Reduction in body size of organisms following mass extinctions is well-known and often ascribed to the Lilliput effect. This phenomenon is expressed as a temporary body size reduction within surviving species. Despite its wide usage the term is often loosely applied to any small postextinction taxa. Here we assess the size of bivalves of the family Limidae (Rafineque) prior to, and in the aftermath of, the end-Triassic mass extinction event. Of the species studied only one occurs prior to the extinction event, though is too scarce to test for the Lilliput effect. Instead, newly evolved species originate at small body sizes and undergo a within-species size increase, most dramatically demonstrated by Plagiostoma giganteum (Sowerby) which, over two million years, increases in size by 179%. This trend is seen in both field and museum collections. We term this within-species size increase of newly originated species in the aftermath of mass extinction, the Brobdingnag effect, after the giants that were contemporary with the Lilliputians in Swift's Gulliver's Travels. The size increase results from greater longevity and faster growth rates. The cause of the effect is unclear, although it probably relates to improved environmental conditions. Oxygen-poor conditions in the Early Jurassic are associated with populations of smaller body size caused by elevated juvenile mortality but these are local/regional effects that do not alter the long-term, size increase. Although temperature-size relationships exist for many organisms (Temperature-Size Rule and Bergmann's Rule), the importance of this is unclear here because of a poorly known Early Jurassic temperature record.

The enigmatic fissure deposits of south-western England and southern Wales are famous for their unique assemblage of Late Triassic vertebrates, although their age is contentious. While recent studies of palynomorphs have dated some as Rhaetian, their conchostracan (Crustacea, Branchiopoda) assemblages have not been described in detail nor used in biostratigraphy. We find that species determination of British Late Triassic conchostracans requires detailed observations of size, shape and ornamentation. We provide evidence that although Euestheria brodieana is invariably smaller than E. minuta, with some slight differences in carapace ornamentation, the traditional view that they are very similar is upheld. The use of conchostracans as a biostratigraphical tool is here tested by application to the British Triassic fissures at Cromhall quarry where the usual stratigraphical evidence provided by superposition is absent. We find no distinction between conchostracans from bedded Rhaetian deposits of the UK and specimens collected from the fissure deposits of Cromhall Quarry, Gloucestershire, supporting a late Rhaetian age for these deposits.

Unresolved taxonomic issues regarding spinicaudatans, clam shrimps that formed the most abundant faunal element in the lacustrine Barremian to Aptian Yixian Formation, have hampered palaeoecological and evolutionary interpretations of this key fossil group. Here, we analyse morphological variability in East Asian clam‐shrimp taxa by quantifying: (1) size and shape; and (2) ornamental features (radial lirae distances). Intergeneric variability was examined using 51 specimens of various East Asian Mesozoic taxa, 16 of which were chosen for a taxonomic revision of the 10 species described from the Yixian Formation of western Liaoning. Geometric morphometrics proved to be effective for the separation of genera, while the quantification of ornamental features was species‐diagnostic. Various authors have previously indicated the possibility that East Asian clam‐shrimp species have been split excessively, a criticism that has been confirmed by our analyses. According to our results, four of the ten species described from the Yixian Formation are valid, of which one might represent a junior synonym of Diestheria jeholensis; five taxon names represent junior synonyms of Eosestheria middendorfii (Jones), and one a nomen dubium. According to lirae distances and analysis of shape, Eosestheria fuxinensis, the original type species of Eosestheria, is synonymous with the type of Diestheria. Therefore, a new type species for Eosestheria is warranted and here fixed as E. middendorfii. This taxonomic revision questions the high level of clam‐shrimp diversity recognized within the Yixian Formation, and indicates that many of the species described in fact represent various ontogenetic stages of E. middendorfii.

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