Gsa - 2014 Abstracts - Pennsylvania Arthropoda

[piranha]

Northeastern Section - 49th Annual Meeting - 23-25 March 2014 - Lancaster, Pennsylvania, USA

 

 

THE EVOLUTION OF LAURENTIAN (NORTH AMERICAN) SPECIES OF TRETASPIS (ORDOVICIAN TRILOBITA)

Paper No. 39-12 - Presentation Time: 8:00 AM-12:00 PM

 

PFAHLER, Benjamin S. and BUSCH, Richard M., Department of Geology & Astronomy, West Chester University of Pennsylvania, West Chester, PA 19383,

 

Discovery of a new species of Tretaspis (trinucleid trilobite) in the Ordovician Myerstown Formation near Lebanon, Pennsylvania sheds new light on the evolution of Laurentian (North American) Tretaspis species. All five known North American species of Tretaspis lived in deep ramp environments of the Taconic foreland basin, on the southern margin of Laurentia. Tretaspis sp. nov. occurs in southeast Pennsylvania, is of early Sandbian age, and is the oldest known North American species of Tretaspis. The fringe of its cephalon has just four anterior (sag.) rows of pits. Tretaspis sp. nov. is likely a common ancestor to T. sagenosus of Virginia (middle Sandbian age) and T. reticulatus of Virginia and New York (middle Sandbian to early Katian age), which have six and seven anterior rows of fringe pits, respectively. T. canadensis of Quebec is also of early Katian age, has seven anterior fringe pits, and may be ancestral to T. reticulatus. T. clarkei of Quebec is of middle to late Katian age and does not appear to be ancestral to any of the older North American species. It has just four anterior rows of fringe pits and is nearly identical to European species of the T. seticornisgroup. It likely represents a migratory species from Baltica.

 

 

ON THE FEEDING BEHAVIOR OF ANOMALOCARIS: A SPECTRUM OF ADAPTATIONS ELUCIDATED BY THE FORM OF SPINES ON THE ‘GREAT APPENDAGE’ OF A NEW FORM FROM THE KINZERS FORMATION (EARLY CAMBRIAN) OF SOUTH-EASTERN PENNSYLVANIA

Paper No. 44-4 - Presentation Time: 8:00 AM-12:00 PM

 

OXMAN, Katherine L., Dept. of Earth & Environment, Franklin & Marshall College, P.O. Box 3003, Lancaster, PA 17604-3003

THOMAS, Roger D.K., Department of Earth and Environment, Franklin & Marshall College, P.O. Box 3003, Lancaster, PA 17604-3003

 

On account of its large size and morphology, Anomalocaris has been interpreted as the top predator in soft-bottom marine faunas of the Early and early Middle Cambrian. For a while, it was supposed to have preyed on the abundant trilobites of that time. However, given the form of its mouth and the mode of operation of its teeth, it is now thought to have been incapable of breaking through the tough carapace of a trilobite (Hagadorn, 2009). Moreover, the ‘great appendages’ are not designed as claws to be used in manipulating and crushing prey. Functional analysis suggests instead that Anomalocaris fed mainly on the worms of several kinds that were so abundant in Burgess Shale-type faunas. Worms would have been a natural target for a predator that could find them and extract them from their burrows. The form of the ‘great appendages’ and their spines is consistent with their use in searching for shallow infaunal prey. Likewise, the form of the mouth was well suited to extract and ingest worms. Four species of Anomalocaris have so far been recognized, notably from the Burgess Shale of British Columbia, the Maotianshan Shale at Chengjiang, and the Emu Bay Shale in Australia. Anomalocaris pennsylvanica occurs in the Kinzers Formation of Lancaster County, Pennsylvania. Now, a recent find appears to represent a previously undescribed species. The new specimen, a single ‘great appendage’, is of particular interest on account of the nature of its ventral spines. These spines are longer than those of any species so far described, they are narrow and uniformly spaced, and they lack any evidence of auxiliary spines.The variety of forms of ventral spines attached along the ’great appendage’ of different species of Anomalocaris implies a range of actions. Long flexible spines have properties that would have enabled the appendages to sweep loose sediment; short rigid spines would have been effective in probing coarser or stiffer materials. The new specimen represents an end member on this spectrum of forms; spines of established species represent the middle and the other end of this range. Recognition of an end member on a spectrum of ’great appendage’ form and function opens a window on the behavior of Anomalocaris species, adapted to feed on worms and other organisms living in substrates of different consistencies.

 

 

[Malcolmt]

Cool would be great to be able to attend the anomalocaris presentation. Now I'm going to have to figure out at some point a way to go collect in Pennsylvania. Definitely one of my top 10 bucket list fossils. Now room for a whole one but an appendage would be spectacular.

[NZ_Fossil_Collecta]

Wow... I always thought anomolacaris fed on trilobites... This must be very recent information as I actually have a DVD at home that still says they fed on trilobites. It also shows how successful trilobites were, as early as the early Cambrian thier exoskeletons were deterring 1-meter predators.

[piranha]

On 1/20/2014 at 4:15 PM, NZ_Fossil_Collecta said:

Wow... I always thought anomolacaris fed on trilobites... This must be very recent information as I actually have a DVD at home that still says they fed on trilobites. It also shows how successful trilobites were, as early as the early Cambrian thier exoskeletons were deterring 1-meter predators.

 

 

Here is the reference cited from the Anomalocaris abstract:

 

Hagadorn, J.W. (2009)

Taking a bite out of Anomalocaris.

In: Walcott 2009—International Conference on the Cambrian Explosion

Abstract Volume pp. 33-34

 

Anomalocaridids are hypothesized to have consumed trilobites. Other than their large size, their midgut glands, and malformed trilobites, there is little direct evidence that they did so. New taphonomic, compositional, and modelling evidence suggests that anomalocaridid mouths were soft, could not close completely or chew, had biting kinematics incompatible with many trilobite malformations, and were well suited to manipulate or suck soft prey.Anomalocaridid mouth plates and their tips are never broken, nor are tips worn. If plates were hard, and were used to manipulate, puncture, crush, or masticate biomineralized prey, they would be expected to show evidence of abrasion or breakage. Absence of this evidence is striking given the frequency (0.01-1%) of healed malformations in extant marine arthropods, most of which are due to prey manipulation or feeding. Moreover, anomalocaridid plates and their biting tips are commonly wrinkled, exhibit preburial shearing and tearing, and mantle or are deformed by biomineralized fossils such as brachiopods, trilobites, and Scenella. Plates are preserved as organic carbon and exhibit fracture patterns typical of desiccating arthropod cuticle. Thus anomalocaridid plates, including their tips, were unmineralized and pliable in life.

 

Computer aided design modelling of the kinematics of mouth opening and closure, together with comparison with muscle movements used by modern circular-mouthed organisms, suggests several plausible models for anomalocaridid mouth movement. These include sphincter-like constricting closure of the circlet of plates, and full- or half-eversion or inversion of the circlet; the latter two movements generate sufficient subambient pressure for suction feeding. In all closure modes, laterally-adjacent opposing plates intersect one another when the mouth closes, which prevents the circlet from closing more than half-way. Orientations of plate tips are consistent with a partial mouth closure model; if full closure was possible, opposing plate tips would not articulate or interlock with one another, as is expected from teeth optimized to masticate or puncture, or teeth which intersect at tooth tips to crush, puncture, or break.

 

Although bilaterally-oriented trilobite malformations can plausibly be explained by a closure of a circular mouth, most trilobite malformations are arc- or U-shaped. Suction-, eversion-, and sphincter-movement of anomalocaridid jaws cannot produce U-shaped bite marks; these are better explained by predators who had opposable jaws or claws. Finite Element Analysis, and modelling of anomalocaridid plates using cuticle yield strengths from modern shrimp (Pandalus) and lobster (Homarus), illustrate that plates could withstand maximum forces of up to 6.2 and 13.0 N, should they have bitten into the thoracic segments of a trilobite. The most commonly malformed Cambrian trilobites had maximum skeletal yield strengths ranging from 3.7–37.1 N, suggesting that only weakly mineralized taxa, such as Elrathia kingii, could have been broken by an anomalocaridid bite.

 

Anomalocaridids may have bitten some soft trilobites, but it is more likely that they were suctorial feeders, perhaps using their preoral appendages to comb soft-bodied invertebrates from the benthos. This feeding strategy makes sense given the recent discovery of multiple rows of inwardly pointing serrated plates inside some anomalocaridids’ oral cavity; these may have prevented prey from exiting the mouth, or may have been part of a buccal cavity or eversible grasping organ.

 

 

[Shamalama]

I didn't think there were any exposures of the Kinzers Fm. around anymore. Figured they were all obliterated by houses and roads. I wonder if that abstract is based on older material collected years ago.