Materpiscis attenboroughi, Long, John A., Trinajstic, Kate, Young, Gavin C. & Senden, Tim, 2008
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publication ID |
https://doi.org/ 10.1038/nature06966 |
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DOI |
https://doi.org/10.5281/zenodo.6229967 |
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persistent identifier |
https://treatment.plazi.org/id/126A8965-FF9F-761A-FF5E-BA4EFD7EFA75 |
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treatment provided by |
Jeremy |
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scientific name |
Materpiscis attenboroughi |
| status |
sp. nov. |
Materpiscis attenboroughi gen. et sp. nov.
Etymology. Generic name from the Latin meaning ‘mother fish’; species name in honour of Sir David Attenborough, who first drew attention to the Gogo fish sites in his 1979 series Life on Earth.
Holotype. WAM 0 7.12.1 ( Western Australian Museum, Perth) View . Age and locality. From the Stromatoporoid camp locality, Gogo Station, near Fitzroy Crossing , Western Australia (Late Devonian, early Frasnian) .
Diagnosis. A small aspinothoracid ptyctodontid fish having an ante- riorly pointed nuchal plate that participates in the posterior margin of the skull roof, broad roughly triangular-shaped preorbitals that meet mesially; the marginal plate has a large postorbital region with parallel rows of tubercles adorning it; the submarginal is strap-like and strongly curved mesially; robust triturating tooth plates that meet only at anterior tips, superognathals with moderately high anterior dorsal process. The body is scaleless.
Description. Materpiscis gen. nov. ( Figs 1–3 View Figure 1 View Figure 2 View Figure 3 ) is readily distinguished from all other known ptyctodontids by the combination of lacking a spinal plate with anteriorly pointed nuchal plate ( Fig. 1 View Figure 1 e), and a much-expanded postorbital region on the marginal plate ( Fig. 1 View Figure 1 f). The nuchal plate participates in the posterior margin of the skull roof and the centrals are unusually broad ( Fig. 1 View Figure 1 e). The skull roof is unusual in having prominent raised ridges for the main sensory-line canals ( Fig. 1 View Figure 1 e). The tooth plates can be moved against each other as in life. This shows that only the anterior-most biting edges of the jaws met in full occlusion ( Fig. 1 View Figure 1 i). The trunk shield plates do not differ significantly from those of many other aspinothoracid ptyctodontids, in particular Austroptyctodus 7, except for proportions and ornamentation, the median dorsal having a low median crest. A restoration of the dermal armour is shown in Fig. 1 View Figure 1 h. A detailed description of the dermal and axial skeleton, braincase and dentition of Materpiscis gen. nov., and its embryonic skeletal morphology, will be published elsewhere.
The Gogo Formation has yielded the earliest phosphatized gnathostome muscle tissues and nerve fibres 9, and the new specimen shows additional soft-tissue preservation never before recorded in any fossil. The new specimen is exceptional in revealing a small partial skeleton located within the upper body cavity of a pregnant, adult female ptyctodontid placoderm ( Fig. 1 View Figure 1 a–d). The relatively complete adult skeleton includes much of the tail ( Fig. 1 View Figure 1 a). The single, partially ossified juvenile skeleton inside the body cavity of the adult clearly belongs to the same species based on characteristic tooth-plate and marginal plate morphology ( Fig. 1 View Figure 1 c, d). The small internal individual must be an embryo, rather than an ingested prey item, because the delicate bones show no breakage or etching from stomach acids, and the dentition is of similar gross morphology to that of the adult. The location of the preserved embryo close to the vertebral column suggests that it is in the uterus rather than the gut, a view supported by the presence of mineralized soft tissue forming a placental connection between embryo and mother. Furthermore, a second specimen from Gogo, previously described as Austroptyctodus gardineri 7, has been re-examined and we have identified three small embryos in the same position posterior to the adult anterior lateral plate as in Materpiscis gen. nov. ( Fig. 1 View Figure 1 g). Cases demonstrating viviparity in the fossil record are extremely rare, the best being Mesozoic ichthyosaurs 10,11 and mosasauroids 12. Presumed fetal specimens of a holocephalan fish from the Lower Carboniferous of Montana 13 may extend the record of viviparity back into the Palaeozoic era, but were not found in or near the body cavity of the mother. Our new example extends the definite record of vertebrate viviparity back by some 200 million years.
The embryos of Materpiscis gen. nov. and Austroptyctodus are about 25% of the adult size, based on proportions of the anterior lateral plate. The embryonic bones are remarkably thin and fragile, yet perfectly preserved, with the upper and lower dentition still in occlusion in Materpiscis gen. nov. ( Figs 1 View Figure 1 b–d and 2g). The skull bones of this specimen are oriented posteriorly, indicating that the embryo was curled. Only some dermal plates are represented in the embryos. Absence of certain bones at an early developmental stage is also recorded in tiny (14–16 mm) juvenile skeletons of the antiarch placoderm Asterolepis 14. Identified embryonic bones comprise paired preorbitals, a paranuchal, anterior dorsolateral, anterior lateral and a marginal plate, and both sets of tooth plates in articulation ( Figs 1 View Figure 1 b–d, g and 2g, f). The supragnathals of Materpiscis gen. nov. meet at a distinct medially directed symphysis (sym, Fig. 2 View Figure 2 g), lending increased structural support for biting ability immediately after birth.
A thin tube of mineralized white material with slight helical twisting (umb, Fig. 1 View Figure 1 c, d) connects the Materpiscis gen. nov. embryo to a region within the upper body cavity of the female, marked by an ovoid mass of coarsely crystalline calcite, possibly the position of the yolk sac ( Fig. 1 View Figure 1 c, d). In modern sharks, the umbilical cord wall comprises multiple small vessels, capillaries and a dense spongy
connective tissue 15. The fossilized tube has similar external shape and position as the umbilical cord in chondrichthyans. High-resolution scanning electron microscopy (SEM) imaging and high-resolution computer tomography scanning of this specimen revealed that the cord loops underneath the adult dorsal fin basal plate ( Fig. 2 View Figure 2 h and Supplementary Information). Its surface is covered with a thin layer of epithelium ( Fig. 2 View Figure 2 e) and has a series of pits of varying sizes ( Fig. 2 View Figure 2 c, d), with the wall of the umbilical cord made up of a series of vessels and a dense matrix of tissue. The path of one major vessel could be determined running through the cord ( Fig. 2 View Figure 2 b). Branching off from the umbilical cord are the remains of filamentous processes equivalent to the appendiculae in extant sharks (app, Fig. 2 View Figure 2 d). Thus, ptyctodonts apparently evolved beyond the first live-bearing stage (oviviparity, in which the mother retains her eggs inside her body, providing only protection, with the yolk sac providing all nutrition) to matrotrophy. The relative size and position of the embryo and yolk sac in relation to the mother fish is shown in Fig. 3 View Figure 3 a, with an attempted restoration of the fish giving birth shown in Fig. 3 View Figure 3 b, based on the observation that several viviparous sharks give birth tail-first to their young. Further discussion of the significance of viviparity and evolution can be found in the Supplementary Information.
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