Tetrapod Tracks Research Articles

Tetrapod track assemblages from Lower Cretaceous desert facies in the Ordos Basin, Shaanxi Province, China, and their implications for Mesozoic paleoecology

Tetrapod ichnofaunas are reported from desert, playa lake facies in the Lower Cretaceous Luohe Formation at Baodaoshili, Shaanxi Province, China, which represent the first Asian example of an ichnnofauna typical of the Chelichnus Ichnofacies (Brasilichnium sub-ichnofacies) characteristic of desert habitats. The mammaliomorph tracks, assigned to Brasilichnium, represent the first report of this ichnogenus from Asia. The assemblages also contain three different theropod trackway morphotypes: one very wide Magnoavipes-like morphotype, one relatively wide, broad-toed, small Eubrontes-like form with short steps and strides, and wide straddle, and an elongate morphotype (Sarmientichnus) with longer steps and narrower straddle representing a didactyl trackmaker, the latter being the first example of the enigmatic ichnogenus found outside its type area in Argentina. The Sarmientichnus occurrence, the first in Asia, has important implications, demonstrating that the trackmaker was not monodactyl, but didactyl with probable affinities to deinonychosaurians which are ichnologically well-represented in the Lower Cretaceous of Asia. Although morphologically distinctive, Sarmientichnus should be recognized as a “form” ichnotaxon compromised by suboptimal preservation. The combination of Brasilichnium isp., Sarmientichnus isp., and tridactyl theropod tracks, indicates mammaliomoprhs and small theropods, and is comparable to ichnofaunas from similar desert facies on other continents. Thus, Cretaceous desert ichnofaunas from China are consistent with global ichnofacies predictions.

On the first description of tetrapod footprints from Italy: re-analysis of the original specimen after 150 years

In Italy, vertebrate ichnology developed rather recently, especially starting from the 70's of the last century. However, fossil footprints from Italian continental successions were known since the 19thcentury. The first scientific note was published by Curioni (1870), after a short report on the same material by Geinitz (1869). Curioni described and drew a small slab with tetrapod tracks from the lower Permian strata of Lombardy (Collio Formation, upper Trompia Valley, Brescian Alps), found by the private collector Don Bruni, Priest of Collio. Subsequent publications always referred to that description, but the original specimen was never restudied, due also to the absence of information about the repository (Curioni, 1870). The original specimen belongs to the prestigious Curioni collection (donated by Curioni to the Regio Ufficio Geologico in 1877) and is nowadays located in the Italian National Institute for Environmental Protection and Research (ISPRA) in Rome. Grounding on the most advanced ichnological methods, in this paper we provide a redescription of the specimen. The study ultimately confirmed the attribution of the three main tracks (a pes-manus couple and a single manual imprint) to the ichnogenus Amphisauropus, tracks probably produced by seymouriamorph reptiliomorphs. Smaller footprints on the same surface were instead assigned to Dromopus, tracks probably left by diapsid reptiles or bolosaurid parareptiles. The note by Curioni thus represents the first report of vertebrate footprints from Italy, the first description of material assignable to Amphisauropus in the world, and one of the earliest on material referable to Dromopus. The studied slabcould also represent the earliest finding of Amphisauropus, althoughuncertainties on timing of Don Bruni's discovery exist. We note that only a careful management of the ancient Italian palaeontological heritage allowed our re-analyses of Curioni's original specimen, almost 150 years after the last study. This study therefore highlights also the role of scientific collections for both preservation and valorisation of geo-palaeontologic heritage.

Non-marine palaeoenvironment associated to the earliest tetrapod tracks

Opinions differ on whether the evolution of tetrapods (limbed vertebrates) from lobe-finned fishes was directly linked to terrestrialization. The earliest known tetrapod fossils, from the Middle Devonian (approximately 390 million years old) of Zachełmie Quarry in Poland, are trackways made by limbs with digits; they document a direct environmental association and thus have the potential to help answer this question. However, the tetrapod identity of the tracks has recently been challenged, despite their well-preserved morphology, on account of their great age and supposedly shallow marine (intertidal or lagoonal) depositional environment. Here we present a new palaeoenvironmental interpretation of the track-bearing interval from Zachełmie, showing that it represents a succession of ephemeral lakes with a restricted and non-marine biota, rather than a marginal marine environment as originally thought. This context suggests that the trackmaker was capable of terrestrial locomotion, consistent with the appendage morphology recorded by the footprints, and thus provides additional support for a tetrapod identification.

First report on swimming trace fossils of fish from the Upper Permian and Lower Triassic of the Dolomites (Italy)

In the Upper Permian continental to marginal-marine succession of the Southern Alps (Dolomites, north Italy), the ichnological record consists of diverse vertebrate footprints and non-diverse invertebrate trace fossils, mainly occurring in the “Bletterbach ichnoassociation” of the Val Gardena Sandstone Formation. After the Permian-Triassic Boundary event, vertebrate ichnoassociations are scarce until the Middle Triassic (Anisian), whereas the uppermost Permian–Lower Triassic Werfen Formation preserves a rich invertebrate trace-fossil record. To date, fish body and trace fossils ( Undichna ) are very rare in the pre- and post-extinction deposits of the Dolomites; only Undichna gosiutensis Gibert, 2001 was identified in the “Voltago Conglomerate” (Middle Anisian), whereas some unidentified fossil fish casts were found in the Permian Val Gardena Sandstone and some fish remains in the overlying Werfen Formation. Recently, for the first time, fish trails have been discovered in the Val Gardena Sandstone (Lopingian) and in the Werfen Formation (Campil member, Early Triassic, Smithian). Val Gardena Sandstone yielded Undichna cf. quina Trewin, 2000 and U. bina Anderson, 1976 and these represent the oldest fish trails found in the Southern Alps so far. Conversely, the specimens found in the Werfen Formation can be assigned to Undichna cf. britannica Higgs, 1988. They represent the oldest Mesozoic record of fish trace fossils in northern Italy and one of the few records of Undichna from marine environments. These trace fossils are consistent with the fossil association found in the two formations and reflect fish swimming activity in different environments: in very shallow, calm, brackish distal-floodplain to marginal-marine environments in the Late Permian, in association with abundant and diverse tetrapod tracks, and non-diverse invertebrate trace fossils, and in inter- to subtidal calm, shallow, marine environments in the Early Triassic, together with abundant, but not diverse invertebrate trace fossils.

Early Jurassic Batrachopus-rich track assemblages from interdune deposits in the Wingate Sandstone, Dolores Valley, Colorado, USA

Late Triassic and Early Jurassic tetrapod track assemblages are abundant and quite well documented from the respective Chinle and Glen Canyon groups of the Dolores Valley region of western Colorado and adjacent regions, especially eastern Utah. However, gaps still exist in our knowledge of the spatial and temporal distribution of representative ichnogenera. The stratigraphic distribution of track assemblages in the cliff-forming Wingate Sandstone Formation, the lower unit of the Glen Canyon Group, underlying the Kayenta and Navajo formations, is difficult to determine because almost all Wingate assemblages are known only from fallen blocks, originating from precipitous, vertical cliffs, which yield both dune and interdune ichnofaunas. Among the characteristic Lower Jurassic biochron ichnogenera Grallator, Eubrontes, Otozoum, Anomoepus and Batrachopus, in the Dolores Valley only Grallator is known abundantly, while Otozoum, and Batrachopus were previously known only from single occurrences, and Eubrontes and Anomoepus have yet to be reported. We here report two large, Batrachopus-rich assemblages that give new insight into the interdune paleoenvironments frequented by the Batrachopus trackmaker, traditionally regarded as a basal crocdylomorph, and the theropodan trackmaker of Grallator. Both assemblages contain the best-preserved and most abundant Batrachopus currently known, locally in high densities. Where individual trackways are clearly visible they indicate that the trackmakers had variable gaits. A third new assemblage containing Batrachopus from Salt Creek is also described, as is a fourth new assemblage from the Uncompahgre Plateau which yields moderately large theropod tracks (cf. Eubrontes), but no Batrachopus. Although diagnostic Late Triassic biochron ichnogenera like Brachychirotherium occur in basal units of the Wingate Sandstone, Batrachopus which is considered an Early Jurassic biochron ichnotaxon, occurs within the formation. Thus, vertebrate ichnotaxa help place the Triassic–Jurassic boundary within the Wingate Formation, shed light on their spatio-temporal distribution, and underscore their utility for paleoecological interpretation, in a unit devoid of tetrapod body fossils.

Revision of Late Permian tetrapod tracks from the Dolomites (Trentino-Alto Adige, Italy)

The Val Gardena Formation of the Dolomites region in northern Italy preserves the most significant assemblage of Late Permian tetrapod footprints in the world. More than 120 years of collecting resulted in about 900 publicly accessible specimens from the study area. This huge amount of data is comprehensively revised in the light of recent advances in the study of Late Palaeozoic – Early Mesozoic tetrapod ichnofossils. According to our analyses, the Val Gardena Sandstone Formation includes tracks that can be assigned to cf. Batrachichnus isp. (temnospondyl amphibian), Capitosauroides isp. (amphibian), Dicynodontipus isp. (cynodont therapsid), Dolomitipes accordii n. igen. n. comb. (dicynodont therapsid), cf. Dromopus isp. (neodiapsid), Pachypes dolomiticus (pareiasaurian parareptile), Paradoxichnium problematicum (archosauromorph neodiapsid), Procolophonichnium tirolensis n. comb. (procolophonoid parareptile), cf. Protochirotherium isp. (archosauriform neodiapsid) and Rhynchosauroides pallinii (neodiapsid). The ichnoassociation is dominated by tracks of neodiapsid and parareptilian tetrapods, whereas synapsid and anamniote tracks are rather minor components. It includes 10 out of 12 tetrapod ichnogenera known from Lopingian deposits and thus it constitutes a reference for the Paradoxichnium biochron. It shows striking similarities with other low-latitude non-aeolian contemporaneous ichnoassociations of Europe and North Africa, differences may be linked to the palaeoenvironment. Moreover, it shows a clear Triassic affinity.The new ichnogenus Dolomitipes was registered in Zoobank.org. urn:lsid:zoobank.org:act:5B4D871C-D16A-4E93-8211-CEE08019BA60

Permian Tetrapod Footprints from Tunisia

ABSTRACTTetrapod footprints have long been known from Permian outcrops of the Cheguimi Sandstone in southern Tunisia, but never described in detail. The only recovered specimen preserves vertebrate tracks of two different biospecies. Ichnomorphotype 1 shows affinity with mid-Permian tetrapod tracks from France (Merifontichnus Gand et al., 2000) and South Africa (unnamed tracks); ichnomorphotype 2 is most similar to Middle to Late Permian tracks of France (Planipes Gand et al., 1995) and Italy (Dicynodontipus Rühle von Lilienstern, 1944), respectively. Both kinds of the Tunisian tetrapod tracks can be referred to non-mammalian therapsid trackmakers. The ichnoassemblage is in agreement with the supposed late Middle to early Late Permian (∼Capitanian to Wuchiapingian) age of the Cheguimi Sandstone, although additional finds are necessary to obtain a more precise age control.

TETRAPOD FOOTPRINT PALEOECOLOGY: BEHAVIOR, TAPHONOMY AND ICHNOFAUNA DISENTANGLED. A CASE STUDY FROM THE LOWER PERMIAN OF THE SOUTHERN ALPS (ITALY)

Vertebrate tracks are linked to the depositional environment where they were formed. Several studies hypothesized a paleoenvironmental control on vertebrate track ichnocoenoses, although this issue was never analyzed thoroughly. A new study of the sedimentology and tetrapod ichnology of two key stratigraphic sections in the Pizzo del Diavolo Formation of the lower Permian continental Orobic Basin of Southern Alps (Italy) tested the link between tetrapod ichnocoenoses and depositional environment. Behavior, taphonomy, and ichnocoenoses of three different lithozones (P-PDV, U-PDVa, U-PDVb) were analyzed and compared, two new census methods for tetrapod tracks were tested (“track/slab” and “weighting size”) and the first was applied to our specimen sample. The possible biostratigraphic meaning of track occurrences/relative proportions were discussed and excluded. Results indicate a predominance of the ichnogenus Erpetopus in a distal floodplain environment (P-PDV), a diverse ichnocoenosis in a proximal floodplain environment (U-PDVa), and a predominance of the ichnogenus Dromopus in a scarcely diverse ichnocoenosis in a floodplain/marginal lacustrine environment (U-PDVb). This encourages further detailed studies on tetrapod track paleoecology, in order to refine and give utility to the concept of tetrapod ichnofacies.

Vertebrate and Invertebrate Trace Fossils in the Late Pennsylvanian (Carboniferous) Fluvio-Lacustrine San Giorgio Basin (South-West Sardinia): Remarks on the Oldest Continental Ichnoassociation of Italy

ABSTRACTA new study of the ichnotaxonomy and palaeoecology of the Late Pennsylvanian San Giorgio Basin's trace fossils was carried out. The tetrapod tracks were attributed to Batrachichnus salamandroides and to indet. tracks with a possible small temnospondyl and/or lepospondyl affinity. The invertebrate trace fossils include locomotion traces (Diplichnites isp.), grazing traces (Cochlichnus anguineus), and feeding structures (Treptichnus bifurcus, Treptichnus isp.). The trace fossils were evaluated by means of ichnofacies, highlighting a transitional Scoyenia-Mermia ichnofacies, typical of Carboniferous freshwater settings. The trace fossil co-occurrence and taphonomy was utilized to give a new interpretation of the fossil-bearing lithofacies, which are dolomitic mudstones-fine sandstones expression of marginal lacustrine environments repeatedly subject to flooding (three different ichnoassociations highlight different bathymetry/emersion). This is the oldest continental ichnoassociation of Italy, and its moderately high diversity and complexity suggest further study of this important Carboniferous trace fossil locality.

Late Carboniferous Tetrapod Footprints from the Souss Basin, Western High Atlas Mountains, Morocco

ABSTRACTThe Late Carboniferous Souss Basin of south-central Morocco exhibits an approximately 1,800 m thick succession of fluvial and lacustrine deposits that have yielded diverse fossil remains of plants, insects, conchostracans, ostracods, jellyfish, fishes, and few tetrapod footprints. Recent exploration of ichnofossils of the Souss Basin led to the discovery of several trampled surfaces including tetrapod footprints assigned to the plexus Batrachichnus (Woodworth, 1900). Limnopus (Marsh, 1894), Dimetropus (Romer and Price, 1940), and Ichniotherium (Pohlig, 1892). These footprints can be referred to temnospondyl, basal synapsid (“pelycosaurian”), and diadectomorph trackmakers. The moderately diverse tetrapod footprint assemblage from the Souss Basin is important because it is the second-oldest record of tetrapod footprints from Africa and only the second record of the well-known ichnogenus Ichniotherium from outside of North America and Europe. Based on the variety of tetrapod tracks and previously collected floral and insect remains, the Souss Basin must have represented a well-established continental ecosystem during the Late Carboniferous.

Korean trackway of a hopping, mammaliform trackmaker is first from the Cretaceous of Asia

A trackway of a small hopping mammaliform trackmaker from the Jinju Formation (Lower Cretaceous) of the Jinju City area, Korea, is the first of this type reported from the Mesozoic of Asia, and globally. The animal left a narrow trackway (∼20 mm wide) with small tetradactyl footprints averaging less than 10 mm in diameter. Only two footprints registered with each hop (mean length 41 mm) thus indicating a bipedal gait. All trackway evidence suggests a small “mouse-like” trackmaker. Previous reports of trackways made by hopping tetrapods from the Mesozoic are rare and presently restricted to ichnogenus Ameghinichnus isp. indet., from the Jurassic of Argentina. Ichnogenus Musaltipes from the Cenozoic of North America, is the only other ichnogenus representing a hopping mammal. The Korean specimen here named Koreasaltipes jinjuensis, is different from these aforementioned ichnogenera in digit count, digit proportion and trackway configuration, as well as lack of tail trace. Koreasaltipes jinjuensis is from a lake shore paleoenvironment associated with nematode tracks (Cochlichnus isp.), other small tetrapod tracks attributed to avian theropods (birds), pterosaurs and crocodylomorphs, as well as larger saurischian dinosaurs.

Middle-Upper Triassic and Middle Jurassic tetrapod track assemblages of southern Tunisia, Sahara Platform

Three tetrapod track assemblages from the early-middle Mesozoic of southern Tunisia are reported. The strata exposed at the Tejra 2 clay-pit near the Medenine and Rehach site, located in the vicinity of Kirchaou, contain the first tetrapod tracks found in the Triassic of Tunisia. The Middle Jurassic (early Aalenian) dinosaur tracks are reported from the Mestaoua plain near Tataouine. In the Middle Triassic outcrop of the Tejra 2 clay-pit, tridactyl tracks of small and medium-sized dinosauromorphs, were discovered. These tracks represent the oldest evidence of dinosaur-lineage elements in the Triassic deposits of Tunisia. Similar tracks have been described from the Middle Triassic of Argentina, France and Morocco. An isolated set of the manus and pes of a quadrupedal tetrapod discovered in Late Triassic Rehach tracksite is referred to a therapsid tracemaker. The Middle Jurassic deposits of the Mestaoua plain reveal small and large tridactyl theropod dinosaur tracks (Theropoda track indet. A-C). Based on comparison with the abundant record of Triassic tetrapod ichnofossils from Europe and North America, the ichnofauna described here indicates the presence of a therapsid-dinosauromorph ichnoassociation (without typical Chirotheriidae tracks) in the Middle and Late Triassic, which sheds light on the dispersal of the Middle-Upper Triassic tetrapod ichnofaunas in this part of Gondwana. The reported Middle Jurassic ichnofauna show close similarities to dinosaur track assemblages from the Lower and Middle Jurassic of northwestern Africa, North America, Europe and also southeastern Asia. Sedimentological and lithostratigraphic data of each new tracksite have been defined on published data and new observations. Taken together, these discoveries present a tantalizing window into the evolutionary history of tetrapods from the Triassic and Jurassic of southern Tunisia. Given the limited early Mesozoic tetrapod record from the region, these discoveries are of both temporal and geographic significance.

A new tetrapod ichnotaxon from Botucatu Formation, Lower Cretaceous (Neocomian), Brazil, with comments on fossil track preservation on inclined planes and local paleoecology

Botucatu Formation is a paleoerg, worldwide famous for its vertebrate and invertebrate ichnofossils. Among Botucatu Formation tetrapod tracks, ichnogenus Brasilichnium Leonardi, 1981 is well known, being generally attributed to mammaliform trackmakers. In this study a new ichnotaxon is described, Brasilichnium saltatorium isp. nov., characterized by a hopping locomotion in phases. The new ichnotaxon differs from B. elusivum Leonardi, 1981 mainly for the locomotion pattern. It also differs from other ichnotaxa by indicating hopping progression regarding limb morphology and track configuration. Fossil evidence shows B. saltatorium and B. elusivum could be produced by the same organism and represent an alternation in locomotory behavior. Neoichnological experiments were conducted to better understand track preservation and aspects of saltatorial dynamics on inclined planes. It was observed differences in heteropody degree may be related to movement direction and locomotion effort on ascending or descending the incluned plane. Due to extramorphological features, heteropody is more evident when the producer climbs the simulated dune. Also, when the movement is ascendent, lack of handprints can occur. This can be explained by total overlap of pes and manus impression and subsurface hand impression. Comparing with recent organisms living in similar environments and conditions, the Botucatu Formation B. saltatorium producer should have been a generalist organism likely with an omnivorous habit. It may have adopted hopping locomotion to gain velocity when hunting, escaping predators, or to facilitate progression on inclined planes and hot sand. São Bento quarry represents a paleodesert environment with relative high humidity, where temporary lagoons may have formed during pluvial events. Paleo-rain episode evidence is preserved through raindrops impact craters on local sandstone. São Bento quarry paleoenvironment sustained a rich paleofauna, represented by abundant ichnofossils. This local diversity suggests a punctual productive desert paleocommunity with several paleoecological interactions, where Brasilichnium producer was one of the fundamental elements.

New Middle Jurassic dinosaur track record from northeastern Sichuan Province, China

Two relatively small tridactyl tracks from the Middle Jurassic Xintiangou Formation of northeastern Sichuan are assigned to cf. Anomoepus based on low length/width and anterior triangle ratios, and a relatively short step and inward rotation of the footprint axes. Anomoepus is typical of many Middle Jurassic dinosaur-dominated ichnofaunas from central and southern China and appears to be allied to the globally widespread Lower Jurassic tetrapod track biochron.

Early Cretaceous dinosaur and other tetrapod tracks of southwestern China

In recent years the Lower Cretaceous red beds of southwestern China have yielded more than 20 significant dinosaur-dominated tracksites. More than half occur in the Jiaguan Formation with the remainder in the Feitianshan and Xiaoba formations. Collectively these sites provide evidence of at least 13 distinct dinosaurian trackmaker morphotypes, in addition to two avian theropod (bird) morphotypes and pterosaur and turtle tracks. Together these total 17 morphotypes provide a data base of 479 potential trackmakers, probably representing the same number of individuals. Such an ichnological database provides a useful proxy paleoecological census of tetrapod communities in the area during the Early Cretaceous, and is especially significant given the complete absence or scarcity of skeletal remains reported from these formations. The composition of ichnofaunas in all three formations is heavily saurischian (theropod and sauropod) dominated with a high diversity of distinctive theropod morphotypes, mostly assignable to known ichnogenera. Moreover, ichnofaunal data from multiple sites are generally consistent between sites and an indication of the reliability and repeatability of track census data. Such regionally-widespread data are rapidly superseding the information available from the skeletal record in the corresponding area, and must therefore be considered of high paleontological value.

Swimming Reptile Tracks in the Lower Triassic Moenkopi Formation, Capitol Reef National Park, UT

Abundant pre-dinosaurian tetrapod tracks, ichnofossil Chirotherium, have been found in the Moenkopi Formation. Swimming reptile tracks are found in the Torrey Member of the Moenkopi Formation in Capitol Reef National Park near Torrey, Utah. The tracks are preserved in a fine-grained sandstone deposited on a flat-lying coastal plain.

A diverse saurischian (theropod–sauropod) dominated footprint assemblage from the Lower Cretaceous Jiaguan Formation in the Sichuan Basin, southwestern China: A new ornithischian ichnotaxon, pterosaur tracks and an unusual sauropod walking pattern

A sample of fallen blocks of fluvial sandstone from the Lower Cretaceous Jiaguan Formation of Sichuan Province yielded an assemblage of dinosaur and pterosaur tracks preserved as natural impressions and casts. Collectively the assemblage reveals 132 tracks representing at least 30 trackways of tridactyl and didactyl theropods, sauropods, ornithopods and pterosaurs. Ichnotaxonomically, the trackways of small tridactyl theropods (pes lengths 7–18 cm) are indeterminable, whereas the trackway of a small didactyl dromaeosaur (pes length up to 7.5 cm) is tentatively assigned to cf. Velociraptorichnus. The sauropod trackways are assigned to cf. Brontopodus based on the medium to nearly wide-gauge pattern. Other characteristics are the U-shaped manus and strong heteropody. One sauropod trackway shows a peculiar pattern with a lack of left manus imprints, and an unusual position and rotation of right manus imprints. Different scenarios and explanations for this phenomenon are discussed. Ornithopod trackways are the most abundant in the sample and characterized by pes imprints of a small biped that are assigned here to the new ichnospecies Caririchnium liucixini. It is characterized by an unusual broad shape and weak mesaxony. Bivariate analysis of different Caririchnium ichnospecies reveals increasing mesaxony toward the larger forms, a trend that is the reverse of typical theropod ichnotaxa, where large imprints have weak mesaxony. Three isolated, small pterosaur tracks (two manus, one pes) are visible on a single surface. They show strong similarities to the widespread ichnogenus Pteraichnus. This is the ninth report of tetrapod tracks from the Jiaguan Formation in recent years and represents one of the most diverse assemblages recorded to date. It is also rare evidence of typical didactyl dromaeosaur tracks and the co-occurrence of sauropod and ornithopod tracks in a fluvial depositional environment representing arid climate conditions.

Thinopus and a Critical Review of Devonian Tetrapod Footprints

Devonian tetrapod tracks and trackways can be recognized by three criteria: morphology of the manus and pes impressions that matches known Devonian tetrapod skeletal morphology, manus smaller than pes, and the alternating trackway pattern that results from lateral sequence walking in quadrupedal tetrapod locomotion. The first reported Devonian tetrapod track, named Thinopus antiquus, from Pennsylvania, is not a tetrapod track and is likely an impression of a fish coprolite(s). A critical review of the published Devonian track record indicates only three can be verified as produced by a tetrapod trackmaker—Genoa River, Australia; Easter Ross, Scotland; and Valentia Island, Ireland. The supposed tetrapod tracks from the Middle Devonian of the Zachełmie quarry, Poland, fail the criteria for identification as Devonian tetrapod tracks. Indeed, no convincing case has been made that the Zachełmie structures are tetrapod tracks. Instead, they are reinterpreted as fish nests/feeding traces (ichnogenus Piscichnus). The oldest Devonian tetrapod trackway is Givetian and this is the oldest record of a tetrapod, but the sparse record of Devonian tetrapod tracks is of no other biostratigraphic and little paleobiogeographic significance. Bona fide Devonian tetrapod tracks are from nonmarine facies, so they do not support a marginal marine origin of tetrapods. They indicate lateral sequence walking and pelvic-limb-propelled, fully terrestrial (subaerial) locomotion in freshwater environments by at least some Devonian tetrapods.

Mid-Carboniferous diversification of continental ecosystems inferred from trace fossil suites in the Tynemouth Creek Formation of New Brunswick, Canada

We report Skolithos, Scoyenia and Mermia Ichnofacies from sub-humid tropical fluvial megafan deposits in the Lower Pennsylvanian Tynemouth Creek Formation of New Brunswick, Canada, and discuss their evolutionary and palaeoecological implications, especially regarding the colonization of continental freshwater/terrestrial environments. The Skolithos Ichnofacies comprises annelid/arthropod spreite in the upper storey of a fluvial channel. The Scoyenia Ichnofacies comprises tetrapod tracks, arthropleurid trackways, and shallow annelid/arthropod burrows in active/abandoned fluvial channels and rapidly aggrading levees/splays in proximal interfluve areas. The Mermia Ichnofacies comprises abundant xiphosuran trackways, along with diverse traces of other arthropods, annelids, mollusks, and fish, in shallow freshwater lakes, ponds, and coastal bays in slowly aggrading distal interfluve areas. Transitional Mermia/Scoyenia Ichnofacies comprise tetrapod, mollusk and annelid/arthropod traces in coastal bay deposits on the distal edge of the megafan. These trace fossil suites (1) provide the clearest documentation yet of the mid-Carboniferous diversification event, when tropical continental environments became more densely populated; (2) suggest that euryhaline visitors (xiphosurans, microconchids, and other taxa) from open marine settings played a key role in this episode of freshwater colonization; and (3) provide empirical support for the “Déjà vu Effect”, the evolutionary concept that new or empty ecospace, recurrent in spatially and temporally variable environments, is colonized by simple ichnocoenoses.

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 r...