Brachiosaurus copyright Andreas Meyers of bigstockphoto.com
|Geomigrations of the Dinosaurs
By Harry Levin
Essay Number Six
Fossil sites of migratory dinosaurs piece together the geography of ancient migration routes.
Those routes were based on positions of five Gondwanaland continents at the same time of travel
– South America, Africa, India, Antarctica, and Australia. They changed position over millions
of years in respect to each other and to Eurasia.
|Dinosaurs originated in
Gondwanaland during the early Mesozoic (about
230 Ma). During the late Paleozoic, a narrow sea channel, here termed
“the Western Tethys,” was configured by close approach between
Gondwanaland and Laurasia. (See frontispiece and Essay # 5) In
premise, with some exceptions, dinosaur herds of herbivores attended by
theropod carnivores made periodic trips back and forth across the
Western Tethys for breeding and feeding purposes from the Triassic
through the Jurassic and early Cretaceous. In season they crossed into
Laurasia to breed; and then they recrossed into their Gondwanaland
feeding grounds. This basic instinct of periodic northward crossing for
nesting safe from predators led to the prevalence of the dinosaur upon
the earth (and is manifest today in the seasonally-migrating bird.)
However, at the beginning of the Cretaceous, came two changes in the pattern, both gradual in nature, which reduced both the capability and the need for periodic crossing:
1. Spreading seas brought continental isolation and increased difficulty of dinosaur passage. As examples, about 90 million years ago, dinosaurs were finding it arduous to cross the waters of the widening channel between South America and Africa or the broadening embayment between South America and North America.
2. Angiosperms set their roots on Laurasian soil; and their new presence reduced the need to re-cross the Western Tethys to feed. In the first instance, angiosperms were introduced into Laurasia by union of Laurasia with a drifting superterrane (in these essays, termed “Austosunda”). In the second instance, the angiosperms entered Laurasia by union of the drifting Indian Plate with Laurasia. These events occurred 150 and 85 million years ago, respectively. At both times, many varieties of monocot grasses, sedges, bamboos, and palms and dicot bushes and trees (leafy, flowering, and fruiting) entered Laurasia and spread a copious table for herbivores under a generally warming climate.
Throughout the early Cretaceous, despite increasing difficulty, the periodic migrations of dinosaur herds back and forth across the Western Tethys continued. However, overpopulation pressures increased, abetted by extinction of the therapsid (the mammal-like reptile) about 150 Mya. Correspondingly, dinosaur populations spread out even to the farthest reaches of North America, Europe, South America, and Africa, filling every available ecological niche. The majority of dinosaurs were not great-distance travelers. With adequate food supply eventually on hand in Laurasia, families that stayed in Laurasia evolved many new genera and species, especially in North America and Europe. This essay, however, will deal with long-distance migrations that involved Africa, Antarctica, Australia, China, and India – thereby coordinating their geography changes with time.
In premise, during the middle and late Triassic the dinosaur achieved dominance by outmaneuvering the therapsid and the placental mammal by the stratagem of crossing over to safe nesting sites on the north shore of the Western Tethys. (See frontispiece.) The resulting new-found numerical superiority of the dinosaur hastened the extinction of therapsids in Gondwanaland and sent the smaller, elusive placental mammal into hiding. However, unhampered breeding caused overpopulation. From the early Jurassic, overpopulation compelled herds of dinosaurs to go forth from their Western Tethys wellspring – to migrate north, south, east and west into new territory in an unending search for other safe nesting sites where at the same time there was an ample food supply.
And to make matters worse, during the Cretaceous, the Western Tethys crossing itself grew ever more daunting, as continents drifted apart from each other. The instinctive compulsion of the dinosaur was to search hither and yon for an ideal safe nesting site, sheltered by water – to seek out “a second Western Tethys,” like that which had been its haven. Thus, confronted time and again with the challenges of overcrowding, nest predation, flooding, food scarcity, and continental drifting, certain genera among the dinosaurs were compelled to search far and wide for ample safe nesting sites with ample food supply. When a herd overextended or depleted one feeding ground, it moved on to another – like the mad hatter’s tea party.
Geographically Significant Dinosaur Migrations
From the early Jurassic and, indeed, until the end of the late Cretaceous, migratory routes spilled eastward into Antarctica, India, China, and Australia. On these continents, the nesting sites provided fossilized identifications of dinosaurs and other attendant creatures for inventory and dating – and pertinent evidence for determination of coeval geography.
These dinosaur migrations under examination may be described as Jurassic Travels (200 to 160 Ma), and the Cretaceous Travels (145 to 65 Ma), as shown Figures 1. The former were marked by the contiguous positions of five Gondwanaland continents in relation to each other during the Jurassic (Figure 1a). The latter resulted from the accelerated dispersion of Gondwanaland (Figure 1b) during the Cretaceous; and were marked by the sequential re-locations of the superterrane, Austosunda, and the Indian Plate on the south coast of Laurasia.
|The Jurassic Travels (208-145 Ma)
The Antarctic Coastal Passage to India and Australia
Significant geographical dinosaur migrations are outlined in Table 1 below. An Antarctic coastal route into India and Australia by way of Africa and Antarctica was available to the dinosaurs during the late Triassic and the Jurassic, as shown in Figure 1a. The route required a clement climate and contiguity of Africa, Antarctica India, and Australia at any one time. This route offered an optional bypass into Antarctica. In premise, a temperate climate and the necessary contiguity of landmasses preserved the route until at least 160 million years ago. The passage to India had begun perhaps 215 million years ago. In Figure 1a, the route started out south from northern Africa to Zimbabwe; then, east through northern Zimbabwe into Mozambique From there, it passed into Antarctica (east of the Weddell Sea). It continued east along the northern coast of Antarctica to Australia.
This route is here termed “the Antarctic Coastal Passage.” Myriad herds migrated over the Antarctic Coastal Passage. They were composed of prosauropods, the earliest sauropods, and the earliest ornithopods, all with their theropod escorts. In their rear, therapsids paced along. Figure 1a shows both the walk-and-swim route taken by the dinosaurs about 200 million years ago and the in-continuum relationship of the four Gondwanaland continents at that time that enabled the migrations.
| The Zimbabwe Gateway
Zimbabwe was a gateway, a “jumping-off place,” forth from Africa to the Antarctic Coastal Passage. As such, its fossil inventories add substantial support that the Antarctic Coastal Passage was the route of the dinosaur on its first migrations to India. This support is manifested both by the locations of its two Zimbabwe early-Jurassic fossil sites and the similarity of their fossil inventories with those of Mount Kirkpatrick in Antarctica, and the Godivari Basin of India. In crossing the northern part of Zimbabwe (Figure 1a), two fossil sites are encountered which are highly relevant to the Antarctic Coastal Passage.The first site is at Forest Sandstone in Matabeleland North, the westernmost district of Zimbabwe. There, one fossil find is Syntarsus rhodesiensis, a coelophysoid theropod. Another find is Massospondylus schwarzi, a prosauropod. Both are dated early Jurassic, 206 to 190 Mya.
Heading east, the route comes to a second fossil site, the Vulcanodon Beds, in Mashonaland, again in northern Zimbabwe. Here, in a fossil find dated 206 to 202 Mya, is a four-meter-long sauropod, Vulcanodon karibaensis, of the family Vulcanodontidae. The Vulcanodontidae are considered the oldest and most primitive of sauropods. Vulcanodontidae routes have a compelling integrating consistency.
Only six early-Jurassic sauropods of the Vulcanodontidae are known. One bed has been noted in Zimbabwe: Vulcanodon karibaensis. In India, in the Godavari Basin in Andhra Pradesh – at a stem terminus of the Antarctic Coastal Passage – are two: Barapasaurus tagorei and Kotasaurus yamanpalliensis. Additionally, one bed is in Germany: Ohmdenosaurus liasicus. Two are in China: Zizhongosaurus chuanchengensis and Kunmingosaurus wudingensis.
Nesting in Antarctica
The early-Jurassic route out of Africa offered the option of a bifurcation of an indefinite stay in Antarctica (Table 1). More than 200 million years ago, Antarctic migration had become practical as a result of a warming of the climate to cold temperate. Far in the interior of Jurassic Antarctica, a dinosaur nesting site took hold. Today that fossil site lies high up on a blizzard-wracked mountain, Mount Kirkpatrick, in the Central Transantarctic Mountains, about 650 km from the South Pole. The site is now at about 3900 meters up the side of that 4500-meter mountain.
At the Mount Kirkpatrick site, fossil remains of four early Jurassic dinosaurs, along with a tritylodont (a therapsid) and a pterosaur, were discovered. The four dinosaurs included a plateosaurid prosauropod along with three theropods. The three theropods were a carnosaurian, Cryolophosaurus elioti; a coelophysoid; and a dilophosaur. (Only C. elioti has been named.) All three theropods were crested; the coelophysoid and the dilophosaur, double crested. (Five of the six fossil dinosaur species were carnivores, an array suggesting a lethal bog close to a prosauropod nesting site. Fancy that the prosauropod may have been isolated from its herd and chased into the bog.)
|It is pertinent to point
out the probable relationship of this site to the Zimbabwe fossil
sites. Both the dilophosaur Dilophosaurus and the Syntarsus species
found at Zimbabwe are among the only three or four coelophysoids that
are known to have paired cranial crests. Syntarsus may have been a
smaller cousin of Dilophosaurus. The theropods Dinophosarus, Syntarsus,
and other ancients such as Coelophysis, were all closely related within
the early Coelophysoidea superfamily. In both the Mt. Kirkpatrick and
Zimbabwe inventories, there was a plateosaurid. The plateosaurid in
Zimbabwe was Massospondylus schwarzi.
The early-Jurassic Mt. Kirkpatrick find of 195 to 190 million years ago predated the rise of the Transantarctic Mountains by about 15 million years. It is easy to imagine that the dinosaurs had come to wetlands of heightened geological activity, of geothermal heating, of hot springs, geysers, and intense vapors. The most interesting occurrence was not the orogeny, to come later, but species adaptation. While the seasonal length of darkness may seem well suited to a characteristically long brood time, endothermy, however, was essential. Fat and perhaps protofeathered, the dinosaurs probably swarmed and huddled for warmth, adults blanketing juveniles, in the deep cold of protracted night.
The stay in Antarctica may have been terminated by greatly increased geophysical activity. About 180 million years ago, there began vast volcanism and great welling up of a coarse basalt, the Ferrar Dolerite, coeval with the newly-rising Transantarctic Mountains, together extending 3500 km across the land, from sea to sea. The dinosaurs were directly in the path of adverse geological change – as it often would occur during their history.
Into India’s Sunny Clime
Dinosaurs, en route in the early Jurassic, that did not opt for Mt. Kirkpatrick entered the Antarctic Coastal Passage at its juncture with Africa and continued on into India, or alternatively into Australia. (See Table 1 and Figure 1a.) The going into India was wet, over delta and swampland, to reach nesting grounds mainly at the Godavari Basin of the Adilabad district, about 300 km from Hyderabad, in the state of Andhra Pradesh on the east coast of the Indian peninsula (at the Bay of Bengal).
There the fossil finds are within calcareous sandstone and shale formations at Maleri, Dharmaram, and Kota in the Godavari Basin. Found at Maleri was a small theropod, Alkwalkeria maleriensis, about 225 million years old, and with it were significant cynodonts (therapsids), amphibians, and pre- crocodilians. Found at Dharmaram were two unidentified prosauropods. In the Kota formation were the remains of lobe-finned fish, pre-crocodilians, and some therapsid teeth. And, remarkably, at Kota were two indicators of the migratory route from Zimbabwe: two species of the early- sauropod Vulcanodontidae. Namely, in an early-Jurassic dig, there was Kotasaurus yamanpalliensis; and in an early-to-middle-Jurassic dig, there was Barapasaurus tagorei.
|The Godavari formations
were laden with egg shells and bone fragments, relics of ancient-island
nesting sites amid shallow water and swamp. The fossil inventories
affirm an aquatic environment by their holdings of fish, amphibians,
and pre-crocodilians. There may well have been lush angiosperm
woodlands nearby. The dinosaurs had to leave the nest to feed, and here
they seemed vulnerable. Large therapsid carnivores and small, agile and
elusive placental mammals may have been vigilant and opportunistic in
pillaging unguarded nesting sites.
This first episode of dinosaur presence in India appears to have ended about 160 million years ago, probably with the inundation of nesting sites by flooding or incursion of sea water. The termination probably occurred soon after the separation of India from Antarctica at a time of the beginning of rapid disassembly of Gondwanaland. The loss of capability of dinosaurs to bridge the gap between Antarctica and India followed in due course. There is no known fossil record of dinosaurs in India between 160 Ma and about 85 Ma when dinosaurs re-entered India via Laurasia.
Early History of Dinosaurs in Australia
The first coming of dinosaurs to Australia occurred during the early Jurassic, by means of migrations along the Antarctic Coastal Passage (Table 1). The herds had entered the passage at its junction with Africa (Figure 1a) and had stayed the course all the way to Australia. Dinosaur footprints appeared in Queensland contemporary with the appearance of the first dinosaurs in India. They were identified as ornithopod (~ 210 Ma) and theropod (~ 200 Ma).
The initial Australian dinosaur of record (175-170 Ma) is Rhoetosaurus brownei, a sauropod. It was found at Roma, Queensland, about 500 km west of Brisbane. And about the same time, on the southwestern Australia coast at Geraldton, a tibia identified as theropod was found and named Ozraptor. This tibia find, and later numerous ornithopod, sauropod, and theropod footprints in sandstone (~120 Ma) at Broome in northwestern Australia, indicate that the western end of the southern coast of Australia, as well as the east end (at Victoria), had been accessible then to dinosaur entry from the Antarctic Coastal Passage. (The dinosaur footprints found at Broome might well have belonged to species that survived in Australia after the cutoff of the Jurassic coastal passage).
The outcome of the Jurassic migrations of the dinosaur to Australia was bleak. The Africa-to-Australia route was severed by the drifting apart of Africa and Antarctica in the late Jurassic about 150 million years ago. About the same time Africa had begun to break off its union with South America and had begun also to move northward, while rotating counterclockwise, and pushing the Arabian Plate ahead of it. The sea invaded Australia and inundated its interior regions from 130 to 100 million years ago. Unresolved questions involve the vast devastation – including the loss of fossil traces – that occurred then among presumed remnants of the dinosaur migrations and, more generally, among other plant and animal life.
Germany Gateway to China
A second geographically significant early Jurassic dinosaur migration route was eastward along what was then a wet, coastal pathway, the “South Laurasia Passage,” as termed herein. It began in Europe in Germany (Table 1). It terminated in three abutting provinces of southwestern China: Sichuan; and south of Sichuan, Yunnan; and east of Yunnan, Guizhou.
In premise, during the early Jurassic, dinosaurs had roamed north into Germany through France and Switzerland. After crossing the Western Tethys, they had opted to remain in Eurasia to forage for food rather than to return in season to the lush angiosperm harvest of Gondwanaland. Early on, those herbivores radiated in Laurasia , without returning to Gondwanaland.
Herds of sauropods and prosauropods entered into Germany with their theropod attendants. From Germany, some of these herds, seeking adequate safe breeding grounds, continued on eastward, over the watery lowland topography of the South Laurasia Passage, to ultimate destinations in southwest China. The migratory sauropods and prosauropods emphasize the relevance of Germany as a second Jurassic gateway, this time for geographically significant dinosaur migrations across the erstwhile Laurasia coastline.
Vulcanodontidae and Plateosauridae strengthen the tie between Germany
and southwest China. Fossils of an early Jurassic vulcanodontid
species, Ohmdenosaurus liasicus, have been found in the southwest
Germany state, Baden-Wurttemberg, bordering France. Vulcanodontids may
well have traveled from Germany along the Coastal South Laurasia
Passage to southwest China, there to be noted as the vulcanodontids
Zizhongosaurus chuanchengensis and Kunmingosaurus wudingensis. Fossils
of the early Jurassic prosauropod family Plateosauridae were found in
many fossil beds in Germany. These prosauropods too may have traveled
the coastal passage to become prosauropods in Yunnan Province in
To China, via the Early Jurassic Coastal South Laurasia Passage
The dinosaurs’ dual needs for accessible food supply and safe nesting grounds kept the early-Jurassic dinosaur on the move. Roving herds from Germany (and perhaps elsewhere in Europe) reached far into China, one quarter of the way around the world. How could they perform so lengthy a journey? They did it by following the South Laurasia Passage, the wet lowland coastline route, which existed 200 million years ago.
In successive herds, dinosaurs went from central Europe to China, season after season, walking and swimming along seashores, wherever practical (Table 1). The South Laurasia Passage crossed where now exist the Black Sea and the Caspian Sea. At the Caspian, the paths were broad, along delta and coastline. They crossed the Caspian, from Azerbaijan and Russia to its west and into Kazakhstan, Uzbekistan, and Turkmenistan to the east. Thence they trekked above Kashmir. The passage then was almost entirely at sea level and not to become mountainous until the Cretaceous. Into China they went, along that southern Asia coastline, where now the Kunlan Mountains rise north of the Tibetan Plateau.
The South Laurasia Passage to China 200 million years ago may seem tendentious because of a paucity of evidence due to upheaval by subsequent orogeny. But yes, there is hard evidence. In the easternmost part of Turkmenistan high up on the Kugitang Mountains are hundreds of dinosaur tracks made as they trudged through the erstwhile muddy lowland. The tracks have been dated as Jurassic, more than 150 million years old.
|The herds of dinosaurs
journeyed on, to the east of Myanmar and into Sichuan and south into
Yunnan and east into Guizhou. Presumably, they found in this
three-province region an ideal watery terminus with plenteous
vegetation. Here again were the vulcanodontids, probably the most
primitive sauropods known. Two were
found here in early Jurassic fossil beds in China: namely,
Zizhongosaurus chuanchengensis in Sichuan, and the other,
Kunmingosaurus wudingensis, in Yunnan. Furthermore, the Jurassic
double-crested theropod, Dilophosaurus, was found in the three China
A Dilophosaurus has been identified in Zimbabwe; and a dilophosaurid was uncovered on Mt. Kirkpatrick in Antarctica, along with a prosauropod plateosaurid. At least two families of prosauropods were found in Yunnan. All of the China specimens are at least of early Jurassic age. It seems amazing that, with small exception, the three provinces should hold all of the Asian fossil sites of early Jurassic dinosaur fossils. It seems amazing that the three Chinese provinces should hold any at all.
The Cretaceous Travels (145-65 Ma)
In Northeast China, Years of the Feathered Dinosaur
A second major migration of dinosaurs into northeastern China began with the Cretaceous about 145 million years ago (Table 1). Competition for safe nesting sites had intensified. The surge was due to an enormous increase in the Laurasia food supply: namely, the superterrane Austosunda (earlier essays) had joined with Laurasia, thereupon releasing the angiosperms into southern Asia for the first time. As a consequence, many families of angiosperm monocots and dicots spread broadly, over several million years, east throughout Asia and west through Europe, Greenland, and North America. Grasses and herbaceous plant provided new ground cover, and broadleaf, flowering shrubs and trees supplanted conifer forests in temperate environments.
These vast biological changes were evidenced in China by the formation of oil fields from Gansu Province northeast across Liaoning Province and up into the major field of Daqine in Heilongjiang Province, and far beyond.
Thus, in the time frame 145 to 100 Ma, dinosaurs migrated in large numbers into northeastern China (including Inner Mongolia), where they rapidly adapted to new floral surroundings and to new eating habits. Northeastern China was hospitable not only to dinosaurs but to placental mammals, and aquatic faunas as well. Notable among the dinosaurs were the many species, of a ceratopsian, Psittacosaurus, which radiated widely. This parrot-beaked ornithischian was well adapted to snapping off plant stalks.
|The biotic influx was
especially eventful in Liaoning Province, about 42 degrees north
latitude, coasting the Yellow Sea and hard by Inner Mongolia to the
northwest. There, a prolific fossil region, the Yixian Formation, as it
is termed, reveals fossils dating from 145 to 100 Ma. The formation
runs from the vicinity of Beipiao southwest to Lingyuan. It consists of
volcanic rock layering sedimentary rock of lake origin, the latter
containing abundant early Cretaceous freshwater and terrestrial
fossils. It is about 2200 m. thick.
Fossil and other evidence suggest that the Yixian Formation was part of a delta of vegetation, of marsh and lake country, with a cool-temperate, damp climate, probably strongly influenced by cold onshore air flow, and well-suited to angiosperms. It is relevant that G. Sun et al. (3) had reported findings of “angiosperm fruiting axes” in the Yixian Formation near Beipiao, dated about 140 million years old, in association with “abundant freshwater and terrestrial fossils.”
In the Yizian Formation, an ankylosaurian nodosaurid, Liaoningosaurus paradoxus, and in the nearby Jiufotang Formation, a ceratopsian, Psitttacosaurus meileyingensis, were reported. Both dinosaur species suggest a cold climate by kinship to polar relatives. For instance, about 115 Ma, in the cold climate below the Antarctic Circle, in Australia, there dwelt Minmi paravertebra, an ankylosaurian nodosaurid, a close cousin of Liaoningosaurus; and there too dwelt the family Hypsilophodontidae, relatives of Psittacosaurus. All of these relatively small bipeds were beaked for snipping off branches of small trees and shrubs.
Many species of theropod maniraptors were reported in the Yixian Formation and in other digs in Liaoning Province. Characteristically, they possessed insulation that also suggest a cold climate. The body coverings ranged from protofeathers to aerodynamically-shaped wing plumes perhaps proficient for gliding. At Beipiao (and elsewhere 120 to 100 million years ago) feathers made it conducive for manirapters to use cold lakes and watery connections for food supply. There too was a phylogenetically absurd therizinosaurian, Beipiaosaurus inexpectus, unearthed in a Yixian dig in Liaoning Province. It was protofeathered, at least clearly on its arms. Likely, it was well suited for stalking for mussels, clams, and other marine morsels as well as for pulling down and snipping off small-tree and shrub branches.
|Return to India, the Second Coming
The second episode of dinosaurs in India was entirely different from the first. It began 85 million years ago with migrations of dinosaurs into India from Laurasia (Table 1). The opportunity to revisit was offered then by the joining of the Indian Plate to an almost immobile Laurasia to the north. From Laurasia, dinosaur populations trekked into India–where, for the previous 80 million years, a drifting Indian Plate had offered no opportunity for dinosaurs to enter India.
The Indian Plate attached itself to Laurasia about 85 million years ago, near to the start of the Campanian. On this second trek of the dinosaurs into India, the traffic continued through the Maastrichtian (71 to 66 Ma). The dinosaurs entered mainly into a wetland region of India, consisting of the bordering states of Gujarat, Maharashtra, Karnataka (all coasting the Arabian Sea) and Madhya Pradesh and Andhra Pradesh, to the east. The region had been inundated during the Permian and held shallow waters interspersed with swamps and islands suitable for nesting sites safely away from placental mammals. The climate was moderately hot. In season, the herbivore herds could make their way to high grounds to feed on abundant angiosperms.
The Lameta Bed Testimony
Unfortunately, almost the only evidence today of that second significant episode of dinosaur migration into India consists of the Lameta Beds, a long strand characterized as “non-marine,” running from Jabalpur in Madhya Pradesh in central India west to Gujarat bordering on the Arabian Sea, then south into Maharashtra. The Lameta Beds were then probably a long stretch of islanded shallows well suited for serving as nesting sites for dinosaurs. Today the region is termed an “intertrappean,” a sedimentary deposit, one of many, positioned between outflows of basaltic lava termed “Deccan Trap.” The uniqueness of the Lameta Beds is that it contains almost all the identifiable dinosaur fossils found in India during the late Cretaceous. The Lameta Beds independently corroborate that the attachment of the Indian Plate to Laurasia occurred about 85 million years ago. None of the Lameta fossils appears to be more than 85 million years old.
|A substantial affirmation
of the 85 Mya attachment of the Indian Plate to Laurasia is among the
sauropod family Titanosauridae. For example, Titanosaurus
madagascariensis, is one of at least four Lameta Bed titanosaurids. It
was taken from a Lameta site in Maharshtra and is Campanian, 84 to 71
million years old. An Antarctosaurus and a Laplatasaurus (perhaps
identical genera) are titanosaurids. They are found in Lameta Bed
sites, from Campanian to Maastrichtian, 84 to 66 million years old.
Moreover, a theropod, Majungasaurus crenatissimus, was found in a
Lameta site in Gujarat and is listed as Campanian. These dinosaurs could have come into India
only from Laurasia to the north. From within the Lameta Beds
there have been described, classified, and named at least four sauropod
genera, nine theropod genera and one ankylosaurian. Many of their names
are open to question. In addition, a clutch of titanosaurid eggs and a
wealth of egg shells and dinosaur fragments have been found.
Of the dinosaurs that crossed the Laurasian border into India, the sauropod genus Titanosaurus is known to have roamed Europe (England) as early as the Valanginian to Barremian, 137 to 121 million years ago. Titanosaurus was widely distributed across South America, North America, Europe, Africa, and Asia during the late Cretaceous. And its titanosauriform cousins were widely distributed as well, even in Australia 100 million years ago. Species differed widely in length, perhaps 10 m to 35 m.
Except for the Lameta Beds and scant parts of other intertrappeans, the store of fossils in the five-state former wetland is almost inaccessible. It is essentially covered by the Deccan Trap lavas. The area extent of the lava upwelling is 1,250,000 square km over the five Indian states.
Return of the Dinosaurs to Australia
The Antarctic Coastal Passage was resumed and lengthened during the middle and late Cretaceous. It was re-started about 120 million years ago by juncture of South America with the Antarctic Peninsula. (See Table 1 and Figure 1b.) The renewed Antarctic Coastal Passage for migratory dinosaurs led from South America eastward to Australia. Its terminus, the southern coast of Australia, presented an inhospitable environment with six months of darkness, a semi-polar climate, and forests of cold-adapted needle-bearing conifers and angiosperms. Nevertheless, dinosaurs did come. There came herbivores such as Hypsilophodontidae, one species of ankylosaurian nodosaurid, a few other herbivores, perhaps a titanosaurid, and with them their theropod followers and the ancestors of penguins.
|Antarctica had joined at 65
degrees south latitude with the Fuegian edge of South America. At the
South American end, the climate was cool temperate. Dinosaurs, among
other flora and fauna, crossed over onto the Antarctic Peninsula. The
Antarctic Coastal Passage became forested from end to end with
angiosperms, notably Proteaceae and Nothofagus.
Dinosaurs entered into Victoria from Antarctica. There they favored two coastal nesting sites about 330 km apart, Strzelecki to the east and Dinosaur Cove to the west (with Melbourne in between). (Figure 1b marks the site of Dinosaur Cove.) From the coast, the migratory herds made their way east then north along the lowlands on the west side of the aged Great Divide Mountains (a 3500 km coastal range). Their destination was a multiple nesting site area in central Queensland referred to as “Fossil Triangle.”
The two coastal sites in Australia were on a flood plain and Fossil Triangle was a shallow, islanded wetland during the early Cretaceous. The environments were suitable to the aquatic nature of the dinosaur. However, the Australian end of the Antarctic Passage was much colder than the South American end. Both the Strzelecki and Dinosaur Cove coastal sites, and Fossil Triangle to the north were below the Antarctic Circle, as had been Mt. Kirkpatrick in Antarctica. To survive the long, inclement polar night in these nesting areas required endothermy; dense coverings of feathers; eye-keen electroreceptors both in spectral range and sensitivity; and the ability to subsist on a coarse diet. Fossils of at least eight genera of ornithopod of family Hypsilophodontidae were found in the colder Dinosaur Cove and Strzelecki sites, which dated 115 to 85 Ma.
In conjecture, their food supply in large measure consisted of the evergreen Banksia ericifolia, followed in season by its flowers, a source of nectar and quick energy. This angiosperm is of the family Proteaceae. It has short, needle-shaped leaves, the impact of the Permo-Carboniferous Ice Age. It is a survivor of the last glacier foray into New South Wales 250 million years ago. Even today, small trees and shrubs of B.ericifolia are abundant in Victoria and New South Wales.
The hypsilophodontidae had closely packed cheek teeth, which were tall and ridged for processing tough or fibrous plant tissue. These teeth were numerous and replaceable. Together, the arrays of teeth in the upper and lower jaws presented two powerful ridged grinding plates. Also likely, these ornithopods had gizzards and gizzard stones. (Gizzard stones have been identified within the rib cages of its early-Cretaceous ceratopsian relative, Psittacosaurus, found in Liaoning Province, above.) Hypsilophodontidae had beaked muzzles, as did Psittacosaurus, and as did the only ankylosaurian notosaurid, Minmi paravertebra, found at Fossil Triangle. The beaks were an essential tool for snipping branches from small trees and shrubs.
|But breeding questions
remain. How did polar dinosaurs, herbivores and carnivores alike,
fulfill the requirements for incubation of eggs and for feeding the
young in a polar environment? The feathery nature of the herbivore
hypsilophodontid genera in the Antarctic suggests that they huddled
rather than hibernated. Undoubtedly, the answer is that every step of
the long nesting period was warmed and sheltered by adult bodies and
body heat. The young were fed by controlled regurgitation, much as in
the penguin manner. The Antarctic Coastal Passage ended about 85 Ma
with separation of
South America and Antarctica.
On the western side of the Antarctic Peninsula, about where the Antarctic Coastal Passage began, are Vega Island and James Ross Island, which are late Cretaceous fossil repositories. See Figure 1b. James Ross Island, in particular, holds fossil sequences of flora from Cretaceous to Tertiary, indicating a climate much warmer than today. James Ross Island digs reveal that during the Campanian (84 to 71 Ma), it hosted dinosaurs in an environment of plesiosaurs, ammonites, etc. On that island were found fossil parts of an ankylosaurian nodosaurid, a kin to Minmi. On Vega Island was found an unusually large (4 to 5 m) late-Cretaceous hypsilophodontid. The traffic to Australia had ceased earlier, about 85 Ma. These islands provide important indication of the climate and the biota present about 100 Ma at the tip of South America.
Fossil inventories at nesting sites of herbivore and carnivore dinosaurs, often together with fossils of therapsid predators, outlined dinosaur migratory routes on now far-flung continents that once formed Gondwanaland or came in contact with it. Indeed, these routes, in turn, are records of the positions of continents in space and time throughout the Mesozoic. Thus, certain dinosaurs marked out the changing geography of the land surface of the earth during the Mesozoic. Noteworthy informants of changing earth geography were the prodigious herbivore travelers, namely: hadrosaurids, hypsilophodontids, nodosaurids, and psittacosaurids of order Ornithischia; and plateosaurids, titanosaurids, and vulcanodontids of order Saurischia.
|Dinosaurs dominated the
earth throughout the Mesozoic by a successful ploy of cyclic migration,
back and forth across the Western Tethys channel, north into Laurasia
to nest in safety (from therapsid and mammal predation of eggs and
hatchlings); and then south again in season to feed on angiosperms in
Gondwanaland. Population pressure and other unfavorable stresses over
time caused them to migrate into Antarctica, India, China, and
Australia. Theropod dinosaurs accompanied herbivores. An optimum
nesting site often involved the protective coastal presence of
plesiosaurs, ichthyosaurs, and mosasaurs.
In particular, the inherent Western Tethys reproductive stratagem of the dinosaur and the migratory impulse of the dinosaur to travel long distances over land and water (far beyond the Western Tethys), established the dinosaur as the dominant animal upon the land over the entire Mesozoic. For 165 million years the dinosaur surmounted hardships of predators, uncertain food supply, geological activity, and flood. By their fossilized traces as dated record where once they traveled coastal wetlands, the dinosaurs were geographers of the Mesozoic.
1. U.S. Geological Survey, GPO Stock No. 024-001-03601-1, W.J. Kious and R.I. Tilling,
This Dynamic Earth: The Story of Plate Tectonics, illustrations by J. Russell,
Washington, D.C., 2001.
2. C.L. Felton and M.A. Felton, The Fossil Book, pp.448-449 and 454, Doubleday, New York,
1989, revised and expanded by others.
3. G. Sun, D.L. Dilcher, S. Zheng, and Z. Zhou, Archaefructus liaoninggensis, Science 282,