However, the Pliosaur was actually from the lower Cenomanian Stage of the Mid Cretaceous/earliest Late Cretaceous Period.
Therefore, it is somewhat hugely anachronistic for it to be the Pliosaur claimed to be the one shown in the episode. Considering that the Cenomanian Stage was between roughly 100.5 Ma and 93.9 Ma, the fact that Plesiopleurodon was from the lower Cenomanian roughly 98 Ma (also being based on limited though relatively high quality fossil evidence) and that the episode in which this Pliosaur apparently appears, is set 127 Ma, the likelihood is that the show never intended this Pliosaur to be regarded as Plesiopleurodon, but simply a generic example of a Pliosaur (blatantly using the Liopleurodon model, albeit recoloured)
A potential reason behind why the inclusion of this mysterious Pliosaur, is regarded to be an attempt to allude to Plesiopleurodon, is the fact that, in naming the specimen, Carpenter (1996, p. 264) noted "Of all known pliosaurs, Plesiopleurodon wellesi most closely resembles Liopleurodon ferox from the Oxfordian of Europe, hence the generic reference."
Perhaps some people took notice of those similarities and looked at the general region of where the Ornithocheirus (Tropeognathus) really was at this point in the episode - that is, flying across the younger Atlantic Ocean, not far from what is now North America - and pointed at Plesiopleurodon to be the intended Pliosaur portrayed. However, even this explanation seems unlikely, though it does superficially make sense. Essentially, it could just be considered an error, by either the show or the fans. In other words, it is unsubstantiated by the makers of Walking With Dinosaurs, and possibly mere fan speculation. Whatever the case, it is erroneous and anachronistic to call this a Plesiopleurodon in truth.
For now, the name Plesiopleurodon has been casually used to describe the unnamed Pliosaur shown in the episode here; though perhaps it'd be more appropriate to call this page, "Unnamed Pliosaur" - because whatever Pliosaur we want to call it, it certainly cannot be a Plesiopleurodon in truth, due to there being 29 million years in between the evidenced time in which Plesiopleurodon lived as far as we know (98 Ma; though it may have been much more long lived, but no evidence for this has been found as of yet) and the setting of the fourth episode, 127 Ma.
It was found and collected in the Belle Fourche Shale, in the Rattlesnake Hills of Wyoming, USA. The species is characterised by a moderately long symphysis bearing 8 pairs of teeth, teeth that are nearly circular in cross-section and which are smooth on the outer surface (except near the base), ribs of the neck vertebrae being singled-headed (double-headed in Jurassic Pliosaurs), and a long slender interpectoral bar on the coracoid.
Plesiopleurodon (supposedly) makes a cameo appearance in Giant of the Skies. While the Ornithocheirus (Tropeognathus) is flying over the ocean, Plesiopleurodon is seen to eye the huge Pterosaur passing above the water surface in low flight. Although a genuine threat to a delicately built Pterosaur, and easily powerful enough to launch itself out of the water to a low height to grab the Pterosaur from the air, this Plesiopleurodon seemed simply more curious than hostile. It raised its head up briefly to look at what had passed overhead, and then it dipped its head back down as it carried on moving through his mysterious waters.
Though the CGI model for Liopleurodon was clearly the basis for this unidentified "hungry monster", having been recoloured in rendering to look sort of Matt-Brown in colour, or some mottled dull colour covering the entire body, this cameo species was not as well animated. It looks more like the pilot episode rough CG designs of a Pliosaur; and likely was only given slightly better animation. Nevertheless, its appearance lasted for less than 10 seconds, so this was clearly included to add further drama to the migration of the old Ornithocheirus (Tropeognathus) yet perhaps was rushed slightly as a minor addition only seconds long. Also this recoloured model was misidentified as Liopleurodon in the U.S. dub narrated by Avery Brooks.
This episode is set 127,000,000 years ago, and therefore this creature certainly wasn't intended to represent Liopleurodon, which had died out long before this time. In general, it is considered that Liopleurodon lived between the Callovian to Kimmeridgian Stages of the Jurassic Period (roughly 165-155 Ma; across the Callovian, Oxfordian and Kimmeridgian Stages, respectively) This means that around 28 million years had passed since the last Liopleurodon, before the events of the fourth episode of the series.
At most - and this is simply pushing it as far as speculation will allow - it could be speculated that (going off the ever changing definitions of the geological timescale when it comes to Stage boundaries, and the fact that Liopleurodon were quite successful for a long time as far as we can tell) there may have been some Liopleurodon making it into the Tithonian Stage, the last Stage of the Jurassic Period (there is no evidence for that as of yet, and potentially never will be)
Therefore, there is absolutely no chance that the deliberately remodelled/re-skinned Pliosaur we see in Giant of the Skies, could be a Liopleurodon (though as explained above, the Liopleurodon model was obviously used for convenience) 127 Ma is actually right in the middle of the Barremian Stage of the Early Cretaceous Period - and a full three Stages of the Early Cretaceous had already passed prior to this Stage (in respective order starting from oldest to youngest; the Berriasian, Valanginian and Hauterivian Stages) None of which have any evidence of Liopleurodon. Meanwhile, Plesiopleurodon, is only known from the lower Cenomanian Stage, at least as far as we know.