Titanosaurs were the largest animals ever to roam on land; they were sauropod dinosaurs that survived to the end of the Cretaceous (most sauropods went extinct at the end of the Jurassic, certainly all non-Titanosaurian Sauropods were extinct by the Mid Cretaceous), and grew to sizes far in excess of their earlier relatives, which were big animals even by dinosaur standards. The biggest Titanosaur for which we can estimate a size, Argentinosaurus, grew up to 35 m in length and weighed 80-100 tonnes; it is quite possible that other Titanosaurs grew bigger, but most are only known from highly fragmented remains; in order to be fossilized efficiently an animal needs to be buried quickly, not easy for a creature as large as a Titanosaur.
Titanosaurs were first discovered in South America, where they seem to have originated and reached the peak of their diversity, and have subsequently been discovered in Africa, Europe, Asia, Australia and, most recently, North America. This month a team lead by Ignacio Cerda of Consejo Nacional de Investigaciones Científicas y Tecnológicas - INIBIOMA and the Museo de Geología y Paleontología at the Universidad Nacional del Comahue in Buenos Aeries published a paper in the German journal Naturwissenschaften in which they describe the discovery of a Titanosaur on James Ross Island, Antarctica.
The location of the Titanosaur find.
The discovery comprises only a part of a single vertebra; this is large and distinctive enough that it could not come from anything other than a Titanosaur, though Cerda et al. have not attempted any more detailed classification due to the limited nature of the material. The sedimentary beds in which the vertebra was found are thought to be of Upper Campanian age, between roughly 75 and 70 million years old.
The James Ross Island vertebra; (a & d) front view, (b & e) side view, (c & f) rear view.
Dinosaurs are not very well known from Antarctica, not so much because they were absent as because they are hard to find there now. Much of the continent is covered in snow and ice, and what is exposed has been scoured repeatedly by glaciation. Thus it is unsurprising that this is the first Titanosaur, and only the second Sauropod, found in Antarctica. Titanosaurs arose in South America and dispersed during the Early Cretaceous. Since they are known to have been present in Australia and New Zealand, areas that were still connected to Antarctica during the Early Cretaceous but not to any other land mass, then Titanosaurs must have been present in Antarctica at that time. It is possible that the new Titanosaur is descended from Titanosaurs that moved to Antarctica during this initial dispersal, but it is also possible that it is more closely related to the Titanosaurs present in South America during the Late Cretaceous, as South America and Antarctica were still connected till quite late in the Period (how late is still a matter of conjecture among geologists.
A reconstruction of the position of the continents during the Late Cretaceous.
See also An American Titanosaur and Dinosaurs on Sciency Thoughts YouTube.