Protea hybrid 'Jack Clark' family Proteaceae Photo by the Author
Nature’s Riddle of the Proteace
As cited by C. Venkata Rao in 1971 (1), there are present in Australia no fewer than thirty-three native genera of Proteaceae. More than two-thirds are G-oides. In Africa, there are fifteen native genera, and all except two are P-oides. In South America, there are eight genera of G-oides, but no P-oide.
Here is an astonishing fact. Four of these G-oides – Gevuina, Lomatia, Oreocallis, and Orites – are native to both South America and Australia. None is native to Africa – which, 300 million years ago, stood between South America and Australia and was attached to both. South America is today some 10,000 km away from Australia and some 5,000 km away from Africa.
For ready distinction, here Proteaceae genera native to Australia are also named Austrops; those native to Africa, Afrops. For example, a P-oide genus native to Australia is an Austrop P-oide; a P-oide genus native to Africa is an Afrop P-oide. No Austrop is native to Africa; no Afrop is native to Australia.
Man’s Riddle of the Sphinx was never more intriguing than Nature’s Riddle of the Proteaceae:
•Austrops in Australia and South America -- but not in Africa.
•Afrops in Africa -- but not in Australia or South America.
There have been previous attempts to solve the Riddle of the Proteaceae. This essay points to the Permo-Carboniferous Ice Age as the impacting factor in its resolution.
The Permo-Carboniferous Ice Age
The Permo-Carboniferous Ice Age was a momentous event in earth history. It began about 300 million years ago. It lasted 50 million years and recorded heights of glacial rubble that dwarfed those of the relatively recent Pleistocene.
The vectors of ice thrust kept changing during the 50-million-year ice age (2), thereby reflecting translational and rotational movements of continents, mountain building, changes of sea level, and changes of sea current, wind direction, and climate.
Laurussia, consolidating to the north, contributed to the pattern of climate change. Ice advance was uneven. In the early stages, Southern Africa and Southeastern South America became large ice fields. A long icy finger reached into Central Africa. Parts of India and Madagascar were iced over. In South America, ice extended north into the lower part of Brazil.
Glaciations at the end of the ice age, 250 million years ago, extended from Antarctica into Australia. Reaching through New South Wales, they attended the Permian uplifting of a chain of mountains. In Australia, the northwest was iced over. But southwestern Australia was not; nor was eastern Australia. Today, more than half of all genera of Proteaceae are found in eastern Australia, and about a third of all species are found in southwestern Australia.
Solution to the Riddle
Gondwanaland provided a connected land route for Proteaceae and other angiosperms and gymnosperms prior to 300 Ma. It stretched roughly from Australia through South America. Evidence of the disruption of this plant route in Africa by the Permo-Carboniferous Ice Age 300 to 250 million years ago (2) strongly indicates that Proteaceae and other plant families had spread throughout Gondwanaland before the Ice Age, and thus have dwelt on earth for more than 300 million years. Thus, the Permo-Carboniferous Ice Age is a linchpin that holds the time frame to 300 million years ago, with all its geological and biological consequences.
An almost unbroken sequence of rocks in the South African Karoo Basin confirms that the region during the Permo-Carboniferous was dominated by gigantic glaciers. The frost, followed by other adverse conditions, wiped out almost all Proteaceae from Africa. Only a few genera survived the ice, perhaps sheltered in warmer pockets to the north. G-oides survived the ice in South America and are there to this day. No P-oides are there.
But questions persist.
Why then are there today fifteen genera of Afrops in Africa, all but two considered to be P-oides? One remarkable answer may be in the detail: Only a few genera of Proteaceae in Africa escaped extinction by the advancing glaciation – ones that reasonably could have already become adapted to warmer regions. (Other angiosperm families trapped in Africa, notably Winteraceae and Nothofagaceae, did not escape at all.)
Of the fifteen Afrop genera, twelve are of the P-oide tribe Proteeae – just one of fourteen tribes. Each of the other three genera is of a different tribe:
• Dilobeia, native only to Madagascar, belongs to tribe Persoonieae;
• Aulax, a unisexual P-oide, belongs to tribe Aulaxeae; and
• Brabejum, the sole G-oide, belongs to tribe Macadamieae.
Together these three genera provide only 5 out of 400 extant Afrop species. The Persoonieae are probable ancestors of both G-oides and P-oides.
For the tribe Proteeae, after the ice age, Africa became a secondary center of evolution. Venkata Rao noted (1): “Separation occurred before evolution.” And subsequently, twelve genera of the tribe Proteeae evolved in Africa out of perhaps one or two original genera of that tribe.
Furthermore, the Proteeae bear clear witness to the overland movement westward from Australia to Africa. The morphological and taxonomic primitives of the Proteeae are found today in Australia. Today the genus Protea, the most widespread of the tribe, shows the same ability to travel from a temperate to a warmer climate – by moving north in Africa – that its ancestor might have used to escape extinction 300 million years ago. Protea (the first frontispiece) has 136 species, 54 of which are native to tropical regions of Africa. Over time, most of the other genera of the tribe Proteeae went south, along the east coast of Africa, to present Cape Province habitats.
A Second Watershed Event
A second major geophysical event which marks the presence of the Proteaceae in Gondwanaland prior to the Permian era was the biological isolation of a huge landmass, a superterrane from northwestern Australia, (in these essays termed “Austosunda”). It occurred at the start of the Permian about 280 million years ago (3). At that time, Austosunda began to drift away from Gondwanaland; and subsequently (about 150 million years ago), near the beginning of the Cretaceous, it found land. Austosunda joined then with the northern supercontinent Laurasia, then to become the southeastern continental core of Laurasia, and to introduce there its biotic cargo, including angiosperms.
In summary, the remarkable present-day distribution of Proteaceae is an end-effect of two principal events: the Permo-Carboniferous Ice Age and the breakaway of a continent-sized landmass, Austosunda, from Australia about 280 million years ago. About 150 million years ago, Austosunda brought Proteaceae to Laurasia.
The above events are keystone to the premise that the Proteaceae inhabited the entire length of Gondwanaland, from Australia to South America, more than 300 million years ago. Hypothetically, the angiosperm phylum originated before the end of the Devonian, more than 360 million years ago. Over the vast, ancient consolidated expanse of Gondwanaland, the unique and unmistakable sexual organ identity of the proteaceous flower had then been already established.
Stability of the Proteaceae
The Proteaceae have no close natural relatives. The proteaceous flower is a primitive organization of flower petals (here called perianth segments) embracing adnate anthers, stigma, style, and a minute (superior) ovary. Proteaceae are among the earliest angiosperms.
There are some 1400 species of Proteaceae today. Stability of the basic floral components over hundreds of millions of years is evincive of capability to ward off disease, inclement weather, and aggression. Early diversification
and radiation could be significant factors in survival. But how could the Proteaceae have existed to this day with almost no sex organ change?
The answer points primarily to the angiosperm phylum invention of the bisexual flower – the crucial factor in its watershed disengagement from seed fern. The bisexual flower is the successful (stable) mutation in the transition from unisexual seed fern to flowering plant. By reason of the invention of the bisexual flower, the angiosperm found an early new independence, an enhanced ability to diversify, and a greater freedom to roam far and wide.
While by no means the only survival factor, the bisexual nature of the proteaceous flower has been highly significant to its long, stable survival – and in particular, to early survival in an increasingly cold Gondwanaland. The three most cytologically primitive surviving genera of Proteaceae are all bisexual. They are Bellendena, Placospermum, and Persoonia, all generally classified in the subfamily Proteoideae. Each has a diploid species (chromosome number 5, 7, and 7 respectively) native to Eastern Australia.
Bisexuality provides the potential for inbreeding – the crucial timeliness of which needs emphasizing. Inbreeding was an essential solution to the problem of transition from seed fern to the fully established cross-pollinating
Early on, there would have been too few plants of the same species to perform cross-pollination successfully; and the fauna would have had too little adaptability to be effective. Some inbreeding persists today among Proteaceae. It decreases change at the cost of diversity. Inbred seeds of Proteaceae have been remarked to be of poorer quality than cross-pollinated seeds. Yet inbreeding can sustain generations in isolation.
Among angiosperms as a phylum, bisexuality and cross-pollination, together, work to augment adaptability and hence to augment the ability to survive, as, for example, in the family Proteaceae. This adaptability to environmental change, which is mainly due to the bisexual flower, is the largest factor in their prolonged survival. Rao, in 1971 (1) noted: “The [Proteaceae] family seems to have originated under rain-forest conditions and spread into arid and exposed regions, to which the taxa got adapted by evolutionary modifications in habit, leaf and fruit.” If the Proteaceae had remained in the Gondwanaland rainforests relatively unmodified, they would probably have died out along with the dominant seed fern, Glossipteris.
The inferred widespread presence of the Proteaceae in Gondwanaland indicates as well that their precursors and consociates – both seed ferns and the earliest angiosperms – lived in the very same places in the early Carboniferous. It is probable that the Proteaceae and other angiosperms propagated initially within communities of Gangamopteris, Glossipteris, and other ferns in Australia, India, Africa, South America, and Antarctica
Melville’s Gonophyll Theory of Angiosperm Origin
This inquiry about the ancient roots of the Proteaceae began by chancing upon an important paleobotanical theory by Ronald Melville, set forth in 1960, (4) and in 1983, (5), regarding the origin of the angiosperm (and in the course of events, its family Proteaceae). It is the gonophyll theory – in explanation of the evolution of the gynoecium (the female sex organs) and the androecium (the male sex organs) of the angiosperm flower. The theory holds that flowers were first built of modified seed fern leaves bearing either ovules or microsporangia.
The consequences of this theory apparently disturb a generally accepted time line: to wit, the angiosperm division of the plant kingdom evolved about 150 million years ago. Hence, the gonophyll theory finds itself ignored rather than disproved. However, the time of origin of angiosperms as deduced by Ronald Melville is consistent with the time of Proteaceae origin as provided by the two independent events discussed herein: the Permo-Carboniferous Ice Age (300 to 250 Mya) and the early-Permian breakaway of a continental-sized block from northwestern coastal Australia (about 280 Mya).
|Ronald Melville reported:
“The primary diversification of the pre-angiosperm stock appears to
have taken place....during the late Carboniferous or early Permian.
Many angiosperm lineages must date back to this period as distinct
lines of evolution. . . ” He observed that to varying degrees,
fern characteristics are conserved among the Proteaceae. See Figure 2.
Ronald Melville reported incipient transitions from seed ferns to angiosperms in 1960 (4) and in later papers. He noted that the parallel veining found in the leaves of Proteaceae and in other primitive plants could have evolved from Gangamopteris, an extremely ancient (Devonian) Gondwanaland seed fern (without a large frond midrib). Observe in Figure 2 that the offset-opposite pattern of the fern leaves is conserved in Grevillea robusta.
Although he found divergence as far back as he was able to look, he continued: “The great disparity between the floral vascular systems of Ranunculaceae and Magnoliaceae . . . implies a very ancient separation of these stocks. A number of other lineages must be as old.” However, Melville, peering into a dim and distant past, sought but was unable to find the primogenitor, the earliest ancestor in the angiosperm phylum.
Melville perceived and even acknowledged (what others pointed out) that his studies, taken in conjunction with the doctrine of Cretaceous origin, implied extreme polyphylesis (i.e., numerous distinct lines of angiosperms originating about the same time, e.g., the Ranunculaceae and Magnoliaceae cited above). Yet, with better-available fossil information, Melville might have gone further back into the Carboniferous than he did, to a more distant past than 300 million years ago, to allow for gradual evolution from a single ancestral stock. Indeed, the apparent extreme polyphylesis is deceptive and that the ancestral stock may, indeed, go far back, in a monophyletic way, even into the Devonian.
(The issue is yet to be resolved among earth historians.) However, a chart on fossil records of Gondwanaland (Patrick Hurley, 1971(6)) supports this inference. It suggests sufficient time for monophylesis. It shows Gangamopteris (the seed fern cited by Melville as a possible ancestor of Proteaceae) to have been present in Eastern Australia during the Devonian 408 to 360 million years ago.
|The remarkable survival of
the Proteaceae is etched in time and place by momentous geological and
climatological events. Furthermore, the ice age and the breakaway
superterrane are found to be concordant both with the Ronald Melville’s
theory of flower origin (4, 5) and with Venkata Rao’s researches on
Proteaceae (1) in accounting for the present world distribution of
Proteaceae and in indication of the place and time of origin: Australia, more than 300 million years
Venkata Rao Researches on Proteaceae
Eastern Australia is described by Rao (1) as the center of origin of the Proteaceae. In the words of Rao: “The concentration of genera and tribes, the high degree of endemism, the abundance of morphological, taxonomic, and cytological primitives and the great community at the genetic level with other land masses show that the eastern Australian region on a once connected land mass (Gondwanaland or Pangaea) was the original home of Proteaceae.” These words summarize Rao’s endeavor whereby, point by point, he demonstrated that the Proteaceae originated in Eastern Australia.
Venkata Rao characterized the ancestry of the Proteaceae as southern hemisphere exclusively. He wrote (1) that fossil records show the Glossipterid flora originated in the south under extremely cold conditions. In regard to Proteaceae, however, Rao noted that today eight genera extend into the tropics. By his count, the other fifty-four genera are confined to southern temperate regions.
The similarity of component floristic elements of the Proteaceae of Africa and Australia leads to Rao’s conclusion below that in the historic past there existed a continuous land expanse between Africa and Australia.
“The similarity in plant associations and the component floristic elements in the two widely separated geographical regions [Africa and Australia] presupposes the existence of similar edaphic and climatic conditions not only at the present time but also in the historic past and through the period of their evolution. The occurrence of a stray genus or species common between two widely separated land masses may be attributed to accidental dispersals, but we cannot adequately explain the existence of similar floras without supposing that they once formed a continuous expanse as Hooker (1860) believed. The conclusion that Proteaceae originated on a connected southern continent which subsequently fragmented, therefore, seems to be unassailable.”
(The research observations of Venkata Rao are presented frequently throughout this paper (1). Rao wrote seventeen journal papers on Proteaceae.
Rao tersely rejected any idea of effective seed dispersal on widely separate land masses by flying creature, wind, sea or other agent. (In rejecting such speculations, Rao remarked, on the “incapacity of the taxa” to cross ecological barriers and to root in unfamiliar soils. He pointed out that the fruit of the Proteaceae family, with few exceptions, are unsuited to avian consumption and carry. For example, seeds of the Lomatia and Oreocallis trees are encased in fruiting heads of hard, large woody follicles.
These seeds are released only after fire or drought. Moreover, it has been observed that migratory birds travel with empty stomachs and clean feathers. Nor does the sea qualify as an agency. Ocean currents flow eastward in temperate zones (i.e., from Africa to Australia); but the pattern of radiation of Proteaceae has been mostly westward.
|Rao noted that the
Proteaceae show high specificity in regard to altitude, temperature,
water, and soil chemistry, all of which can limit their range.
Even on a connected land mass, they were hardly capable of crossing
ecological barriers. Rao emphasized that this inability “should put a
limit to speculations regarding the efficiency of long range dispersals
in the family.”
Rao was quick to note, however, that the “element in which Proteaceae predominate is common between Africa and Australia." He concluded from his studies that Western Australia was the center from which there occurred a significant lateral movement of Proteaceae from Australia into Africa. (Essay # 1 elaborates that Australian and African Proteaceae have the same unique sexual parts though they have no genus in common, and they too are now an ocean apart.)
The Route of the Proteaceae
What was the route that brought the Proteaceae from Australia to South America more then 300 million years ago? Could the primary route of the Proteaceae have been passage from Australia to Africa across Madagascar, then land-linked to India? The Proteaceae genus Dilobeia provides an answer in an unexpectedly strong linkage of Madagascar and Australia. It belongs to the tribe Persoonieae. Rao, in 1971(1), described Persoonieae as the most primitive tribe, the most ancient stock, of the Proteaceae.
Today there are eight genera of Persoonieae. Five are native to Eastern Australia (where Rao sites the origin of Proteaceae). Two more are native to New Caledonia. And one, Dilobeia, is native only to Madagascar. Considering that a single genus of that most primitive tribe of Proteaceae is found only in Madagascar while five other genera are found native to Australia – assuredly, Dilobeia is living evidence that the Proteaceae passed into Madagascar in spreading from Australia to Africa.
The Winteraceae join in the answer. They are probably the oldest family of angiosperms. Like the Proteaceae, they probably originated in Eastern Australia. The Winteraceae too manifest a “living fossil” genus, like Dilobeia, in Madagascar. It is the lone species Takhtajania perrierii. In South America today, there are endemic Winteraceae and Proteaceae, 9000 kilometers from eastern Australia.
Both of the above ancient living angiosperm families mark essentially the same overland route west from Australia through Madagascar (then part of India) through Africa and into South America more than 300 million years ago – before the Permo-Carboniferous Ice Age (300-250 Ma). Thus, the presence of Dilobeia and Takhtajania today in Madagascar suggests that the primary route of Proteaceae from Australia to Africa more than 300 million years ago was across Madagascar, then joined or contiguous to India, in a continuous land passage. The phytogeographic studies of Rao, 1971(1) are strongly persuasive in qualifying the actual route as “a continuous expanse.”
Whitmore in 1981 and 1988 (7, 8) cited a remarkable companion to the Proteaceae: the southern beech, Nothofagus, the only genus of the family Nothofagaceae. A similar African hiatus, or disjunction, occurred with this angiosperm family, as it had with the family Proteaceae. Today Nothofagus has thirty-five species. Its seeds must travel over land because they are killed by salt water. Nothofagus exists in temperate forests in both Australia and South America. It is abundant on Australasian islands: in the temperate rainforests of New Caledonia, New Zealand, and Tasmania and in the montane regions of New Guinea and New Britain.
Nothofagus is entirely absent from Africa and have no fossil traces in Africa. Here again, almost in refrain, Nothofagus in Australia and South America – but not in Africa. Whitmore, furthermore, noted: “Nothofagus has a very complete and long fossil record and highly distinct pollen . . . ” And he added: “[The southern hemisphere distribution of Nothofagus is] one of the remaining great puzzles of phytogeography.”
Indeed, absence of Nothofagus from Africa is a remarkable substantiation to the stark reduction of Proteaceae tribes in Africa. Viewed in context with the Proteaceae, the present Nothofagus phytogeography strongly implies that more than 300 million years ago, Nothofagus consociated with the Proteaceae. Before the Gondwanaland Ice Age, Nothofagus, together with the Proteaceae, inhabited Australia and had already spread across Africa and into South America.
Like most Proteaceae, Nothofagus in Africa fell victim to the oncoming ice. Although its pollen is distinct and readily traceable, Nothofagus left no imprint there. Ice had destroyed all fossil record of its early African existence. Its present phytogeography supports a premise that in the early Permian, or before, Nothofagus, along with Proteaceae, was rafted from Australia on drifting terranes that became cores of Southeast Asia.
|The Rifting of Austosunda
A watershed geological occurrence took place at the beginning of the Permian about 280 million years ago. A tectonostratigraphic terrane, named herein Austosunda,, broke away from the northwestern margin of Australia. It was comprised of three conjoined continental blocks: Sibumasu, Lhasa, and Changtang. The separated Austosunda quickly became isolated from Australia by intervening sea level rise. Tens of millions of years later, the superterrane drifted into contact with the Eurasian Plate to form then the southeastern coastal core of Laurasia. See Figure 3.
That core material today bears evidence of Permo-Carboniferous marine and terrestrial faunal affinity to the northwestern Australia of 280 million years ago. Ian Metcalfe in 1988 (3) examined the huge rifted continental blocks in their present locations as continental core of Southeast Asia. According to Metcalfe: “Stratigraphic, palaeontological, and palaeomagnetic evidence suggests that all of these crustal blocks probably had their origin in the north-eastern margin of Gondwanaland where they formed part of a complex continental margin.”
Quoting Metcalfe: “Since South China and Indo-China were at low northern palaeolatitudes in the Permian, Sibumasu must have already rifted from Gondwana by latest early Permian times. It is considered here that Sibumasu, [and Lhasa and Changtang regions of] Tibet (between the Indus-Yarlung- Zangbo suture and the Langcangjiang Fracture Zone ) . . . were in continuity and rifted together at the same time from Gondwanaland.”
Metcalfe offered diagnostic evidence that Sibumasu, had once been a part of Australia. Metcalfe wrote: “This terrane remained on the [north-west Australian] margins of Gondwanaland until early Permian, as indicated by the late Carboniferous-early Permian glacial-marine diamictites, cool-water faunas, absence of warm climate floras, and presence of faunas of Gondwanaland (north-west Australian) affinities.”
A basic facet of Proteaceae existence, therefore, comes to light.
Certain terranes, or continental blocks, which were coastal regions of northeastern Gondwanaland and which were biologically detached from Australia and India during the early Permian, are now parts of Southern Asia, as seen in Figure 3.. They carried with them to South China, to Indochina, and indeed, to the whole of Laurasia – in a sea voyage of many millions of years – Proteaceae and other angiosperms, and fauna as well, which at that time of biological detachment were not only denizens of Australia but were living elsewhere throughout Gondwanaland and were present in those places for millions of years prior to the separation.
Today the Sibumasu continental block extends (Figure 3) icicle-shaped, south through large parts of Myanmar, Thailand, Malaya, and the island Sumatra. The Sibumasu block and Australia are now about 2500 km. apart from each other at their closest approach. Nevertheless, there is a genus of Proteaceae, Helicia, which is both native to the now-distant Sibumasu and has nine species in Australia. Helicia and Heliciopsis (found in New Guinea) are the only two genera that extend into the Malayan tropics. Native to less moist regions of Sulawesi are Grevilleae and Macadamiae. All belong to the subfamily Grevilleoideae.
At least eleven genera of Proteaceae (primitives and Grevilleoides) are found today in Indonesia, Indo-China, and Australasia. In description of this biogeological transition, T. C. Whitmore, (7, 8) wrote: “It is now known that there are several substantial areas of Gondwanaland rocks, terranes, embedded in continental south-east Asia. These terranes are shards, rifted off Northern Australia and which drifted north to collide with Laurasia. There is some evidence that they were dry land, and hence were available as rafts for plants and animals, or as stepping-stones between Laurasia and Gondwana.”
|This breakaway of
Austosunda, which occurred at the beginning of the Permian, joins
independently with the Permo-Carboniferous Ice Age to extrapolate the
time of origin of the Proteaceae beyond the Carboniferous, to far more
than 300 million years ago.
Arborial Hopscotch, Australia to South America
and to the South Pacific
Australia became biologically isolated from Gondwanaland about 280 million years ago. As previously noted, four genera of Proteaceae, all Grevilleoideae, are common to Australia and South America today, but absent from Africa. These are Gevuina, Lomatia, Oreocallis, and Orites. Their respective species are remarkably similar. Species of Orites of South America and Orites of Australia appear to be identical “though they come from the ends of the earth.”
At least three of these genera include trees among their species. They were a part of the forests that spread from Australia and across Africa more than 300 million years ago, to enter South America from Africa. Perhaps, by fortunate earlier acclimatizing, all four survived in warmer parts of South America, beyond the lethal reach of ice. Today, by the same predisposition to warmth, at least one species of each of these four genera exists under tropical conditions elsewhere, on distant South Pacific lands.
Insect and Flower: Each an Instrument
in the Evolution of the Other
Nurturing bounty must well attest that insects even at the flower origin were active in fashioning the flowers of the Proteaceae to their own advantage. The insects were first among faunal pollinators, along with other arthropods. During the late Paleozoic and thereafter – even in such times of stress that could mean the sudden absence of a major cross-pollinating vertebrate – insects might have been ubiquitously available to carry out pollinations. Early traces of insects have been found in Devonian rocks. Some 800 species of cockroaches (including winged ones) were extant during the late Carboniferous; and dragonflies of many sizes were then abundant.
Flying beetles, moths, and butterflies came conspicuously into fossil record during the Jurassic, which began 208 million years ago; and some paleontologists note that insects have undergone little change in the last 200 million years (9). Yet the diversity of present-day pollination-specialized insects speaks vividly that long before the Jurassic, lively adaptations in their form and function took place. Today, moths and butterflies flit from flower to flower with body-length proboscises, or sucking tubes, drawn out to drink up nectar. Today, pollination-specialized scarabs like the African Trichostetha fascicularis – whose name means “hairy-chest, with hair in tufts” – move pollen effectively from proteacean flower to flower.
|Assuredly, in the remote
pre-Jurassic past, long before 208
million years ago, the predecessors of the earliest known moths,
butterflies, and beetles had been enticed by entomophilous flowers to
evolve bodies especially suited to perform cross-pollination. By
sustaining the phylogenetic invention of the bisexual flower, insects
have been essential in fostering the survival of the Proteaceae’s
almost-eternal flowers. They have been the mainstay in pollination of
Proteaceae and other angiosperms from the late-Paleozoic to this day.
An Almost Eternal Courtship
More than 300 million years ago, the Proteaceae had evolved their nectar-producing glands and nectar reservoirs to attract and reward pollinators.
The cross-pollination potential was ever high among Proteaceae, more than enough to sustain phylogenetic survival. Well-attended flowers provided a plenitude of nectar within their perianths, attracting in the course of time reptiles, possums, mice, bats, birds etc. and a myriad of arthropods – the latter, in turn, providing mammals and birds with a nectar-and-protein menu. An evolutionary reciprocity started and ensued from the Paleozoic years to the present, in which the Proteaceae induced the pollinating fauna to coevolve with them in order for both to utilize the floral bounty effectively.
The Proteaceae then (as even today) ranged in size from small, prostrate bushes to tall, massive trees which were, in aggregate, forests. The Proteaceae and other angiosperms must have created evolutionary challenges to those then-living reptiles to climb, to cling, and to move freely among their branches; to find shelter there from Gondwanaland cold and predators; and to reach nectar-and-pollen-laden Proteaceae flowers, which, characteristically are at the tips of leafy branches that sway in the wind. Reptiles were early, important contributors to cross-pollination. Fossil records reveal that reptiles were present in the late Carboniferous, some 300 million years ago, and flourished throughout the Permian as a dominant vertebrate land fauna. Small, agile herbivores abounded among them.
Adapting to challenge, some Permian reptiles, mammal-like reptiles among them, became tree climbers and tree dwellers. Some began to evolve a capability of gliding, or even of flying (before the advent of the flying Pterosauria of the Mesozoic). The hordes of insects that fed on tree flowers surely were an important source of nourishment to tree-associated reptiles.
|In the Mesozoic, other
types of plant-induced faunal adaptations
occurred, notably among a new reptilian subclass, the dinosaur. Many
dinosaurs characteristically evolved large bodies, long necks, and
small heads in order to reach the leaves, flowers, fruit,
and insects high up among the Proteaceae and other angiosperms. Triassic
prosauropods were first examples. Among later examples, there was the
Jurassic quadrupedal Brachiosaurus, which could dine twelve meters up a
towering tree, while keeping all fours on the ground. Curiously,
bird-ancestral dinosaurs, from Velociraptor to crudely-flying
Archaeopteryx, evinced little or no phylogenetic tendency to climb
trees. But many mammals did. (The miacids, late Cretaceous ancestors of
placental order Carnivora, are believed to have included tree
From the last 100 million years, from the late Cretaceous into the present, birds have taken part in that almost-eternal courtship of Proteaceae. They have evolved specialized adaptations that bring about cross-pollination in fields of flowering Proteaceae. Today many species of birds testify by their form and function to effective cross-pollination. Effective tools of their own design for nectar sipping are the slim, downcurving bills (about 20 % of body length) of the sugar birds and sunbirds of Southern Africa. Effective as well are the brush-tipped tongues of the brilliantly feathered lorikeets and the nomadic honeyeaters of Australia. And even among the mammals of Southwest Australia, there are brush-tongued, hairy-bodied possums adept for pollination. Some species of Proteaceae, in evolutionary reciprocity, are said to smell like possums.
Legacy of the Paleozoic
From the Paleozoic to this day, the Proteaceae and other angiosperms have sustained their existence by trading nutriment for pollination. Conversely, vertebrates and hordes of insects have been sustained by angiosperms. The adaptations of present-day animals and insects for effective sipping of nectar and spreading of pollen are echoes of the Paleozoic – heirlooms of ancient gene pools. Even in that distant past, those adaptations were essential to the phylogenetic survival of the Proteaceae.
The late Paleozoic was a time of evolutionary development not only for the angiosperms including Proteaceae, but for their faunal associates as well. Food and shelter offered by the angiosperms formed the basis of reptile and mammal evolution from the Paleozoic onward. Co-evolutionary adaptations of flora and fauna help put to rest a basic question of both biophysics and geophysics: namely, the time and place of the origin of the angiosperm, the flowering plant division of the plant kingdom. That origin belongs to the late Paleozoic of Eastern Australia – As long ago as the Devonian more than 360 million years ago.
|Summary and Conclusion
This essay demonstrates that presently living angiosperms, and in particular Proteaceae, are crucial to the realistic reconstruction of earth history. The plant family Proteaceae, among the earliest angiosperms, originated in Eastern Australia during the late Devonian, more than 360 million years ago. Long before the Permo-Carboniferous Ice Age, which began 300 million years ago, they had propagated overland throughout Gondwanaland, Their reproductive organs, unchanged by the passage of time, speak firmly of the late-Paleozoic existence of the angiosperm and of the drift of continents.
The Proteaceae are more than the saga of one plant family. Were it not for the presence of Proteaceae today and consociated angiosperms and gymnosperms, there would be almost no evidence of the early evolution of flowering plants and of their interactions with early vertebrate fauna in the southern hemisphere – sequences of earth’s history essentially untraced by fossils, from the Carboniferous through the Permian, 360 to 245 million years ago.
The Proteaceae, therefore, are living repository of a large store of earth history.
This intermeshing of biophysics and geophysics brings to light a singularly significant biogeophysical era: the late Devonian. In providing sufficient time for divergence from a single progenitor species, the hypothesis of Devonian origin 408 to 360 million years ago provides a time line adequate for angiosperm monophylesis.
The biogeophysical milepost of the time of origin of the angiosperm is the adjustment needed to re-read the earth’s clock for the true accounting of the interactive histories of flowers, mammals, dinosaurs and birds. To reiterate: the remarkable survival of the Proteaceae over Paleozoic and Mesozoic history calls for reexamination of man’s records of earth history in order, for the first time, to take into account the profound effects of the angiosperm on the evolution of mammals and dinosaurs. A basic understanding of the evolution of mammals, dinosaurs and birds cannot be derived without knowledge of the history of the angiosperm.
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