Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

Abstract

The Tuştea vertebrate locality, at Oltoane Hill (northwestern part of the Hațeg Basin, Romania), has provided a rich and diverse assemblage of Late Cretaceous (Maastrichtian) continental vertebrates. More than 800 vertebrate fossils were recovered from this locality; the isolated and associated remains represent 21 different taxa including amphibians, turtles, lizards, snakes, crocodyliforms, pterosaurs, dinosaurs and mammals. The local assemblage is overwhelmingly dominated by dinosaurs, with the rhabdodontid Zalmoxes as the most abundant taxon. The bonebeds that yielded this fossil material occur in a stacked series of mudstone/calcrete units belonging to the middle member of the Densuş-Ciula Formation. The taphonomical investigations suggest that the Tuştea assemblage is made up of attritionally accumulated politaxic remains and that it is a parautochthonous assemblage with no evidence for significant bone transport or reworking.According to the synthesis of all available field data two outstanding fossiliferous levels can be identified within the Tuştea locality, where Megaloolithus eggs and hadrosauroid hatchling material are preserved together, recognized here as two superposed nesting grounds. Such co-occurrence was considered controversial, since there is a longstanding and quasi-general consensus that eggs of the Megaloolithus oogenus were laid by titanosaurian sauropods. We present several alternative scenarios to account for the cooccurrence of Telmatosaurus hatchling remains and megaloolithid eggs in the nesting horizons and explore these alternative hypotheses by weighing the arguments supporting or contradicting them. The burden of evidence derived from our sedimentological, taphonomical and palaeoecological investigations at Tuştea is still in favor of the autochthony of the hatchlings, preserved within their own nesting grounds, whereas there is no such support for a titanosaurian origin of the Tuștea megaloolithid eggs.

A Catalog ofZalmoxes(Dinosauria: Ornithopoda) Specimens from the Upper Cretaceous Nălaţ-Vad Locality, Haţeg Basin, Romania

“…Below the posterior corner of the greater trochanter, the posterolateral edge of the shaft is marked by a prominent bulge, a morphological feature mentioned previously by Weishampel et al (2003) and Vremir et al (2014) as present in the femora of Zalmoxes. The specimen is similar to both NHMUK R.3834 (assigned previously to Z. robustus by Weishampel et al, 2003) and LPB (FGGUB) R.1608 (assigned tentatively to Z. shqiperorum in Botfalvai et al, 2017) in the overall appearance of the proximal region. Accordingly, we conclude that the specimen is too fragmentary to assign it definitively to either of the two Zalmoxes species known from the Hațeg Basin.…”

“…The fossiliferous layers are exposed within the old riverbed downstream from the Totești-II hydropower station, now only shallowly covered by water because in the mid-1980s the river was diverted to a new water channel with the construction of the power plant. Thus, the uppermost Cretaceous rocks are well exposed, and only rarely waterlogged or covered by gravel as would have been the case in Nopcsa's time, more than a Nopcsa, 1904Nopcsa, , 1928; 2, Godefroit et al (2009); 3, Csiki et al (2010c), Botfalvai et al (2017); 4, this paper. * = series of cranial elements (NHMUK R.3389, R.3393, R.3395, R.3396, R.3398 and R.3402) considered to represent disarticulated parts of the same skull as the holotype right dentary (NHMUK R.3392), cf.…”

“…In most Hațeg locales, rhabdodontid bones and teeth usually rank among the most commonly occurring vertebrate remains (e.g., Csiki et al, 2010c;Vasile and Csiki, 2010;Botfalvai et al, 2017). The same also appears to be true in other parts of Transylvania that preserve latestCretaceous dinosaur fossils, such as the southwestern Transylvanian Basin (Brusatte et al, 2013b;Vremir et al, 2014) and even the very poorly sampled northwestern Transylvanian Basin (Codrea and Godefroit, 2008).…”

“…Unfortunately, these diagnoses are hampered by some unavoidable difficulties. First, except for a few cases of positive and well-documented field association (e.g., Nopcsa, 1904Nopcsa, , 1928Weishampel et al, 2003;Godefroit et al, 2009;Csiki et al, 2010c;Botfalvai et al, 2017), the vast majority of the previously known Zalmoxes fossils have been disarticulated and/or isolated, making their referral to one or the other of the two species largely conjectural. There are many features that may be diagnostic of either Zalmoxes or one of the two species, but these cannot be assessed in close relatives (such as Rhabdodon) and/or in one of the two Zalmoxes species because of a lack of comparable bones.…”

“…); TOT = Totești (M.V., personal obs. ); TU = Tuștea (Botfalvai et al, 2017); VL = Vălioara (Kadič, 1916;Buffetaut et al, 2002;Weishampel et al, 2003); SP = Sânpetru (Nopcsa, 1928;Godefroit et al, 2009; M.V., Z. Cs.-S., personal obs. ); PU = Pui (Van Itterbeeck et al, 2004;Csiki et al, 2005Csiki et al, , 2010c; M.V., Z. Cs.-S., personal obs.…”