The sponge pump as a morphological character in the fossil record

Abstract

The timing of early animal evolution remains one of the biggest conundrums in biology. Molecular data suggest Porifera diverged from the metazoan lineage some 800 Ma to 650 Ma, which contrasts with the earliest widely accepted fossils of sponges at 535 Ma. However, the lack of criteria by which to recognize the earliest animals in the fossil record presents a challenge. The sponge body plan is unchanged since the early Cambrian, which makes a sponge-type animal a good candidate for the earliest fossils. Here we propose a method for identifying an organism as sponge grade by translating the sponge pump character into a quantifiable morphological trait. We show that the ratio between the two major components of the aquiferous system, the cross-sectional area of the osculum (OSA) and the surface area of the whole sponge (SA), is an effective metric of the pump character of extant sponges and that the slope of this ratio is distinct for three classes of Porifera: Demospongiae, Calcarea, and Hexactinellida. Furthermore, this metric is effective at distinguishing as sponges both extant taxa and fossils from two extremes of the Phanerozoic, the Cambrian and Paleogene. We tested this metric on the putative Ediacaran sponge Thectardis avalonensis from Mistaken Point, Newfoundland, and found Thectardis fits both with Cambrian sponges and with modern demosponges. These analyses show that the OSA/SA ratio is a reliable character by which to identify fossils as sponge grade, opening up exciting possibilities for classifying new fossils as sponges.

Keratose sponges in ancient carbonates – A problem of interpretation

“…2E). In Turner's (2021) study no mesoscopic body fossil with its overall shape and organization (architecture) that might help to determine its nature, is reported; and at the microscopic scale, there is a problem because no sponge‐specific attribute such as the canal system (Aragonés Suarez & Leys, 2022) is preserved, although the enclosing microcrystalline phase is interpreted to represent automicrite resulting from mummification (Luo & Reitner, 2014, 2016). However, automicrite is not normally seen in published interpretations of keratose sponges (for examples, see Figs 4C, 13E and 13F).…”

“…1A, B). Recently, Aragonés Suarez & Leys (2022) proposed a model for fossil sponge recognition based on the presence of a canal system. However, there are no verified canals in all the fossil examples illustrated here and in publications interpreting keratose sponges examined in this study.…”

Adaptive specialization of a unique sponge body from the Cambrian Qingjiang biota

“…Admittedly, the body shape of sponges is across a wide range of variety [ 48 – 51 ]. Beside the common and idealized shapes, such as spherical, cylindrical, conical and crustose forms [ 49 , 52 ], there are a number of modern deep-sea sponges with peculiar morphology. For examples, glass sponges of Rossellidae and Farreidae (Hexactinellida) usually have a long, distinctive stalk and a bulged, ramulous main body part, reminiscent of a porous mushroom or a thick plume; carnivorous sponges of Poecilosclerida (Demospongiae) look like flowers of dandelions or slender tree branches with dense, tiny and horrible spinules [ 53 ].…”

Decline and fall of the Ediacarans: late‐Neoproterozoic extinctions and the rise of the modern biosphere

“…Externally opening compartments with putative ciliary pumping in rangeomorphs (Butterfield, 2020) and the fluid-dynamics of radialomorphs (Rahman et al, 2015;Cracknell et al, 2021) and erniettomorphs (Gibson et al, 2019;Darroch et al, 2022) suggest suspension feeding (although see Darroch et al, 2023a), with possible commensalistic aggregates (Gibson et al, 2019;Darroch et al, 2022) enhancing vertical mixing while exploiting turbulence for nutrient advection. If ocean oxygenation during the Shuram NCIE (Zhang et al, 2019) stemmed at least in part from the assembly of the poriferan (Suarez & Leys, 2022) and eumetazoan (Butterfield, 2020) Laakso et al, 2020), which may in turn precipitate nitrogen limitation by favouring nitrate-reducing bacteria (Tyrrell, 1999). Nitrogen or, perhaps more plausibly, phosphorus (Xiang et al, 2018) limitation itself may have driven the decline in primary productivity proposed by Brasier (1992) to account for late-Neoproterozoic NCIEs.…”

“…Externally opening compartments with putative ciliary pumping in rangeomorphs (Butterfield, 2020) and the fluid‐dynamics of radialomorphs (Rahman et al ., 2015; Cracknell et al ., 2021) and erniettomorphs (Gibson et al ., 2019; Darroch et al ., 2022) suggest suspension feeding (although see Darroch et al ., 2023 a ), with possible commensalistic aggregates (Gibson et al ., 2019; Darroch et al ., 2022) enhancing vertical mixing while exploiting turbulence for nutrient advection. If ocean oxygenation during the Shuram NCIE (Zhang et al ., 2019) stemmed at least in part from the assembly of the poriferan (Suarez & Leys, 2022) and eumetazoan (Butterfield, 2020) DOC‐removal pumps, its disruption in ‘depauperate’ late‐Ediacaran communities might have promoted a shift from oxygenated, low‐suspended‐carbon to turbid, stratified anoxic waters.…”