First sorry for my poor English, my Mother Tongue is French.

Perhaps (probably) some of you already know these finds and the papers that describe. These finds are Birds-Like fossil footprint from the late Triassic.

The first description of these footprints were published in a Nature’s Paper in 2002.

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 150Myr 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 birds7. 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 55Myr 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.

Ricardo N. Melchor, Silvina de Valais & Jorge F. Genise, Bird-like fossil footprints from the LateTriassic, Nature 2002

These footprintsare very bird-like because we can see a probably reversed Hallux. But there’s a problem these footprints are dated from the Triassic period perhaps  the lower Jurassic period.

Note, the footprints show en reversed Hallux but in the Nature’s Paper the Argentina team says that the Hallux is probably not in a position adapted for  perching.

The shallow hallucal impression, commonly disconnected with the rest of the foot, suggests that the hallux contacted the ground, but that it was slightly raised and probably not adapted for perching as in some  birds.

Ricardo N. Melchor, Silvina de Valais & Jorge F. Genise, Bird-like fossil footprints from the Late Triassic, Nature 2002

Some people in the dinosaur mailing list proposed that the animal who made these  footprints can be a unknow Heterodontosauridae. After all Heterodontosauridae  have convergent characters with modern birds, like a tarsometatarsus, so perhaps  some unknow Heterodontosauridae have also a reversed Hallux.

But  recent studies of the footprints reveal another unsettling thing. According to  the Argentina Team the animal that makes these footprints was capable of  flight!

The purpose of this study is to apply neoichnological observations to the behavioural and taphonomic interpretation of a Late Triassic–Early Jurassic track surface from the Santo Domingo Formation (Argentina) containing hundreds of bird-like tracks and trackways. In addition, the factors affecting the formation and preservation of bird tracks in lacustrine settings are particularly addressed. The 5.5 m2 fossil track surface contains different types of trace fossils: the avian ichnotaxa Gruipeda dominguensis (the most abundant), bird-like tracks with elongated hallux impressions, small epichnial rounded pits, and invertebrate traces (Skolithos, Taenidium). The modern environmental analogue chosen for the neoichnological studies was a coastal freshwater pond (the Bajo de los Huesos, Chubut, Argentina) seasonally occupied by sandpipers (Calidris bairdii and Calidris fuscicollis; Charadriiformes). The comparison  between the fossil succession and the modern example suggests that they share lithology and sedimentary structures and that sedimentary processes and local palaeoenvironment were fairly similar and do not bias ichnological comparisons.  Field observations allowed to distinguish twenty one behaviours that produced  distinct traces and four modern footprint types (1 to 4) related to specific  substrate conditions. In particular, the preferential formation of bird tracks  parallel to the waterline, also confirmed by studies on droppings and  invertebrate fauna of the pond, and other associated sedimentary features  (ripple marks, wrinkle marks, mud drape thickness) and trace fossils were important for recognition of the shoreline in the fossil example. These  observations also allowed us to distinguish the adjacent deeper and shallower  parts of the fossil pond and can be applicable to other similar case studies.  Contrasting sediment properties and footprint types, some relationships and  constraints on the formation and preservation of modern footprints are proposed;  although these are very complex processes that will require further studies.  Five of the behaviours recognised in the modern pond were inferred from the sixteen trackways distinguished on the fossil track surface, including walking, walking with a zig-zag path, short runs, probing, and landing with legs directed  forward (possible trace of flight). The recognition of traces of flight  (Volichnia), probing marks, and tracks showing morphology similar to modern  shorebirds (G. dominguensis), strongly suggest an avian affinity for the  producers of the fossil tracks and, in consequence, the Santo Domingo track site would be younger than supposed.

Jorge F. Genise , Ricardo N. Melchor, Miguel Archangelsky, Luis O. Bala, Roberto Straneck, Silvina de Valais, Application of neoichnological studies to behavioural and taphonomic  interpretation of fossil bird-like tracks from lacustrine settings: The Late  Triassic–Early Jurassic? Santo Domingo Formation, Argentina, 2008

The authors of this paper suggest that the footprints would be younger but nothing seems indicate the tracks would be younger than supposed.

The studied fossil track site is located in the Quebrada (gulch) de Santo Domingo situated in the Reserva Provincial Laguna Brava, in the precordillera of La Rioja Province, Argentina. The track surface belongs to the Santo Domingo Formation, which is considered of Late Triassic– Early Jurassic age. This age is based on characteristic fossil wood remains (Caminos et al., 1995), on a 40Ar/39Ar radiometric age from interbedded basalt flows (Coughlin, 2001), and palaeomagnetic studies (Vizán et al., 2005). The formation reaches a minimum thickness of c. 1950 m and is in fault contact with Carboniferous igneous and sedimentary rocks (Caminos and Fauqué, 2001). The Santo Domingo Formation is a red bed succession that displays, from base to top, a transition fromalluvial fan, fluvial braided (with calcretes), ephemeral fluvial and shallow lakes, and eolian environments (Vizán et al., 2005). The described track surface with bird-like footprints was recorded from a succession from the upper part of the Santo Domingo Formation, which had been interpreted as an ephemeral fluvial system. The main track surface is located at 1650mfrom the base of the section, a second trampled surface with similar tracks has been recorded, although not studied to date.

Jorge F. Genise , Ricardo N. Melchor, Miguel Archangelsky, Luis O. Bala, Roberto Straneck, Silvina de Valais, Application of neoichnological studies to behavioural and taphonomic interpretation of fossil bird-like tracks from lacustrine settings: The Late Triassic–Early Jurassic? Santo Domingo Formation, Argentina, 2008

As some of you can guess, some BAND (Birds Are Not Dinosaurs) think that these footprints prove that advanced birds already existed in the Triassic period and that the dino-bird theory has to face to a important challenge.

I have personallyno doubt that birds are dinosaurs but I don’t know what to think about these footprints. Are the birds originate from the Triassic period or is there a unknown archosaur with some convergences with modern birds? But most important, has the Argentina team proved that the animal that made these footprints was capable of flight? The Argentina team says that the drag mark of the hallux that we can see in some footprints, is a proof of landing and so a proof of ability of flight.

In another paper published in PLoS ONE, I noticed that other theropod’s footprints with a possibly reversed Hallux were described.

Anchisauripus was thought to differ from either Grallator or Eubrontes by possessing a short, caudally-directed hallux impression that was frequently detached from the remainder of the print [43], but this has been interpreted (based on a specimenmisidentified as the holotype [38]) as a fragment of a mud crack that intersectsthe impression [46]. However, in modern bird tracks, digit impressions,including the hallux, have been known to precipitate mud cracks.

Andrew R. C. Milner, Jerald D. Harris, Martin G. Lockley, James I.
Kirkland, Neffra A. Matthews, Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace, PLoS ONE 2009

I know  that we can’t have a definitive answer without new discoveries.  But I’m interested by your opinions about these footprints and the possible ability of flight of the animal that made these footprints (the footprints of Argentina).

Thank you for reading this long message.

Genise et al 2009 interpret a landing trace among the tracks due to a couple of traces with elongated halux impressions.  I've seen traces like this several times, including mid-way along a trackway, so would be rather more cautious about interpreting landing behaviour from such tracks, and perhaps instead interpreting them as something else, maybe a claw drag mark from unusual limb kinematics.  Sediment properties can vary so locally that trackways can come and go and tracks can change in morphology without any change from the animal.

Having said that, the tracks really do look very avian.  But then most small theropod tracks do - in particular some of the small Amherst tracks from the early Jurassic look quite similar.  And I've definately seen a lot of theropod tracks of all sizes with a reverse halux.

As someone who specialises in dinosaur tracks, I'm among the first to urge caution in interpreting behaviour from tracks.  These are very interesting tracks, but personally I would be very wary of stating flight abilities 


HOWEVER I have not seen these tracks in person, and only have figures to work with so I would not want to openly and fully disagree with the author's interpretation outside of the literature.

[edit] Also, remember they are comparing behaviour with tracks made by pretty derived wading birds (Calidris. sp.).  How comparable are the traces associated with given behaviours between Sandpipers and ancestral birds/dinosaurs.

[Edit 2] Finally, The elongated halux impressions interpreted as landing behaviour could equally be produced from a small hop or jump.

So basically, you summed it up nicely yourself; these are very interesting tracks and raise some interesting questions, but aren't conclusive on their own.

Last edited by Peter Falkingham (1st Oct 2010 15:22:21)