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Fig. 120: The heart and blood vessels. Cv: cardiac vessels, bw: body wall.

Fig. 119: Position of the organs within the fossil (top) with a reconstruction of the fossil (bottom).

PRINCIPAL PUBLICATION AND AUTHORS

Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte, K. Trinajstic (a), J.A. Long (b), S. Sanchez (c), C.A. Boisvert (a), D. Snitting (c) P. Tafforeau (d), V. Dupret (c) A.M. Clement (b), P.D. Currie (e), B. Roelofs (c) J.J. Bevitt (f), M.S.Y. Lee (b), P.E. Ahlberg (c), Science, 377(6612), 1311-1314 (2022); https:/doi.org/10.1126/science.abf3289 (a) School of Molecular and Life Sciences, Curtin University, Bentley (Australia) (b) College of Science and Engineering, Flinders University, Adelaide (Australia) (c) Department of Organismal Biology, Evolutionary Biology Center, Uppsala University, Uppsala (Sweden) (d) ESRF (e) ARMI, EMBL Australia Building, Monash University, Clayton (Australia) (f) Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights (Australia)

REFERENCES

[1] K. Trinajstic et al., Science 341, 160-164 (2013). [2] D. Goujet, Comptes Rendus Palevol 10, 323-329 (2011). [3] J.A. Long et al., Nature 457, 1124-1127 (2009).

revealed greater complexity than had been predicted [1]. Most recently, the first organs of a 380-million-year-old arthrodire placoderm fish were shown, and these not only represent the earliest organs, preserved in 3D for a jawed fish, but provide information on the timing of the evolution of key jawed vertebrate traits.

A key question in palaeontology has been whether lungs were a basal character common to all jawed vertebrates or if lungs were a synapomorphy of the bony fishes. The identification of lungs in placoderms has been controversial [2]. The data showed a large liver overlain by a glandular stomach (Figure 119) in the position that the presumed lungs occupied. No living animal has the stomach positioned over the lungs. In addition, the presence of embryos [3], recovered directly behind the shoulder girdle, indicate the position of the uteri in females and other reproductive organs leaving no room for lungs (Figure 119). It was therefore concluded that placoderms lacked lungs and, like many sharks, used a large liver for buoyancy.

Direct evidence for feeding in fossils is also rare but, in addition to the stomach, the last meal of the placoderm the remains of the legs and spines from a phyllocarid arthropod (Montecaris gogoensis) were also recovered from the stomach and spiral intestine.

The heart was identified in two specimens, one using ID19 and one using neutron radiography (Dingo beamline) at the Australian Nuclear Science and Technology Organisation (ANSTO). The S-shaped heart with the associated blood vessels (Figure 120) was located under the gills in a more anterior position to that of jawless fishes. This discovery provided the first fossil evidence that the development of the neck, also a characteristic of the jawed vertebrates, is linked with the anterior migration of the heart and the evolution of jaws.

These results provide the most complete information on the internal anatomy of a stem-group jawed vertebrate and shed light of the anatomical changes from jawless to jawed vertebrates, one of the greatest evolutionary steps.