The Lestaillats Marls Formation (Formation des marnes de Lestaillats) is a geological formation in southwestern France whose layers date back to the early late Maastrichtian, approximately 69 to 68 million years ago. It consists of dark marls deposited in a coastal marsh area. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.

Location

The Lestaillats Marls Formation first appeared in the scientific literature in 1999. This formation had not been distinguished in earlier studies, and the vertebrate fossils discovered there in the early 1990s were initially attributed to the Marnes d'Auzas Formation.

The Lestaillats Marls Formation is located in the Plagne anticline in the central part of the Haute-Garonne department (Petites Pyrénées) in Occitania region. As this region is covered with very dense vegetation, outcrops of this formation have mainly been studied in active or abandoned quarries located in particular near the villages of Mauran and Ausseing.

The Lestaillats Marls Formation is the second of the three formations of the Ausseing Group. It overlies conformably the Nankin 2 Limestones Formation and is overlain conformably by the Calcarenites du Jadet Formation. The Lestaillats Marls Formation corresponds to a more continental environment (estuarine marsh) than that of the two underlying and overlying formations deposited in a shallow marine environment.This tripartite subdivision is only present in the Plagne and Saint-Martory anticlines. In the Aurignac anticline, located to the north of the two previous ones, the Lestaillats marls are absent and the layers equivalent to the Ausseing Group are designated as Nankin limestones facies.

Lithostratigraphy and depositional environment The Lestaillats Marls Formation reaches approximately in thickness and is composed solely of gray to black marls, rich in organic matter, and highly bioturbated. These marls can be more or less indurated and contain lignites. The richness of organic matter (indicating a reducing environment), the overabundance of cynenid bivalves (indicator of an environment with variable salinity), the joint presence of euryhaline marine and freshwater fish, plant remains and terrestrial reptiles, make it possible to reconstruct a depositional environment corresponding to an estuarine marsh area.

The Lestaillats Marls Formation was deposited on the west coast of the former Ibero-Armorican island, which included a large part of France and the Iberian Peninsula.. The rocks of the Ausseing Group and the overlying Marnes d'Auzas Formation show the alternation of shallow marine sediments and coastal continental deposits (estuarine and fluvial) corresponding to sea level fluctuations and shoreline shifts during the Late Maastrichtian in this part of the Ibero-Armorican island.

Fossil content

The first vertebrate fossils from the Lestaillats Marls Formation were discovered in 1993 at the Lestaillats 1 site near the village of Mauran in the basal part of the formation. Two excavation campaigns carried out in 1994 and 1997 by a team of the Musée des dinosaures d’Espéraza unearthed numerous vertebrate remains. Other specimens come from the Lestaillats 2 site discovered in 1994. Another site located in the middle part of the formation was discovered in 1997 near the village of Ausseing and excavated in 2000 by the same team. It also yielded a diverse fauna.

The most common vertebrate fossils from the formation belong to undetermined hadrosaurid dinosaurs. Most of the available hadrosaur bones do not allow their definitive attribution to a particular hadrosaur clade, with the exception of an ischium from the Ausseing site which shows characteristics of Lambeosaurinae. Lambeosaurines are the only known Hadrosaurids from the Ibero-Armorican domain and it is likely that the other hadrosaur remains from the Lestaillats Marls Formation belong to this clade. The very good state of preservation of their bones reveals that they did not undergo significant transport before their burial, which indicates that these hadrosaurs probably lived in the tidal plain in which their remains were found. Most of the hadrosaur bones unearthed show bite marks, particularly on the neural spines of several dorsal vertebrae, ischia, as well as on one femur, revealing that the bodies of these specimens were consumed by crocodiles or theropod dinosaurs.

Dinosaurs

Ornithischians

Ankylosaurs Ankylosaurs of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Struthiosaurini indet. Indeterminate Lestaillats 1 Lower MDE-Les-69, osteoderm (smal scute) MDE-Les-09, osteoderm (oval keeled plate) MDE-Les-68, osteoderm (oval keeled plate) A struthiosaurin nodosauridae

Hadrosaurs Hadrosaurs of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Hadrosauridae indet. Indeterminate Lestaillats 1 Lower MDE-LES-73, a dentary tooth MDE-Les-06, a complete dorsal vertebra MDE-Les-07, a complete dorsal vertebra MDE-Les-08, a complete dorsal vertebra MDE-Les-14, a dorsal rib MDE-Les-25, a complete left scapula MDE-Les-04, a complete caudal vertebra MDE-Les-05, a complete caudal vertebra MDE-Les-20, a complete caudal vertebra MDE-Les-03, an incomplete left pubis MDE-Les-01,19, two incomplete ischia belonging probably to the same individual MDE-Les-02, an incomplete ischium (which is more robust and less laterally flattened than the other two) A squamosal and an anterior fragment of a maxilla are cited (but not figured) by Laurent and colleagues.The slender shape of the scapula, with its two extremities of equal width (a dominant morphology in Hadrosaurinae, although there are exceptions), suggests a different taxon from the lambeosaurine Canardia found in the same region in the younger strata of the Marnes d'Auzas Formation. In the latter, the scapular blade is shorter, its distal end being wider dorsoventrally than its proximal end, a typical characteristic of most lambeosaurines, although there are also exceptions. The dorsal and caudal vertebrae have very tall neural spines, a feature more common (but not exclusive) in lambeosaurines. A dentary tooth of the Lestaillats hadrosaurid has a crown with a median carina but without a secondary carina.. This tooth therefore differs from the dentary teeth of Canardia which have a main carina slightly offset posteriorly relative to the axis of the tooth (asymmetrical position) and which are equipped with a thin secondary carina located anterior to the main carina. Indeterminate Lestaillats 2 LowerMDE-Les2-10A proximal half of a right femur. Shows numerous bite marks Indeterminate Ausseing Middle MDE-Aus-160, a cervical rib MDE-Aus-01, a nearly complete right femur ( in length) MDE-Aus-03, a left tibia ( in length) MDE-Aus-09, a right fibula ( in length) MDE-Aus-184, a left metatarsal IV MDE-Aus-47, an ungual phalanx Fragmentary teeth and lower jaw are also cited but not figured. Lambeosaurinae indet. Indeterminate Ausseing Middle MDE-Aus-185, a nearly complete left ischium ( in length)In 2013, Prieto-Márquez et al. identified diagnostic lambeosaurines features in the left ischium MDE-Aus-185 (iliac process with dorsal margin caudally recurved producing a “thumb-like” lateral profile).. The other hadrosaur remains from the Ausseing site reported by Yves Laurent in 2003 may belong to the same taxon.

Saurischians

Sauropods Sauropods of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Titanosauria indet. Indeterminate Ausseing Middle MDE-Aus-129, a right tibia ( in length) with both ends incomplete MDE-Aus-177, a metacarpal

Theropods Theropods of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Theropoda indet. Indeterminate Lestaillats 1 Lower MDE-Les-76, an incomplete tooth Possibly an indeterminate dromaeosaurid

Crocodilians Crocodilians of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Crocodyliformes indet. Indeterminate Lestaillats 1 and 2, Ausseing Lower and Middle Teeth (including MDE-Aus-187, osteoderms (including MDE-Aus-06 and 112) Thoracosaurus Indeterminate Ausseing Middle Teeth Musturzabalsuchus? Indeterminate Ausseing Middle MDE-Aus-230 and 124, teeth A probable Allodaposuchidae eusuchian Acynodon A. cf. iberoccitanus Ausseing Middle MDE-Aus-74, anterior spatulate tooth MDE-Aus-77, posterior globular tooth MDE-Aus-71, posterior globular tooth A hylaeochampsid eusuchian

Squamates Squamates of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Lacertilia indet. Indeterminate Ausseing Middle Vertebrae (including MDE-Aus-254) Scincomorpha indet. Indeterminate Ausseing Middle MDE-Aus-255, a dentary bearing teeth

Turtles Turtles of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Pleurodira indet. Indeterminate Lestaillats 1 and 2 Lower MDE-Les-15, xiphiplastron ; dermal plates Indeterminate Ausseing Middle MDE-Aus-10, a scapulocoracoid MDE-Aus-133, epiplastron MDE-Aus-214, hyoplastron MDE-Aus-136, hyoplastron MDE-Aus-29, xiphiplastron with pubis and ischium MDE-Aus-146, xiphiplastron MDE-Aus-56 and 58, peripheral plates MDE-Aus-14 and 118 pleural plates MDE-Aus-51 and 88 neural plates Foxemys? Indeterminate Ausseing Middle MDE-Aus-18, entoplastron A bothremydid turtle Solemys? Indeterminate Ausseing Middle MDE-Aus-16 and 183, dermal plates A helochelydrid turtle

Amphibians Amphibians of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Albanerpetontidae indet. Indeterminate Ausseing Middle MDE-Aus-251, a dentary fragment bearing seven teeth Discoglossidae indet. Indeterminate Ausseing Middle MDE-Aus-252, distal end of a humerus MDE-Aus-253, skull roof fragment

Fish Fish of the Lestaillats Marls FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage Chondrichthyes indet. Indeterminate Lestaillats 1 and 2 Lower Teeth (including MDE-Les2-09) Osteichthyes indet. Indeterminate Ausseing Middle Vertebrae Lepisosteidae indet. Indeterminate Lestaillats 1, Ausseing Lower and Middle MDE-Les-67 and MDE-Aus-250, ganoid scales MDE-Aus-242, vertebra cf. Lepisosteus? Indeterminate Ausseing Middle Teeth (including MDE-Aus-243) cf. Atractosteus? Indeterminate Ausseing Middle Teeth (including MDE-Aus-244) Phyllodontidae indet. Indeterminate Lestaillats 1 and 2, Ausseing Lower and Middle Teeth (including MDE-Aus-245) Phyllodontinae indet. Indeterminate Lestaillats 2 Lower MDE-Les2-06, a partial tooth plate Amiidae indet. Indeterminate Ausseing Middle Tooth plates (including MDE-Aus-246) ; vertebrae (including MDE-Aus-247) cf. Palaeolabrus? Indeterminate Ausseing Middle MDE-Aus-248, a tooth plate Sparidae? indet. Indeterminate Lestaillats 1 and 2, Ausseing Lower and Middle Teeth (including MDE-Aus-249)

Notes

References

Bibliography

Books

See also

List of dinosaur-bearing rock formations List of stratigraphic units with indeterminate dinosaur fossils