Counillonia and Repelinosaurus Type Locality: Early/Lower Triassic, Laos
collected by P. Taquet and colleagues 1993 - 2003

List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
Anomodontia
Counillonia superoculis n. gen., n. sp. Olivier et al. 2019
1 specimen
LPB 1993-3 (holotype), partial skull without mandible
Repelinosaurus robustus n. gen., n. sp. Olivier et al. 2019
2 specimens
LPB 1993-2 (holotype), partial skull without mandible; LPB 1995-9, partial skull without mandible
see common names

Geography
Country:Laos
Coordinates: 19.9° North, 102.1° East (view map)
Paleocoordinates:0.6° South, 94.4° East
Basis of coordinate:stated in text
Geographic resolution:outcrop
Time
Period:Triassic Epoch:Early/Lower Triassic
10 m.y. bin:Triassic 1
Key time interval:Early/Lower Triassic
Age range of interval:251.90200 - 247.20000 m.y. ago
Age estimate:maximum 251.0 ± 1.4 Ma (U/Pb)
Stratigraphy
Formation:Purple Claystone
Stratigraphic resolution:group of beds
Stratigraphy comments: "Three samples from the Purple Claystone Formation, including one collected at the dicynodont site, were dated using U-Pb geochronology on detrital zircon (Rossignol et al., 2016). The sample collected at the dicynodont fossil site yielded a maximum depositional age of 252.0 ± 2.6 Ma, whereas the other volcaniclastic samples collected in the same formation yielded maximum depositional ages of 251.0 ± 1.4 and 300.5 ± 3.7 Ma. The various volcaniclastic textures, their roundness, and the relatively low volcaniclast content (below 20%) implying an important and protracted mixing with other detrital particles, as well as the fact that some of the volcaniclasts underwent at least two sedimentary cycles (Bercovici et al., 2012; Blanchard et al., 2013), suggest that these dates, obtained from zircon grains interpreted as being detrital in origin, represent maximum depositional ages. The actual age of deposition of the Purple Claystone Formation is therefore likely to be younger. Both youngest maximum depositional ages (i.e., 252.0 ± 2.6 and 251.0 ± 1.4 Ma) encompass the P-Tr boundary (251.902 ± 0.024 Ma; Burgess et al., 2014) within uncertainties. The consideration of a late Permian age, potentially plausible, would nonetheless imply that the reworking of the zircon grains took place within an unlikely brief time span. Given the age of the overlying formation (224.9 ± 1.0 Ma; Blanchard et al., 2013), an age up to the Carnian could be proposed as the theoretical upper age limit for the Purple Claystone Formation. However, the occurrence of a regional Middle Triassic unconformity (e.g., Racey, 2009), probably superimposed onto the reverse fault separating the Purple Claystone Formation from other sedimentary units to the southeast, reduces the likely time span for the deposition of the Purple Claystone Formation. Consequently, an Early Triassic age for the Purple Claystone Formation and its enclosed fossils is considered to be the most likely." (Olivier et al. 2019)
Lithology and environment
Primary lithology: silty claystone
Lithology description: "The Limestone and Sandstone Formation is overlain by the Purple Claystone Formation, from which various fossil remains have been excavated (dicynodonts and a chroniosuchian; Steyer, 2009; Arbez et al., 2018). The Purple Claystone Formation is mainly composed of homogeneous silty claystones, silts, and more rarely clays (Bercovici et al., 2012). The formation also comprises volcaniclastic siltstones and sandstones, with millimeter- to centimeter-sized rounded and highly weathered volcaniclasts (up to about 20 vol.%). These volcaniclasts exhibit a variety of volcanic textures (microlithic, trachytic, porphyritic) and are sometimes embedded within lithic fragments, attesting to multiple reworking events for these volcaniclasts (Bercovici et al., 2012; Blanchard et al., 2013). The Purple Claystone Formation also contains subordinate amounts of coarser deposits, including sandstone and conglomeratic facies with three-dimensional megaripples typical of braided river deposits. The conglomeratic levels consist of rounded pebbles of highly fossiliferous limestones (foraminifers, corals, bryozoans), subangular to rounded pebbles of volcanic rocks, black cherts, red quartzites, red sandstones, and siltstones. Paleosols, sometimes exhibiting vertical root traces, are developed within this formation (Bercovici et al., 2012)." (Olivier et al. 2019)
Environment:"floodplain"
Geology comments: "The sedimentary facies association indicates braided river depositional environments, evolving vertically to alluvial plain environments, probably including ponds (Bercovici et al., 2012)." (Olivier et al. 2019)
Taphonomy
Modes of preservation:body
Size of fossils:macrofossils
Collection methods and comments
Collection methods:field collection
Reason for describing collection:taxonomic analysis
Collectors:P. Taquet and colleagues Collection dates:1993 - 2003
Collection method comments: LPB - Luang Prabang Basin specimens stored in the Savannakhet Dinosaur Museum, Savannakhet, Laos
Metadata
Also known as:Luang Prabang Basin
Database number:201493
Authorizer:A. Dunhill Enterer:B. Allen
Modifier:B. Allen
Created:2019-05-10 05:31:36 Last modified:2019-05-10 05:43:34
Access level:the public Released:2019-05-10 05:31:36
Creative Commons license:CC BY
Reference information

Primary reference:
68957. C. Olivier, B. Battail, S. Bourquin, C. Rossignol, J.-S. Steyer and N.-E. Jalil. 2019. New dicynodonts (Therapsida, Anomodontia) from near the Permo-Triassic boundary of Laos: implications for dicynodont survivorship across the Permo-Triassic mass extinction and the paleobiogeography of Southeast Asian blocks. Journal of Vertebrate Paleontology [A. Dunhill/B. Allen]