Megahertzia, A. S. George & B. Hyland (George and Hyland, 1995

Carpenter, Raymond J. & Rozefelds, Andrew C., 2023, Leaf fossils show a 40 - million-year history for the Australian tropical rainforest genus Megahertzia (Proteaceae), Australian Systematic Botany 36 (4), pp. 312-321 : 318-319

The past distribution of Megahertzia

As well as at Anglesea, Megahertzia - type cuticle (‘ Proteaceae sp. 7’) occurs in the mid-Eocene Hotham Heights foliar assemblage of south-eastern Victoria ( Carpenter et al. 2004, their fig. 56). This assemblage represents a rainforest-derived flora very similar to that which was present at Anglesea, sharing Athertonia - and Musgravea -like cuticles, Ebenaceae , Gymnostoma , and abundant evidence of Lauraceae , Cunoniaceae and Elaeocarpaceae . An even greater past distribution of Megahertzia is indicated by fossil occurrence records of the Megahertzia -like ( Macphail 1999) pollen morphospecies Proteacidites latrobensis W.K.Harris. This species was not included in the phylogenetic study of Proteaceae pollen by Sauquet et al. (2009), but its distinctive small sexine spines ( Harris 1965, 1966; Stover and Partridge 1973) could be homologous with the supratectal spines recorded by Sauquet et al. (2009) for M. amplexicaulis . Proteacidites latrobensis was described by Harris (1965, 1966) from the Princetown Member (Dilywn Formation – Otway Basin) of western Victoria (Early Eocene: e.g. McGowran et al. 2004) and has since been widely recorded in Cenozoic sediments from across Australia (e.g. Stover and Partridge 1973, 1982; Nott and Owen 1992; Alley et al. 1996; Itzstein-Davey 2004), including Tasmania ( Hill and Macphail 1983), the Northern Territory ( Truswell and Marchant 1986) and the Pilbara of north-western Australia ( Macphail and Stone 2004). Records of P. latrobensis from Queensland include from the Eocene of the Yaamba Basin ( Foster 1982), the Early–Late Miocene inland of Mackay ( Beeston 1994) and the Early Miocene sequence of Sandy Cape, K’gari (Fraser Island) ( Wood 1986). Adding to our inference that Megahertzia had an extensive past distribution, P. latrobensis is also found within the Neogene of New Zealand ( Raine et al. 2011).

Megahertzia paleoamplexicaulis adds to the list of proteaceous taxa that belong to lineages that were widespread in the past, but are now confined to the northern Queensland Wet Tropics and Gondwana Rainforests of Australia World Heritage Area of north-eastern New South Wales and south-eastern Queensland. These taxa include Athertonia (Rozefelds 1992, 1995), Eidothea ( Douglas and Hyland 1995; Rozefelds et al. 2005), Musgraveinae ( Christophel 1984; Carpenter et al. 2016) and Orites excelsus ( Carpenter and Jordan 1997).

Christophel et al. (1987) found Megahertzia leaves in two of the six lenses they studied, the ‘Mesophyll Lens’, and ‘Site II Lens A’. Only a few of their highly diverse leaf taxa have been identified, but both lenses are known to also host the extinct cycad Pterostoma R.S.Hill as well as Ebenaceae , Cunoniaceae and Elaeocarpaceae , Musgraveinae and abundant and diverse Lauraceae ( Christophel et al. 1987; R. J. Carpenter, pers. obs.). As well as these taxa (except Pterostoma ), the greater Anglesea flora reportedly has numerous other taxa with extant relatives in tropical and subtropical rainforests of eastern Australia, including Bowenia , largeleaved Podocarpus Labill. , Gymnostoma , Brachychiton Schott & Endl. and Myrtaceae ( Christophel et al. 1987; Christophel and Greenwood 1988; Christophel 1994). Undoubtedly, the disappearance from much of Australia of mesic rainforest elements, including Megahertzia and the other Proteaceae discussed above, was a consequence of a general decline over millions of years in the availability of equably wet and warm conditions, especially since the final separation of Australia from Antarctica (reviewed by Byrne et al. 2011).