Red Roughed Lemur photo by Eric Isselee copyright

On The Ubiquity and Diversity of Placental Mammals

By Harry Levin
Essay Number Nine


Some of the earliest placental mammals were carried on the backs of the dinosaurs – in an astonishing and beneficial relationship that brought fragile but adaptive creatures across thousands of miles to
eventually help establish the 4,000 species of mammals we know today.

On the Ubiquity and Diversity of Placental Mammals
discloses for the first time a paramount
symbiotic relationship between early mammals and dinosaurs involving ectoparasitology.

Harry Levin

Florida Wildflowers presents Dr. Harry Levin's essay on the diversity of mammals and their relationship with dinosaurs, in which he proposes an astonishing solution to another puzzle of prehistory.

It is one of 10 ground -breaking essays in natural history published for the first time. These essays are accessible from the contents page, along with his philosophy of how an engineer can  analyze, synthesize, and contribute to new scholarship in the natural sciences,

Michael E. Abrams
Florida Wildflowers

This symbiosis was the cause of extremely accelerated evolution of placental mammals and of their great diversity and ubiquity. The symbiosis is offered also in explanation of the rapid evolution from oviparous to viviparous mammals.

The symbiosis resulted from extremely small, insectivorous mammals – with scansorial abilities – feeding on dinosaur skin parasites while breeding on the backs of the dinosaurs.

This symbiotic relationship between early mammals and dinosaurs, in hypothesis, can explain in the main the ubiquity and diversity that exists among placental mammals. The cooperative arrangement provided the dinosaur protection against deep-time ectoparasites. It provided the mammal with food and shelter.

This symbiosis involved the transport of early scansorial mammals on the backs of dinosaurs as they migrated in herds from nesting site to nesting site thousands of kilometers apart. 

The symbiosis gave the mammal great opportunity for secondary evolution in divers ecologies by the shedding of their offspring from the backs of the migrating or nesting dinosaurs. An abnormally high degree of mammalian speciation resulted from this “seeding” all over the earth.

For placental mammalian, this symbiotic relationship was far more effective than other methods of diversification and radiation.

Three early mammal migratory episodes, widely scattered in time and location in the fossil record, are cited in introduction to the symbiotic relationship. A fourth symbiotic relationship involved gondwanathere and titanosaurid; and this time the unwelcome intruder was the  barnacle. It explains the hypsodont molars of the gondwanathere and the late-Cretaceous “armor” of the titanosaurid.

The ancient dinosaur-mammal symbiosis is the key, the instrumentality–

• in explaining the wonder of the four families of lemurs being the only
primates native to Madagascar; and

• in explaining the wonder of cattle and deer, grazing and reposing in magnetic (north-south) alignment, as statistically shown.

During the late-Paleozoic and all of the Mesozoic, continental movements and other geophysical effects strongly influenced both the migrations of dinosaurs and the secondary evolutions of placental mammals.



Placental mammals, Eutheria, present and past, have had amazing diversity. The orders of these mammals today are variously listed from nine to twenty six, depending on the criteria that rule their selection. Within the orders are whales, bats, elephants, shrews, monkeys, armadillos, pandas, dogs, squirrels, deer, rhinos, rats, pigs, otters, seals, cats, horses, etc.– some 4000 species, expressing extreme diversification.

With the extinctions of the therapsid about 150 million years ago and the dinosaur 65 million years ago, the placental mammal has gained animal kingdom ascendancy and has spread into almost every ecological niche on the surface of the earth.

In accounting for the extraordinary diversity of placental mammals, a hypothesis is offered herein of a unique symbiotic relationship of dinosaur and scansorial mammal for riddance of ectoparasites, to wit: minute mammal “travel companions” protected dinosaurs from ectoparasites; and in exchange for such protection, dinosaurs provided minute mammals “room and board” on their backs and tails. These symbiotic conditions were conducive, over millions of years, to fostering diverse secondary evolution of mammals, especially placental mammals, upon conveyance by migrating dinosaurs into distant diverse ecological regions.

The present placental mammal diversity may, in considerable part, be the result of these many occurrences of secondary evolution in diverse environments. Three fossil episodes of earlier probable symbiosis are given; and a fourth later episode involving gondwanatheres is cited. All are supported by a live fifth episode, namely, the unique presence of the lemur on Madagascar.

The fourth episode of pertinent early mammal symbiosis involves the baffling finds of unmistakable mammalian gondwanathere teeth (with hypsodont molars) in three far-apart late Cretaceous sites. In astonishing explanation, hard but toothsome barnacles clinging to the hides of late-Cretaceous titanosaurids triggered the evolution of the  gondwanathere hypsodont molars. Such is the explanation of early hypsodont development  – to feed on hard-bodied barnacles. Again astonishingly, these same barnacles provided the so-called armor that covered the hides of late-Cretaceous titanosaurids unearthed in fossil finds.


Episode 1

Episode 1 concerns Hadrocodium wui. It suggests that symbiotic cooperation had an early start as early as the Triassic or perhaps even earlier between reptilian archosaurs and dawn mammals. In the early Jurassic, 195 million years ago, Hadrocodium wui existed in the Lufeng Basin, about 100 km northwest of Kunming in the Yunnan Province of China. H.wui was 3.2 cm long, about half the size of the smallest hummingbird. It left a skull about 1.2 cm long. This skull was found in 1985, and that was the only part ever found.
Hadrocodium is described by Zhe-Xi Luo and co-authors as an early Jurassic mammaliaform (1). The paper observes that Hadrocodium could have existed alongside the ancestor of living mammals: “Hadrocodium is considered to be a sister taxon to living mammal groups, the closest relative to all extant mammals. Its very small size suggests . . .  that it adds a new lineage to early mammal diversity.” The authors note that the new species has a large brain and the middle ear of modern mammals. It had teeth that, according to the authors, “suggest it ate small insects.” 

By inference, H. wui was pediculophagous; i.e., it ate bird lice, such as the Hemiptera order Phthiroptera, suborder Mallophaga, probably little changed over the past 195 million years. Mallophaga today feed on the feathers and skin fragments of living birds. About 195 million years ago Mallophaga, or variants, may have infested the backs and tails of dinosaurs, especially those that were in early stages of evolving downy back and tail quills. A symbiotic accommodation seems likely to have existed between H. wui and dinosaurs in control of bird lice and other minute insects.    
The Lufeng Basin, where H. wui was found, was an early-Jurassic dinosaur nesting site. It contains a 1000-meter-thick formation of dinosaur-fossilbearing rock formed from sediments of lake and river origin. In the Lufeng Basin, two families of prosauropods, one Yunnanosauridae and the other Plateosauridae, have been identified. In the latter family, the 6-meter-long  Lufengosaurus, with some 30 complete or partial skeletons, constitutes the bulk of the animal fossils thus far found. Because of the wetland nature of its environment, Lufengosaurus likely was beset on back and tail by many external parasites in addition to Mallophaga. 

Dinosaurs of the family Plateosauridae 195 million years ago had traveled far and wide. They have been cited importantly in Africa (Zimbabwe), in Antarctica (Mount Kirkpatrick), in Laurasia (in several places), and in southwestern provinces of China. In accompaniment, Hadrocodium wui may have been a welcome guest on the back and tail of host Plateosauridae. It may have traveled long distances with them and with other dinosaurs from the Triassic on, perhaps from an initial place of origin such as the far-away Karoo Basin of southern Africa.


Episode 2

Episode 2 concerns Eomaia scansoria. It lived 125 million years ago in the early Cretaceous near Beipiao in the Liaoning Province of China. The Yixian Formation, where its well-preserved fossil was found, consists of volcanic rock layering sedimentary rock of lake and river origin, the latter containing abundant early Cretaceous freshwater and terrestrial fossils.

Eomaia scansoria may be a major development in animal history, the earliest known placental mammal. The fossil represents a mammal at least well advanced toward placental. It possessed a key feature in transition to placental mammal – more premolar teeth than molar.

E. scansoria has been examined in skeleton detail by Qlang Ji et al (2). Among the morphological features, the prehensile hands and feet are of special interest here. The Ji research found that the manual bones are “comparable to the condition in the grasping hands of living scansorial and  arboreal mammals.” The first joint of the forefoot digit is curved and in evidence of a strong muscle for grasping. The pedal bones show similar  “proportion and curvature to the grasping feet of extant arboreal mammals.” The Ji paper suggests that these features are more typically scansorial than arboreal.

The species name “scansoria” itself points out a noteworthy scaling ability possessed by this mouse-sized mammal, 9 cm long from head to rump.  Both its hands and feet were apparently adapted for scaling, grasping, and  clinging securely. Onto what? In all likelihood, onto the bodies and tails of feathered dinosaurs. To feed thereupon on abundant arthropod ectoparasites;  and to engage thereupon in their own brooding among downy quills – especially during the dinosaur nesting season in a cool wetland environment.

The presence of herbivore dinosaurs in and around the Yixian Formation 125 million years ago is noted; but few species have been described. Those include a Psittacosaurus (a sheep-sized, parrot-beaked, biped ceratopsian) and a Liaoceratops (a dog-sized, two-horned, frilled, quadruped ceratopsian). The presence of many species of feathered theropods suggests a chilly climate.

Life there for E. scansoria must have been precarious. Agility too must have been required for such small animals to survive among theropods that accompanied herbivore dinosaurs on migrations and at nesting sites. Among the carnivore theropods that surrounded the brooding sites of herbivore dinosaurs were feathered maniraptors such as Sinornithosaurus, a grasping-clawed, chicken-sized dinosaur, amid whose fossil bones was the last-meal jawbone of an early mammal. And there was Microraptor, about 0.5 m long, that most surely ate mouse-sized mammals as well as arthropods, mollusks, and worms. The early-Cretaceous fossil records witness an increase in maniraptors. The best chance of survival for mammals at that time was to remain small, agile, and as inconspicuous as possible – and, perhaps best of all, to stay within the protection of the herds of herbivores.


Episode 3

Episode 3 concerns Ausktribosphenos nyktos. Here is another indication (along with E. scansoria) of mammal evolution long before the  Cretaceous. A. nyktos connotes also a long previous history of dinosaur symbiosis with mammals which were near to the root of the eutherian tree.

In the Cretaceous 115 million years ago, A. nyktos existed in Victoria, Australia, where there are two main southern coastal dinosaur nesting sites, about 330 km apart, Strzelecki to the east and Dinosaur Cove to the west (with Melbourne in between). The two Victoria nesting sites at that time were well within the Antarctic Circle.

The find of A. nyktos was made by Thomas Rich in 1997 near Strzelecki. It consisted only of a 1.6-cm-long lower jaw with teeth. The length of mammal was estimated to have been 8.5 cm. Rich et al. recognized A. nyktos as a “generalized insectivore” (3). A tribosphenical (grinding and shredding) toothed mammal, A. nyktos is opined by Rich and others to be a placental mammal.

Within seven years of 1997, more than twelve other jawbone specimens were found; and all were given the taxon Australosphenida. Some were smaller, some larger than A. nyktos; and some, such as two Bishops whitmorei, were more confirmatory of placental mammal nature. The Bishops show a mandibular angle in evidence. A main criterion in its acceptance as a placental mammal was the presence of 4 or 5 premolars and 3 molars.

On the other hand, other tooth characteristics are cited to show that the austrosphenids were (egg-laying) monotremes. However, the data are undeniable that this mammal existed in Australia at least 115 million years ago. Size differences within the family suggest lengthy habitation and continued evolution at the Strzelecki site. In extrapolation, antecedents existed elsewhere. The smallest austrosphenid, half the size of A. nyktos, could have come to Strzelecki on the back of a dinosaur.

With A. nyktos, here again symbiosis is suggested in control of dinosaur ectoparasites. The teeth of the mammal indicate that it defended the dinosaur from larger external parasites than bird lice. Leeches, for example, might have been prime targets of opportunity. The jaw and the teeth of A. nyktos indicate that it was well adapted to chewing on leeches. Leeches are no less than 500 million years old; are generally found in still waters; and species are known to exist within polar zones such as early-Cretaceous Victoria. Some are carnivorous to turtles and reptiles, as well as to mammals. Today leeches are rife in the still waters of Victoria, New South Wales, and Queensland – no doubt, awaiting patiently the return of the dinosaur.

Australian fossil records cite the presence of dinosaurs in Strzelecki and Dinosaur Cove 120 to 85 million years ago. During that time, the dinosaur migratory route in Australia extended northward along icy wetlands on the west side of the Great Divide Mountains to a large marshy dinosaur nesting expanse known as Fossil Triangle in the center of Queensland. Essay # 5 The Dominance of the Dinosaur and Essay #6 The Geomigrations of the Dinosaurs describe the migrations of dinosaurs out of Antarctica across into Australia in the above time period.


It is important to realize that the two Victoria nesting sites at that time were well within the Antarctic Circle. For survival, the long, inclement polar night required protection, such as a dense covering of hair and endothermy for the mammal and a dense covering of feathers and (indicated) endothermy for the dinosaur. There is no clear indication of hibernation among dinosaurs.

The Hypsilophodontidae family of ornithropods (bipedal cousin to the better-known hadrosaurs, or duck-billed dinosaurs) appear to have been the main dinosaurs at Strzelecki and Dinosaur Cove, where at least five genera  have been cited. Hypsilophodontids were among the small dinosaurs, about 2 m in length. Being herbivores, like the duckbills, with beaked snouts, closely packed cheek teeth, gizzard, and gizzard stones, they could extract  nourishment from tough, fibrous plant tissue, such as perhaps the needles of the cold-adapted Banksia ericifolia.

Here again, symbiosis is suggested. The warm, downy backs and tails of hypsilophodontids could have been important survival havens to a minute, early A. nyktos in symbiotic adaptation with these dinosaurs. A. nyktos was likely scansorial and hitched its rides on hypsilophodontids and other dinosaurs all the way from South America or Africa probably across Antarctica to cold Strzelecki and Dinosaur Cove, while nesting and feeding on dinosaur ectoparasites. Thomas Rich pointed to an insectivore, the hedgehog, as a modern analog of A. nyktos. The hedgehog is an exemplar of hibernation, an intriguing hint that A. nyktos hibernated through the long polar night at Strzelecki – and perhaps an indication of placental mammal hibernation as far ago as the end of Permo- Carbonaceous Ice Age 250 Mya. 


In three separate instances, examples have been pointed out of probable dinosaur-mammal symbiosis at dinosaur fossil sites millions of years and thousands of kilometers apart – decidedly out-of-joint in respect to current belief of time and place of origin of placental mammals. 

In perception, the minute mammals, after climbing and clinging onto broad dinosaur backs, would have completed their life cycles and produced young, (mammal “seedlings”) while the dinosaur herds made their journeys over dry land and marshes and onto nesting sites This view meshes with the realization that dinosaurs were characteristically aquatic in their migrations and in their choice of (arthropod - infested) wetland nesting sites for long months of brooding. And what commodious living quarters there must have been for these tiny mammals! Two-to-sixty meters of neck, back, and tail, often protofeathered. 

The nesting sites were frequently in lowlands, in rivers, lakes, and brackish-water environments, which, by their nature, stocked many of the familiar pernicious parasites – for example, lice among insects; amphipods among crustaceans; and leeches among annelids. Yet vegetation abounded, and many of the mammal “seedlings” would evolve into herbivores.


An Astonishing Gondwanathere–Titanosaurid Relationship

The gondwanathere might be considered as Episode 4. Explorations of three late-Cretaceous nesting sites of titanosaurids in Madagascar, in India, and in South America each unearthed a cluster of mammalian teeth, including distinctive hypsodont molars, that belonged to a single unknown mammal, given the name of gondwanathere. The only gondwanathere information obtained consists of these few isolated similar hypsodont (high-crown) molar teeth, which link Madagascar, India, and South America and at the same time link the titanosaurid with the gondwanathere. These vastly far-apart but essentially coeval findings are compelling indications of symbiotic gondwanathere conveyance on the backs of titanosaurs. 

Here, in hypothesis, is a symbiotic relationship between the gondwanathere (likely a small scansorial mammal) and the herbivore titanosaurid, as disclosed by the few recovered gondwanathere teeth and a relatively well-documented fossil record of the titanosaurid. Curiously, while there is not enough information to classify the gondwanathere, its mammal hypsodonts (with their protective coating of enamel) seem to be anachronistic to the late Cretaceous. Why these wear-resistant teeth? Astonishingly, those few teeth of the gondwanathere that were found speak eloquently of the titanosaurid.

During the late Cretaceous, titanosaurids had become especially indigenous to tidal wetlands. By deduction, titanosaurid bodies in many locations became host to species of intertidal calcareous crustaceans – one or more species of barnacles – during the late Cretaceous. The barnacles, which incidentally were not ectoparasites, spread like wildfire, gluing themselves to titanosaurids in their aquatic environments. The hides of titanosaurids quickly became beaded with dense-packed, permanent exoskeletal structures of barnacles – with the hard armor of accreted barnacle plates of calcium carbonate. (In paleontological studies to-date of late-Cretaceous titanosaurids, the unrecognized epidermal biofouling of titanosaurids by barnacles appears to have led to the false impression that many of the titanosaurids rapidly evolved their own armor.) 

At the same time, hard but toothsome barnacles triggered evolution of the gondwanathere hypsodonts. Thus, the explanation of the early hypsodont development is, namely: it enabled the gondwanatheres to feed effectively on the hard barnacles adhering to the hides of late-Cretaceous titanosaurids. 


The Titanosaurid and Its Role in Symbiosis

Consider the titanosaurids. The sauropod family Titanosauridae (4) had available the entire 89-million-year Cretaceous to adapt to symbiosis with the early mammals. During that time, the titanosaurids (some genera 18 to 20 meters long) spread out abundantly almost everywhere upon the earth.  Their fossil bed locations include Kazakhstan, France, Romania, Spain, the United States, Argentina, Brazil, Chile, Uruguay, Egypt, Niger, Malawi, Madagascar, and India. 

Titanosaurids were especially wide-spread during the last two epochs of the late Cretaceous: the Campanian (84 to 74.5 Ma) and the Maastrichtian (74.5   to 65 Ma). For example, species of titanosaurids, Antarctosaurus and Laplatasaurus, that existed in Argentina during the Campanian and Maastrichtian appear to be similar to species that existed in India during that time. Also, in these epochs, Rapetosaurus krausei found in Madagascar appears to be similar to Titanosaurus madagascariensis found in India. In Argentina, there are more than eleven Campanian and Maastrichtian titanosaurid fossil beds. In Madagascar, there are two such titanosaurid fossil beds, i.e., less than 85 million years old; and in India, there are four.

At specific locations in these countries, in delta river basins and other wetland  regions, titanosaurid herds (accompanied by theropods) sought out their nesting sites. The particular Campanian and Maastrichtian titanosaurid fossil beds of Argentina, Madagascar, and India are of special interest here in connection with the obscure gondwanathere (5).  
Explanation of the baffling, abrupt presence of a few identical teeth of the gondwanathere at Campanian and Maaastrichtian dinosaur fossil sites in Argentina, Madagascar, and India fits the concept of symbiosis and is in context with the symbiotic relationships described in the first three episodes of tiny-mammal fossils. The titanosaurids too must have given room, board, and passage to the gondwanathere, whose few unmistakable teeth and a jaw fragment (like a Cheshire cat grin) had been left behind in fossil beds at specific titanosaurid wetland nesting site locations. 
It is striking that in one of the gondwanathere-tooth sites, namely, the Maevarano Formation in the Mahajanga Basin in Madagascar, the titanosaurid, Rapetosaurus krausei, was found. Incidentally, it has been pointed out (6) that “many of the relic roots of the Maevarano Formation are encrusted with calcium carbonate or interspersed with irregular clumps of that material.” Was this calcium carbonate the copious remains of the aforementioned barnacles that might densely have been glued to the hides of R. krausei?


It is striking that near to the gondwanathere-tooth site in the Lameta Formation Beds in Andhra Predesh in Central India, was found the titanosaurid, T. madagascariensis, similar to R. krausei of Madagascar.

And “curiouser and curiouser!” Like the gondwanathere teeth in their abrupt appearances, the fossils of a theropod family, Abelisauridae, have been found halfway around the world, in Argentina, in Madagascar, and in India; and none pre-dated the late Cretaceous. Abelisaurid fossils are found  among the late - Cretaceous titanosaurid fossils in Madagascar and India (7); namely, in fossil sites in the Maevarano Formation in Madagascar and in the Lameta Formation in India, this time at Gujarat. The Abelisauridae, relatively large carnivores, about 4 to 9 meters in length, resembled T Rex in  silhouette, except for small forelimbs and much shorter skulls. Abelisaurids presumably journeyed with titanisaurids, circling and culling the herds.

Continental Movements and Other Geophysical Effects

The above information, moreover, appears to be of the utmost paleogeographic significance. The India interrelationship of the gondwanathere, the abelisaurid, and the titanosaurid resulted from the linkage of the Indian Plate to the Eurasia Plate to a degree that permitted biotic passage from Eurasia onto the Indian subcontinent. This linkage occurred about 85 million years ago. The Indian Plate previously had been a part of Gondwanaland.

About the same time (85 million years ago), a linkage of Africa and Madagascar provided a roughly concurrent interrelationship for the gondwanathere, the abelisaurid, and the titanosaurid. A land bridge (shown in Figure 1) that had connected Africa and Madagascar during the late Permian and the Triassic was again crossable by dinosaurs during an extended period of low sea level that began about 85 million years ago and continued into the Tertiary. In its crossable stages, the land bridge probably  was partially submerged, with patches of land of unstable high-tide elevation amid large stretches of shallow sea.


Figure One

Conceptual sketch of Madagasar and Africa geography 250 to 240
million years ago, showing an overland passage, a land bridge, existing between Madagascar and Africa, placed there by reason of mainland proximity, prevailing ice-age low sea level, and the movement of ice-field till and other sediment off both lands. Sketch is not to scale.


The land bridge in Figure 1 is of such importance that it is here delimited, as follows. On the African side, it was built by sediment (initially glacial till) washed from the Zambezi Basin watershed of Malawi, Tanzania, and Mozambique. During its existence, its upper and lower latitudes were roughly those of Lake Malawi.

On the Madagascar side, it received sediment in coastal continuity from the southern part of the Mahajanga Basin to the northern part of the Morondava  Basin – attrition (initially glacial till) washed down from the west versant of the central mountains. In width, the land bridge included both the latitudes of the Maevarano Formation (site of titanosaurid and abelisaurid fossils and gondwanatheres) and the latitude of the 230 - million-year-old fossil site of prosauropods. Could the fossil sites such as in the Maevarano Formation have resulted from whirlpooling effects of torrential mountain-side rainstorms?

The biotic passageway from Eurasia to India and the dinosaur-crossable land bridge connecting Africa to Madagascar were concomitant geophysical occurrences (i.e., events that were essentially geophysically independent of each other).

The concurrence does, however, point out that as early as 85 million years ago, titanosaurids, conveying gondwanatheres (and escorted by abelisaurids) were enabled to make overland passage from Eurasia into India. And, about the same time, they were able to make land bridge crossings Africa into Madagascar, conveying gondwanatheres. The fossil inventory of the Madagascar Maevarano Formation implies that the land bridge in Figure 1 was difficult to cross except by aquatically-adept creatures such as titanosaurids, abelisaurids, and crocodilians.
Furthermore, this hypothesis connotes a migratory compulsion and a wetland preference of the family Titanosauridae in search of safe nesting grounds with nearby vegetation. It is noteworthy here that the Abelisauridae, as theropods, had hollow-boned buoyancy and aquatic ability; so they could keep pace with the larger titanosaurids hither and yon, over both marshes and dry land. The aquatic ability of the theropods has been confirmed (8).

It is significant to note that, in keeping with their migratory compulsion to venture into wetlands, the dinosaurs were able to swim across a narrow sea between Africa and South America (to Patagonia) until about 80 million years ago. The result was that symbiosis of dinosaurs and tiny scansorials on migration into South America eventually led to a plethora of species of placental mammals throughout South America (9). 


The Lemuriformes

The lemur may be considered a live episode in this account of mammalian diversity through symbiosis. Lemurs are the only primates ever found to have existed on Madagascar. Today, lemurs are native nowhere else, presumably because they were losers elsewhere in competition with later-evolved suborders of primates.
(Madagascar had been isolated from land approach ever since India broke away from Madagascar about 240 million years ago—except for approach by dinosaurs and other aquatic reptiles over that land bridge (Figure1) on two low-sea-level occasions. Other exceptions were birds, bats and large amphibians. Also in exception, in the late-Cretaceous and early Tertiary, were mammals with high aquatic ability, such as Tenrecidae which could bridge the gap.)

In brief, lemurs exist today on Madagascar solely by reason of its geographic isolation providing protection against other primates (except recently, man and his works). In hypothesis, about 230 million years ago, herbivore dinosaurs of infraorder Prosauropoda, traveled from Africa over the land bridge (Figure 1) to nesting sites in Madagascar. Evidence of their habitation is known from two prosauropods jawbones found in Madagascar and dated to 230 Ma.  On their backs rode minute, scansorial ancestral lemurs in symbiotic passage into Madagascar. There, the lemurs dismounted offspring.

Here again, symbiosis is imputed, this time between an ancestral lemur and the dinosaur – at an early Triassic time involving a crucial land bridge (the same land bridge that later was to re-emerge between Africa and Madagascar during the late Cretaceous). The inference here is that the ancestral lemur crossed from Africa to Madagascar in the Triassic, not in the Cretaceous, based on:

     • The absence of other mammalian fauna, particularly primates, from Madagascar. (Surely there was a diversified mammalian fauna extant in Africa in the late Cretaceous. If the lemur had crossed over at that time it would have been accompanied by other mammals); 

     • Hibernation habits of certain lemurs, an evolutionary response to cope with the cold winters associated with the Permo-Carboniferous Ice Age which ended about 250 Ma; and

     • The observation that the pigmy mouse lemur (at 35 grams) is small enough to suggest that a similar-sized ancestor could have had a scansorial relationship with the kangaroo-sized prosauropod.

The land bridge (Figure 1) between Africa and Madagascar probably originated at the end of the Permo-Carboniferous Ice Age, during the Permian 250 million years ago, as ice-field till (under rapid climate change) was swept beyond the shorelines of both Africa and Madagascar (then part of India) to fill the intervening low-sea-level channel. The initially emergent land bridge probably existed in a partially submerged condition until about 220 Ma – before it became fully submerged by rising sea level.  


About 240 million years ago, India had begun a lengthy process of rifting away from Gondwanaland. But the land bridge effectively restrained Madagascar to Africa. The gradual breakaway led to increasingly difficult traffic between India and Madagascar, a traffic which ended about 220 Ma. 

The Madagascar prosauropod fossil site (10) contained the oldest dinosaur remains yet found – well - preserved jawbones of two 230-year-old prosauropods estimated to have been about the size of kangaroos. Ergo, any back-riding symbiot would have been extremely tiny. (The 195-million-yearold Hadrocodium wui, previously cited as found also at a prosauropod site, has been estimated as 3.2 cm in length.) In order to inhabit the back of a dinosaur the size of a kangaroo, a very tiny lemur, indeed, needs to be called forth; and today there exists that improbable figure of its ancient symbiot ancestor. This lemur, of the family Cheirogaleidae, is the pigmy mouse lemur. It is native to the Kirindy Forest in the northern part of the Morondava Basin. It weighs 35 grams.

Hibernation too may have played a part as a significant defense against the bitter cold of 250 million years ago especially in the Karoo Basin of southern Africa, where mile-high ice fields had risen. But by 240 Ma, the ice had melted away and the Karoo basin had become warm. Hibernation, as a defense against the cold, likely evolved in the late-Permian among the earliest mammals. Today hibernation persists among mouse lemurs of Kirindy Forest and the Ampijoroa stands of timber near Mahajanga further north. In fact, the fat-tailed dwarf lemurs of Kirindy Forest are observed to store fat in their tails and to hibernate for an eight-month period each year.

(The reader will recall that at 115 Ma in the Antarctic Circle, at Strzelecki, Australia, there existed the warm-blooded mammal, an indicated symbiot, Ausktribosphenos nyktos. T. Rich (3) noted that its fossil jaw is suggestive of the hedgehog – which insectivore is exemplary of hibernation. A. nyctos may have hibernated through the long, inclement winter night.)

Today on Madagascar there are four families of lemurs, order Primates, suborder Prosimii, infraorder Lemuriformes. These are Lemuridae, Indridae, Megalopadidae, and Cheirogaleidae. The latter family includes the mouse lemur and the fat-tailed dwarf; and it is, in all likelihood, the most ancient.  The lemurs were so successful, until recently, that they had diversified to about 50 species. Many are tree dwellers with remarkable agility, able to leap long distances, even with their young, from tree to tree. Some of the largest species are diurnal and spend much time upon the ground. The smallest are nocturnal and fill niches in trees.

Here in the above paragraphs is a paleobiogeophysical implication of high significance, namely: the placental mammal had evolved before the dinosaur and perhaps as far back as the end of the Gondwanaland Ice Age about 250 million years ago. It could be rewarding to search in the Karoo Basin fossil-bearing formations of 240 to 220 million years ago especially for jaw fragments or extremely tiny teeth resembling those of the mouse lemur.


Mammalian Deductions

Placental mammals were ascendant, and not marsupials, where dinosaur conveyance (symbiosis) was feasible for both.  The placental mammal consistently displaced the marsupial from competitive territories.

However, monotremes and marsupials are native to Australia, but placental mammals are not. In conjecture, it might follow that monotreme and marsupial ancestors were in Australia before it severed its biological connection to Gondwanaland; and placental mammal ancestors were not. (There is no evidence of hedgehogs in ancient Australia.) According to Essay # 3,
Origin of flowering plants , Australia biologically rifted from Gondwanaland about 280 million years ago. The implication is that in Gondwanaland early forms of monotremes and marsupials originated more than 280 years ago; and placental mammals originated there at a later date.

Monotremes are oviparous; and it seems probable that among the multituberculates, marsupials, and placentals as well, some species were oviparous during the Mesozoic. Again in conjecture, the symbiosis of dinosaur and mammal could have had a rapid and decisive effect in displacing oviparous birth with viviparous birth entirely among the marsupials and the placentals. In a few words, egg layers may have become extinct because their eggs would have tended to roll off the backs of symbiotic dinosaurs.

Here, in hypothesis, is a startling three-way relationship; for it involves anacronistic hypsodont teeth, false titanosaurid “armor”, and barnacles. A symbiotic relationship between the gondwanathere (likely a small scansorial mammal) and the herbivore titanosaurid, is disclosed by a few recovered gondwanathere teeth and a relatively well-documented fossil record of the titanosaurid.


Addendum to Essay #9
Explanation of Cattle and Deer Orientation in a North-South Direction

    Begall et al (11) statistically established that cattle and deer align their body axes in roughly a north-south direction when grazing or resting. Magnetic alignment is offered by these authors and others as “the most parsimonious explanation.”
     The basis for the behavior pattern of north-south orientation in cattle and deer finds a logical explanation here in Essay #9 of Tectonic Genesis. The following prefatory information is essential for the comprehension of this phenomenon:
     · For more than 120 million years (from about 200 Ma until about 80 Ma), the dinosaurs in herds travelled north and south, back and forth in season, across a narrow water channel, north to Laurasia to breed, south to Gondwanaland to sample bountiful provender.
     ·That water channel, described here as the Western Tethys, extended thousands of kilometers east and west and was a main factor for the dominance of the dinosaur.

      ·The thesis of dinosaur travel in season north and south across the Western Tethys is expatiated in Essay #5 of Tectonic Genesis, entitled “The Dominance of the Dinosaur.”
      ·Today, in magnetically imprinted memory of those millions of years of sustained dinosaur crossings, birds – the last of the dinosaurs -- in flocks, travel forth, in season, north to a nesting site and south again to an ancestral homeland. That birds fly north to nest is among the strongest evidence that birds are direct descendents of dinosaurs.
       With the above information, the why and wherefore can now be understood.
        Cattle and deer have been statistically shown to graze and rest in a north-south direction. At this latter day, Bovidae (cattle) and Cervidae (deer), both of order Artiodactyla, obey magnetically imprinted ancestral voices from afar – a chord of genetic memory, habituated by millions upon millions of years of repeated ancestral prototype north-south travel on the backs of dinosaurs.
     These artiodactyls monophyletically trace their lineage back to a single placental mammal precursor that lived in the age of dinosaurs 235 to 65 million years ago.
       By deduction, this progenitor of cattle and deer was characteristically extremely small, inconspicuous, scansorial, and insectivorous. It was adroit and able to crawl up and cling to the backs of resting dinosaurs and to nest thereon in delta-like environments where edible ectoparasites abounded -- in a symbiotic dinosaur-mammal relationship similar to those described in this essay for Hadrocodium wui, Eomania scansoria, the austrosphenids, the gondwanathere, and the forerunner of the lemuriformes.
       These extremely small mammals (as had the others above) fed on dinosaur skin parasites, while they traveled with the herds north and south for more than 120 million years.  During this course of time, they bred on the backs of the dinosaurs and dropped off their new-born broods, which diversified in various ecologies.

      Thus, in the premises of this essay, artiodactyls, (both cattle and deer), in magneto-genetic behavioral memory of ancestral travel, orient their bodies north-south in grazing or resting.
         At the time of dinosaurs, the earth’s magnetic field was significantly stronger than it is today.



In accounting for the extraordinary diversity of placental mammals, a hypothesis is offered herein of a unique symbiotic relationship of dinosaur and scansorial mammal for riddance of ectoparasites, to wit: minute mammal “travel companions” protected dinosaurs from ectoparasites; and in exchange for such protection, dinosaurs provided minute mammals “room and board” on their backs and tails.

These symbiotic conditions were conducive, over millions of years, to fostering diverse secondary evolution of mammals, especially placental mammals, upon conveyance by migrating dinosaurs into distant diverse ecological regions. The present placental mammal diversity may, in considerable part, be the result of these many occurrences of secondary evolution in diverse environments.  
For the tiny mammalian passengers aboard the dinosaurs, ample opportunity likely prevailed over millions of years to shed (dismount) their offspring – i.e., to sow progeny – into many wide-spread dinosaur nesting sites and into migratory stops along the way. Nutriment was often on hand for the dismounted young in diverse ecologies. Opportunities for secondary evolution into many different species were often right over millions of years for these mammals, especially placental mammals.

In truth, it might be said that the placental mammal strode forth to inherit the earth on the backs of dinosaurs. Dinosaur-mammal symbiosis has taken a remarkable twist. Long years ago, nit-picking mammals may well have protected dinosaurs. Today, a descendent of dinosaurs, the oxpecker, protects antelopes and cattle.



1.  Luo, Z.-X., Crompton, A.W., and Sun, A.-L., A new mammaliaform from the early Jurassic and evolution of mammalian characteristics,  Science 292, 1535-40 (2001).

2.  Ji, Q., Luo, Z.-X., Yuan, C.-X., Wible, J. R., Zhang, J.-P., and  Georgi,  J.A., The earliest known eutherian mammal, Nature 416, 816-22 (2002).

3.  Rich, T.H., Vickers-Rich, P., Constantine, A., Flannery, T.F., Kool, L., and van Klaveren, N., A tribosphenic mammal from the Mesozoic of Australia, Science 278, 1438-42 (1997).
4. Wilson, J.A. and Upchurch, P., A revision of Titanosaurus Lydekker (Dinosauria-Sauropoda), the first dinosaur with a ‘Gondwanan’ distribution, Journal of Systematic Paleontology 1, 125-60 (2003) The Cambridge University Press.

5.  Krause, D.W., Prasad, G.V.R., von Koenigswald, W., Sahni, A., and Grine, F.E., Cosmopolitanism among Late Cretaceous Gondwanan mammals, Nature 390, 504-07 (1997).

6. Rogers, R. R. and Krause, D. W., Tracking an ancient killer, Scientific American, 296 (2), 43-51 (2007).

7. Sampson, S.D., Witmar, L.M., Forster, C.A., Krause, D.W., O’Conner, P. M., Dodson, P., and Ravoavy, F., Predatory dinosaur remains from Madagascar: Implications for the Cretaceous biogeography of Gondwana, Science 280, 1048-51, (1998).

8.  Ezquerra, R., Doublet, S., Costeur, L., Galton, P. M., and Perez-Lorente, F., Were non-avian theropod dinosaurs able to swim? Geology, 35 (6) 507-510 (2007) Geological Society of America.

9.  Flynn, J.J., Wyss, A.R., and Charrier, R., South America’s missing mammals, Scientific American, 296 (5), 68-75, (2007).

10.  Flynn, J.J., Parrish, J. M., Rakotosamimanana, B., Simpson, W.F., Whatley, R.L., and Wyss, A.R.,  A Triassic fauna from Madagascar,  including early dinosaurs, Science, 286, 763-65 (1999).

11. Begall, S., Cerveny, J., Neef, J., Vojtech, O., and Burda, H., Magnetic  alignment in grazing and resting cattle and deer, published online before print, August 25, 2008, doi 10.1073/pnas 0803650105.