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Palaeoentomology: towards the big picture

100%

Jarzembowski E. A.

Acta Zoologica Cracoviensia

2003

tom 46

nr Suppl.

Insects (Superclass Hexapoda) are the most palaeodiverse as well as the most biodiverse organisms of all time but probably total under 20 million species. Familial/generic data agree with an exponential growth model of the evolution of terrestrial life. Ordinal data is consistent with a logistic model but with a major perturbation superimposed (the Triassic extinction). The global taxonomic carrying capacity is about 31 for orders whereas familial and species data suggest power functions. Key events in the Phanerozoic insect record are briefly discussed.

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Palaeobiology and evolutionary context of Angulithes mermeti, a streamlined early Late Cretaceous shallow - water nautiloid

67%

Wilmsen M., Nagm E.

Acta Palaeontologica Polonica

2019

tom 64

nr 4

Cretaceous nautiloids are commonly characterized by inflated shells and prolonged stratigraphic ranges. In the Albian, the species of Angulithes appeared and compressed, short-lived forms with narrow venters emerged during the Cenomanian age. Based on a new description, the late Cenomanian nautiloid Angulithes mermeti is discussed with its palaeobiological background and placed in an evolutionary context of the Cenomanian lineage of Angulithes, considering contemporaneous palaeoenvironmental changes and inferred functional traits. A. mermeti is characterized by a nearly oxycone shell with sharp venter and narrow umbilicus, a fairly sinuous suture, low inter-septal distances, and an almost dorsal siphuncle. Its palaeobiogeographical occurrence was latitudinally restricted to shallow tropical–subtropical shelf seas with a preferred habitat depth between 5–50 m. Several morphological trends reflected by the Cenomanian species of the genus culminated in the late Cenomanian species A. mermeti, i.e., (i) increasing shell compression and sharpening of the venter, (ii) increasing folding of the septa, (iii) reduction of inter-septal distances, and (iv) dorsally directed migration of the siphuncle. The hydrodynamically efficient form was favorable to successfully populate the wide and shallow epicontinental seas that formed during the Cenomanian age. The increasing sutural sinuosity and the dense septal spacing aimed to buttress the shells against shell-breaking predators while the functional reason for the dorsal- directed migration of siphuncle is more elusive; it may have improved the efficiency of the hydrostatic apparatus and its internal position is beneficial in the case of predation, too. The gradual morphological change in the Cenomanian lineage of the genus Angulithes provides a well-constrained case study of rapid evolutionary response to major environmental pressure, i.e., the opening of newly available niches in the course of the great early Late Cretaceous transgression, in an otherwise rather bradytelic biotic group.

Ograniczanie wyników

1 Acta Palaeontologica Polonica

1 Acta Zoologica Cracoviensia

1 Jarzembowski E. A.

1 Nagm E.

1 Wilmsen M.

1 2019

1 2003

Wyniki wyszukiwania

Palaeoentomology: towards the big picture

Palaeobiology and evolutionary context of Angulithes mermeti, a streamlined early Late Cretaceous shallow - water nautiloid