Zby is an extinct genus of non-neosauropod eusauropod sauropod dinosaur which lived during the late Jurassic (Kimmeridgian) in Portugal. It belonged to the unranked clade of large sauropods called Turiasauria and was related to the large European Turiasaurus.
Zby was described in 2014 and was named after Georges Zbyszewski, who studied the geology and palaeontology of the Portuguese landscape.
Zby is only known from its holotype, which is a partial skeleton, containing a complete tooth with root, a fragment of cervical neural arch, an anterior chevron, and an almost complete right pectoral girdle and forelimb.
Currently only one species of this animal is known: Zby atlanticus.
Zby is closely related to Turiasaurus riodevensis, which is known from contemporaneous deposits, in Spain.
However, there is enough difference in the morphology of this animals to distinguish these two genera.
The anatomical features present suggest that Zby is a non-neosauropd eusauropod, confirming its position in the clade Turiasauria.
An interesting fact is that turiasaurs seem to have been restricted to Europe. However, there some dinosaur genera that are found in both Europe (in the Lourinhã Formation, in Portugal) and in North America (in the Morrison Formation, USA), such as Ceratosaurus, Allosaurus, Torvosaurus, Stegosaurus and Supersaurus, albeit of different species.
Zby isn´t the only sauropod found in Portugal. In fact, it is the forth genus of sauropod from the late Jurassic.
One thing that Mateus et al point in the paper that describes Zby atlanticus is the fact that all adult sauropods found in Portugal are very big individuals. It seems that there weren´t any small to medium-sized ones.
One possible answer given in the paper is, and I quote: «it is possible that the apparent absence of small- or medium-sized adult sauropods might be related to the occupation of lower-browsing niches by non-sauropods such as the long-necked stegosaur Miragaia longicollum.»
Miragaia longicollum is known to have a a very long neck. It had 17 vertebra. This is unsual even to sauropds, but what is odd is that this animal is a stegosaur. Animals like Miragaia had probably already occupied the niche of medium browsers and sauropods had to grow to bigger sizes so as to compete less with these herbivores.