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Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode

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Bohaty J.

Acta Palaeontologica Polonica

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2011

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tom 56

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nr 3

The lecanocrinid Ammonicrinus(Flexibilia) is newly interpreted based on new material from the Middle Devonian of the Rhenish Massif (Eifel and Bergisches Land, Germany). The species have echinoid−like tubercles on the attachment and on the column, which bear articulated spines. The intraspecific variability of the column is discussed for three facies−controlled morphotypes, herein classified as standard “exposed−” or “encased roller−type” and the rare “settler−type”. New specimens have floating transitions between different plate sculpturing and between those individuals with none or one to several columnals with herein termed “lateral columnal enclosure extensions” on the proximal−most, barrel−like dististele and the following mesistele, which is solely distinguished by these extensions. Based on this interpretation, Ammonicrinus kongieli is evaluated as a subjective junior synonym of Ammonicrinus sulcatus. The latter species was first recognised from the Eifel (Germany). “Ammonicrinus wachtbergensis”, from the upper Eifelian of the Eifel, is declared a subjective junior synonym of Ammonicrinus doliiformis. The first nearly complete specimen of Ammonicrinus kerdreoletensis is described from the lower Eifelian of Vireux−Molhain (southern Ardennes, France). Two new species are described: Ammonicrinus jankei sp. nov. and Ammonicrinus leunisseni sp. nov. A functional morphologic trend in perfecting the crown encasement by continuous modification of the lateral columnal enclosure extensions of the mesistele from the Eifelian to the Givetian, indicates a vagile benthic “predator”−driven evolution of ammonicrinids in the Eifel area. Several ammonicrinid species are herein defined as spined soft−bottom dwellers, feeding in low−intensity current water, possibly through a self−produced water flow. The first known postmortem encrusting epizoans on ammonicrinid endoskeletons are reported.

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Sublethal injuries in Early Devonian cephalopod shells from Morocco

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Klug C.

Acta Palaeontologica Polonica

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2007

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tom 52

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nr 4

Internal moulds of the relatively small− to moderate−size shells of Early Devonian ectocochleate cephalopods (typically <150 mm diameter) occasionally display traces of repaired shell damage. Presumably, these animals with their highly specialized buoyancy device, the phragmocone, lived in the water column. It is uncertain as to how the shells of these animals were damaged; one likely cause would be predatory attacks but the identity of the perpetrator remains uncertain. So far, no remains of arthropods capable of breaking or cutting shells have been found in the fossiliferous outcrops of this age in the Anti−Atlas (Morocco). The only macrovertebrate remains of this age are of acanthodian and placoderm fish which probably lived a more or less benthonic life style. Additionally, a fish attack on these cephalopods would probably have destroyed most of the thin−shelled conch and killed the animal. Most of the repaired shell breaks are triangular in shape which is characteristic for cephalopod bite marks. Additionally, the paired arrangement of the fractures in over 70 bactritoids supports the hypothesis that it was a cephalopod attacking another cephalopod. It cannot be excluded with certainty that occasional vertebrate attacks left traces on their shells. Fossil evidence indicates that the development of tightly coiled conchs was a rapid evolutionary event in the Ammonoidea in the Early Devonian; however, the evolution of coiling is probably not directly related to predation pressures because the ratio of injured to healthy specimens is roughly the same in Zlíchovian bactritoids with orthoconic and ammonoids with coiled shells.

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Concentration of juvenile and small cephalopods in the Hirnantian cherts [Late Ordovician] of Porkuni, Estonia

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Kroger B.

Acta Palaeontologica Polonica

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2007

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tom 52

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nr 3

The quarry in the north Estonian village of Porkuni provides a succession of shallow−water limestones and cherts spanning the Ashgillian Normalograptus? extraordinarius graptolite Biozone. This interval comprises the initial pulse of the end−Ordovician extinction. The succession of Porkuni contains abundant and extraordinarily well−preserved fossils. 71 cephalopod specimens were extracted from these strata at Porkuni. Many of these specimens are fragments of juvenile shells or small adults. The embryonic shells of the cephalopods are usually preserved and provide insight into their early ontogeny. The faunal composition is considered as autochthonous and reflects a “palaeo−nursery” in a Hirnantian reef environment. The collected specimens represent twelve genera and four orders. Small oncoceridans and orthoceridans dominate the association. The rate of endemism is very high, since only two genera found in Porkuni, are known from outside Baltoscandia. The new genera Parvihebetoceras, Pomerantsoceras, Porkunioceras, and the new species Parvihebetoceras wahli, Pomerantsoceras tibia, Porkunioceras tuba, and Strandoceras orvikui are erected.

Ograniczanie wyników

3 Acta Palaeontologica Polonica

1 Bohaty J.

1 Klug C.

1 Kroger B.

1 2011

2 2007

Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode

Sublethal injuries in Early Devonian cephalopod shells from Morocco

Concentration of juvenile and small cephalopods in the Hirnantian cherts [Late Ordovician] of Porkuni, Estonia