608


Journal of Paleontology 91(4):604–617


2015), but the presence of oral frame plates and the nature of the floor plates cannot be clearly seen.


of oral frame plates, oral plates, and abradial floor plates. The presence of both oral plates and oral frame plates is confirmed from a few exposed oral area interiors seen on specimens of Edriophus levis Bather, 1914 (see Bell, 1976; Kammer et al., 2013). The oral frame plates form the peristomial opening and preclude the oral plates from contact with the peristome (Fig. 2.8). Distally, they articulate to the proximal-most abradial ambulacral floor plates, terminating in a point along the midline. The interradial oral plates are the only peristomial bordering plates seen from the exterior of the theca (Fig. 2.7). Apparent facets on oral plates of edrioblastoids suggest the presence of oral frame plates, but none have been directly observed because of the nature of the preservation (Kammer et al., 2013). The abradial floor plates are widely exposed externally and show nearly identical morphologies to those seen of the abradial floor plate series of Kailidiscus (Fig. 2.2, 2.7), and they bear sutural pores for podia (Fig. 2.8). Furthermore, they are in line with the oral plate series as in Kailidiscus, strongly suggesting that these are the abradial floor plates. In pyrgocystid isorophid edrioasteroids, the oral frame


Edrioasterine edrioasteroids appear to have a combination


two sets of floor plates—uniserial and imbricating adradial floor plates and biserial and laterally positioned abradial floor plates (Sumrall and Zamora, 2011). The abradial floor plates bear sutural pores, presumably for podia, and have the ambulacral cover plates mounted upon them. Later isorophinid edrioasteroids lost the abradial floor plate series (see the following). This results in an axial skeleton composed of interradial oral frame plates articulating to uniserial adradial floor plates that are entirely internal. These structures can only be seen from specimens exposing the interior of the theca or reconstructed from isolated thecal plates (Sumrall and Parsley, 2003).


Oral-frame-plate-/adradial-floor-plate-bearing taxa


Several Cambrian eocrinoid-grade taxa and isorophinid edrioast- eroids share an axial skeleton composed of radial oral frame plates and adradial floor plates as a basic constructional design, though through different lineages. Unfortunately, these plates are all internal and difficult to observe in taxa unless preserved with a broken interior view or similar preservation. Consequently, this is much more poorly understood than oral plate/abradial floor plate designs discussed in the following. These structures are also present in only a few taxa, and therefore, the known diversity of these structures is limited in comparison to systems based on oral plates and abradial floor plates. In the middle Cambrian eocrinoid-grade echinoderm


Lepidocystis, the oral area can be observed from both the interior and exterior surfaces (Sprinkle, 1973). The exterior surface is poorly documented, but the five ambulacra radiate in 2-1-2 symmetry from a centrally located peristome covered by an oral cone.Where interradial oral plates would be positioned, there are only small platelets of the interambulacral plating documenting the absence of these plates. The floor plates (thought to represent


is constructed only by interradial oral frame plates (Sumrall and Zamora, 2011). The floor plate system is plated with


adradial floor plates) are poorly exposed on the oral surface except where brachioles mount, but details are lacking because of the disrupted nature of these specimens. Similar construction in the better-preserved Kinzercystis shows epispires right up to the food groove (Sprinkle, 1973, pl. 4.1), showing that these plates are not


broadly expressed as they typically are in taxa bearing the abradial floor plates. Brachioles arise alternately from these floor plates mounted adjacent to the food grooves rather than alongside ambulacra (Sprinkle, 1973). Exposed interior views of two specimens show the nature


of peristomial border and floor plates (Sprinkle, 1973; Kammer et al., 2013). The peristomial border bears a frame of radially positioned oral frame plates bordering bean-shaped peristomial opening (Fig. 2.3). Each of the five main plates leads to an ambulacrum, and the CD side apparently has an extra plate of unknown origin. Again, the absence of oral plates can be clearly shown by the presence of small interambulacral plates filling the areas between the oral frame plates and adradial floor plates in the proximal-most interambulacral areas (Fig. 2.3). Although poorly seen, the floor plates appear to be biserial because of the presence of angled sutures (Fig. 2.3) and show a narrow expression in the interambulacral areas. Gogiids are less well known, but there is evidence that


these too have oral frame plates as peristomial bordering plates. Specimens of the gogiid Sinoeocrinus (Parsley and Zhao, 2006) from the middle Cambrian of China have a reduced oral surface in which the peristome is bordered by radially positioned oral frame plates (Fig. 2.4) that give rise to terminal brachioles (Kammer et al., 2013). In some larger specimens, there are groups of terminal brachioles, but how these structures are related to floor plates is presently unknown. Other gogiids with preserved oral surfaces do not expose obvious floor plates externally, and it is assumed that this is evidence that they are internal and likely the adradial set. Isorophinid edrioasteroids show a second example of the


axial skeleton being formed from oral frame plates and adradial floor plates. More plesiomorphic forms such as pyrgocystids


floor plates, roofing the food groove. In many taxa, there are pores along the hinge line passing between the cover plates and the floor plates, possibly forming podial basins and passage- ways for podia (Fig. 2.5). In these taxa, the cover plates are long with broad intrathecal extensions. In more-derived taxa, the cover plates lack these extensions and apparently lack the pores as well.


bear only oral frame plates around the peristome but retain both adradial and abradial floor plates in the ambulacra (Sumrall and Zamora, 2011, fig. 14). In isorophinids, the abradial floor plate set is lost, leaving only the adradial set to form the food groove (Fig. 2.5). The oral frame plates and the adradial floor plates are strictly internal features and only visible from fortuitous interior views of the oral surface (Fig. 2.5). A bean-shaped peristome is bordered by five radially positioned oral frame plates of whichC and D are extended into the CD interray (Fig. 1.2) associated with the hydropore and gonopore (Sumrall and Parsley, 2003). The distal ends of the oral frame plates become U-shaped and align with U-shaped, uniserial floor plates that floor the rest of the ambulacral length (Fig. 2.5). Floor plates can be either adjacently or imbricately sutured. Cover plates mount atop the oral frame plates and adradial


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228  |  Page 229  |  Page 230  |  Page 231  |  Page 232  |  Page 233  |  Page 234  |  Page 235  |  Page 236  |  Page 237  |  Page 238  |  Page 239  |  Page 240  |  Page 241  |  Page 242  |  Page 243  |  Page 244  |  Page 245  |  Page 246  |  Page 247  |  Page 248  |  Page 249  |  Page 250  |  Page 251  |  Page 252  |  Page 253  |  Page 254  |  Page 255  |  Page 256  |  Page 257  |  Page 258  |  Page 259  |  Page 260  |  Page 261  |  Page 262  |  Page 263  |  Page 264  |  Page 265  |  Page 266  |  Page 267  |  Page 268  |  Page 269  |  Page 270  |  Page 271  |  Page 272  |  Page 273  |  Page 274  |  Page 275  |  Page 276  |  Page 277  |  Page 278  |  Page 279  |  Page 280  |  Page 281  |  Page 282  |  Page 283  |  Page 284  |  Page 285  |  Page 286  |  Page 287  |  Page 288