Collection of the thinnest: A unique eggshell assemblage from the Late Cretaceous vertebrate locality of Iharkút (Hungary)

Abstract

As a result of several years of screen-washing activity, a remarkable assemblage of eggshell fragments has been recovered from the Late Cretaceous vertebrate locality of Iharkút, Hungary. Detailed investigation of the assemblage by multiple visualization techniques (scanning electron microscopy, polarizing light microscopy, X-ray micro-computed tomography), quantitative morphometric analyses, and micro X-ray fluorescence spectrometry revealed a diverse composition of five different eggshell morphotypes (MT I-MT V) and three subcategories within the second morphotype (MT II/a, b, c), with MT I being by far the most abundant (83%) in the assemblage. MT I, MT III, and MT V represent theropod dinosaurian eggshells, whereas MT II and MT IV show characteristics of crocodilian and squamate eggshells, respectively. Hence, despite their fragmentary nature, these eggshells represent the first clear evidence that various sauropsid taxa had nesting sites near the ancient fluvial system of Iharkút. Besides the implied taxonomic diversity, two unique features add to the significance of this eggshell assemblage. First, it contains the thinnest rigid crocodilian (MT II/c) and squamate (MT IV) eggshells ever reported. Moreover, one of the identified theropod morphotypes, MT I, is also among the thinnest fossil dinosaurian eggshells, the thinness of which is only rivalled by the eggshells of the smallest Mesozoic avian eggs known to date. Second, the Iharkút eggshell assemblage consists exclusively of thin eggshells (≤300 μm), a condition unknown from any other fossil eggshell assemblages described to date. Combined with the knowledge acquired from skeletal remains, these peculiarities give additional insights into the paleoecology of the terrestrial sauropsid fauna once inhabiting the ancient island of Iharkút. Finally, the presence of well-preserved eggshells recovered from two different sites representing different depositional environments provides further evidence for previous taphonomic and sedimentological conclusions, and also expands our knowledge of the special conditions that allowed the preservation of these delicate eggshell fragments.

Comparative crystallography suggests maniraptoran theropod affinities for latest Cretaceous European ‘geckoid’ eggshell

“…In contrast, Prondvai et al . () concluded recently that the most abundant fossil eggshells (‘morphotype I’ or ‘MT I’) from the Santonian of Iharkút, Hungary, which resemble both Pseudogeckoolithus and the French ‘geckonoïde’ morphotype, have a theropod affinity based on the presence of a mammillary layer, in agreement with Vianey‐Liaud & Lopez‐Martinez (). Furthermore, Prondvai et al .…”

“…Furthermore, Prondvai et al . () suggested that, along with the Hungarian MT I eggshells, putative ‘gecko‐like’ eggshells from the Upper Cretaceous deposits in Romania, Spain and France might have theropod affinities as well, consistent with the interpretation of North American dispersituberculate eggshells (e.g. Zelenitsky et al .…”

A comparative study of eggshells of Gekkota with morphological, chemical compositional and crystallographic approaches and its evolutionary implications

“…This crystallographic disparity between gekkotan and archosaur eggshells casts doubt on the hypothesis that all rigid sauropsid eggshells have the same mechanism of eggshell formation [ 8 ]. Moreover, if these features are autapomorphies of gekkotan eggshells, they can be used for verification of several “gecko-like” egg fossils from the Cretaceous deposits in Europe [ 54 – 59 ] and North America [ 60 ], the Eocene deposits in North America [ 23 ], the Oligocene deposit in Europe [ 2 ], and the Miocene deposit in Kenya [ 61 ].…”

The dirty dozen: taxonomical and taphonomical overview of a unique ankylosaurian (Dinosauria: Ornithischia) assemblage from the Santonian Iharkút locality, Hungary

“…Depositional area of Unit 1 of site SZ-6 acted as a trap where the current velocity suddenly decreased and the poorly sorted sediments and different density (i.e. bones, plant and eggs) and sized (microfossils and partial ankylosaur skeletons) fossils were accumulated altogether at same time (Botfalvai et al 2015;Prondvai et al 2017;Segesdi et al 2017). The stacked series of Unit 1 (and thus most of the vertebrate fossils in the Iharkút assemblage) was deposited in a relatively short time (e.g.…”

“…The accumulation of these skeletons began after the culmination of a high flood process, when current strength suddenly decreased and different density (i.e. bones, plant and eggs) and sized (microfossils and partial ankylosaur skeletons) fossils accumulated together at the same time (Botfalvai et al 2015;Prondvai et al 2017).…”