Bryozoans are epibenthic suspension-feeders and use their ciliated tentacles to generate feeding currents. Modern bryozoan mouth size limits the size of the particles that can be ingested, and lophophore diameter is linked to water pumping rates. In fossil bryozoans these soft parts are absent, however, mouth and lophophore dimensions can be inferred from preserved skeletons. Gondwanan Permian palaeostomate bryozoans show distinct order-level trophic partitioning across warm to cold-water faunas. In diverse warm-water faunas of southern Thailand fenestrate bryozoans consume the smallest food particles, cryptostomes and trepostomes consume mid-size particles, and cystoporates consume the largest, and widest range, of particles. In contrast, in low diversity cold-water faunas of eastern Australia, where cystoporates and cryptostomes are uncommon, fenestrate bryozoans again consume the smallest food particles, however the abundant trepostomes have much larger mouths than their warm-water counterparts and consume the largest food particles. This plasticity in mouth size, especially in the trepostomes, suggests that mouth size is not controlled by systematics and that sessile benthic organisms are trophically structured to utilise different sized food particles from a suspended food source. Gondwanan Permian palaeostomates have much larger mouth and lophophore sizes than modern stenolaemates (cyclostomes) and are more comparable to gymnolaemate (cheilostome) bryozoans. This suggests that palaeostomates were able to access and consume the same range of food resources as modern bryozoans, and feed at similar rates, prior to the marine environmental changes at the close of the Palaeozoic, and that modern cyclostome stenolaemates are probably limited by the more successful cheilostomes.

PERMIAN DATA
Zooecial aperture dimension and apertural spacing data for Permian bryozoans were gathered from measurements provided in systematic descriptions of eastern Australia (Crockford 1941a-b, 1943, 1945; Wass 1968; Reid 2003; Morozova 2004), Western Australia (Crockford 1944a-c, 1957; Ross 1963) and the Rat Buri Limestone of southern Thailand (Sakagami 1966, 1968a-c, 1970, 1971, 1973, 1975, 1999; Reid 2001). The data for apertural size and closest spacing (centre to centre) were used in the form of averages, either directly as reported by the source, or calculated from maximum and minimum if only the range data were available. Where spacing data was not available in measurements, they were either taken from figured material, or calculated from quoted number of apertures in a given distance, or are left missing. Expected polypide mouth size and lophophore diameter (in millimetres) was calculated from mean skeletal aperture size using the regression formula of Tamberg & Smith (2020) derived from modern stenolaemate bryozoans.

MD = 0.22 x [(AW+AL)/2] + 0.011mm
where MD is mouth diameter, AW aperture width and AL aperture length.

LD = 1.9 x [(AW+AL)/2] + 0.1639mm
where LD is lophophore diameter.

The equation of Snyder (1991) was also to calculate lophophore diameter as it utilises an alternative predictor.
LD = 1.5 x AS
where AS is closest apertural spacing.

MODERN DATA
Mouth and lophophore diameter measurements of living cheilostome and cyclostome bryozoans were gathered from published literature (Borg 1944; Rogick 1949; Ryland 1967, 1975, 1977; Winston 1977, 1978, 1979; Best & Thorpe 1986; Pouyet & Herrera-Anduaga 1986; Ryland & Hayward 1991; Riisgård & Manríquez, 1997; Nielsen & Riisgård 1998; Gordon & Taylor 2001; Shunatova & Ostrovsky 2001; Ramalho et al. 2009; Ryland et al. 2009; Tamberg & Smith 2020) and new measurements collected by YT following techniques in Tamberg and Smith (2020). Lophophore diameter may be listed as tentacle crown diameter in publications on modern bryozoans.

All measurements are in millimetres.

Refer to ReidTamberg2021bryozoaReadMe.txt.