Small terrestrial non-eusuchian mesoeucrocodylians are common components of Cretaceous
assemblages of Gondwanan provinces with notosuchians and araripesuchids as flagship
taxa in South America, Africa and Madagascar, well into the Late Cretaceous. On the
other hand, these are exceedingly rare in Laurasian landmasses during the Late Cretaceous.
Small terrestrial mesoeucrocodylians from Europe were often referred to the genus
Theriosuchus, a taxon with stratigraphic range extending from the Late Jurassic to
the late Early Cretaceous. Theriosuchus is abundantly reported from various European
localities, although Asiatic and possibly North American members are also known. It
has often been closely associated with the first modern crocodilians, members of the
Eusuchia, because of the presence of procoelous vertebrae, a widespread key character
diagnosing the Eusuchia. Nevertheless, the relationships of Theriosuchus have not
been explored in detail although one species, Theriosuchus pusillus, has been extensively
described and referred in numerous works. Here, we describe a new basal mesoeucrocodylian,
Theriosuchus sympiestodon sp. nov. from the Maastrichtian of the HaA eg pound Basin,
Romania, suggesting a large temporal gap (about 58 myr) in the fossil record of the
genus. Inclusion of the new taxon, along with Theriosuchus guimarotae, in a phylogenetic
analysis confirms its referral to the genus Theriosuchus, within a monophyletic atoposaurid
clade. Although phylogenetic resolution within this clade is still poor, the new taxon
appears, on morphological grounds, to be most closely related to T. pusillus. The
relationships of Atoposauridae within Mesoeucrocodylia and especially to Neosuchia
are discussed in light of the results of the present contribution as well as from
recent work. Our results raise the possibility that Atoposauridae might not be regarded
as a derived neosuchian clade anymore, although further investigation of the neosuchian
interrelationships is needed. Reports of isolated teeth referable to a closely related
taxon from the Upper Cretaceous of Romania and France, together with the presence
of Doratodon and Ischyrochampsa, indicate a previously unsuspected diverse assemblage
of non-eusuchian mesoeucrocodylians in the Late Cretaceous European archipelago.
