Patrick R. Getty

Reinterpretation of Climactichnites Logan 1860 to Include Subsurface Burrows, and Erection of Musculopodus for Resting Traces of the Trailmaker

Abstract Based on a thorough examination of field and museum Climactichnites specimens, two species of this trace are recognized, each representing a unique behavioral variant produced by a soft-bodied animal in Late Cambrian intertidal environments. C. wilsoni represents surface-produced trails, whereas C. youngi is re-erected for burrows produced below the surface. Burrowing behavior is supported by: 1) the presence of C. youngi within, rather than on, the surface of beds; 2) the orientation of some burrows inclined to bedding; and 3) the occasional presence of distinct burrow fills. Burrows can also be distinguished morphologically from surface traces by the absence of lateral ridges and the presence of fine, mm-scale striations or grooves superimposed on the transverse bars and furrows. Burrowing behavior for the Climactichnites trailmaker was previously unknown and thus represents a new, although not entirely unexpected, behavior for this mollusk or mollusk-like animal. The body impression of the sedentary animal is removed to Musculopodus sedentarius n. igen. and isp. In the future, Musculopodus may be expanded to include the resting traces of other soft-bodied animals known from the fossil record. Currently, Climactichnites is known only from very shallow to emergent strata of North America; reports of this fossil in other parts of the world are misidentified trails produced by other animals.

Variation in wingless insect trace fossils: insights from neoichnology and the Pennsylvanian of Massachussetts

ABSTRACT Trace fossils of basal, apterygote (wingless) insects from the Pennsylvanian-aged Rhode Island Formation of southeastern New England include the body imprint Tonganoxichnus buildexensis and the trackways Mitchellichnus cf. ferrydenensis, Siskemia elegans, Stiallia pilosa, and Stiaria intermedia. Trackways with double and triple medial impressions (S. elegans and M. ferrydenensis) are rare among trace fossils attributed to such insects. To determine how these unusual trackway morphologies were produced, and why they are so rare, experiments were conducted over a range of media ( = sedimentary substrates) with modern archaeognathans (jumping bristletails) and thysanurans (silverfish). Our experimental results suggest that archaeognathans produced the fossil body imprints, as well as trackways exhibiting opposite symmetry, but cannot rule out thysanurans for trackways exhibiting alternate symmetry. The results also show that a variety of appendages leave medial impressions. The rarity of fossil trackways with more than one medial impression results from the low mass of the animal and the delicate nature of the appendages making such structures, coupled with behavior (jumping and landing) and media properties (saturation and cohesiveness). The production of different numbers of medial impressions by a single archaeognathan species suggests that fossils should show similar variety, albeit in rare cases, and that the named ichnotaxa are likely derived from a single biological taxon. Finally, the experimental work provides new insights into the production and preservation in Stiallia and Tonganoxichnus.

Was the Eubrontes Track Maker Gregarious? Testing the Herding Hypothesis at Powder Hill Dinosaur Park, Middlefield, Connecticut

Abstract The theropod footprint taxon Eubrontes is common in Early Jurassic rocks of the Hartford Basin. Aligned Eubrontes trackways at one site in Holyoke, Massachusetts, have led to the hypothesis that the track makers were gregarious; however, trackways are not aligned at several other sites. To test the gregariousness hypothesis, we measured trackway orientations at Powder Hill Dinosaur Park in Middlefield, Connecticut, where exposed rocks were deposited in an ephemeral lake environment, and compared these orientations to those of two additional track sites from similar sedimentary facies. The Eubrontes trackways produced in the ephemeral lake environments have no preferred orientation and provide no evidence of gregarious behavior. We suggest that the alignment of tracks in Holyoke reflects behavior in response to environmental settings rather than group behavior. Trackways may be aligned next to large, permanent lakes because of shoreline-parallel travel, but random orientations characterize other habitats. This study underscores the value of examining track sites from different paleoenvironments when inferring dinosaur behavior.

A new reconstruction of continental Treptichnus based on exceptionally preserved material from the Jurassic of Massachusetts

Abstract. Continental deposits of the Early Jurassic East Berlin Formation in Holyoke, Massachusetts, have yielded an exceptional occurrence of the ichnogenus Treptichnus. Here, burrows are preserved in full relief within thin mud laminae between layers of fine-grained, cross-bedded sandstone. We studied these burrows to evaluate whether earlier explanations of burrow morphology are applicable to all Treptichnus. Our research focused on three questions. (1) Do the Holyoke Treptichnus have significant vertical relief? (2) Does the lack of projections in some of the Holyoke Treptichnus result from stratinomic sectioning through the bottom of the burrow? (3) Do expanded, bulbous ends of burrow segments result from sediment compaction? While addressing these questions, the Holyoke fossils were compared to syntype and topotype material of Treptichnus from the Carboniferous of Indiana. The Holyoke Treptichnus did not exhibit significant vertical relief, and the presence and absence of projections is explained by the positioning of new segments at different points along older ones. The bulbous ends of burrow segments resulted from trace-maker behavior, not sediment compaction. Drawing on the analysis of the Holyoke material, a new reconstruction is proposed that presents continental Treptichnus as a shallow mole-tunnel-like burrow produced just below the sediment surface. This reconstruction is consistent with the morphology of Recent Treptichnus-like burrows produced by fly (dipteran) larvae, which are considered the most likely makers of the Holyoke Treptichnus.

RETRODEFORMATION OF CARBONIFEROUS TRACE FOSSILS FROM THE NARRAGANSETT BASIN, UNITED STATES, USING RAINDROP IMPRINTS AND BEDDING-CLEAVAGE INTERSECTION LINEATION AS STRAIN MARKERS

Abstract Retrodeformation of fossils can improve taxonomic and paleobiologic interpretations, but fossils that lack symmetry or other regular geometric properties are difficult to retrodeform unless strain markers are preserved within the fossil-bearing strata. Strain markers, however, are generally distributed unevenly, and their use can be problematic if strain varies among specimens and the markers do not occur in close association with the fossils. We use two approaches to retrodeform Carboniferous tetrapod tracks from the Narragansett Basin of southern New England: (1) a direct method in which the strain ratio (Rs) is obtained from deformed raindrop imprints preserved on the same specimens as the tracks and (2) an indirect method in which the range in orientation of the bedding-cleavage intersection lineation is used as a proxy for Rs. The latter follows from a strong correlation between the range in orientation of the bedding-cleavage intersection lineation and Rs values obtained from the deformed raindrop imprints, and allows the retrodeformation of tetrapod tracks not preserved in close association with deformed raindrop imprints. Our methodology was applied to both anamniote and amniote traces and was tested by retrodeforming originally bilaterally symmetric insect traces from the same location. In all cases, the trace fossils return to their expected morphology. This work shows that deformed raindrop imprints and bedding-cleavage intersection lineation are useful strain markers for the retrodeformation of trace fossils and expands our understanding of the fossil record of early tetrapods in southern New England.

On the Ichnotaxonomic Status of Haplotichnus indianensis (Miller, 1889)

ABSTRACT The type specimens of the ichnospecies Haplotichnus indianensis and Treptichnus bifurcus were compared under low-angle light. H. indianensis was found to exhibit segments with projections, which are morphological characteristics of T. bifurcus. Consequently, H. indianensis is reinterpreted here as a shallow, subsurface burrow and is considered to be a subjective junior synonym of T. bifurcus. Traces assigned to H. indianensis, other than the type, should be reassigned to other ichnotaxa. Looping surface trails, for example, should be called Gordia isp.