Early Triassic Archosaur-Dominated Footprint Assemblage from the Argana Basin (Western High Atlas, Morocco)

Abstract

An assemblage of abundant and well-preserved tetrapod footprints has been discovered in the Tanamert Member (T3) of the Triassic Timezgadiouine Formation (Argana basin, western High Atlas, Morocco). It is the first fossil record from T3. Surfaces from different localities show a uniform tetrapod ichnofauna that consists of chirotherian and small lacertoid forms. The chirotherians are assigned to the plexus Protochirotherium-Synaptichnium, their trackmakers interpreted as basal archosaurs. The lacertoid imprints show close affinities withRhynchosauroides and may reflect archosauromorphs or lepidosauromorphs. Protochirotherium-Synaptichnium assemblages are characteristic of the Early Triassic and were known previously only from units of this age in central Europe. Biostratigraphically, the European record implies a wide-spread pre-Anisian Protochirotherium-Synaptichnium dominated assemblage preceding the first appearance of Chirotherium barthii near the OlenekianAnisian boundary. The stratigraphic position of T3 between Late Permian (uppermost T2) and Middle Triassic (T4) and the European correlatives suggest an Early Triassic age of this unit. It is the first record of Early Triassic continental deposits in Morocco. The surfaces from T3 open up perspectives for further contributions to ecology, biogeography and locomotion of early archosaurs. Furthermore, excellent outcrops and quality of footprint preservation in the Argana basin offer a potential for clarification of ichnotaxonomic and biostratigraphic issues.

Climate changes during the Early–Middle Triassic transition in the E. Iberian plate and their palaeogeographic significance in the western Tethys continental domain

“…The Ateca-Montalbán High was a geographical boundary with the more humid areas towards the equator, in the E Argana Basin (Morocco). Here, no aeolian sediments were recorded during the Early Triassic (Tourani et al, 2010;Klein et al, 2010). These climate boundaries are consistent with mean annual precipitation simulations by Bourquin et al (2007), indicating more than double precipitation in Argana with respect to the Iberian Plate (from <0.1 mm/day to >1 mm/day) during the Olenekian.…”

The Origin and Early Radiation of Archosauriforms: Integrating the Skeletal and Footprint Record

“…Digits and clawmarks possess medial and lateral striations, documenting the dynamics and movement of the pes in the substrate. All features, especially the shape of digit V and relative length of digit IV, closely resemble those observed in Protochirotherium [47], an ichnogenus particularly abundant in the Lower Triassic deposits of central Europe (Germany and Poland) and northern Africa [32,47–49]. Chirotheriid apomorphies are present in this specimen (e.g., massive posterolateral digit V, compact digit group I–IV), allowing an attribution to the ichnofamily Chirotheriidae [50].…”

“…Supposed archosauriform footprints from the Late Permian of Morocco [31] have recently been redated as Early Triassic [32]. …”

Peer Review #3 of "Archosauriform footprints in the Lower Triassic of Western Alps and their role in understanding the effects of the Permian-Triassic hyperthermal (v0.1)"

“…Manuscript to be reviewed or as long as digit I. However, the first character occurs in archosauriforms and non archosauromorphs diapsids (Haubold, 1971a(Haubold, , 1971bSmith & Evans, 1996) whereas the second is present in archosauromorphs (including non-archosauriforms) and lepidosaurs (Haubold, 1971a(Haubold, , 1971bEvans & Wang, 2005;Gottman-Quesada & Sander, 2009).Other features suggesting an archosaur-grade affinity for chirotherian footprints (observed also in the here described traces), are narrow trackways linked to the disposition of limbs under the body, and the presence of small manus relative to the pes, which indicate a possible early tendency toward bipedal posture and gate (see Haubold, 1971aHaubold, , 1971bHaubold, , 1984Haubold, , 2006Klein et al, 2010).…”