Aug 4, 2015

Earliest known - 565 million year old - seafloor breeding strategy

The way that some of Earth’s earliest large multi-celled organisms reproduced is turning out to be surprisingly complex according to new research.
Category: Aug 2015
Posted by: Sarah

A reconstruction of reproductive clusters of the 565 million year old rangeomorph fossil Fractofusus on a Newfoundland seabed in late Precambrian times (Artwork by co-author/Cambridge palaeontologist Charlotte G. Kenchington)

Lead palaeontologist Emily Mitchell from the Department of Earth Sciences in Cambridge and colleagues from Oxford and Bristol have been studying the 565 million year old remains of some very curious seabed dwelling organisms called Fractofusus, one of a number of extinct organisms known as the rangeomorphs. The spindle-shaped fossils (1-42 cm long) of Fractofusus are only known from late Precambrian age rocks exposed on the barren wind-swept cliffs of, Newfoundland, Canada.

Mistaken Point, Newfoundland on a good day, showing the fossil bearing strata and the GPS transmitter used for spatial positioning at a millimetre-scale.

Amongst the most puzzling fossils known, the immobile and soft-bodied rangeomorphs grew to between 10 cm and almost two metres in size and had a unique self-similar, fractal-like, branching construction and are quite unlike any living organisms. Their fossils have been subject to intense research for several decades but researchers have been frustrated by the lack of anatomical evidence of reproductive structures or internal biology preserved in the rock. It is only now that new techniques are beginning to reveal aspects of their biology.

Close-up, a sediment mould of a Fractofusus surface shows its distinctive self-similar, fractal branching (photo E.G. Mitchell)

By using sophisticated spatial analysis of over 3000 specimens, the clustering patterns of different sizes of Fractofusus, it can be seen that small ‘juveniles’ occur close to larger, more widely and randomly spaced larger ‘mature’ forms. Similar patterns are found in plants with a dual mode of asexual and sexual reproduction. In the rangeomorphs, the asexual mode, through a stolon-like process similar to strawberry plant runners, produced numerous small but clearly separate forms in close proximity to the larger ones; whilst the rarer water-borne stage involved the release of propagules, possibly sexually-produced gametes, into the surrounding seawater, producing the more widely distributed larger forms. This dual mode of reproduction allowed Fractofusus to colonise new areas of seabed, and then to rapidly establish itself.

The rocky surface of a Late Precambrian seabed with its scattered clusters of Fractofusus marked up for spatial data collection

The research is published in advance online on the 3rd August, 2015 for the journal Nature.