The Earliest Evidence of Holometabolan Insect Pupation in Conifer Wood

Background: The pre-Jurassic record of terrestrial wood borings is poorly resolved, despite body fossil evidence of insect diversification among xylophilic clades starting in the late Paleozoic. Detailed analysis of borings in petrified wood provides direct evidence of wood utilization by invertebrate animals, which typically comprises feeding behaviors.\ud \ud Methodology/Principal Findings: We describe a U-shaped boring in petrified wood from the Late Triassic Chinle Formation of southern Utah that demonstrates a strong linkage between insect ontogeny and conifer wood resources. Xylokrypta durossi new ichnogenus and ichnospecies is a large excavation in wood that is backfilled with partially digested xylem, creating a secluded chamber. The tracemaker exited the chamber by way of a small vertical shaft. This sequence of behaviors is most consistent with the entrance of a larva followed by pupal quiescence and adult emergence — hallmarks of holometabolous insect ontogeny. Among the known body fossil record of Triassic insects, cupedid beetles (Coleoptera: Archostemata) are deemed the most plausible tracemakers of Xylokrypta, based on their body size and modern xylobiotic lifestyle.\ud \ud Conclusions/Significance: This oldest record of pupation in fossil wood provides an alternative interpretation to borings once regarded as evidence for Triassic bees. Instead Xylokrypta suggests that early archostematan beetles were leaders in exploiting wood substrates well before modern clades of xylophages arose in the late Mesozoic

<i>Shajia</i>, a new genus of polyconitid rudist from the Langshan Formation of the Lhasa Block, Tibet, and its palaeogeographical implications

A new polyconitid rudist Shajia tibetica gen. et sp. nov., of late Aptian to Albian age, is described from the Langshan Formation of Nyima County, northern Lhasa Block, Tibet. Though comparable in size and external morphology with Horiopleura haydeni Douvillé, which is a common endemic species in southwestern Asia, Shajia differs from the latter species in its possession of an inwardly inclined, instead of outwardly facing, posterior myophore in the right valve. In addition, a single specimen from Ladakh, which was previously assigned to Polyconites? sp., on account of a similar myophoral distinction from H. haydeni, is transferred to the new genus. Shajia is considered most likely to have been derived from one of a group of Horiopleura species that lived on the southern margin of the Mediterranean Tethys. The so-called ‘Yasin fauna’ represented by the late Aptian to Albian Horiopleura haydeni/ Auroradiolites gilgitensis rudist association, is considered to be restricted to southwestern Asia, including Afghanistan, Kohistan in northern Pakistan and Ladakh in northern India, though those two species in particular have not so far been recorded from the Lhasa Block of Tibet. Nevertheless, S. tibetica co-occurs with Auroradiolites biconvexus (Yang et al.), which probably evolved directly from A. gilgitensis (Douvillé), and the age of the latter association is in accordance with the generally accepted age of the Yasin fauna as late Aptian to Albian. Hence the S. tibetica and A. biconvexus association can be considered a regional variant of the Yasin fauna, which had evidently already dispersed to the Lhasa Block by the late Aptian. So the Langshan Formation can be considered palaeogeographically linked with other mid-Cretaceous shallow-marine carbonate deposits in adjacent southwestern Asian regions. These findings also provide new evidence that the age of the rudist assemblage of the Lhasa Block is late Aptian to Albian, although a slightly younger age cannot be excluded