HERBIVORE PERSISTENCE AND CHANGE ON BROAD-LEAVED CONIFERS BETWEEN THE MIDDLE JURASSIC AND EARLY CRETACEOUS OF NORTHEASTERN CHINA

A continual theme in conifer history is the production of a recurring leaf type that consists of a broad, planted, lanceolate-shaped blade with entire margins and parallel veins that originate basally and are differentiated into major veins and minor veinules. Examples of these leaf isomorphs include Late Triassic voltzialean conifers (Heidiphyllum), mid-Mesozoic Podozamites, Lindeycladus and Liaoningocladus, and Agathis, the Podocarpaceae (e.g., Podocarpus, Nageia, Dacryidium) and Araucariaceae (e.g., Araucaria bidwillii) of mostly the Cenozoic. Because of this structural convergence of leaf form, we established an hypothesis that taxonomically disparate species would host very similar herbivore communities. To test this hypothesis, we sampled from the Inner Mongolia Autonomous Region and Liaoning Province, in northeastern China, three broadleaved conifer taxa from three sites near Daohugou and Yangcaogou (Jiulongshan Fm., latest Middle Jurassic), and the 40 million-year younger three sites at Dwangzhangzi, Liutiaogou and Duolun (Yixian Fm., late Barremian). The Middle Jurassic taxa were Podozamites lanceolatus and Lindeycladus; the Earl Cretaceous provided Liaoningocladus boii and the long-ranging L. lanceolatus. We found 19 damage types (DTs) on all three plant hosts from both periods, consisting of external foliage feeding (6 DTs), piercing and sucking (4 DTs), oviposition (3 DTs) and leaf mining (1 DT). Four of these DTs were restricted to the Middle Jurassic; five were found exclusively in the Earl Cretaceous. An assessment of DT diversity and relative abundance data indicated that DT diversity and abundance was greater in the Cretaceous, and a higher proportion of host specialization occurs for L. boii, suggesting a more saturated component community of generalist and specialist herbivores for the Early Cretaceous. These data imply that structurally similar plant-host lineages may accumulate herbivore associations gradually through time, asymptoting to a saturated component community. Alternatively, undetected factors in plant-host biochemical or structural tissue defenses may have disallowed herbivory in certain broadleaved plant hosts that otherwise appear physiognomically similar.