An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania

Abstract

Islands are noted for the occurrence of aberrant, endemic, and dwarfed taxa (the "island effect"). Late Cretaceous vertebrate assemblages of Romania and elsewhere in Europe are classic examples of island faunas in the fossil record, and are characterized by dwarfed herbivorous dinosaurs and other endemic taxa that are noticeably primitive relative to their mainland contemporaries. Fossils of the predators inhabiting the European paleoislands, however, are exceptionally rare and fragmentary. We describe a new dromaeosaurid theropod, based on an articulated skeleton from the Maastrichtian of Romania, which represents the most complete predatory dinosaur from the middle to Late Cretaceous of Europe. This taxon is characterized by a peculiar body plan, most notably extensive fusion in the hand and distal hindlimb, a highly retroverted pelvis with enlarged femoral muscle attachments, and a pair of hyperextensive pedal claws. However, unlike the island-dwelling herbivorous dinosaurs, its closest relatives are contemporary similar-sized Laurasian taxa, indicating faunal connections between Asia and the European islands late into the Cretaceous. This theropod provides support for the aberrant nature of the Late Cretaceous European island-dwelling dinosaurs, but indicates that predators on these islands were not necessarily small, geographically endemic, or primitive.Dromaeosauridae | endemic | Europe | island fauna | Theropoda

Dinosaur morphological diversity and the end-Cretaceous extinction

“…We calculated the terminal Cretaceous disparity patterns of every dinosaur subgroup that is represented by a reasonable number of Campanian-Maastrichtian specimens that could be scored for large matrices of discrete characters. Analysed clades include: non-avian coelurosaurian theropods 28 , tyrannosauroid theropods 29 , pachycephalosaurs 30 , ceratopsids (most of which are chasmosaurines, because there is no available global phylogeny of ceratopsids that includes comprehensive sampling of centrosaurines and chasmosaurines 31 ), hadrosauroids 32 , sauropods 33 , and ankylosaurs 34 . Other groups, such as abelisauroid theropods, non-hadrosauroid ornithopods, and non-ceratopsid ceratopsians, could not be analysed because large samples of reasonably complete CampanianMaastrichtian specimens scored for discrete character data are not yet available, almost entirely due to poor fossil sampling [41][42][43] .…”

“…The seven discrete character datasets record the presence, absence, number, and form of skeletal features in each species of the clade being analysed, and, therefore, comprise a database of overall morphological form for the group. Each of the seven discrete character datasets [28][29][30][31][32][33][34] was used to derive a Euclidean distance matrix, which quantifies the pairwise differences between the taxa in question, using the freeware program MATRIX. The seven distance matrices were next subjected to individual principal coordinates analyses (PCO), a multivariate statistical technique that assimilates information from the distance matrix into a more manageable set of coordinate axes, using the freeware program GINGKO (Universitat de Barcelona, http://biodiver.bio.ub.es/ginkgo/).…”

“…We calculated four measures of range and variance-based disparity for seven major Late Cretaceous non-avian dinosaur groups [28][29][30][31][32][33][34] , to test whether disparity increased, decreased, or stayed consistent during the final two stages of the Cretaceous (Campanian and Maastrichtian). Taxa were temporally binned using two schemes (equal-length late Campanian and Maastrichtian bins (Fig.…”

An unusual dinosaur from the Late Cretaceous of Romania and the island rule

“…One of the most exciting discoveries, reported by Csiki et al (11) in PNAS, is a previously unknown taxon of theropod dinosaur, Baldaur bondoc. Baldaur (named using an ancient Romanian word for dragon) is referable to the Dromaeosauridae (the "raptors" of Jurassic Park fame), which are the closest relatives of birds.…”

“…These unusual features suggest that Baldaur was capable of delivering powerful strikes with its feet. Based on what is known about insular faunas past and present, Csiki et al (11) hypothesize that the peculiar body plan of this predatory dinosaur is probably caused by the island effect. The body size of Baldaur is comparable with that of most other known dromaeosaurids.…”