Ricardo N. Melchor

Ichnotaxonomy of Bird-Like Footprints: An Example from the Late Triassic-Early Jurassic of Northwest Argentina

Abstract The ichnotaxobases previously used to classify avian-like footprints, at the ichnogeneric, ichnospecific, and ichnofamily level, are varied and contrasting. Consequently, an agreement on the most adequate taxobases to use for classifying these vertebrate trace fossils is necessary. The authors follow an ichnotaxonomy treatment independent to the age, locality provenance, and possible tracemaker of the trace fossils. The ichnotaxobases used to classify tracks with avian affinities at ichnogeneric and ichnospecific levels are evaluated and a proposal is made for useful and appropriate ichnotaxonomic criteria, considering those currently in use. Previous criteria used to distinguish avian footprints from non-avian theropod or ornithischian tracks are discussed. These concepts are applied to the avian footprints from the upper part of the Late Triassic-Early Jurassic Santo Domingo Formation from La Rioja province, northwest Argentina, which has yielded a diverse assemblage of trace fossils. The most conspicuous avian footprint is Gruipeda dominguensis isp. nov. The ichnogenus Gruipeda Panin and Avram, 1962 is revised and an emendation of its diagnosis is suggested. Trisauropodiscus Ellenberger, 1972, from South Africa and Antarctichnus Covacevich and Lamperein, 1970 from Antarctica are considered as junior synonyms of Gruipeda. Three other morphotypes of avian footprints are left under open nomenclature: one is assigned as cf. Alaripeda isp., other as bird-like footprints type C, and the third bird-like footprint with elongated drag marks. These specimens could be related to avian origin, but the possibility of a case of convergence with birds is not discarded. The presence of tracks with a wide total divarication produced in ephemeral fluvial systems with shallow ponds and mudflats suggest that it is likely the attainment of a convergent avian-form feet to improve controlled movements.

Ichnology, Sedimentology and Paleontology of Eocene Calcareous Paleosols From a Palustrine Sequence, Argentina

Abstract Integrated analysis of the ichnology, sedimentology, geochemistry, and fossil content of three trace fossil-bearing calcareous paleosols from the early Eocene Gran Salitral Formation is used to reconstruct the detailed paleoenvironmental and paleoecological setting of this insect-dominated ichnofossil association. This continental sequence, located in southwestern La Pampa province (Argentina), is composed of palustrine marls and minor lacustrine mudstones and sandstones arranged in shallowing-upward cycles. The ichnologic association is the first comprehensively described from a palustrine sequence and could be used for future comparisons with other similar assemblages. The ichnofauna is dominated by bee cells, Celliforma germanica, C. roselli, and Rosellichnus isp.; Teisseirei barattinia, an insect trace fossil that is redescribed and recorded for the first time outside its type locality; Taenidium barretti; and Skolithos linearis. The ichnologic association also includes ovoid structures, ornamented burrow fillings, and plant trace fossils (rootlets, rhizoliths, and a tree / shrub stump). Abundant freshwater (Pomacea sp.) and terrestrial gastropods (Plagiodontes spp., Bostryx sp., and Bulimulus sp.) are used to characterize the paleoenvironmental setting. The weakly developed paleosols are interpreted as Inceptisols, developed in a low-gradient lake margin periodically exposed to pedogenesis with low (probably saline) vegetation and sparse shrubs. They developed under a semi-arid and warm climate (mean annual temperature higher than 20°C). Short saline / alkaline conditions were prevalent during lake lowstands, accompanied by incipient karst development. The association of trace fossils is attributed provisionally to the Coprinisphaera ichnofacies, although its distinctive features and recurrence in time and space may deserve recognition as a separate ichnofacies.

Bird-like fossil footprints from the Late Triassic.

The study of fossilized footprints and tracks of dinosaurs and other vertebrates has provided insight into the origin, evolution and extinction of several major groups and their behaviour; it has also been an important complement to their body fossil record. The known history of birds starts in the Late Jurassic epoch (around 150 Myr ago) with the record of Archaeopteryx, whereas the coelurosaurian ancestors of the birds date back to the Early Jurassic. The hind limbs of Late Triassic epoch theropods lack osteological evidence for an avian reversed hallux and also display other functional differences from birds. Previous references to suggested Late Triassic to Early Jurassic bird-like footprints have been reinterpreted as produced by non-avian dinosaurs having a high angle between digits II and IV and in all cases their avian affinities have been challenged. Here we describe well-preserved and abundant footprints with clearly avian characters from a Late Triassic redbed sequence of Argentina, at least 55 Myr before the first known skeletal record of birds. These footprints document the activities, in an environment interpreted as small ponds associated with ephemeral rivers, of an unknown group of Late Triassic theropods having some avian characters.

Small Amphibian and Reptile Footprints from the Permian Carapacha Basin, Argentina

This paper contains a taxonomic study of the Permian tetrapod ichnofauna from the Carapacha Basin. Tetrapod traces are analyzed in their environmental context and compared with similar faunas from Europe and North America. This ichnofauna is particularly relevant because of the scarcity of Permian tetrapod tracks from South America and also of Permian tetrapod fossils from Argentina. Ephemeral fluvial and shallow lacustrine deposits compose the sedimentary succession of the basin, which is represented by the Carapacha Formation. Most of the tracks have been collected from the upper member of the formation (Urre-Lauquen Member), mainly from freshwater ephemeral lake deposits as well as from playa-lake mudflats. The deposits of this member have been attributed to the early Late Permian on the basis of a Glossopteris fossil flora. Ichnotaxonomic designations of tetrapod traces are made on the basis of morphologic features that reflect the anatomy of the producer and special attention has been paid to extramorphologic deformations observed in the track assemblage. A total of four footprint ichnotaxa have been recognized, namely Batrachichnus salamandroides (Geinitz, 1861), Hyloidichnus bifurcatus Gilmore, 1927, cf. Amphisauropus isp. and cf. Varanopus isp. These track taxa are associated with two forms of vertebrate swimming traces (Characichnos isp. and type A swimming trace) and a possible fish trail. Invertebrate trace fossils include abundant arthropod locomotion traces and Scoyenia isp. The ichnofauna is composed of six tetrapod ichnocoenoses that are dominated by tiny amphibian tracks attributed to Temnospondyli (Batrachichnus and type A swimming trace) and Seymouriamorpha (Amphisauropus), and also contain the footprints of small reptiles, mostly Captorhinomorpha and possibly Pelycosauria (Hyloidichnus and Varanopus). Even if the ichnofauna of the Carapacha Basin is slightly younger than typical examples from the literature of the Early Permian “red bed ichnofacies” (Hunt et al., 1995b), a comparison is made. However, further detailed case studies are needed to formally define this “red bed ichnofacies” and its prospective subdivisions.

Spongeliomorpha in nonmarine settings: an ichnotaxonomic approach

The authors revise the occurrences of burrow networks with striated walls having dominantly transverse to oblique striae, which have been assigned to the ichnogenera Spongeliomorpha Saporta, 1887, and Steinichnus Bromley & Asgaard, 1979. The taxonomic status of the ichnogenus Steinichnus Bromley & Asgaard, 1979 is examined and it is suggested that this ichnogenus is a subjective junior synonym of Spongeliomorpha Saporta, 1887. Spongeliomorpha is best reserved for an unlined network of burrows having distinct surface ridges or grooves of different orientation and massive filling. The diagnosis of Spongeliomorpha is emended accordingly and the proposed ichnospecies revised for consistency with the diagnostic features of the ichnogenus. Spongeliomorpha milfordensis Metz, 1993a is considered a subjective junior synonym of Spongeliomorpha carlsbergi (Bromley & Asgaard, 1979) after a visual comparison and statistical analysis of the angle of striation with respect to the burrow midline in the type material. Nevertheless, the use of statistical techniques is not advocated for distinction of ichnotaxa, but may support observations. Spongeliomorpha carlsbergi is considered as an indicator of nonmarine settings and was probably produced by burrowing insects. Proposed ichnospecies of Spongeliomorpha that fit the emended diagnosis include S. sudolica (Zareczny, 1878); S. iberica Saporta, 1887; S. sicula D’Alessandro & Bromley, 1995; S. chevronensis Muniz & Mayoral, 2001; and Spongeliomorpha isp. nov. aff. sicula Lewy & Goldring, 2006.

Tectonic implications of post-folding Permian magnetizations in the Carapacha Basin, La Pampa province, Argentina

Paleomagnetic results from Permian clastic and igneous rocks of the Carapacha Basin of the Gondwáides orogenic zone of central Argentina are mainly consistent with results reported previously from the same zone further east, e.g., in the Sierra de la Ventana. Three lithologic entities were analysed: the lower member and upper member of the Carapacha Formation, and an andesite intrusive into the upper member. The directions of their characteristic remanences are similar, differ significantly from the present field direction, and are post-folding. The in situ magnetization directions are moreover consistent with directions expected for late Permian poles of the APWP for South America. The in situ pole for the lower Carapacha Formation is 70°S, 049°E, A95=11° (San Roberto pole); the pole for the upper Carapacha, combined with similar directions from the intrusive, is 64°S, 005°E, A95=5° (Río Curacó pole). These magnetizations imply that the Carapacha Formation, with a minimum age of early Late Permian (about 260 Ma.), was deformed before the end of the Permian. Structural evidence, as well as paleomagnetic, IRM, and AMS experimental results, support the interpretations. The paleogeographic implications of these results are interpreted as a significant counterclockwise movement of Gondwana between the early and the late Permian.

Comment—Advanced Early Jurassic Termite (Insecta: Isoptera) Nests: Evidence from the Clarens Formation in the Tuli Basin, Southern Africa (Bordy et al., 2004)

“The characteristics of termite nests are better understood if the main requirements of these insects are kept in mind (Noirot, 1970, p. 102). More than the gross architecture, some details may be significant…A very precise description of the chambers and galleries would be necessary…” (Noirot, 1977, p. 179) Insect paleoichnology, being a young discipline, needs to gain acceptance and recognition as a sister counterpart of paleoentomology and entomology. Accordingly, the analyses and discussions to ascertain the attribution of continental trace fossils to insects should be carried out very carefully. Such analysis (e.g., Machado, 1983; Sands, 1987) for fossil termite nests, which is lacking in the recent contribution by Bordy et al. (2004) on supposed Jurassic termite nests, is critical, because their results are at odds with our previous knowledge of the evolutionary history of termites and their relationship with coevolving groups of plants and fungi. Many invertebrate trace fossils are more preservable than their constructors are. For example, fossil bee nests predate the oldest known bees by about 25 My (Elliot and Nations, 1998; Genise, 2000; Engel, 2000), which is an expected gap. In contrast, the gap between the oldest termites, which come from the Lower Cretaceous (Jarzembowski, 1981; Martinez-Delclos and Martinell, 1995), and the supposed termite nests described by Bordy et al. (2004) would be about 60 My. However, it is neither the time involved nor the difficulties of imagining fungus-growing termites in an early Jurassic environment deprived of Basidiomycotina and grasses that promoted this comment. Instead, it is the understanding that the description and affinities of the Tuli structures are not treated with the necessary detail and their termitic origin was not demonstrated. Termite nests comprise closed and dynamic systems, largely isolated from the external environment, within which the microclimate can be …

Chapter 7 Invertebrate and Vertebrate Trace Fossils from Continental Carbonates

This chapter presents a review of trace-fossil assemblages from carbonate sediments deposited in continental settings, including carbonate-rich paleosols, lacustrine and eolian carbonates, and examples from travertine and tufas. Carbonate-rich paleosols from the Paleozoic are scarce and trace fossils are mostly only briefly described; Mesozoic examples are more abundant and better studied, although associations of trace fossils cannot now be included in the ichnofacies model because of a lack of recurrence. The Cenozoic shows the largest and best-studied cases of trace fossils in carbonate-rich paleosols. Two Seilacherian ichnofacies can be recognized: the Coprinisphaera ichnofacies, which occurs in paleosols, probably with a relatively lower carbonate content, and the Celliforma ichnofacies, which occurs in deposits with a higher carbonate content. The latter, developed in calcretes and mostly in palustrine carbonates, displays a recurrent association of insect trace fossils dominated by bee and wasp ichnofossils, particularly Celliforma ichnospecies and Rebuffoichnus sciuttoi, associated with freshwater and terrestrial gastropods and hackberry endocarps. Seven cases and three additional possible examples of these assemblages are reviewed in detail. They range in age from Late Cretaceous to Miocene and are known from South and North America, Europe, and Africa. These examples are used to further support an incipient Celliforma ichnofacies. When occurring in calcretes, the Celliforma ichnofacies would be indicative of drier paleoenvironments, such as scrubs to woodlands, than those represented by the Coprinisphaera ichnofacies. When occurring in palustrine carbonates, it would reflect the presence of bare soils exposed after periodic waterlogging under subhumid to sub-arid climates. The examples of trace-fossil assemblages from lacustrine carbonates are more numerous (39 cases cited in this chapter) as well as more varied. These examples can be subdivided into assemblages from carbonate-dominated, mixed carbonate/siliciclastic, and evaporite lacustrine basins. The Mermia ichnofacies is represented by a few cases of subaqueous trace-fossil assemblages. Carbonate microbial/caddisfly mounds constitute a distinctive biogenic structure from carbonate-dominated and wave-agitated littoral lacustrine facies, although no ichnofacies assignment is possible to date. Some cases of intermittently exposed and submerged shallow-lacustrine deposits, where the subaerial exposure was not enough to allow insects to nest, can be ascribed to the Scoyenia ichnofacies. Many trace-fossil assemblages contain tetrapod tracks and invertebrate traces in shallow-lacustrine facies that were frequently exposed and submerged. Some of the Mesozoic examples have been attributed to the Brontopodus ichnofacies, whereas the Cenozoic examples (containing shorebird and mammal footprints) have been regarded as representing the “shorebird ichnofacies” or Grallator ichnofacies. A case assignable to the later ichnofacies, from the Triassic Ischichuca Formation (Argentina), is discussed in more detail. In addition, a few examples of trace-fossil assemblages from Late Cenozoic carbonate eolianites are summarized. One of these examples was tentatively considered as representative of the Psilonichnus ichnofacies.

A Late Eocene date for Late Triassic bird tracks

Arising from R. N. Melchor, S. De Valais & J. F. Genise 417, 936–938 (2002)10.1038/nature00818Bird-like tracks from northwest Argentina have been reported as being of Late Triassic age. They were attributed to an unknown group of theropods showing some avian characters. However, we believe that these tracks are of Late Eocene age on the basis of a new weighted mean 206Pb/238U date (isotope dilution–thermal ionization mass spectrometry method) on zircons from a tuff bed in the sedimentary succession containing the fossil tracks. In consequence, the mentioned tracks are assigned to birds and its occurrence matches the known fossil record of Aves.

Permian floras fromCarapacha Basin, central Argentina. Description and importance

Abstract This paper completes the taxonomic description of the recently discovered Permian “Glossopteris”taphofloras from Carapacha Basin and compares its entire paleofloristic assemblage with other known Permian plant associations from Argentina. Carapacha Basin was a halfgraben located in the southern region of La Pampa province (central Argentina) that received fluvial/lacustrine sediments from Early Permian to Late Permian times. On the basis of their Glossopteris leaves, two paleofloristic associations are recognized. The older Estancia San Roberto (ESR) association contains leaves with scarce and narrow anostomoses, whereas the younger Curaco River (CR) association has glossopterid leaves with distinct and complex anastomoses, plus glossopterid fructifications. In both taphofloras sphenopsid stems, ferns, and petrified gymnosperm wood were also identified. Curaco River association -described in this paper- includes eleven types of glossopterid leaves, as follows: Gangamopteris sp., Glossopteris browniana Brongniart ,, 1828, G. damudica Feistmantel ,, 1881, G. cf. G. euryneura Maheshwari ,, 1965, G. pampeana Melchor & Cesari nov. sp., G. argentina Archangelsky ,, 1958b, G. wilsonii (Seward) Archangelsky et al. 1981, G. communis Feistmantel ,, 1876, G. tortuosa Zeiller ,, 1902, G. cf. G. pandurata Pant & Gupta ,, 1971, and Glossopteris sp. From the same association we also describe scale leaves, Dictyopteridium sp., Neomariopteris sp., Phyllotheca sp., and Cordaites sp. The composition of both associations allows to relate them to the Gangamopteris biozone (ESR association) and Dizeugotheca superzone (CR association) of early Early Permian and late Early Permian to Late Permian age, respectively. In particular, the last association has strong affinities with the exuberant flora from La Golondrina Basin (Patagonia). The paleoflora recovered from Carapacha Basin is meaningful because it is a new permian record from a geographic area with intermediate position among basins of northwest and west Argentina, Buenos Aires Province, Patagonia and Malvinas/Falkland Islands. The compositional differences among these paleofloras can be accounted for paleoenvironmental, local geographic and taphonomic factors. Furthermore, its presence does not support the hypothesis of allochthony of Patagonia for Permian times.