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Journal of Paleontology 91(5):981–986 Discussion
Taxonomy.—The new ichnospecies belongs to the genus Palaxius because of the crescentic, internal canals. To our knowledge, seven Palaxius ichnospecies with ten internal canals have been described (Elliot, 1962; Palik, 1965; Kennedy et al., 1969; Senowbari- Daryan, 1979; Kuss and Senowbari-Daryan, 1992; Senowbari- Daryan and Kuss, 1992; Blau et al., 1993; Blau and Grün, 2000; Becker and Chamberlain, 2006; Peckmann et al., 2007;Kietzmann and Palma, 2010, 2014; Kietzmann et al., 2010). From the size and arrangement of crescentic canals, the south Florida specimens resemble the Oligocene P. decemlunulatus (Paréjas, 1948), how- ever, there are some marked differences. In P. decemlunulatus,the openings of the two central crescents are inclined away from each other in cross-section; they are facing in the same direction in the Florida specimens (Fig. 3.1, 3.2). Also, the opening of the two upper, lateral crescents in P. floridanus n. isp. are pointed inward, towards each other (Fig. 3.1), and oriented outward in P. decem- lunulatus (Fig. 3.2). Two Mesozoic microcoprolites, assigned to
Figure 3. Schematic cross-section through P. floridanus n. isp. and other microcoprolites that resemble the new ichnospecies. (1) P. floridanus n. isp. from the Miami Limestone showing the details of internal structuring by ten crescentic canals. Note the slight ventral depression of the pellet. Drawn based on pellet shown in figure 2.4 (ichnoholotype). (2) Cross-section through P. decemlunulatus from Paréjas (1948). (3) Cross-section through coprolite identified by Kennedy et al. (1969) as Favreina decemlunulatus.(4) Schematic cross-section through microcoprolite assigned to P. decemlunulatus by Kuss and Senowbari-Daryan (1992) and Senowbari-Daryan and Kuss (1992). The bilateral symmetry plane (SP) runs vertically through the center of all examples.
Because these cores were taken in the early 1960s, no GPS- coordinates of the exact drill locations exist.
Occurrence.—The samples from Coral Gables and Everglades National Park come from surface outcrops and belong to MIS 5e (thin-sections Cocoplum #7, 8, 9, 10; Pinelands # 9, 10). The sample in core W9 is from a core depth of 3.0m (thin-section W9-10) and belongs to MIS 7. The sample in coreWPcomes from a core depth of 14.4m(thin-section WP-46/49) and can be assigned to MIS 5a or
5c.Twosamples from coreWBderive from 9.7mand 12.4m core depth, thin-sections WB-32 and WB-41, respectively, in MIS 7. The sample from coreW2is from a core depth of 41.0m (thin-section W2-132/139) and belongs most likely in MIS 11.
Description.—The microcoprolites consist of fine-grained detrital material. They are cylindrical with round to slightly oval cross-sections (Fig. 2). They are as long as 3.5mm and have diameters of 0.7–1.2mm. In some specimens, a shallow indentation or ventral groove may be seen on one side (Figs. 2.4, 3.1). The microcoprolites have ten crescentic or U-shaped internal canals 20–30 µm across, which are widest at the ends. The canals are filled with small crystals of blocky calcite. The total diameter of the canals ranges from 100–150 µm. In cross- section, the microcoprolites are bilaterally symmetrical. Eight of the ten crescents are oriented with their openings towards the center; the two central crescents have their openings directed in the same direction towards the outside, usually towards the shallow indentation (Figs. 2.4, 2.5, 3.1).
the latter ichnospecies resemble P. floridanus n. isp. as well at first glance. However, the Jurassic form, reported as Favreina decemlunulatus (Kennedy et al., 1969), and the Late Cretaceous (Cenomanian) form, described as Palaxius decemlunulatus (Kuss and Senowbari-Daryan, 1992; Senowbari-Daryan and Kuss, 1992), are different from P. floridanus n. isp. based on the orientation of the cross-sections of the two central crescents, the openings of which are oriented outward, in opposing directions (Fig. 3.3, 3.4). The openings point in the same direction in P. floridanus n. isp. and slightly away from each other in P. decemlunulatus (Fig. 3.1, 3.2). For these reasons, the Cretaceous form belongs to neitherP. decemlunulatus nor P. floridanus n. isp., but to a new Cretaceous ichnospecies of Palaxius yet to be described. The stratigraphic occurrence of P. decemlunulatus, previously described as reaching from Cenomanian to Oligocene (Senowbari-Daryan and Kube, 2003), should be restricted to the Oligocene. The internal canals in the Jurassic F. decemlunulatus are relatively thin and more “comma-shaped” as compared to the wider and U-shaped canals in the Cenomanian, Oligocene, and Pleistocene specimens. Furthermore, the Jurassic form has an exter- nal sediment envelope that is lacking in the three younger forms, and in Palaxius in general. Therefore, for the Jurassic F. decemlunulatus (Kennedy et al., 1969) a new ichnogenus should be erected, as suggested already by Senowbari-Daryan and Kuss (1992).
Aspects of paleoecology and preservation.—Microcoprolites of P. floridanus n. isp. were mostly found in packstone-facies (i.e., in moderate-energy environments) locations >20km away from the former platform margin. The Coral Gables outcrop and the WP-core (Basin Hill Shoals) locations are closer to the platform margin, but still several kilometers inboard. The fact that P. floridanus n. isp. microcoprolites occur also in an oolite grainstone facies suggests that the producer also inhabited somewhat higher energy depositional environments. Today, considerable areas in the intertidal and shallow subtidal zones of the south Florida carbonate platform interior are inhabited by burrowing callianassid and thalassinidean shrimps along with the endobenthic crustacean Alpheus (Shinn, 1968). In the Pleistocene Miami Limestone, Ophiomorpha trace fossils are common (Halley
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