thiolliericrinid crinoids from the lower cretaceous of crimea

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— 657 —occupying nearly the whole centrodorsal surface inthe oldest specimens. The stem facet, being flat in theyoung specimens, turned into concave in the adultones.The centrodorsal grew quicker than the radiais inH. heberti (fig. 17C). Therefore, the upper centrodorsalsurface is very concave. The basais, being visible inthe young specimens, disappeared in the adult ones.The height of the radiais decreased. The diameter ofthe centrodorsal was roughly equal to that of theradial ring in the young specimens. However, the centrodorsalwas considerably wider than the radiais inthe adult specimens. The stem facet was almostalways flat.7 — ORIGIN OF THE THIOLLIERICRINIDAEMany thiolliericrinids have the quite developed cirriwith the mobil bifascial articulation of cirrals on theircentrodorsals. Only Comatulida and Pentacrinida *may have such cirrus construction among postpaleozoiccrinoids. So specialized cirral organs couldnot originated twice in the phylogeny of crinoids.Therefore, the origin of Thiolliericrinidae must beconsider in the close connection with the origin ofcomatulids and pentacrinids in one phylogeneticsequence with these groups.Three hypothesis are possible in the comprehensionof the development of three given groups, namely :(1) stalked pentacrinids, (2) stalked thiolliericrinids or(3) stemless comatulids are initial. The embryologicalinvestigations showed that young stages of comatulidswere stalked (Thomson 1865 ; A .H . Clark 1921). Thefine and peculiarly constructed perforation on thelower centrodorsal face of some (relatively primitive?) comatulids (A.M. Clark 1973, fig. 1—3) are alsothe illustration of the stalkness of comatulid ancestors.Available facts testify to the origin of Comatulidafrom stalked forms and to the unacceptability ofthird (see above) hypothesis respectively.Earliest pentacrinids known beginning with earlyTriassic (Holocrinidae) had a number of specific features.One should note the following primitive signs :the distal attachement disc (replaced later into unattachedbulge), the infrabasals which can be seen on thecalyx surface, the narrow spot of the crown on theradial = brachial suture. The newly-gained feature isthe only one : the nodals in proximal stem part withshort cirri (mostly not more than three in a whorl).The recent Proisocrinidae are the analogue for theseancient stages. Known finds of young pentacrinids(Carpentier 1884, pi. 30a, 35, 36) and encrinids (Hagdorn1978, Abb. 21 ; 1982, Abb. 18, 19) also showthat pentacrinids have been developed from attached* Pentacrinida T o r t o n e s e (1938, p. 171, 177, 212) = IsocrinidaSie v e r t s -D o r e c k , 1952.and cirriless forms with quite large infrabasals, andthat they had many features common with encrinids.Then, the development of pentacrinids followed apath of perfection of the cirral organs (with a mountingof the five-rayed nodal symmetry and an appearanceof the cryptosymplectial sutures : Hagdorn1983, p. 357 ff.), transm utation of the calyx fromdicyclic to cryptodicyclic and disappearance of themorphological isolation of the calyx from the arms.Cited data show that origin and development of thepentacrinids followed without any connection withthe considerably more late Thiolliericrinidae. Consequently,only one of above mentioned hypothesisremains acceptable : the pentacrinids are the ancestorof the cirriferous Articulata.By subsequent consideration of this hypothesis, twoversions are possible : (1) Pentacrinida —» Thiolliericrinidae—> Comatulida (De Loriol 1880, p. 11 ; Kirk1912, p. 75 ; Jaekel 1918, p. 71 and others) or (2) Pentacrinida—> Comatulida —> Thiolliericrinidae (Rasmussen1978b, p. 314 ; 1978c, p. 867, 879).One can make out two stages in the skeleton developmentof the recent comatulids. Deltoid plates,large basais, minute infrabasals and columnals arelaid at early cystidean stage. Absence of cirri and theconstruction of the calyx basis permit to see, in thisstage, an analogy with the initial forms for articulatecrinoids (possibly, with Encrinidae). Further, thenodal plates on which cirri can developed subsequentlyare laid under the calyx in pentacrinoid stage.We can see here the transition from Encrinidae toPentacrinida. The cirri develop on all the proximalnodals of pentacrinids. The cirri appear but only onone or two most proximal nodals of comatulids,however some discoidal cirriless columnals which arehomological to pentacrinid nodals are formed belowthem. Then, the detachment of the comatulid larvafrom the stem takes place. By that, the free animalhad not carried yet that indivisible plate which shouldbe called as a centrodorsal. This very important circumstanceshows that the comatulid centrodorsal wasformed by some proximal nodal plates (Thomson1865, p. 536).
— 658 —At the same time, all the Thiolliericrinidae withoutexception possessed of a centrodorsal. And what ismore, this plate assumes the relatively greater size inyoung specimens (fig. 8 E, 9 C). This indicates thatThiolliericrinidae originated from the forms having awell developed large centrodorsal, and Comatulida -from the forms with the centrodorsal consisting ofseveral plates.Paracomatula Helvetica (H e s s , 1951, fig. 1—7) hasthe centrodorsal consisting of several nodal columnalsand crown already typical for comatulids, and servesa good example for the forms transitional from Pentacrinidato Comatulida (see fig. 18). Carpenterocrinusmollis (C a r p e n t i e r , 1884, p. 338, pi. 33, fig. 7-10) can be an example of such transitional formsamong recent crinoids.Thus, the hypothesis on the origin of the Thiolliericrinidaefrom comatulids and that on the origin of thelatter, in its turn, from pentacrinids seems to be themost substantiated ones.The explanation of the origin of Thiolliericrinidaefrom the family Solanocrinitidae seems to be mostconvincing. Adutl individuals of this latter familyhave large centrodorsals where, under each radial,two vertical rows of the cirrus sockets are placed.Each row can contain up to five sockets and more.The basais are well visible on the calyx surface, theradiais have high external surface and the centrodorsalbasis is flattened and smooth. In the enumerationof these features one can see an evident coincidencewith the calyx construction of Solonaerium, the firstand most primitive genus of the family Thiolliericrinidae(fig. 18).8 — DEVELOPMENT OF THE THIOLLIERICRINIDAEDuring settling of the reefs, one of the groups of theorder Comatulida (possibly Solanocrinitidae) obtainedthere the most favourable conditions for its life(pure water, an abundance of the light, heat, oxygen,food). There was no necessity to change the place oflife, and therefore the moment of the larval stem tearingoff began to be delayed. The individuals of Solonaeriumand Thiolliericrinus were free when theybecame adult. After detaching from a stem theseforms lived freely using their powerful centrodorsalcirri to attaching to the bottom (see fig. 16). Therefore,it seems to me that the determination of Thiolliericrinusas « a permanent larval form » (Carpenter1881b, p. 377) is quite good.The sessile mode of life appeared so successful, atthe time, that it began to be the cause of subsequentmorphological adaptations of the skeleton. The cirribegan to be lost as useless now (Gislén 1924, p. 206 ;Rasmussen 1978a, p. 273), the stem became morepowerful and more flexible. Here we witness thechange from cirriferous forms to Burdigalocrinus andUmbocrinus, having rudimentary cirrus fossae on thecentrodorsal, and then to Conoideocrinus and Heberticrinuswith no traces of cirri. The basais and partlythe radiais were reducing (Bather 1900, p. 195 ; Kirk1912, p. 78). The crown became more compact andmore strongly constructed (see fig. 16). The animalswere attached during the whole life. By that, theattachment organs (the stem and the distal disc) weresimilar to the larval structures of the « true » comatulids.Just so « Thiolliericrinidae appear to be aproterogenetic evolution from the Solanocrinitacea »(Rasmussen 1978b, p. 314). Thiolliericrinidae are evidentlynot an unique example of the conservation oflarval features by adult animals adapted to the life inthe reef conditions.The morphological variations of Thiolliericrinidaecalyxes are presented on fig. 18, according to theirsupposed phylogenetic correlation.Solonaerium seems to be the initial form with highradiais, large basais and a regular disposition of thecirrus sockets. Subsequently the disposition of thesockets lost the regularity but the basais were still preserved(Thiolliericrinus). The radiais can be high orlow. Then the number of the cirrus sockets decreased,some sockets turned into structureless fossae. Laterthe sockets disappeared completely, but the fossaewhich had been scattered on the centrodorsal remained(Burdigalocrinus). The full disappearance of thecirri on the centrodorsal, with the preservation ofhigh radiais and large basais, is typical for Conoideocrinus.The centrodorsal fossae can remain on theradial-centrodorsal suture. The gradual disapearanceof these fossae can be observed simultaneously withthe atrophy of the basais and the preservation of thehigh radiais (Loriolicrinus). Otherways, fossae andbasais could remain (and even decrease in size) withthe considerable reduction of the radial ring (Umbocrinus).The final disappearance of the fossae and thebasais, and the decrease of the relative size of radiais,are marked in the genus Heberticrinus in which theprincipal morphological types can be determinedaccording to the form and size of the centrodorsal.
Page 1 and 2: THIOLLIERICRINID CRINOIDS FROM THE
Page 3 and 4: TABLE OF CONTENTS1 - Introduction..
Page 5 and 6: — 628 —Name of s p ecies L o ca
Page 7 and 8: 630 —
Page 9 and 10: — 632 —not only specific but al
Page 11 and 12: — 634 —Fig. 3 — Calyxes and c
Page 13 and 14: — 636 —Fig. 4A scheme of the di
Page 15 and 16: — 638 —Thiolliericrinus elongat
Page 17 and 18: — 640 —Fig. 7 — Calyxes and c
Page 19 and 20: — 642 —cavity. The primaxillary
Page 21 and 22: — 644 —D e s c r i p t i o n :T
Page 23 and 24: — 646 —T y p e s p e c ie s :Ge
Page 25 and 26: — 648 —Fig. 12 — Calyxes and
Page 27 and 28: — 650 —T y p e l e v e l :Upper
Page 29 and 30: — 652 —5 — RECONSTRUCTION OF
Page 31 and 32: — 654 —SIS rllAxsurface (Loriol
Page 33: primaxillaries but are asymmetrical
Page 37 and 38: — 660 —AcknowledgementsThis art
Page 39 and 40: ROMAN F. (1897) - Recherches strati
Page 41 and 42: PLATE
Page 43: Geobiosn° 20, fasc. 5Pl. 1V.G. Kli

thiolliericrinid crinoids from the lower cretaceous of crimea

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