A New Turtle Dominated Fossil Biota from the Late Triassic (Norian) of Poland

This paper documents a newly discovered fauna from the Norian of Poland that is important because it is dominated by fossils of what is most likely a new taxon of turtle. Of course Late Triassic terrestrial turtles are very rare so we will watch further research from this site with interest. The locality also includes other vertebrate taxa including a coelophysoid dinosaur and an aetosaur.  The aetosaur is of interest because the dorsal vertebra possesses a distinct hyposphene, a character previously only found in Desmatosuchus from North America and Aetobarbakinoides from Brazil.  This new site is also significant because it preserves micro and macrofloral fossils, which are generally uncommonly associated with vertebrate remains. Large temnospondyls are also rare in the Norian, but this site has one as well.

Sulej, T., Niedźwiedzki, G., and R. Bronowicz. 2012. A new Late Triassic vertebrate fauna from Poland with turtles, aetosaurs, and coelophysoid dinosaurs. Journal of Vertebrate Paleontology 23: 1033-1041. DOI:10.1080/02724634.2012.694384

Abstract - We report a new site with an occurrence of isolated bones of a Palaeochersis-like turtle in Norian-Rhaetian fluvial sediments from southern Poland. The turtle remains are associated with bones of a medium-sized aetosaur, a coelophysoid dinosaur, and a larger carnivorous archosaur, as well as a hybodontid shark, ganoid and dipnoan fishes, and a large temnospondyl.

More Evidence for Long Norian and Rhaetian Stages

This is a new paper looking at Triassic magnetostratigraphic correlations between Europe and North America.  The findings essentially support the early conclusions of Muttoni et al. (2004; 2010) arguing for long Norian and Rhaetian stages.  Correlations between the Steinbergkogel sections in Austria and the Newark Supergroup in the eastern U.S.A., suggest the following timescale revisions:

Carnian-Norian boundary: ~226.6 Ma;
Lacian-Alaunian boundary: ~216.4 Ma (fairly equivalent to the old Carnian/Norian boundary);
Alaunian-Sevatian 1 boundary: 211.8 Ma;
Norian Rhaetian boundary: ~209.8 Ma.

Thus according to these data the early Norian is approximately 10 million years long, the middle Norian is 4.5 million years old, and the late Norian is 2 million years old for an approximately 17 million year long Norian stage.  The Rhaetian is approximately 9 million years long.

Proposed biostratigraphic data from palynomorphs and conchostracans suggesting a shorter Norian are refuted.

Hüsing, S. K., Deenen, M. H. L., Koopmans, J. G., and W. Krijgsman. 2011. Magnetostratigraphic dating of the proposed Rhaetian GSSP at Steinbergkogel (Upper Triassic, Austria): Implications for the Late Triassic time scale.  Earth and Planetary Science Letters 302: 203-216

Abstract - The Global Stratotype Section and Point (GSSP) for the Rhaetian Stage has recently been proposed at Steinbergkogel in Austria. We re-sampled the Steinbergkogel sections (STK-A and STK-B + C) in high-resolution to establish a robust magnetostratigraphy that allows global correlation. The palaeomagnetic signal at Steinbergkogel is composed of three components, which can be separated by thermal demagnetization. The highest temperature component, revealed between 280/300 and maximum 600 °C is of dual polarity and is interpreted as primary. Rock magnetic experiments showed that the signal is carried by magnetite. Our results allow correlation between the two individual Steinbergkogel outcrops. Subsequently, we correlate the two key biostratigraphic horizons for the base of the Rhaetian, the FO of M. hernsteini and the FAD of M. posthernsteini to other sections of the Tethys domain. The correlation to the astronomically dated continental successions of the Newark basin indicates that these positions for the base of the Rhaetian are most likely determined in chrons E16n and E16r, respectively. This correlation is confirmed by cyclostratigraphic control on the marine Pizzo Mondello (Italy) section, where a combination of long period Milankovitch cycles (~ 175-Myr) and short-eccentricity cycles (~ 100-kyr) provide additional correlation constraints, respectively supporting a long duration of the Rhaetian. Our study implies that the Norian and Rhaetian Stages have durations of ~ 17 and ~ 9 Myr.


REFERENCES

Muttoni, G., Kent, D.V., Jadoul, F., Olsen, P.E., Rigo, M., Galli, M.T., and A. Nicora. 2010. Rhaetian magneto-biostratigraphy from the Southern Alps (Italy): constraints on Triassic chronology. Palaeogeography, Palaeoclimatology, Palaeoecology 285: 1–16.

Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily)and correlation to the Late Triassic Newark astrochronological polarity time scale. Geological Society of America Bulletin 116: 1043–1058.

New Biostratigraphical Constraints for the Norian⁄Rhaetian Boundary

Once even questioned as a valid stage the Rhaetian has made quite a comeback research-wise, especially since the GSSP for the Norian/Rhaetian boundary has yet to be determined.

Giordano, N., Rigo, M., Ciarapica G. & Bertinelli A. 2010. New biostratigraphical constraints for the Norian ⁄Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy. Lethaia, 10.1111/j.1502-3931.2010.00219.x.

Abstract - Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola-Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro-palaeontological data set based on conodonts and radiolarians for the characterization of the Norian ⁄Rhaetian interval. The studied sections represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate characteristics between the Calcari con Selce and Scisti Silicei Formation, in particular the progressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian ⁄Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hernsteini and Misikella posthernsteini, here represented by all the transitional forms characterized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian ⁄ Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well-preserved, radiolarian associations of Pignola-Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, highlighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage.

I've Been Waiting For This For A Long Time

Walker, J., & Geissman, J. (2009). 2009 GSA Geologic Time Scale GSA Today, 19 (4) DOI: 10.1130/1052-5173-19.4-5.60

The Geological Society of America has just released its updated geological timescale for 2009 (here and here). A significant revision of this timescale is the Triassic section based on recent studies by Furin et al. (2006) and Kent and Olsen (2008). Most notably is the incorporation of the "long Norian" stage. In the previously published version of the timescale, the Carnian/Norian boundary was dated at 216.5 Ma. Now this boundary is dated at 228 Ma, which in the previous version was the date for the Ladinian/Carnian boundary (Middle/Late Triassic boundary).

The beginning of the Late Triassic is now dated at 235 Ma (previously a strong Middle Triassic date). Incredibly the majority of the Triassic now consists of the Late Triassic. In fact just the Norian stage (24 my) of the Late Triassic is longer than the combined Early (6 my) and the Middle (17 my) Triassic Epochs! The base of the Triassic is still at 251 Ma (defined by a GSSP); however, the age of the Triassic/Jurassic boundary has changed from 199.6 Ma to 201.6 Ma.

As it is now "official" the "long Norian" will have significant implications for the age of the Chinle Formation and other supposed "Carnian" fossil assemblages worldwide as suggested recently by studies such as that of Furin et al. (2006) and Irmis and Mundil (2008). As more GSSPs are established for the Triassic these dates should stabilize.

REFERENCES

Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi: 10.1130/G22967A.1.

Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.

Kent, D.V., and Olsen, P.E.,2008, Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in association with the central Atlantic magmatic province: Journal of Geophysical Research, v. 113, B06105, doi: 10.1029/2007JB005407.

Rethinking Turtle Origins - Odontochelys

What an exciting time it must be to work on basal turtles. Hot on the heels of Chinlechelys and Eileanchelys comes a new basal turtle, Odontochelys semitestacea, from the Norian (~220 Ma) of China. The article and commentary came out today in the journal Nature and you can also read about it here and here.

Odontochelys predates other earliest known turtles by at least 5 million years and is from marine rocks suggesting a marine origin for turtles. The complete fossil (see these photos from the Nature News website), known from four specimens, possesses a ventral plastron but not a dorsal carapace suggesting that the plastron formed first (but see argument by Reisz and Head, 2008).

Finally, as also hinted at by the name, Odontochelys is the first known turtle to possess teeth.

Whereas, the marine origin is surprising given the terrestrial nature of other Triassic turtles overturning what was thought to be a stable hypothesis, the teeth are a nice find, but not so surprising given that turtles must have originated from a toothed reptilian ancestor.

As to the ventral carapace forming first, Reisz and Head (2008) argue against the interpretation provided by Li et al. (2008); however, based on a statement made by Li that "here, in our hands, there is an ideal missing link for turtle evolution. It has no osteoderms on its back, but only ossified neural [central] plates and expanded ribs." I wonder if what we are looking at is a preservational artifact. Maybe the plastron fully ossifies earlier on in ontogeny. Not being a turtle specialist or seeing the specimens I may be completely wrong, but that is the explanation that first popped into my head.

Sounds like there is a lot more exploration and work to be done on basal turtles.

REFERENCES

Chun Li, Xiao-Chun Wu, Olivier Rieppel, Li-Ting Wang, Li-Jun Zhao (2008). An ancestral turtle from the Late Triassic of southwestern China Nature, 456 (7221), 497-501 DOI: 10.1038/nature07533

Robert R. Reisz, Jason J. Head (2008). Palaeontology: Turtle origins out to sea Nature, 456 (7221), 450-451 DOI: 10.1038/456450a

No Carnian aged deposits in the Chinle Formation?

For the last couple of years one of the more intriguing hypotheses regarding the Chinle Formation is the possibility, based on proposed revisions of the Late Triassic time scale (Muttoni et al., 2004; Furin et al., 2006), that the entire unit was Norian-Rhaetian in age, rather than Carnian-Norian. The Carnian-Norian age was based on palynology (e.g., Litwin et al., 1991) as well as vertebrate biostratigraphy (e.g., Lucas and Hunt, 1993). In fact, a faunal and floral turnover near the middle of the Chinle Formation was hypothesized by many workers to possibly represent the Carnian-Norian boundary and was evidence for an end-Carnian terrestrial extinction. First noticed by Camp (1930) and Gregory (1957) this turnover was more fully documented by Long and Ballew (1985) who noted the presence of two distinct faunas differentiated by the phytosaurs “Rutiodon A” and “Rutiodon B”, as well as the aetosaurs Calyptosuchus and Typothorax. Lucas and Hunt (1993) subsequently named these the Adamanian and Revueltian land-vertebrate faunachrons.

Considered controversial, the hypothesis that most if not all of the Chinle is actually Norian received strong support by the recent announcement of a new 206Pb/238U age of 219.2 ± 0.7 Ma from the base of the Blue Mesa Member in New Mexico (Mundil and Irmis, 2008). This is important for several reasons, firstly, the Chinle Formation has very well documented vertebrate, invertebrate, plant and trace fossil assemblages and is arguably a keystone unit for study of the Late Triassic terrestrial record. Second, it is the basis for the Adamanian land-vertebrate faunachron which has been used to correlate the first appearance of dinosaurs globally (e.g., Heckert and Lucas 1999, 2000). The implications of this will be the focus of Randy Irmis’ presentation at the Society of Vertebrate Paleontology annual meeting next month and therefore will not be discussed further here. What I would like to discuss is the slight possibility that despite these new findings maybe not all of the lower Chinle is now Norian.

In the four corners are of the western United States (Arizona, Utah, Colorado, New Mexico), the Chinle Formation uncomformably overlies the Middle Triassic (Anisian) Moenkopi Formation and consists of seven members which from oldest to youngest are the Shinarump, Bluewater Creek, Blue Mesa, Sonsela, Petrified Forest, Owl Rock, and Rock Point (Note: another unit, the Mesa Redondo Member, is locally situated between the Shinarump and Blue Mesa members but is lithologically distinct from the Bluewater Creek and the relationships between these units are not completely understood). The date provided by Mundil and Irmis (2008) is near the Bluewater Creek/Blue Mesa contact. As the new hypothesized date for the Carnian-Norian boundary is now around 230 ma, this would still leave approximately 10 million years of Norian time below this contact and would presumably include the Shinarump and Bluewater Creek. This is important because instead of just having an uncomformity between the Moenkopi and Chinle that encompasses the Ladinian, this unconformity would now encompass the Ladinian-Carnian as well as a portion of the early Norian. Whereas this might possibly explain the lack of rhynchosaur material (believed to have died out at the end of the Carnian or in the early Norian) from the Chinle Formation, it would also suggest that the Chinle is not temporally equivalent to all of the Dockum Group (eastern New Mexico and Texas) or most of the Newark Supergroup (eastern U.S.) as previously supposed. I’m getting dangerously close to the contents of Randy’s SVP abstract here which is embargoed for the next month, so I will stop this line of thought, but what I want to look at in more detail is the possibility that the Shinarump may not be Norian.

The Shinarump member consists mainly of extrabasinal conglomerates and sandstones that fill paleovalleys carved into the underlying Moenkopi Formation. Once considered its own formation, the Shinarump is now considered to represent the basal member of the Chinle Formation. Unfortunately, the high energy environment that deposited the conglomerates and sands is not conducive to preserving fossils; however in some places mudstone facies do preserve material, most notably near Cameron Arizona. Ash (2005, 2006) has documented this flora and found that it is distinct from the rest of the Chinle Formation in possessing several forms, most notably a seed fern, that more closely resembles archaic forms from the Paleozoic. This suggests that the Shinarump, although still Late Triassic, may be much older than the rest of the Chinle. Unfortunately the vertebrates are not any help. Heckert et al. (2003) documented material that is purportedly from the Shinarump near Cameron, and found that the fauna contains metoposaur and phytosaur material typical of the rest of the Chinle. Furthermore, the flora does also contain forms found in the younger Chinle units including the pollen (Litwin et al., 1991; Ash, 2005). Finally in his excellent dissertation, Jeff Martz discusses in detail that Riggs et al. (1996), in an important but often overlooked paper, used detrital zircons to correlate the Shinarump (and the Santa Rosa Formation of the Dockum) with the marine Auld Lang Syne Group, which is early Norian in age (Martz, 2008). Thus, these authors (Riggs et al., 1996) had suggested a Norian age for the entire Chinle over a decade ago. Despite this, the idea that the Shinarump may still be Carnian is intriguing because it would suggest the presence of a sizeable unconformity (TR-4?) between that unit and the rest of the Chinle Formation.

One final note is that the faunal turnover mentioned at the beginning of this post is close to the base of the Sonsela Member based on detailed mapping and revised biostratigraphic work done by Jeff Martz and myself in Petrified Forest National Park. Thus this turnover (which may also correspond with a floral turnover) is in the early-middle Norian and does not represent an end-Carnian event. More on this later.

REFERENCES

Ash, S.R. 2005. A new Upper Triassic flora and associated invertebrate fossils from
the basal beds of the Chinle Formation, near Cameron, Arizona. PaleoBios 25:17–34.

Ash, S.R. 2006. Chilbinia gen. nov., an archaic seed fern in the Late Triassic Chinle Formation of Arizona, USA. Palaeontology 49:237–245.

Camp, C. L. 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California 10:1-174.

Furin, S., Preto, N., Rigo, M., Roghi., G., Gianolla, P., Crowley, J.L., and S. A. Bowring. 2006. High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs. Geology 34:1009–1012.

Gregory, J.T. 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America. Report of the 20th Session of the International Geological Congress 1956, Section II:7-25.

Heckert, A.B., and S.G. Lucas. 1999. Global correlation and chronology of Triassic theropods (Archosauria: Dinosauria). Albertiana 23:22-35.

Heckert, A.B., and S.G. Lucas. 2000 [imprint 1998]. Global correlation and chronology of Triassic theropods. Gaia 15:63-74.

Heckert, A.B., Lucas, S.G., and J. W. Estep. 2003 [imprint 2002]. Lower Chinle Group (Upper Triassic: Upper Carnian) tetrapods from the vicinity of Cameron, Arizona. New Mexico Museum of Natural History and Science Bulletin 21:73-76.

Litwin, R.J., Traverse, A., and S.R. Ash. 1991. Preliminary palynological zonation of the Chinle Formation, southwestern U.S.A., and its correlation to the Newark Supergroup (eastern U.S.A.). Review of Palaeobotany and Palynology 68: 269-287.

Long, R. A. and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45-68.

Lucas, S.G., and A.P. Hunt. 1993. Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States. New Mexico Museum of Natural History and Science Bulletin 3:327-329.

Martz, J.W. 2008. Lithostratigraphy, chemostratigraphy, and vertebrate biostratigraphy of the Dockum Group (Upper Triassic), of southern Garza County, West Texas. Unpublished PhD dissertation. Texas Tech University, Lubbock, 504p.

Mundil, R., and R. Irmis. 2008. New U-Pb age constraints for terrestrial sediments in the Late Triassic: Implications for faunal evolution and correlations with marine environments. International Union of Geological Sciences (IUGS) meeting abstracts Oslo 2008 (online at: http://www.cprm.gov.br/33IGC/1342538.html).

Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004 Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale: Geological Society of America Bulletin 116:1043–1058.

Riggs, N. R., T. M. Lehman, G. E. Gehrels, and W. R. Dickinson. 1996. Detrital zircon
link between headwaters and terminus of the Upper Triassic Chinle-Dockum
paleoriver system. Science 273:97-100.