[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Early vertebrate evolution (free pdf) + other non-dino papers



Ben Creisler
bcreisler@gmail.com



A number of recent non-dino papers that may be of interest:

In open access:

Philip C. J. Donoghue and Joseph N. Keating (2014)
Early vertebrate evolution.
Palaeontology (advance online publication)
DOI: 10.1111/pala.12125
http://onlinelibrary.wiley.com/doi/10.1111/pala.12125/abstract

Debate over the origin and evolution of vertebrates has occupied
biologists and palaeontologists alike for centuries. This debate has
been refined by molecular phylogenetics, which has resolved the place
of vertebrates among their invertebrate chordate relatives, and that
of chordates among their deuterostome relatives. The origin of
vertebrates is characterized by wide-ranging genomic, embryologic and
phenotypic evolutionary change. Analyses based on living lineages
suggest dramatic shifts in the tempo of evolutionary change at the
origin of vertebrates and gnathostomes, coincident with whole-genome
duplication events. However, the enriched perspective provided by the
fossil record demonstrates that these apparent bursts of anatomical
evolution and taxic richness are an artefact of the extinction of
phylogenetic intermediates whose fossil remains evidence the gradual
assembly of crown gnathostome characters in particular. A more refined
understanding of the timing, tempo and mode of early vertebrate
evolution rests with: (1) better genome assemblies for living
cyclostomes; (2) a better understanding of the anatomical
characteristics of key fossil groups, especially the anaspids,
thelodonts, galeaspids and pituriaspids; (3) tests of the monophyly of
traditional groups; and (4) the application of divergence time methods
that integrate not just molecular data from living species, but also
morphological data and extinct species. The resulting framework will
provide for rigorous tests of rates of character evolution and
diversification, and of hypotheses of long-term trends in ecological
evolution that themselves suffer for lack of quantitative functional
tests. The fossil record has been silent on the nature of the
transition from jawless vertebrates to the jawed vertebrates that have
dominated communities since the middle Palaeozoic. Elucidation of this
most formative of episodes likely rests with the overhaul of early
vertebrate systematics that we propose, but perhaps more fundamentally
with fossil grades that await discovery.

***
Mammals across K-Pg boundary

Lauren B. DeBey & Gregory P. Wilson  (2014)
Mammalian femora across the Cretaceous–Paleogene boundary in eastern Montana.
Cretaceous Research 51: 361–385
DOI: 10.1016/j.cretres.2014.06.001
http://www.sciencedirect.com/science/article/pii/S0195667114001128


Highlights

We investigate femora diversity across the K–Pg boundary in eastern Montana.
The latest Cretaceous assemblage comprises small multituberculates.
Paleocene immigrant taxa increased first mean specimen size then, maximum size.
Paleocene taxa include archaic ungulates, a large taxon, and a possible primate.
We preliminarily suggest locomotor diversity expanded across the K–Pg boundary.

Abstract

Our understanding of latest Cretaceous and earliest Paleogene
mammalian evolution is based almost entirely on the dental fossil
record. Mammalian postcranial fossils are rare and mostly found as
isolated elements in latest Cretaceous and earliest Paleogene
vertebrate microfossil assemblages of North America. Although placing
these fossils in a tooth-based taxonomic framework is difficult, they
can provide insight into locomotor diversity and habitat preference to
complement diet reconstructions and diversity estimates from dental
fossils. Here, we describe 64 femora of mammals recovered from latest
Cretaceous (Lancian) and earliest Paleogene (Puercan) localities in
eastern Montana. We sorted these based on morphology and size
(morphotypes). In some cases, morphotypes were tentatively assigned to
dentally based taxa that are known from these strata.

Although our resulting femoral dataset is small relative to the study
area's dental dataset, we show several key findings. First, there is a
greater morphological diversity of multituberculate femora than
previously recognized, especially in the latest Cretaceous sample. In
contrast, metatherians, which have a high relative abundance in
Lancian Hell Creek Formation dental assemblages, are absent from our
postcranial samples; eutherian femora are only present in the Puercan
assemblages. Second, we record a minor decrease in morphotype richness
across the K–Pg boundary that is associated with an increase in mean
specimen size, due to the appearance of a few significantly
larger-bodied, immigrant taxa. Among the eutherians, there are two
specimens of larger-bodied early Puercan archaic ungulates, a very
large specimen of a middle/late Puercan taeniodont, pantodont, or
triisodontid, as well as a specimen possibly attributed to a
“plesiadapiform” archaic primate. Third, preliminary functional
morphologic analyses of the more complete specimens suggest that
locomotor diversity increased from mainly arboreal or
terrestrial/saltatorial multituberculates in the latest Cretaceous to
include a fossorial multituberculate and potentially an arboreal
eutherian in the early Paleocene. These patterns parallel those
previously reported from a dental dataset and indicate that
postcranial data are valuable as an independent means to test
hypotheses of taxonomic and ecomorphological diversity across the K–Pg
boundary.

***
Ichthyosaur taphonomy, paper in open access:

Achim G. Reisdorf, Gail S. Anderson, Lynne S. Bell, Christian Klug,
Annette Schmid-Röhl, Hans-Joachim Röhl, Michael Jung, Michael Wuttke,
Michael W. Maisch, Mark Benecke, Daniel Wyler, Roman Bux, Peter
Fornaro & Andreas Wetzel (2014)
Reply to “Ichthyosaur embryos outside the mother body: not due to
carcass explosion but to carcass implosion” by van Loon (2013).
Palaeobiodiversity and Palaeoenvironments 94(3): 487-494
http://link.springer.com/article/10.1007/s12549-014-0162-z#page-1


****

Crocodile taphonomy

Caitlin E. Syme & Steven W. Salisbury (2014)
Patterns of aquatic decay and disarticulation in juvenile Indo-Pacific
crocodiles (Crocodylus porosus), and implications for the taphonomic
interpretation of fossil crocodyliform material.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
DOI: 10.1016/j.palaeo.2014.07.031
http://www.sciencedirect.com/science/article/pii/S0031018214003861

Highlights
We monitored decay patterns of juvenile Crocodylus porosus carcasses
in freshwater.
Most disarticulation occurred at the sediment-water interface when
carcasses sank.
The results are useful for interpreting patterns of decay for fossil specimens.
Decay in low energy settings alone does not guarantee high degrees of
articulation.
Freshly dead carcasses will begin to float unless weighed down by burial media.

Abstract
High levels of skeletal articulation and completeness in fossil
crocodyliforms are commonly attributed to rapid burial, with
decreasing articulation and completeness thought to result from
prolonged decay of soft tissue and the loss of skeletal connectivity
during ‘bloat and float’. These interpretations are based largely on
patterns of decay in modern mammalian and avian dinosaur carcasses. To
address this issue, we assessed the decay of buried and unburied
juvenile Crocodylus porosus carcasses in a controlled freshwater
setting. The carcasses progressed through typical vertebrate decay
stages (fresh, bloated, active decay, and advanced decay), reaching
the final skeletal stage on average 56 days after death. Unburied
carcasses commenced floating five days post-mortem during the bloated
stage, and one buried carcass only commenced floating 12 days
post-mortem. While floating, skeletal elements remained articulated
within the still coherent dermis, except for thoracic ribs, ischia and
pubic bones. The majority of disarticulation occurred at the
sediment-water interface after the carcasses sank during the advanced
decay stage, ~ 36 days post-mortem. Based on these results we conclude
that fossil crocodyliform specimens displaying high levels of
articulation are not the result of prolonged subaerial and subaqueous
decay in a low-energy, aqueous environment. Using extant juvenile C.
porosus as a proxy for fossil crocodyliforms, rapid burial in an
aquatic setting would have to occur prior to the carcass floating, and
would also have to continually negate the positive buoyancy associated
with bloating. Rapid burial does not have to be the only avenue to
preservation of articulation, as other mechanisms such as physical
barriers and internal physiological chemistry could prevent carcasses
from floating and subsequently disarticulating upon sinking. The
inference that a large proportion of skeletal elements could drift
from floating carcasses in a low energy setting with minimal
scavenging, thereby causing a loss of completeness, seems unlikely.

****
Wildfire evidence from Triassic

http://www.livescience.com/47316-oldest-forest-fire-scar-fossil.html

Paper:

Bruce A. Byers , Sidney R. Ash, Dan Chaney & Lucía DeSoto (2014)
First known fire scar on a fossil tree trunk provides evidence of Late
Triassic wildfire.
Palaeogeography, Palaeoclimatology, Palaeoecology 411: 180–187
DOI: 10.1016/j.palaeo.2014.06.009
http://www.sciencedirect.com/science/article/pii/S0031018214003216


Highlights
We describe a scar on a fossil tree trunk from the Late Triassic of
southeast Utah.
We compare it with modern tree scars to determine the cause of the ancient scar.
Macro- and microscopic characteristics most closely match those of
modern fire scars.
No ancient fire scar resembling those in modern trees has previously
been described.
Fire could have been an ecological and evolutionary force in Late
Triassic forests.

Abstract

Fire scars are well known to fire ecologists and dendrochronologists
worldwide, and are used in dating fires and reconstructing the fire
histories of modern forests. Evidence of fires in ancient forests,
such as fossil charcoal (fusain), is well known to paleontologists and
has been reported in geologic formations dating back to the Late
Devonian. We describe what we conclude is a fire scar on a fossil tree
trunk from the Late Triassic Chinle Formation of southeastern Utah (~
200–225 Ma). The external features of the prehistoric scar match those
of modern fire scars better than those of scars created by other kinds
of wounding events. The fossil specimen also exhibits a number of
changes in wood anatomy similar to those reported in modern
fire-scarred trees, including a band of very small tracheids that
indicate growth suppression immediately associated with the scarring
event; an area with a tangential row of probable traumatic resin
ducts; and a significant increase in tracheid size following the
scarring event that indicates a growth release. No fire scar
resembling those in modern trees has previously been described in
petrified wood as far as we can determine. The presence of a fire scar
not only provides further evidence of ancient fires, but also shows
that at least some individual trees survived them, indicating that
fire could have been an ecological and evolutionary force in forests
at least as early as the Late Triassic.


***
K-Pg impact effect on nearby plant life

Takuya Mizukami, Kunio Kaiho & Masahiro Oba (2014)
A spike of woody plant biomarkers in the deep-sea iridium layer at the
Cretaceous/Paleogene boundary.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
DOI: 10.1016/j.palaeo.2014.07.041
http://www.sciencedirect.com/science/article/pii/S0031018214004003

Highlights

We examined biomarkers from the Cretaceous-Palaeogene boundary in Haiti.
Accumulation of woody plant to the deep sea occurred in a year after
the bolide impact.
The supply of terrestrial organic matter into the deep sea led to low
dissolved oxygen.

Abstract

At the Cretaceous/Paleogene (K/Pg) boundary, 66 million years ago, the
Chixulub impact resulted in significant environmental changes and a
mass extinction of dinosaurs and marine invertebrates such as
ammonites. Here, we report that accumulation of woody plant biomarkers
in the deep water occurred in the iridium anomaly at ~ 700 km from the
impact crater. The results reveal that the concentration of
terrestrial organic molecules derived from woody plants, namely
biphenyl and dibenzofuran, shows synchronized changes and increases
abruptly in the red layer (fine ejecta), which has an iridium spike,
above tsunami-like coarse deposits indicating a significant increase
in the influx of woody plant fragments into the ocean a few years
after the impact. Long-chain n-alkanes and cadalene derived from land
vegetation in the tsunami-like coarse deposits prior to the
transportation of trees were also transported to the deep sea. This
implies that transportation of grass to the deep sea started within a
few days of the bolide impact. Transportation of trees then began a
few years later. A rapid increase in the concentration of
dibenzothiophenes also occurs in the red layer, indicating that
low-dissolved-oxygen conditions had expanded in the bathypelagic zone
over the seafloor. An increase in the influx of terrestrial organic
matter into the deep ocean could have resulted in the
low-dissolved-oxygen conditions. Furthermore, the stratigraphic
distribution of planktonic foraminifera at Beloc shows that Cretaceous
planktonic foraminifera became extinct as the result of an asteroid
impact.