to be intermediates in the evolution of Catinaster coalitus coalitus to Catinaster calyculus calyculus. The first occurrence of C. coalitus is shown to be in the lower part of C5n.2n at 10.7–10.9 Ma in the low to mid–latitude Atlantic and Pacific Oceans. The last occurrence of C. coalitus coalitus varies from the upper part of C5n.2n to the lower portion of C4A. Magnetobiostratigraphic evidence suggests that the FO of C. calyculus rectus is diachronous. Catinaster mexicanus occurs in the late Miocene and has been found only in the eastern equatorial Pacific, the Indian Ocean and the Gulf of Mexico.


INTRODUCTION
The genus Cutinaster and two of its species were first described by Martini & Bramlette (1963) from the 'middle' Miocene of Trinidad. The first occurrences of Catinaster coalitus and Catinaster calyculus are nannofossil zonal markers in the widely used zonations of Martini (1971) and Okada & Bukry (1980). As Berggren et al. (1995) noted, there are discrepancies of > I m.y. in published correlations of these and a few other early Tortonian markers making this interval one of the most unclear in the entire Tertiary for nannofossil-magnetostratigraphy integration. The stratigraphic distribution of C. mexicanus is known only from a few locations, and the relationship among these and other undescribed species of Catinaster have yet to be established. In this paper, we present data on the stratigraphic range, evolution and geographic distribution of catinasters from various Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites from low to mid-latitudes (Fig. 1). We also describe a new subspecies, Catinaster coalitus extensus and document its stratigraphic distribution along with a transitional form between Discoaster and Catinaster. A new subspecies C . calyculus rectus is described which is older than Catinaster calyculus calyculus.
All species assigned to Catinaster are closely related to discoasters, hence to determine evolutionary relationships of this group a basic understanding of homology in Neogene discoasters is essential (Fig. 2m). These homologies have been dealt with in a number of papers (e.g. Stradner & Papp, 1961;Prins, 1971;Theodoridis, 1984;Perch-Nielsen, 1985). Typical 60" I I I I I I I I I I 120' 90" 60" 30" 0" 30" 60" 90" 120" 150" 180" 150"   (1971). Sequence a-d-e: alternative homologies suggested by Theodoridis (1984). Morphological details such as the rim breaks and central area sutures shown in figs 2b and 2c suggest that sequence a-b+ is most likely. (f-k) Neogene discoasters (Fig. 2m) are star-shaped and formed of five or six rays often with bifurcate tips. Many species are concavoxonvex which allows proximal (concave) and distal (convex) sides to be defined. In addition, central area structures can be used to consistently separate these two sides. On the distal side of the central area, low ridges usually run along the sutures, and if a stellate boss is developed, then it will show the same inter-radial orientation. Conversely, on the proximal side radially-directed stellate bosses and radial ridges are developed. These central area structures are developed to varying degrees in different species but their orientations are entirely consistent whenever they are present (Fig. 2m).

MATERIALS AND METHODS
Samples were taken from DSDPjODP sites ( Fig. 1) for which moderate to good magnetostratigraphies have been established for the chron 4-5 interval. These included Holes 519, 558, 563, 588/588A, 710A, 710B, 782A and 845A. A few sites without magnetostratigraphic records were also used to determine the occurrence and stratigraphic distribution of C. mexicanus and to study the evolution of catinasters. Relevant observations from a previous study of Indian Ocean DSDP Sites (Young, unpublished PhD Thesis) are also incorporated. Smear slides were made from unprocessed marine sediment samples mounted with Norland optical adhesive and cured under ultraviolet light. Some mobile mounts in Canada balsam were made to photograph the same specimens in different orientations. Observations were done on a Zeiss Axioskop light microscope at 400x and lOOOx magnification. All counts were done in phase contrast illumination.
Nannofossil abundances were estimated under 400 x magnification using the following scheme modified from Gartner (1992): A = abundant: 6 2 5 specimens per field of view. C = common: 1-5 specimens per field of view. F = few: 1 specimen in 2-10 fields of view. R = rare: 1 specimen in 11-50 fields of view. T =trace: 1 specimen in 51-200 fields of view.
Extra scanning time (45-60 minjslide) was spent to establish endpoint occurrences or null occurrences in the next few samples.
Magnetostratigraphies for Sites 519, 558, 563, 588, 710, 782 and 845 are from Poore et al. (1984), Kahn et al. (1985), Miller et al. (1985), Barton & Bloemendal (1986), Backman et al. (1990), Ali et al. (1992) and Mayer et al. (1992) and Schneider (1995), respectively. Detailed information about these sites such as core recovery, lithology, etc. can be found in DSDPjODP Volumes 73,82,90,115,125 and 138. First and last occurrences of nannofossil species are assigned as the midpoint depth between productive and non-productive core samples. This midpoint depth is correlated to site magnetostratigraphy and later assigned an age, based on calibrations to the revised geomagnetic polarity time scale (GPTS) of Cande & Kent (1995). The quality of the magnetostratigraphy is assessed for each of the DSDPjODP sites selected. For most of the sites, magnetostratigraphic interpretation is only broadly constrained by nannofossil biostratigraphy, thereby the problem of circularity in interpretation is minimal. Uncertainties in chron assignments and their bearing on the reliability of nannofossil datums are discussed in the text. It should be noted that in the calibration of datum depths to chron C5n.2n for sites with missing chrons C5n.ln and C 5 n . l~ (Sites 519,558,563,588 and 782), the duration of C5n.211 (9.920-10.949 Ma) is calculated from the top of C5n.ln to the bottom of C5n.2n (9.740-10.949 Ma). Chron terminology is from Cande & Kent (1992,1995). Chron placements and age estimates of nannofossil datums from this study are compared with other DSDPjODP nannofossil logs and with the revised Cenozoic biochronology of Berggren et al. (1995). Use of this biochronology places the entire Catinaster lineage in the late Miocene. All age estimates from previously published work are converted to the Cande & Kent (1995) GPTS.
Type specimen slides of new taxa presented here are deposited at the Scripps Institution of Oceanography Nannofossil Laboratory Collection with catalogue numbers recorded in the systematic descriptions.

RESULTS AND DISCUSSION
Abundance and range charts of Catinaster taxa from the different DSDPjODP sites, arranged in chronological order are shown in Figs 3 and 4. The distribution patterns of Catinaster coalitus coalitus. C. calyculus rectus and C. calyculus calyculus from eight DSDPjODP sites are summarized in Fig. 5. A section is devoted to these Catinaster taxa because they are more abundant in the sediments and have a more widespread occurrence than the other catinasters; this makes them good biostratigraphic markers for the Miocene. A separate section is presented for Catinaster mexicanus to synthesize data on this poorly documented species.

Evolutionary trends in Catinaster
Catinasters and their various transitional forms were documented from nine DSDPjODP drillholes (519, 558, 563, 588, 710A, 710B, 758A, 782A and 845A). The following Discoaster and Catinaster taxa were recognized (Fig. 2  Because of the susceptibility of catinasters to overgrowth, all six forms were rarely recognized in a single site. A probable evolutionary scheme for genus Catinaster is shown in Fig. 6. These species and subspecies are described in detail in the sytematics section. Evolution of the genus Catinaster from Discoaster has previously been suggested based on morphology i.e. similarity of the two genera, and partly on stratigraphic occurrence. Martini & Worsley (1971) proposed that C. coalitus evolved from 'a small discoaster resembling D. extensus by becoming highly concavo-convex and reducing the interray areas until they are closed' (Fig. 2 a s ) . Bukry (1973) suggested a possible derivation of C. coalitus from Discoaster bollii by reduction of the rays while Martini (1981) proposed that D. musicus gave rise to Catinaster. An alternative view was given by Theodoridis (1984) who defined C. coalitus (Eu-discoaster coalitus group) as 'asteroliths with . . . pronounced sutural ridges on the distal face of the central area' and stated that they lack arms (Fig. 2 a, d,e).
This implies a different evolutionary scheme from that proposed by the previous nannofossil workers. Structures considered as by Martini & Worsley (1971) and Bukry (1973) are sutural ridges to Theodoridis (1984). The interpretation favouring rays instead of sutural ridges is supported by the following observations: (a) the presence of C. coalitus specimens with slight breaks in the rim on the distal side that suggest incomplete fusion of the bifurcated rays ( Fig. 2g; P1. I, fig. I; P1. 2, figs 12-13); a feature that would not be compatible with Theodoridis' sutural ridges ; (b) a proximal view of a well-preserved specimen in Miiller (1974; pl. 10, fig. 4) shows a stellate central structure which is oriented parallel to the ridges on the opposite face suggesting that the ridges on the distal face are rays; (c) ridges extend as free rays in C. calyculus; and (d) the presence of sutures between rays in the centre of C. coalitus (pl. 1, figs 1-3, 10; pl. 3, fig. 1 in Martini, 1981). Thus, we interpret the basic morphology of catinasters as consisting of a cup formed by fusion of the bifurcations. This cup is open distally and closed proximally. The rays are arranged inside the cup as six radial plates, rather like the septa of a coral. They protrude distally above the cup, where they are surmounted by a concave disk derived from the reduced central   Peirce et al. (1989). Sources for magnetostratigraphy: ODP Holes 710A/710B, Backman et al. (1990) and Schneider & Kent (1990); ODP Hole 782A, Ali et al. (1992); and ODP Hole 84SA, Mayer et al. (1992) and Schneider (1995) (1995). Sites are arranged from north to south according to latitude. In some sites, only FO and LO can be shown either due to a gap in the magnetostratigraphic record or absence of samples. Vertical bars represent the time interval between productive and non-productive samples. Horizontal bars represent the midpoint of this time interval at which the datum age is designated. Calibrations for both shorter and longer C5n.2n interpretations for Site 558 are included within the uncertainty values.
area. The proximal view is often complex showing both the base of the rays and the convergent bifurcations. Rays and bifurcations are usually readily identifiable in proximal view due to the presence of openings between the rays (PI. 1, figs 5-6, 9, 13-14). They are less obvious in specimens without such openings (e.g. PI. 1, fig. 15; PI. 2, fig. I).
In light microscopy, a key feature of Catinaster is that the rays extend through from the top to the base of the specimen, hence as one focuses through the specimen the orientation of the rays does not change. Discoasters such as D. musicus with massive central areas can produce specimens which look very similar to catinasters if they lose their rays, but they have a sutural star on the distal side with inverse orientation. Aubry (1993a) illustrated specimens of this type as Catinaster sp. (PI. 3,(17)(18)(19), and they strongly resemble specimens of D. musicus and D. sanmiguelensis from the same sample (Pl. 3, figs 5-7, 9-10).
The earliest forms we recognize are small discoasters with unusually thick cross-sections, converging on the cupshaped morphology of Catinaster. These specimens have small central areas and strongly bifurcate rays but the tips of the bifurcations do not meet. We term these forms Discoaster transitus (PI. 2, figs 9-1 1). Another small discoaster species has been described from sediments of this age -Discoaster micros (Theodoridis, 1984)  present only in relatively well preserved specimens. Its stratigraphic range is mostly limited to the middle-upper part of magnetic chron C5n.2n although it extends to chron C5r.l and C4Ar.2n in Site 710.
Catinaster calyculus rectus subsequently evolved from C. coalitus extensus with six straight rays forming the corners of the hexagonal basket (Pl. 1, figs 10-14; P1. 3, figs 7-8). In C. calyculus, the shape of the distal cup has changed as a result of the extruded rays. The simple hexagonal cup in C. coalitus whose corners are formed by fusion of adjoining bifurcating rays, has retracted towards the proximal pole in C. calyculus. Instead, the distal rim in C. calyculus is a modified hexagon with protruding corners formed by the extended rays and the retracted cup edges (compare P1. 1, figs 1 4 with figs 1&12). Evidence from Holes 519, 558, 563, 588, 710A, 710B and 758A shows the later development of curved rays in C. calyculus calyculus (Pl. 1, figs 1&20; P1. 3, figs 14-15) as suggested by Martini & Bramlette (1963) and Martini (1981). Ray curvature is consistently counter-clockwise in distal view (Pl. 1, figs 18-20). A new subspecies is erected to distinguish the form with straight rays, C. calyculus rectus, from the one with curved rays, C. calyculus calyculus. The first occurrence (FO) of Catinaster calyculus calyculus from different sites remains within subchron C5n.2. The last occurrence (LO) of C. calyculus rectus usually occurs at the same level as C. calyculus calyculus but in three sites (558, 563 and 588), it disappeared earlier.
Because of its very limited occurrence, it is difficult to ascertain whether Catinaster mexicanus (PI. 2, figs 2-8; P1. 3, figs 17-20) evolved from the rest of the catinasters. We know that it evolved later than the rest of the Catinaster species based on reported occurrences and its association with CN7-CN9a nannofossils. Young (unpublished) suspects that C. mexicanus is an unrelated homoeomorph of the catinasters that evolved by ray reduction (evolutionary sequence a 4 -e of Fig. 2) because of the presence of 'sutural ridges on the distal side', a feature absent in typical catinasters. Alternatively, Young (unpublished) believes that C. mexicanus could be a 'preservational fragment of a discoaster rather than a genuine species ' and Pujos (1985) considered it as a relict of D. tristellifer (syn. D. altus).
Our SEM illustrations (especially P1. 2, fig. 2) clearly show sutures running through the ridges on the distal side. Thus these ridges cannot be homologous with the ridges in the distal side of C. coalitus or C. calyculus. This suggests an independent origin of C. mexicanus from discoasters. On the other hand, C. mexicanus has the hexaradiate symmetry and cup shape that is characteristic of the catinasters. C. mexicanus could be a second derivation from Discoaster, separate from the two other species or it could have been the result of mutation at the end of the Catinaster line. A more specific possible explanation is that it evolved from C. coalitus by infilling of the spaces between the rays followed by expansion of the central area and development of new sutural ridges. Affinity with the catinasters is also suggested by the stratigraphic co-occurrence of C. mexicanus and C. calyculus rectus in three sites (Sites 3, 710A and 845A). Lacking any other evidence for definitive relatives of this species, we tentatively continue to include it with the catinasters, but exclude it from our evolutionary scheme.  Wei, 1995). Previously, the main distinction between C. coalitus and C. calyculus is the extension of the rays beyond the rim in the latter. We define the species concept of C.

FO and LO of
All figures are SEM micrographs. White bar = I pm. coalitus coalitus as catinasters whose rays connect to the middle of the segments of the basket rather than the corners when observed under the light microscope. On the other hand, the rays of C. calycttlus calyculus and C. calyculus rtctus extend to form corners of the rim (see systematic descriptions). This distinction between the two species is due to modifications in the shape of the distal rim as a result of ray extension in C. culyculu.~ (refer to discussion in evolution). This definition is especially helprul in classi,fying transitional morphotypes (e.g. C. coalitus with rays extending out of the rim) whose identification was based on the old distinction between the two species (i.e. whether the rays extend out of the basket).
Berggren et (Zl. (1995) provide two alternative placements for the FO of C. coalitus, either at 10.9 Ma (Chron Cjn.2n) based on data from equatorial Pacific sites or at 11.3 Ma (subcron C5r,2r), based on Atlantic sites. From our examination of several Miocene Atlantic and Pacific sites with magnetostratigraphies, the 1-0 of C. coalitus coalitus is consistently in the lower part of subchron C5n.2n (10.55-10.95 Ma). This result coincides with the report of Berggren et a/. (1995) from the equatorial Pacific (10.9 Ma; based on Raffi & Flores, 1995 andRaffi et ul., 1995) but is significantly different from the placement of this datum in subchron C5r.2r (1 1.3 Ma). One of their bases for this latter datum report is Miller et a/. (1985) who recorded C. coalitus coalitus down through the bottom of core 4 in Hole 563. As in Parker et a/. (1985), we did not find any C. coalitus coalitus in the lower part of core 4 despite extensive search. Berggren et al. (1995) also cited Site 710 (Raffi et al., 1995) as another reference for placement of this datum in C5r.2r, as was reported by Miller et ul. (1994) in the Buff Bay Section of Jamaica. Our observations of the FO of C. coa1itu.s coalitus at Hole 710A is consistent with that of Raffi et al. (1995) but a proper chron calibration is not possible because this core (7 10A-10H) has evidence of slumping, hence no magnetic chron was designated in the ODP reports. Our results from other sites are consistent with previous reports from Hole 782A  Site 588 (Lohman, 19861, Hole 845A (Raffi ei ul., 1995) and Site 519 (Poore et a/., 1984). An equivalent age was adopted by Young e t a/. (1994). The rarity and presence of overgrowth on C. coalitus coalitus specimens in some sites can pose a problem in establishing a consistent age estimate for this datum. Identification of the long normal Chron 5n.2n where the FO of C. coalitus coalitus occurs is straightforward for most of the sites. The lower boundary of C5n.2n in Site 558 may be reinterpreted to include the next indeterminate interval which extends the bottom depth of this subchron to 208 mbsf. This results in a younger estimated age for the FO datum (Fig. 5). Although discontinuities in the magnetostratigraphic record of Hole 782A exist, a datum calibration consistent with other sites was found.
In most of the sites, the LO of C. coalitus coalitus corresponds to the upper part of C5n.2n (9.75-10.0 Ma) but in ODP Holes 710A and 710B and DSDP Hole 558, it corresponds to C4A. In these three cores, the magnetostratigraphy can be subject to reinterpretation especially at this interval (C4A-C5) because of the slumped reworked sediments above and below core 710A-9H, no recovery above and below core 710B-9H, and an incomplete record at Site 558. A reliable age estimate for this datum cannot be made at Site 558 due to difficulty in interpreting specific subchrons above C5n.2n. Our results closely agree with previous work from Site 519 (Poore eta/., 1984), Site 558 (Parker et a/., 1985), Site 563 Parker et a/., 1985;Peleo--Alampay & Wei, 1995), Site 710 Backman et a/., 1990) and Hole 782A . The discrepancy between our LO datum depth (219.35 mbsf) in Site 588 and that of Lohman (1986) at 213.96 mbsf may be attributed to differences in species concepts of C. calyculus reccus and C. coalitus coalitus although we did not find C. calyculus rectus up to that depth (refer to Hole 588/588A abundance chart).
The FO of c'. calyculus rectus is in the lower portion of C5n.2n  in Sites 519 and 563, and coincides with the FO of C . caulitus coalifus in Site 519. In other sites (558, 588 and 782) however, C. culyculu.~ rectus appeared later in midupper C5n.2n. At Holes 558, 563, 588 and 782A, we found this datum lower than previously reported, resulting in a 0-0.3 m.y. variation in age. Our datum depth of 186.35 mbsf at Site 563 is close to 185.1 mbsf as reported by Parker et a/. (1985),  and Peleo-Alampay & Wei (1995)   . In Site 519 however, we got a significantly deeper depth (148.1 mbsf; 10.95 Ma) for this datum than Percival (1984) and Poore et ul. (1984) who reported it at 141.55 mbsf (10.1 Ma). This discrepancy can be due to a difference in species concepts of C. coalitus coalitus and C. calq'culus rectus (refer to Hole 519 abundance chart). We were not able to establish reliable FO and LO datums for C. calyculus subspecies at Hole 845A where they had a very limited occurrence although Raffi et al. (1995) were able to determine a FO datum for C. calyculus by analysing samples from both Hole 845A and 845B. Raffi et a/. (1995) reported the FO datum depth at 158.72 mcd (10.45 Ma). The discrepant age estimates for this datum signify possible diachroneity of the FO of C. calyculus rectus as suggested in Peleo-Alampay & Wei (1995). The coincidence of the FO of C. coalitus coalitus and C. calyculus rectus (with straight rays) at Site 519 might seem to contradict the nannofossil zonation of Okada & Bukry (1980) which utilizes the FO of C. coalitus coalitus and C. calyculus culyculus (with curved rays) to delineate the base of Zone CN6 and Subzone CN7b, respectively. Similarly, this apparent coincidence violates the evolutionary sequence presented in our Fig. 6, and therefore, reflects the missing section at Site 519 or incomplete sampling of the local ranges.
Most detailed studies, including this one, support the sequence of C. coalitus coalitus preceding C. calyculus calyculus. For example, Takayama (1993) detailed species events from five ODP drillholes (803D, 804C, 805B, 806B and 807A) on the Ontong-Java Plateau in the tropical Pacific and showed that the FO of C. coalitus coalitus is consistently found earlier than the F O of C. calyculus calyculus. These consistent results support the utility of catinaster occurrences for identifying Zone CN6 and Subzone CN7b of Okada & Bukry (1980) for low latitude floras.
The LO of C. calyculus calyculus is in the lower part of C4A (9.3-9.6 Ma). Results from our analysis of this datum are exactly consistent with previous reports from Site 563 (Parker et al., 1985;Peleo-Alampay & Wei, 1995), Hole 782A  and Site 519 (Poore et al., 1984). Our calibration of this datum at Site 588 is at a shallower depth (212.73 mbsf) than the 213.96 mbsf observed by Lohman (1986), corresponding to a 0.1 m.y. difference in age estimates. The older age estimate of 9.85 Ma from Hole 782A could be due to poor preservation in that site as compared to others.

Catinaster mexicanus
CatimWr mexicanus was described by Bukry (1971) from DSDP Site 3 in the Gulf of Mexico where it was given an upper Miocene age. It has only been recorded in a few sites since. Ellis et al. (1972) also recorded C. mexicanus, along with C. coalitus, in Site 3. Aside from DSDP Site 3, C. mexicanus has been reported from the Somali Basin in the western Indian Ocean (DSDP Leg 25) by Miiller (1974) where it was assigned an upper Pliocene age (NNI 5) although specimens were considered atypical. The bifurcation of the rays seemed less distinct than those described from the Miocene. In Leg 85, Pujos (1985) noted the similarity of C. mexicanus specimens in mid-Pliocene zones C N l l and CN12a to the knobbed centre of D. tristellifer and classified it under the latter. Bukry (1981) documented C. mexicanus from the west coast of Mexico and found it associated with Zone CN8 and CN9 coccoliths in the late Miocene. Jiang & Watkins (1992) documented the occurrence or C . mexicanus in nannofossil subzone CN9a (late Miocene) from the northern Gulf of Mexico. In the same region, Aubry (1993a) reported the presence of c . coalitus coalitus with c . mexicanus in two Eureka drill sites (Coreholes E68-136 and E6G73). In both drill sites, this co-occurrence cannot be firmly established due to reworking and mixing in the older sediments (Zones CN4-CN6). The same is true for the younger intervals (Subzones CN7a and CN9a) where poor preservation and low abundance hampered definite identification of C. coalitus coalitus (particularly in Corehole E68-136). It is also possible that the C. coalitus specimens identified (especially in the critical sample 2433'9", Hole E68-136 where they are most abundant) are D. musicuslD. sanmiguelensis with reduced rays. Aubry (1993~) however, recognized C. mexicanus without C. coalitus coalitus in one sample in Subzone CN9a.
We found C. mexicanus in Hole 845A in the eastern equatorial Pacific Ocean, Hole 710A in the Indian Ocean and Site 3 in the Gulf of Mexico. We did not find it in the Miocene sediments we examined from Holes 364, 518A, 519, 563, 575A, 577A, 588, 588A, 710B, 758A and 848B. At Hole 845A, it co-occurs with Catinaster calyculus rectus cf. in Subzone CN9a where the nannofossil assemblage primarily consists of Discoaster quinqueramus, D. brouweri, D. challengeri, D. variahilis, D. berggrenii, D. surculus and D. pentaradiatus with the noticeable absence of Amaurolithus. This is similar to the report of Bukry & Bramlette (1969) from Site 3. C. calyculus rectus specimens observed (by A. P,-A,) in Hole 845A are similar to those observed in Site 3 co-occurring with C. mexicanus where the rays do not extend beyond the rim. Most of their rims are dissolved and the ray tips show some overgrowth. At Hole 710A however, C. mexicanus is associated with D. hamatus in Zone CN7.
Locations of reported occurrences of C. mexicanus suggests a preference for particular environments such as semi-enclosed basins or in locations proximal to the continental borderland (Sites 241, 470A and 845A). Correlation with site water depths has not been found.

CONCLUSIONS
The evolution of Catinaster from Discoaster and among the Catinaster species is established with the documentation of a transitional form, Discoaster transitus and a new subspecies, Catinaster coalitus extensus. New subspecies, Catinaster calycurectus gave rise to C. calyculus calyculus which is used to identify Subzone CN7b.
The FO of C. coalitus coalitus is shown to be consistently at the lower part of C 5 n . h at 10.55-10.95 Ma. The LO of c . coalitus coalitus is at the upper part of C5n.2n (9.75-10.0 Ma) in most sites but extends up to the lower portion of C4A (9.4-9.6 Ma) in some sites. The FO of C. calyculus rectus appears earlier at the lower part of C5n.2n in some sites, even coinciding with the FO of C. coalitus coalitus, while it occurs later in others (mid-upper C5n.2n). This suggests diachroneity of this subspecies. Similarly, C. calyculus calyculus appears in lower to mid-C5n.2n at five of our sections and higher at two others.
Catinaster mexicanus has a very limited geographic distribution and seems to prefer specific environments. It usually occurs in the late Miocene within nannofossil zones CN7-CN9a.

Diagnosis. Discoaster transitus is a transitional species between
Discoaster and Catinaster. It is a simple six-rayed discoaster with bifurcating ray ends. The sides of the rays are parallel until they reach the point of bifurcation. It has a small central area with no distinctive knob or suture pattern. In side view it is thicker than regular discoasters, a feature that is typical of C. coalitus coalitus. The bifurcated ray ends are not fused to form the outer rim as in typical catinasters. These transitional forms are generally smaller than typical discoasters. Size. 3-6pm.
Remarks. It is differentiated from D. micros by the presence of a reduced central area resulting in longer free rays, the long bifurcations, the lack of notched ray ends and a consistent sixrayed symmetry. Its small size distinguishes it from the larger D. extensus and D. divaricatus aside from being more robustlooking and lacking the distinct notch present in D. divaricatus.
Remarks. C. coulitus typically has six rays and a circular or hexagonal rim (PI. 1, figs 1-4). This rim/basket is formed by the bifurcation of the rays. The hexagonal rim in C. coalitus has corners formed by the fused bifurcations. In the light microscope, this can be seen as rays that connect to the middle of the segments of the rim rather than the corners as in C. c~alyculus (Peleo-Alampay & Wei, 1995). The rim continues to the proximal side of the catinaster producing the basket-like body. In earlier forms, the bifurcated rays can have gaps between them, producing an incomplete rim (Fig. 2). In large C. coalitus specimens, pseudo-rays or nodes can be formed along the rim where the bifurcations meet, changing the overall rim shape into a 12-sided polygon (PI. 1, figs 5, 6; PI. 3, fig. 2; Aubry, 19936, PI. 16, figs 4-6). The proximal side of C. coalitus features a stellate ray pattern whose orientation mirrors that of the same features on the distal side (PI. 1, figs 5-6; P1. 2, figs 16, 18) . Remarks. This subspecies is the type of the specks C. coalitus. It is characterized by confinement of the rays within the rim. There may be gaps betwen the bifurcation tips, or they may meet neatly, or protrude to form pseudo-rays.
Cutinaster coalitus extensus n. subsp. Occurrence. This nannofossil is found in well-preserved sites from mid to low latitudes. Abundance of this species is quite low. It usually occurs in nannofossil zones CN6 and CN7 and mostly correlates with the middle to upper part of magnetic chron C5n.2n but can extend to subchrons C5r.l and C4Ar.2n in some sites. Its stratigraphic range is limited within the range of C. coulitus coulitus.
the simple hexagonal rim found in C. coalitus. Each of the extended rays of C. calyculus forms protruding corners with the simple hexagonal rim which has protracted proximally. This results in a modified hexagonal rim whose sharp corners are formed by the extended rays. When seen under the light microscope, the rays appear to meet the corners of the hexagonal basket rather than the middle of the segments as in C. coalitus (Peleo-Alampay & Wei, 1995). As in C. coalitus there are usually either well defined sutures or gaps between the rays on the proximal side which makes it easy to distinguish them (e.g. PI. 1, figs 13-15). It is clear from such specimens that the ridges on the distal side are true rays, not inter-radial ridges (as in C. mexicanus). The parallelism of the distal and proximal structures can easily be observed in light microscopy by focusing through the specimens. It is a useful test that the specimen is a true catinaster.
Jiang & Watkins (1992) also showed micrographs of C. calyculus that are considered here as C. coalitus coalitus. Micrographs in Aubry (1993b;pl. 16, figs 11-14) identified as C. calyculus are considered as C. coalitus coalitus since the rays mostly hit the middle of the segments of the basket and its side view is more typical of C. coalitus coalitus.
Catinaster calyculus calyculus Martini & Bramlette, 1963 (Pl. 1, figs 1620; P1. 2, fig. 1; P1. 3, figs 12-16) Remarks. C. calyculus calyculus is the type of the species C. calyculus. It is distinguished from a new subspecies, C. calyculus rectus by its curved rays that bend counter-clockwise in distal view. This is the opposite sense of rotation to that shown by the c w v a l Discoaster species D. hamatus and D. calcaris, which confirms that there is no direct evolutionary cause for the coincidence of ray curvature in two separate lineages at this time.
Occurrence. This subspecies occurs later than C. calyculus rectus. Catinaster with straight rays that may or may not extend out of the outer rim. Each ray extends to form a corner of the modified rim instead of meeting the rim at mid-segment as in C. coalitus (see C. calyculus description).
Occurrence. The FO of C. calyculus rectus is in the lower part of C5n.211 in some sites but has also been documented to occur later (mid-upper C5n.2n), suggesting diachroneity. Its LO is similar to that of C. calyculus calyculus but is slightly earlier in DSDP Sites 558, 563 and 588.

Remarks.
Catinaster mexicanus has short bifurcate rays (Bukry, 1971) which do not extend beyond the rim of the basket. Adjacent bifurcations meet to form double-peaked protrusions of the rim. This results in an overall digitate appearance of the basket which makes it distinct from the other catinasters. Unlike the other catinasters, sutural ridges occur on the distal side of C. mexicanus between the rays and in opposite orientation to the radial ridges on the proximal side. This can easily be seen in light microscopy while focusing through the specimen, stellate structures are clearly visible on both sides of the specimen but with opposite orientation. In this respect Cmexicanus is similar to normal Neogene discoasters and differs from true catinasters.
It differs from C. calyculus calyculus in the absence of long curved arms. The C. mexicanus micrographs in Muller (1974) and Xu & Wise (1992) do not show the characteristic digitate basket of this species. Size. 4-6 MMMm. Occurrence. C. mexicanus has been found in nannofossil zones CN7-CN9a (late Miocene), correlating to magnetic chrons C4A to C4n.