Where in the World is Rotodactylus?

Rotodactylus ichnites (Peabody 1948, Lower Triassic, Moenkopi Formation, Arizona, Utah; Grès d’Antully Formation, France, Middle Triassic Haizer-Akouker Unit at the Belvédčre (Bkherdous) locality in Algeria; Fig. 1) are distinguished from all others by the impression of pedal digit 5 far behind the other asymmetric digitigrade toes.

Peters (2000) matched Rotodactylus tracks to basal fenestrasaurus, including Cosesaurus (Fig. 2). We can also include a Cosesaurus sister, Langobardisaurus, as a possible trackmaker, following several days of Langobardisaurus news here and here. We can probably also include Pteromimus and Amotosaurus, more sisters to Langobardisaurus and Cosesaurus.

Cosesaurus and Rotodactylus, a perfect match.

Figure 1 Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

Here (please check this link) is a good Rotodactylus track along with a model of a  Cosesaurus-like hypothetical trackmaker. Note pedal digit 5 does not include an ungual imprint, as the model indicates it should and Peabody (1948) noted. No, the pedal 5 imprint is a smal round impression, the sort made by the impression of the dorsal side of a flexed interphalanageal joint, as in pterosaurs.

Cosesaurus foot in lateral view matches Rotodactylus tracks.

Figure 2. Cosesaurus foot in lateral view matches Rotodactylus tracks. The center of balance is over the anterior toes. Digit 5 was more like a kickstand bouncing and flexing with each step but distant from the weight-bearing digits.

Amy Barth of Discover magazine reported, “Rotodactylus is believed to be a dinosaur or a surviving dinosaur ancestor that lived just after dinos and crocodilians split into separate branches.” This is the traditional consensus, following the paper by Brusatte et al. (2011) even though no archosaur had an elongated digit 5. She reported, “Footprints in southern Germany, for example, may extend the entire dinosaur lineage back four to five million years. The tracks were formed 240 to 245 million years ago by a cat-size reptile called Rotodactylus, known from its footprints alone; no bone evidence of dinosaurs dates this far back, says paleontologist Hartmut Haubold of Martin Luther University in Halle-Wittenberg, Germany.”

The Triassic World with Rotodactylus areas in pink.

Figure 4. The Triassic World with Rotodactylus areas in pink.

Rotodactylus in white along with other Triassic tracks in red

Figure 3. Rotodactylus in white along with other Triassic tracks in red. Even the manus of this specimen extended posteriorly, but also notice, you see the tip of the digit, unlike the pes.

Thirty years ago Harmut Haubold (1983) reported, “Rotodactylus somewhat resemble those of Lagosuchus (Marasuchus). Trackway pattern shows relatively broad trackways, pes angulation up to 160°, and very long stride from which results overstep of manus by pes  impressions. Stride and trackway pattern show an extremly variable speed, something quite rare in reptilian trackways generally.”

Haubold continues, “The digit group II-IV is subparallel and closed-together. Digits I and V are only impressed as points, V in the characteristic heel-like backward position. The only reasonable interpretation, seems to be that these animals belonged to an ear!y specialised thecodontian group. The pes joint was probably mesotarsal because,  of the very digitigrad impressions and the closed digit group II-IV, but possibly it showed the transitional lacertoid and rabbit-like habit, as in Lagosuchus, the most ‘similar’ genus of Middle Triassic age. Rotodactylus may be characterised as a progressive lacertoid type.”

Here Lagosuchus nests as a theropod with pedal digit 3 far exceeding digit 4 and digit 5 was absent a far cry from the ichnite Rotodactylus. Cosesaurus and Langobardisaurus are better matches.

Paleontologists see Rotodactylus as digitigrade and consider it archosaurian, close to dinosaurs. They also note that digit 4 is longer than digit 3, which occurs in lizards, proterosuchians and protorosaurs, far from dinosaurs. The presence of pedal digit 5 also knocks archosaurs, out of contention. What we’re looking for is a match on all counts. Such a match occurs in basal fenestrasaurs.

Rotodactylus tracks have been found from the US southwest to central Europe and Algeria (Fig. 3). That’s a large area and it increases hope that more Pteromimus/Langobardisaurs/Cosesaurus-types will be found someday as fossils in this zone.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Brusatte SL Niedźwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Demathieu G and Gand G 1973 Deux espèces ichnologiques nouvelles des Grès à Empreintes du Trias du Plateau d’Antully [Two new ichnological species from the Triassic Grès à Empreintes of the Antully plateau]. Bulletin Trimestriel de la Société d’Histoire Naturelle et des Amis du Muséum d’Autun 67:11-27
Demathieu G and Gand G 1974. Une nouvelle espèce du genre Rotodactylus découverte dans les grès du Trias moyen du plateau d’Antully: Rotodactylus velox [A new species of the genus Rotodactylus discovered in the Middle Triassic sandstones of the Antully plateau: Rotodactylus velox]. Bulletin Trimestriel de la Société d’Histoire Naturelle et des Amis du Muséum d’Autun 72:9-23
Ellenberger P 1970. Les niveaux paléontologiques de première apparition des mammifères primoridaux en Afrique du Sud et leur ichnologie. Establissement de zones stratigraphiques detaillees dans le Stormberg du Lesotho (Afrique du Sud) (Trias Supérieur à Jurassique) [The paleontological levels of the first appearance of primordial mammals in southern Africa and their ichnology. Establishment of detailed stratigraphic zones in the Stormberg of Lesotho (southern Africa) (Upper Triassic to Jurassic). In: S. H. Haughton (ed.), Second Symposium on Gondwana Stratigraphy and Paleontology, International Union of Geological Sciences. Council for Scientific and Industrial Research, Pretoria 343-370.
Haubold H 1983. Archosaur evidence in the Buntsandstein (Lower Triassic) Acta Palaeontologica Polonica 28 (1-2), 1983: 123-132.
Peabody FE 1948. Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah. University of California Publications, Bulletin of the Department of Geological Sciences 27(8):295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.