1. Faunal Distribution and Supercontinents
Ike Ross
Michigan State University Geological Sciences
ABSTRACT
Continental based faunal distribution through the final periods of the
last three supercontinents (Gondwanaland, Laurasia and Pangea) can
be described as a spike in continental based migration prior to the
break up of Pangea forming the two supercontinents, Gondwanaland
and Laurasia. A shift of gradual distribution of fauna on Laurasia and
Gondwanaland is documented after the increased range of distribution
from Pangea. While internal migration allowed for species distribution
on the main lands of Laurasia and Gondwanaland respectively,
common species found on both supercontinents can be attributed to
marine and land bridge based migration upon continental separation.
By negating the Devonian and the periods prior, this eliminates the
need to focus on the migration pattern of fish and other marine species
whose distributions were not inhibited by travel over land masses
during periods of supercontinents. By using reconstructed maps with
tetrapod fossil distribution combined with previous research on
migratory patterns of existing fauna from the end of the Devonian
through the Jurassic (150 Mya to 225 Mya) it is be possible to
reconstruct a geologic explanation for the fossils found due to the
migration of fauna from southern Pangea through northern Laurasia.
Based on fossil records of the
Lystrosaurus, there is definitive
evidence of Lystrosaurus presence in
southern Pangea, current day South
Africa, India, and Antarctica, however,
there is also evidence of Lystrosaurus
fossils reaching as far north as
northern Laurasia, the U.S.S.R. region,
during later periods.
CONCLUSIONS
While the faunal distribution of the Permian through early Triassic has been
easily explained by the connected continents that formed Pangea, the
distribution of families of tetrapods from the mid Triassic through the early
Jurassic periods is more difficult to explain. The separation of Laurasia and
Gondwanaland would impede the distribution of land based tetrapods.
REFERENCES
1. Watson, J.M., 2012, Historical perspective [This Dynamic Earth, USGS]:
Historical perspective [This Dynamic Earth, USGS]
2. Colbert, E.H., 1982, OF THE DISTRIBUTION LYSTROSAURUS IN
PANGAEA AND ITS IMPLICATIONS : Geobios, v. 15, p. 375–383, doi:
10.1016/S0016-6995(82)80126-5.
3. Records of Life: Fossils as Original Sources Athena Review, v. 5.
4. Cox, C.B., 1974, Vertebrate Palaeodistributional Patterns and Continental
Drift: Journal of Biogeography, v. 1, p. 75–94, doi: 10.2307/3037956.
5. Cox, C.B., 1974, Vertebrate Palaeodistributional Patterns and Continental
Drift: Journal of Biogeography, v. 1, p. 75–94, doi: 10.2307/3037956.
Fig. 1 Position of continents from the Permian through the Cretaceous (USGS, 2012)
METHODS RESULTS
Fig. 2 Distribution of Lystrosaurus during the early Triassic
represented by black dots (Colbert, 1982)
INTRODUCTION
By focusing on vertebrates having evolved after the Devonian period
(~360 Mya), it is possible to construct a brief history of the continental
distribution patterns of fauna, specifically tetrapods, across the last 3
existing supercontinents. Based on fossil records of tetrapods and
dinosaurs, it is evident that these fauna had begun to disperse themselves
across the southern ends of Pangea during periods in which the
supercontinent had limited inland seas. Once Pangea began to break into
Laurasia, to the north, and Gondwanaland, to the south, the resulting
formation of seas and a probable land bridge allowed for fauna to migrate
northward to Laurasia from the central and southern regions of
Gondwanaland.
The distribution of known fossils
found of the tetrapod
Cynognathus correlates with the
distribution of the Lystrosaurus,
spreading mainly throughout the
southern reaches of Pangea. The
Cynognathus, however, has a
greater reach throughout present
day South America with no
noticeable reach into India.Fig 3 Regional distribution of Cynognathus through the early
Triassic
As Pangea split into Laurasia
and Gondwanaland in the late
Triassic, there is evidence of
tetrapod family distribution
through the northern parts of
Laurasia as well as regions in
the central to lower portions of
Gondwanaland. Faunal
distribution records show
similar results with families of
tetrapods on either side of the
Tethys Sea as well as the
southwest Americas and
northeast African regions.
Because there is evidence of tetrapods and dinosaurs of the same
families distributed across Laurasia and Gondwanaland, there must have
been a land bridge The presence of a land bridge would also explain the
high percentage of species with similar families found in northern
Laurasia and southern Gondwanaland. During the early phases of
continental separation, reptiles could have crossed the shallow seas prior
to their oceanic formation which would explain the presence of similar
fauna on either side of the Tethys Sea.
Fig. 5 Faunal distribution during the middle Jurassic represented by
black dots (Cox, 1974)
Europe (41) Asia (18.5) S. America
(19)
Africa (42.5) India (16)
N. America
(16)
87.5% 44% 56% 75% 59%
Europe 80% 74% 59% 81%
Asia 51% 89% 41%
S. America 74% 56%
Africa 75%
Fig. 4 Table of terrestrial faunal similarities at family level by percent during the Triassic. Number in
brackets represents number of families found on each present day continent. Incomplete families
were given an additional size of 0.5 (Cox, 1974)