Rangeomorph nutrition

Rangeomorphs were ancient seafloor organisms with branching bodies that could look like fronds or rows of small fans. Their deep-water fossils leave a basic question: how did they obtain food? Possibilities include absorbing dissolved nutrients across a body surface, collecting particles from moving water, or relying on microbial partners. None is established for all of them.[1] [2]

Rangeomorphs were branching organisms in ancient seafloor communities; their deep-water fossils preserve form more readily than feeding function. How did these bodies acquire nutrients, and how did their living position affect that process? Pectinifrons, for example, had two rows of branches arranged like a fence.

Absorbing dissolved nutrients through a surface is called osmotrophy; capturing food particles from water is suspension feeding. Each needs a suitable interaction between the body and flowing water. Darroch and colleagues simulated flow around Pectinifrons reconstructions and found problems with both feeding interpretations under their assumptions. Fine surface details, flexibility and current direction limit the test.

A separate hypothesis proposes that some rangeomorphs reclined on the sediment and benefited from microbial partners. That changes the relevant water–sediment contact, but neither the position nor the partnership supplies a demonstrated feeding mechanism for every rangeomorph.[1] [2]

Their anatomy and water flow constrain possible answers, but feeding and living position remain debated.[1] [2]

Pectinifrons simulations constrain absorption and suspension-feeding interpretations under model assumptions. Reclining reconstructions and symbiotic proposals require further evidence and cannot be generalized to every taxon.[1] [2]

Different feeding modes put an organism in different relationships with its surroundings: dissolved nutrients, drifting particles or living partners. Working out which applied would reconstruct how some of the earliest large seafloor communities obtained energy, rather than just what their members looked like.[1] [2]

A branching surface might serve food uptake, gas exchange or another function; similar shapes need not perform the same job. Discriminating among these possibilities changes how we reconstruct the movement of nutrients and energy through early large-organism communities. It also tests how much function can be inferred from fossil form when soft tissues and living behavior are missing, rather than treating a plausible reconstruction as an observation.[1] [2]