Changes in the timing of mantle formation and larval life history traits in linguliform and craniiform brachiopods

The distribution of embryonic and larval mantles is documented in linguliform and craniiform brachiopods. Criteria are presented for identifying these mantle types. The mantle type is related to planktotrophic and lecithotrophic larval life history patterns. In the Linguliformea and Craniiformea, all Lower Palaeozoic families with adequate preservation had larval mantles, indicating the presence of a planktotrophic larva. Heterochronic changes in the time of mantle origin, from the larval to the embryonic stage of development, has occurred several times. In the Lingulidae this change appears to have taken place at about the time the family originated in the Devonian and has been retained in extant genera. The family Discinidae has also retained a planktotrophic larval stage from the Lower Palaeozic to the present. The extant genus Crania in the Craniidae has a short-lived lecithotrophic larva that lacks a mantle. Through the Lower Jurassic, this family had planktotrophic larvae with a larval shell. During the Upper Jurassic, genera with a lecithotrophic larva that lacked a larval shell began to appear; however, the last genera in this family with a planktotrophic larva and a larval shell did not become extinct until the Tertiary.