Connecting the Fifth Ape to the Sixth Mass Extinction

Recent research conducted out of UC Berkeley and Penn State University has quantitatively demonstrated that mammal diversity in North America has plummeted since the arrival of humans about 13,000 years ago. The study (Available at PLoS One) examines changes in the number and variety of mammal species from several different biogeographic provinces within the United States and over a time period ranging from the Oligocene up to about 500 years ago.

To conduct the study, researchers established a ‘diversity baseline’ by calculating species-area relationship values from counts of fossilized mammals. Species-area relationship values are basically ratios of species occurrence to geographic area. Once this base line was determined, time intervals without human presence were compared to periods since the arrival of humans into North America about 13,000 years ago.

After finding a correlation between humans and declining mammal diversity, the scientists concluded that if “mass extinctions are defined as loss of at least 75% of species on a global scale, our data suggest that North American mammals had already progressed one-fifth to more than halfway (depending on biogeographic province) towards that benchmark, even before industrialized society began to affect them.”

The study is unique in that it utilized fossil evidence to establish a diversity base line covering a thirty million year period. The quantification of this paleontological data aids in giving greater empirical support to qualitative assessments of declining diversity worldwide. As stated in the paper’s conclusion, “[w]orldwide, about 60 mammal species have gone extinct in the past 400 years, and some 25% of remaining species are considered under threat of extinction, observations which contribute to notions we are experiencing a sixth mass extinction.”

Carrasco, M., Barnosky, A., & Graham, R. (2009). Quantifying the Extent of North American Mammal Extinction Relative to the Pre-Anthropogenic Baseline PLoS ONE, 4 (12) DOI: 10.1371/journal.pone.0008331

Part 3 - Darwins Dilemma, Creationist Propaganda and Corrupt Christians

The previous post is available here.

Having ‘proved’ that fossils predating the Cambrian radiation are non-existent, and that all modern animal phyla appeared out of nowhere - in what the narrator describes as a “burst of creativity” - Darwin’s Dilemma the movie, then proceeds to ridicule Darwin the scientist. In their distorted reasoning, the creationist filmmakers think that if they can discredit a scientist that lived 150 years ago in Victorian England, somehow the audience will be convinced that the whole of modern science is erroneous. To initiate the strike against their biology bent Beelzebub, another carefully cropped quote is thrown to screen;

“Nothing distressed him more than the Cambrian explosion…” - Stephen J. Gould

For some unknown reason, creationists love Stephen Gould. Their infatuation may have something to do with a distorted view of Gould’s ‘punctuated equilibrium’ model; perhaps somehow the idea of a long stasis followed accelerated change translates to divine creation in the minds of simpletons? At any rate, Stephen Meyer or some other failed scientist from the Discovery Institute must have gotten this Gouldian morsel shorthand in a text message. They certainly didn’t get it from the page 238 of The Panda’s Thumb, the book in which Gould uses it to illustrate the lack of discrepancy between long past Darwinian predictions and modern paleontology.

It is certainly true that Darwin struggled with the lack of fossils predating the Cambrian radiation, speaking to intermediate fossils in Chapter 10 of the Origin of Species he wrote;

“Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against my theory.”

Of course, as with the Richard Dawkins quote yesterday and the Gould quote above, Darwin is here using the presupposition of a question as a lead to his explanation. And although the film in question is in the habitat of mining only the presumptive portions of these literary tools, the authors’ answers usually follow. In the case of Darwin’s true dilemma alluded to in the Origin of Species quote, he explains later in chapter 10 that,

“The explanation lies, as I believe, in the extreme imperfection of the geological record…. we continually overrate the perfection of the geological record, and falsely infer, because certain genera or families have not been found beneath a certain stage, that they did not exist before that stage. In all cases positive paleontological evidence may be implicitly trusted; negative evidence is worthless, as experience has so often shown…
Those who believe that the geological record is in any degree perfect, will undoubtedly at once reject my theory. For my part, following out Lyell's metaphor, I look at the geological record as a history of the world imperfectly kept and written in a changing dialect. Of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved, and of each page, only here and there a few lines. Each word of the slowly-changing language, more or less different in the successive chapters, may represent the forms of life, which are entombed in our consecutive formations, and which falsely appear to have been abruptly introduced. On this view the difficulties above discussed are greatly diminished or even disappear.”

Basically stated, what Darwin was implying was that, due to erosional processes, fossils are rare in the first place, and the oldest of all-the-fossils on Earth are rarer still. And he further predicts that despite these natural conditions, predecessor fossils are there and will be found as time proceeds and paleontological excavations are made. Darwin was right on-target with this prediction. In the 150 years since publication of the Origin of Species, numerous fossils have been unearthed, including those of the Ediacara biota, some from the Doushantuo formation and even the fascinating Markuelia fossil embryos – all predating the radiation vent! But, alas I guess these fine fossils don’t count… After all, as Paul Chien the head of the Discovery Institute’s paleontology section tells us in the film,

“to the paleontologist, the lack of intermediate fossils is well known.”

And Paul Chien should know, because he’s Chinese! As he later explains, “the Chinese community is honest about these problems and tries to explain them outside of Darwin.”

In addition to having an Asian heritage on his side, Paul Chien is a fellow of the Discovery Institute where he helps ‘spread the good word’ by translating Christian pseudo-science into the Chinese language. The worst part of Chien’s resume is that he’s also a biology professor at the University of San Francisco – tsk tsk San Fran.

Chien’s appearance marks a second transition point in the film’s diabolical plot. Leaving the fossils in the past, the modern sciences of evolutionary development and molecular genetics take center stage. In concert with this changeover is implementation of a new strategy – drawn the audience with science-ish jargon and convince them of life’s irreducible complexity. Leading this new front is Steven Meyer himself; holstered at his side is information theory. Brandishing this weapon he aims to shoot down “Neo-Darwinist storytelling” – by showing that modern genetics has nothing to do with evolution…


CONCLUDED - IN PART 4



Condon, D. (2005). U-Pb Ages from the Neoproterozoic Doushantuo Formation, China Science, 308 (5718), 95-98 DOI: 10.1126/science.1107765


Dong, X., Donoghue, P., Cunningham, J., Liu, J., & Cheng, H. (2005). The anatomy, affinity, and phylogenetic significance of Markuelia Evolution Development, 7 (5), 468-482 DOI: 10.1111/j.1525-142X.2005.05050.x

Morris, SC (1995). Ecology in deep time Trends in Ecology & Evolution , 10 (7), 290-294

Sex was a Costly Affair for Ceratopsian Dinosaurs

In a recent article published in The Anatomical Record several scientists, including Florida State University’s resident dino-osteologist Gregory Erickson, constructed a life table for a population of 80 bird-hipped dinosaurs.

Note, a ‘life table’ is a common tool used by population ecologists/biologists to interpret the birth-to-death maturation cycle of an organism. Essentially, a life table can be thought of as a listing of a population’s members with a corresponding age identified for each individual. Through examination of how the table’s age-ranges are distributed scientists can make inferences regarding the population’s ecology.

Drawing reliable conclusions on the subject of population-level processes can be difficult, particularly when that population happens to be extinct and is only known from the fossil record. Without numerous, quantitatively significant, representatives from a population, discussions of maturation rates, reproductive cycles and mortality rates are all but impossible. However, a mass kill event documented in the Lujiatun Bed of the Lower Cretaceous (Yixian Formation, Liaoning Province of China) provided the Erickson led team with the rare opportunity to do just that, study the demography of an extinct population of dinosaurs – specifically the species Psittacosaurus lujiatunensis.

Compared to the ‘lizard-hipped’ dinosaurs (saurischians) relatively little research has been undertaken in understanding the life history and population dynamics of the Ornithischia (bird-hipped), this makes the case of P. lujiatunensis all the more significant. Through histological analysis of the growth rings found within the fossil bones of the ceratopsians, – analogous to counting the growth rings in a tree – Erickson was able to estimate the age of each population member; the frequency of the age-ranges were then correlated to body size estimates. The result was that, like modern birds and mammals of comparable size, the life history of Psittacosaurus lujiatunensis reflected a pattern in which

“[h]igh attrition in young individuals gives way to lower stabilized values once a threshold size is obtained; however, later in ontogeny mortality rates increase (typically from the effects of senescence) leading to the extinction of the cohort.”

In other words, risk of death was found to be at its greatest when the dinosaurs were young and small – possibly because of vulnerability to predation. Once achieving a certain size and becoming less vulnerable, mortality rates decreased. Mortality risks would then increase again as the dinosaurs got old; through the natural ageing process the senior members of the population would once again become vulnerable to predators, disease, and etcetera.

In addition to the vulnerable young and old members of the Psittacosaurus lujiatunensis population, incidences of increased mortality were also found for those ceratopsians around the age-range associated with reaching sexual maturity. In this case, energy and resources devoted to the pursuit and winning of mates, as well as the rearing of young once a mate was found, likely conspired to cause escalated mortality levels during the reproductive years.


Erickson, G., Makovicky, P., Inouye, B., Zhou, C., & Gao, K (2009). Initial Insights Into Ornithischian Dinosaur Population Biology
The Anatomical Record, 292 (9), 1514-1521

Taking a Bite out of Niche Conservatism

In efforts to quash assumptions associated with niche conservatism, scientists from the Florida Museum of Natural History and the New York State Museum have enlisted the teeth of several fossil mammals to better understand the ecology of climate change.

Recently published at PLoS One, the research holds critical the idea that niches remain constant over extended periods of time. This idea, called niche conservatism, essentially holds that niches are highly specialized, ancestrally –linked, relatively inflexible and are therefore exceedingly susceptible to disturbance and rapid degradation in the face of change - particularly climate change.

While biologic response to environmental change is assumed, often such conservatism is overemphasized and is presented in a manner inconsistent with understanding gained through modern ecology and the insights of paleontology, which have both demonstrated incredible plasticity within the Earth’s biota.

Undoubtedly, the changing climate is of great concern and poses tremendous challenges to all organisms, but at the same time life is flexible and extinctions are not entirely unavoidable. As evidence to life’s flexibility, the currently discussed paper uses the testimony of change documented in the isotopic signatures of mammalian tooth enamel to show that the obstacle of climate change has been successfully negotiated in the past. More specifically, glacial-interglacial transitions during the Pliocene and Pleistocene are marked by substantial alterations in plant communities; however the contemporaneous uptake of vegetative food-stuffs by mammals seems to have fluctuated little.

The article is worth a read:
DeSantis, L., Feranec, R., & MacFadden, B. (2009). Effects of Global Warming on Ancient Mammalian Communities and Their Environments PLoS ONE, 4 (6) DOI: 10.1371/journal.pone.0005750


Vertebrates, and in particular mammals, are highly responsive to changes in the environment. Climate fluctuation can lead to an incredible amount of variation in the diet choice, distribution, and even the morphology of vertebrates.

Natural selection is a reflection of the biological and physical environment as transcribed into the genes of flora and fauna; however, the DNA found within living cells functions only as a recipe for ecological fit, the actual ingredients – the building materials - required to construct living tissue are harvested from surrounding chemistry. Because of variability inherit to this chemistry, the isotopic constituents that compose individuals may differ with respect to climate, diet, or a number of other variables.

For example, carbonate apatite - a primary constituent of both skeletal bones and dentition in vertebrates - is incorporated into organisms through diet and water uptake. Some conservationists use the isotopic signatures recovered from this apatite to better decipher the life histories of contemporary species in expectation of aiding in their continued preservation. As a case in point, remains from the world’s largest cavefish (Milyeringa veritas) have been used by Australian conservationists to better examine and comprehend the environment and ecosystem inhabited by the fish. The cavefish resides in deep water columns that are rich in dissolved limestone. Due to relative densities and variable solubility, different depths in the water column are correlated to specific concentrations of dissolved materials. By examining the isotopic signatures of the cavefish’s skeletal apatite, conservationists were able to discover the exact depth the fish occupies.

As demonstrated by the cavefish, uptake of elements within vertebrates (O, C, Sr & others) generates a highly detailed record of the environmentally available isotopes at a given point in time; this availability can even be indicative of climate.As another illustration of application, Thure Cerling and others at the University of Utah have refined the technique of laser ablation to such quality and precision that they can use it to vaporize the apatite found in teeth. They then analyze the resulting gas via spectrometry to determine its isotopic components. The teeth can be examined to such resolution as to be able to report the dietary preferences of mammals between C3 and C4 plants. A similar isotopes-from-enamel strategy was employed by the folks from the University of Florida to expound several fallacies of niche conservatism…

Examinations of isotopic records are commonplace for many paleontologists. Uncountable volumes have been written on Foram O-18 isotopes and their relationship to periods of increased glaciation, and similar correlations of speleothems and C-13, but accurate isotopic records of both of these elements can be obtained from other sources as well - including mammals.

As a side note - skeletal tissues, which possess apatite, are very susceptible to diagenic processes that can cause recrystalization and alter results, but dental samples seem to be far more reliable when it comes to maintaining their original isotopic signatures. This coupled with the knowledge acquired in the past few decades in regarding incorporation of specific O-18 and C-13 isotopes into biological entities has brought to light a highly accurate record of climate change – and the critters that adapted to it.

Cretaceous Billabong Yields New Dinosaurs

Hocknull, S., White, M., Tischler, T., Cook, A., Calleja, N., Sloan, T., & Elliott, D. (2009). New Mid-Cretaceous (Latest Albian) Dinosaurs from Winton, Queensland, Australia PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006190

Two newly identified sauropods and a new theropod have been excavated from the base of the Winton Formation near central Queensland. Fossilized pollens in-strata with the vertebrate remains indicate a Phimopollenites pannosus palynomorph Zone sequence and are thought to be Albian in age - about 100 million years old. In regards to ecology, cursory examinations of taphonomy and sedimentology show that the depositional conditions associated with the finds are akin to those found in modern oxbow lakes, or as the Aussies call them “billabongs”.

Although all three dinosaurs represent significant finds, the predatory theropod in particular is sure to bring publicity to the Australian Age of Dinosaurs Museum of Natural History and the Queensland Museum, which jointly worked on the excavations and diagnoses of the dinos. There’s nothing quite like a giant predatory allosauroid in terms of stirring the public’s interest in paleontology and stimulating museum attendance numbers.

According to Ben Kear of La Trobe University in Melbourne, "Australia is one of the great untapped resources in our current understanding of life from the Age of Dinosaurs. The discoveries...will definitely reinvigorate interest in the hitherto tantalizingly incomplete, but globally significant record from this continent..."


Meet “Matilda”

Named for the Diamantina River and one of Austrailia’a National songs (“Waltzing Matilda”), Diamantinasaurus matilda was a 16-meter long (52-foot) sauropod.


Nicknamed Matilda, she is the more stout of the two new sauropods and left behind a variety of fossils, including a pelvis:

Left reconstructed pelvis in lateral (A) view. Left ilium in anterior view (B) showing the position of the sacral vertebrae. Right pubis and ischium in medial (C), proximal (D) and lateral (E) views. Right ischium in lateral (F) and medial (G) views. Reconstructed right and left ischia in dorsal view. Abbreviations: ip, ischial peduncle; iip, iliac peduncle of ischium; of, obturator foramen; pa, pubio-ischial contact; pip, iliac peduncle of pubis; ppd, pubic peduncle; ppp, preacetabular process of ilium; s, sacrum; sym, fused ischial symphysis.

Meet “Clancy”

Wintonotitan wattsi, or “Watts' Winton Giant" was also around 16-meters in length, but sported a more elongate neck than Matilda.


Nicknamed Clancy, he was diagnosed from a variety of fossils, some partially articulated, including several vertebra:

Partial dorsal centrum in lateral (A) and posterior (B) views. Isolated neural spine in anterior view (C). Anterior caudal vertebrae of Wintonotitan wattsi. Anterior caudal vertebra in lateral (D) and anterior (E) views. Anterior caudal vertebra in posterior (F), lateral (G) and ventral (H) views. Anterior caudal vertebra in anterior (I), lateral (J) and ventral (K) views. Abbreviations: plc, pleurocoel; pcdl, posterior centrodiapophyseal lamina; prel, prespinal lamina; spl, spino-prezygopophyseal lamina.

Last, but not least - Meet “Banjo”

Called “Banjo” after Australian bush poet Banjo Patterson, Australovenator wintonensis was a 5-meter long (16-foot), 500 kilogram (1100 pounds) predator with three slashing claws.

"The cheetah of his time, Banjo was light and agile," "He's Australia's answer to Velociraptor, but many times bigger and more terrifying," said the article’s lead author Scott Hocknull of the Queensland Museum.

As evidence of his ferocity, here are a few of Banjo’s teeth:

Isolated teeth in labial (A, C, E, F, G, I, J, L) and labial (B, D, F, H, J, K) views. A–B. Anterior dentary tooth or premaxillary tooth. C–L. Dentary teeth.

Hocknull, S., White, M., Tischler, T., Cook, A., Calleja, N., Sloan, T., & Elliott, D. (2009). New Mid-Cretaceous (Latest Albian) Dinosaurs from Winton, Queensland, Australia PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006190

All Images from Referenced Article

Associated Press News

Reuters News

Panamanian Treasure Trove

Scientists with the Smithsonian Tropical Research Institute (STRI), the Florida Museum of Natural History and the University of Oregon’s Geology Department seem to be having one heck of a good time down in Panama!

During the last few months, there’s been a variety of paleontology related research coming out of the Panama Canal's spoils; I’ve seen articles on paleoclimate, paleobotany and now vertebrate paleontology.

As copied from STRI materials (PDF available HERE):

Aldo Rincón, STRI paleontology intern, unearthed a set of fossil teeth in the Panama Canal that Bruce MacFadden, curator of vertebrate paleontology at the Florida Museum of Natural History, describes as belonging to Anchitherium clarencei, a three-toed browsing horse the size of the modern donkey, living 15 to 18 million years ago.

Expanding the Panama Canal to make way for super-sized ships is providing geologists and paleontologists with rare finds. Carlos Jaramillo, STRI stratigrapher, has, in collaboration with the University of Florida and the Panama Canal Authority, organized a team of researchers and students who move in following dynamite blasts to map and collect exposed fossils.

"This is one of very few places in the tropics where we have access to fresh outcrops before they are washed away by torrential rains or overgrown by vegetation, and we expect the fossils that we have been salvaging to resolve some major scientific mysteries," said Jaramillo. "What geological forces combined to create the Panama land bridge? Were the flora and fauna of Panama before the land bridge closed similar to those of North America, or did they include other elements?"

The latest finding appears in the Journal of Paleontology, vol. 83: 489-492.

Rincón, MacFadden, Jaramillo

Good stuff…

Gregory Retallack (University of Oregon) and Michael Kirby (STRI) have also been actively publishing on materials from the Canal’s excavations. I plan to post about some of their work over the next few days - so keeping it brief for now.

Anchitherium Image Credits: FMNH

The Devonian Fishes that Got Away

In addition to remembrance ceremonies paying tribute to the men and women of the armed services, Memorial Day has become a day in which Americans head to the great out-of-doors to enjoy friends, family, picnics and nature. With this tradition in mind, I thought it fitting to briefly mention a couple of fish stories. These not so tall-tales are about a couple of good catches from the past year that somehow managed to get away from me.

The first story received quite a bit of publicity, it was in the news about a year ago and may be old news for some - but it's a fish worth a second look!

The fossil Materpiscis attenboroughi is a 380-million year old placoderm that was found with an intact umbilical cord! According to Dr. John Long of the Museum Victoria,“The discovery is certainly one of the most extraordinary fossil finds ever made. It is not only the first time ever that a fossil embryo has been found with an umbilical cord, but it is also the oldest known example of any creature giving birth to live young. The existence of the embryo and umbilical cord within the specimen provides scientists with the first ever example of internal fertilisation - i.e sex - confirming that some placoderms had remarkably advanced reproductive biology. This discovery changes our understanding of the evolution of vertebrates.”

Here's a Youtube Video (originally from Nature):




Long, J., Trinajstic, K., & Johanson, Z. (2009). Devonian arthrodire embryos and the origin of internal fertilization in vertebrates Nature, 457 (7233), 1124-1127 DOI: 10.1038/nature07732

Abstract: Evidence of reproductive biology is extremely rare in the fossil record. Recently the first known embryos were discovered within the Placodermi, an extinct class of armoured fish, indicating a viviparous mode of reproduction in a vertebrate group outside the crown-group Gnathostomata (Chondrichthyes and Osteichthyes). These embryos were found in ptyctodontids, a small group of placoderms phylogenetically basal to the largest group, the Arthrodira. Here we report the discovery of embryos in the Arthrodira inside specimens of Incisoscutum ritchiei from the Upper Devonian Gogo Formation of Western Australia (approximately 380 million years ago), providing the first evidence, to our knowledge, for reproduction using internal fertilization in this diverse group. We show that Incisoscutum and some phyllolepid arthrodires possessed pelvic girdles with long basipterygia that articulated distally with an additional cartilaginous element or series, as in chondrichthyans, indicating that the pelvic fin was used in copulation. As homology between similar pelvic girdle skeletal structures in ptyctodontids, arthrodires and chondrichthyans is difficult to reconcile in the light of current phylogenies of lower gnathostomes, we explain these similarities as being most likely due to convergence (homoplasy). These new finds confirm that reproduction by internal fertilization and viviparity was much more widespread in the earliest gnathostomes than had been previously appreciated.

Check out the Museum Victoria's Website for more info on Mother Materpiscis.

The second Devonian fish story that slipped away is one that has been retold since 1892 and really has some teeth to it!

In fact, teeth are all that it has to it – fossil teeth. Back in 1892 Woodward described the Devonian chondrichthyan Protodus jexi from the Lower Devonian Campbellton Formation in New Brunswick based on teeth recovered from the site. Several months ago, Susan Turner and Randall Miller published a follow-up examination of these teeth in Acta Geologica Polonica and determined the fish to be representative of the first predatory fish.

Here’s their conclusion:
Protodus jexi is known from one locality on the Campbellton shoreline of northern New Brunswick and represents the first chondrichthyan with predator style teeth. Given the nature of shark dentitions, the known 60 or so teeth might belong to one dentition. The paratypes and probably the syntypes include a tooth file of four associated dagger-like teeth with serrated cristae. The large subrectangular to D-shaped Protodus toothbase is similar and might be phylogenetically related to the cladodont type. Contemporaries Celtiberina and Stigmodus might be closely related or the similar tooth features might reflect functionality, with large laterally extended bases providing such ‘protodontidid’ teeth with a ‘solid’ root resisting movement and assisting an efficient predatory bite.

A Couple of Fossil Protodus jexi Teeth. Source Turner & Miller Article

SUSAN TURNER,RANDALL F. MILLER (2008). Protodus jexiWoodward, 1892 (Chondrichthyes),from the Lower Devonian Campbellton Formation, New Brunswick, Canada Acta Geologica Polonica, 58 (2), 133-145

The article is available HERE.

Neil Shubin on Tiktaalik & Transitional Fossils

Neil Shubin, Associate Dean of the Biological Sciences Division at the University of Chicago describes how his diverse fossil findings allow him to devise hypotheses on how anatomical transformations occurred by way of genetic and morphogenetic processes.

Andean to Amazon, an Anuran Account

The tropical rainforests of the Americas are a hotspot of biodiversity and boasts the largest reservoir of amphibian diversity on the planet; but how did such variety arise in our slippery skinned friends?

If I would have been asked this question yesterday, my reply would have a bit different than it would be today – this after reading an article by Juan C. Santos of the Integrative Biology and Texas Natural Science Center recently published at PLoS.



“The unstable coexistence of lineages within a large community for extended periods of time has been hypothesized as a cause of Neotropical diversity. However, our results suggest that such a model is incomplete; rather, the complex pattern of diversification is strongly intertwined with paleogeographic events. Our inferences about the past history of the poison frogs using ancestral area reconstructions and diversification analyses provide new insights on speciation and extinction patterns in the Neotropics. Three species richness patterns are potential explanations for the extant diversity differences among regions of the Neotropics:

(1) high immigration into one region after suitable geoclimatic conditions are established;

(2) gradual in situ diversification of old endemic clades, regardless of the geoclimatic conditions, promoting species accumulation; or

(3) rapid in situ diversification of endemic clades after favorable geoclimatic conditions are established. We found that all three patterns might apply to different areas depending on historical context.

All extant Amazonian species descended from 14 lineages that dispersed into the Amazon Basin, mostly after the Miocene floodbasin system receded. The recurrent immigrations that originated mostly in the adjacent Andes, combined with an increased rate of diversification, explain the high α–diversity of Amazonia. Later, from the Miocene-Pliocene boundary to the present, a rapid in situ diversification gave rise to the extant Amazonian endemic biota. Therefore, most species in Amazonia originated in the last 10 MY. Moreover, lineages immigrating into Amazonia at <8.0>

The diversity in the Chocoan-Central American super-region derived from scattered immigrations from Andes to the early Chocoan rainforest during the late Miocene. However, starting at the Miocene-Pliocene boundary, significant orogenic events gave rise to the Central American archipelago followed by sea level fluctuations, which provided the conditions for repeated dispersal and vicariance events in pre-PLB islands. Evidence of rapid in situ diversification is supported by the high genetic diversity observed among poison frogs and other lineages especially between Western and Eastern Panamá. Interestingly, our results might explain the high β–diversity of other endemic clades within the Chocó-Central America super-region as originating initially from long-distance dispersals between disconnected islands, with diversification later during isolation by high sea levels.

The Andes have undergone extended in situ diversification since the late Eocene. However, our analyses also provided evidence of decline in the diversification rate since the middle Oligocene, which has important implications for history and conservation of the endemic Andean fauna. First, the Andes uplift at the Miocene–Pliocene boundary caused significant changes in the rate of diversification in the lowland transition zone. We found that several poison frog lineages distributed on one or both sides of the Andes had dispersed repeatedly before the Miocene uplift (i.e., five cross-Andean and five Northern to Central Andes migrations). Paleogeological evidence supports introgression of shallow seas across the northern Andes during the Miocene, suggesting a historical connection between the Amazon Basin and the Chocó. Second, the Pliocene Andean uplift (>2,000 m above sea level) formed a significant barrier to dispersal, because no other cross-Andean dispersals were found. The uplift also was associated with dramatic ecological changes and a decrease in diversification rates. These results suggest a role for niche conservatism, in that some lineages may have gone extinct because of failure to adapt. Alternatively, despite greater sampling effort in the Andes region than in other areas, we failed to find some previously common Andean species (e.g., Hyloxalus jacobuspetersi and the Ecuadorian H. lehmanni). Consequently, it is difficult to separate a natural decrease in diversification rates from the current trend of amphibian species extinctions at high altitudes due to anthropogenic habitat alteration, increased UV radiation, climate change, or pandemic infection. In contrast, the montane transition zones of the Andes and adjacent lowlands (Chocó and Amazonia) have become centers of rapid cladogenesis, and species richness in these transition zones might be underestimated because many Neotropical lineages have been shown to contain several cryptic species. Therefore, dispersals within or across the Andes diminished during the Pliocene, but diversification has intensified in the Andes-lowlands interface.

Although some of the oldest lineages of poison frogs originated in the Guiana Shield and the Venezuelan Highlands (>30 species), our results suggest extended in situ diversification followed by a decline in the rate of diversification of endemic clades in both areas since the early Miocene. Along the same lines, the Guiana Shield has high poison frog endemism, which is mostly restricted to the summits of the sandstone tepuis, while recent Amazonian poison frog immigrants occupy lowlands adjacent to the tepuis. Our results suggest that the decline of endemic Guianan diversity might be associated with ecological changes in habitat due to the collapse of the ancient tepuis and repeated dispersals from Amazonian lineages since the Pliocene. However, the diversity of poison frogs in the Guiana Shield is only beginning to be revealed. In contrast, diversification in the Venezuelan region most likely reflects the oldest vicariant event in Dendrobatidae, at 40.9 MYA. The costal ranges of Mérida, Cordillera de la Costa, and Paria peninsula are species rich but their total area is less than 5% of that of the Amazon Basin. No lineage of this endemic fauna has dispersed out to other regions since the early radiation of the poison frog family in the late Eocene. However, Eocene floristic paleoecological reconstruction of the Venezuelan Highlands area showed that it was more diverse than at present, suggesting that the ancestral habitat of the first poison frogs might have been lowland. The depauperate dendrobatid fauna of the Venezuelan llanos and Brazilian Shield plateau is puzzling, but might be related to Holocene aridity.

The recurring dispersals to Amazonia suggests that a large part of dendrobatid diversity results from repeated immigration waves at <10.0>

Santos, J., Coloma, L., Summers, K., Caldwell, J., Ree, R., & Cannatella, D. (2009). Amazonian Amphibian Diversity Is Primarily Derived from Late Miocene Andean Lineages PLoS Biology, 7 (3) DOI: 10.1371/journal.pbio.1000056

Trilobites, Paleoecology and Anomalocaris

The “Explosion,” as the Cambrian Diversification is commonly referred, occurred approximately a half-billion years ago and is represented by the rapid appearance of about fifty phyla of animals. Present day scientists through the study of numerous fossils, as well as, genetic research have identified this uprising from the Kingdom Animalia and have come to the astonishing conclusion that the entire event lasted, at the very most, a mere ten million years. Most would agree that this seems an extremely minute quantity of time to permit such an all-encompassing radiation, which is one reason why this event is not only a topic of current research, but also one of heated debate.

A linear representation of animal evolution would certainly have a spike near the geologic time of the Cambrian Explosion. All present day phyla (i.e. body-plans, or animal “designs”) arose during that time (with the exception of Bryozoa) including that of the most abundant animal, and second most abundant organism (following only bacteria) on earth today, the arthropods.

One of the groups to rise from the Cambrian is the Phylum Arthropoda. Today the most common arthropods are the insects, but in pre-history, deep in geologic time, the title of most abundant arthropod may quite possibly have gone to the class Trilobita.

Trilobites are without a doubt one of the most easily recognized fossils in modern times, their abundance and variety have played a key role in paleontology as they act as wonderful index fossils. Variation in trilobites covers a wide range of morphological deviation, but most hold a few key characteristics in common. These common morphological characteristics include the division of the trilobite exoskeleton into three distinct regions, those being the head, (cephalon), the main body (thorax) and the tail (pygidium). These regions, especially the cephalon, have distinct sub-features that aid in the identification of individual trilobites, some of which are diagramed below in Figure 1.

FIGURE 1

Trilobites were structurally similar to many modern day arthropods; they possessed jointed appendages and hard exoskeletons, which fortunately - in conjunction with the process of molting - provided us with numerous high quality fossils today. The trilobites ranged in size from mere millimeters to over two-feet in length. They occupied primarily calm, deep waters were there was an abundance of fine silts which they plowed through with their flattened cephalons in order to search out rich debris to be used as a food source. Some trilobites however were most certainly predators, and many may have occupied other niches as well. They appeared (or they apparently appeared - some evidence suggests that they may have earlier origins) early in the Cambrian, reached their zenith in the late Cambrian and then began diversifying up till the Permian during which time they became extinct. There have been estimates of greater than 20,000 species of these incredibly successful Paleozoic marine arthropods - making classification rather tedious at times with new finds occurring on a regular basis. Luckily, some fossils retain sufficient detail as to render their classification relatively certain; however fossils don’t always readily describe the ways in which organisms interacted within their ecosystems.

This is one reason why Jennifer Dunne, et al, conducted research focused towards delineating the food-webs and niche interactions of species identified from the Chengjiang and Burgess Shales. From the Author’s Summary of Compilation and Network Analyses of Cambrian Food Webs,

“Our analyses show that for most aspects of network structure, the Early Cambrian Chengjiang Shale and Middle Cambrian Burgess Shale food webs are very similar to modern webs. This suggests that there are strong and enduring constraints on the organization of feeding interactions in ecosystems. However, a few differences, particularly in the Chengjiang Shale web, suggest that some aspects of network structure were still in flux during early phases of de novo ecosystem construction.”

In another paleoecology related story, Mariel Schotenfeld from the University of Massachusetts Amherst has challenged the widely held idea that Anomalocaris preyed on trilobites.

Anomalocaris

From upcomming G.S.A. agenda: “The Cambrian animal Anomalocaris is hypothesized to have eaten trilobites and other biomineralized prey. The lack of broken or abraded teeth on the plates comprising examination of the mouth apparatus of Anomalocaris suggests that it may not have had the ability to break the exoskeletons of any hard-shelled animal. SEM – EDS of the mouth apparatus from Burgess Shale specimens, indicate that the 32 plates are composed of organic carbon, suggesting they were originally unmineralized cuticle.

Mechanical properties of these plates were analyzed using CAD modeling and Finite Element Analysis. Poisson's ratio and Young's modulus of potential Anomalocaris plates, as well as density and fracture strength used for the FEA analyses, were estimated using a range of modern-day arthropods. Two end-member values were used both to approximate the range of strengths exhibited by Anomalocaris' cuticle, and also to encompass the range of exoskeleton strength likely exhibited by trilobites. The hardest skeletal values are from wet lobster (Homarus americanus) crusher claw cuticle; these are most likely to deform in a brittle manner. The softest are from adult dung beetle (Copris ochus) cuticles. In order to bite and successfully break the calcified cuticle of a trilobite, Anomalocaris' mouth plates would have needed to withstand forces that are greater than those required to fracture a trilobite exoskeleton. Results demonstrate that the teeth-like structures of the mouth plates should have deformed or broken when less than 90 N of force was applied perpendicular to the plates.

Additionally, documented trilobite malformations were compared to modern and extinct arthropod malformations. Abnormal trilobites previously attributed to predation of Anomalocaris might also be interpreted as molting failures or genetic mutations; such malformations occur with similar frequency in modern marine clawed lobsters, brachyuran decapods, and limulids. Furthermore, there is no direct evidence for Anomalocaris' feeding habits such as gut contents.”



Dunne, J., Williams, R., Martinez, N., Wood, R., & Erwin, D. (2008). Compilation and Network Analyses of Cambrian Food Webs PLoS Biology, 6 (4) DOI: 10.1371/journal.pbio.0060102

Vertebrate Proxies of Climate Change

Haphazardly racing around the net while pumped-up on Peet’s Sumatra coffee (so good!), I noticed that Jessica Blois and Elizabeth Hadley have an article being published in the Annual Review of Earth and Planetary Sciences this upcoming May. This is great news for me, because I have an interest in Cenozoic climate change and these folks are experts in the subject area; however, unfortunately for any readers of this blog lacking sufficient caffeine-ation, this post may seem a bit rambling… Consider it a refresher on vertebrate proxies of climate change.

"Organisms change through time. " - At first read this simple four-word sentence may seem rather barren of substance but within its basic grammar there exists a world of profound scientific insight and understanding. Evolution lies at the center of our biological universe, its principles are essential to science, and by grasping these principles we are able to efficiently navigate the worlds of ecology, paleontology and other life-linked sciences. Paleontologists and paleobiologists often utilize the ideas and tenants of organismal change as tools to decipher the remnants and records of past life in aspirations of better understanding not only biology and life, but also as a means of interpreting the physical history of our beloved planet Earth - the fundamental constants of chemistry and climate.

Numerous factors or mechanisms may signal biological change; natural selection, genetic drift and other gene flow can all introduce variation into a population, but these are merely the effects, or end products of change, what physically lies at the source of the process - what environmental factor triggered or was driving the selection, drift and flow?

What if, for example, some physical barrier was removed from a geographic region, thereby permitting the migration of a herd into previously unchartered lands, or the founding of a new population? Would the organisms – and their fossil remnants - be disrupted in such a way as to leave clues behind explaining the reason for increased rate of change or distribution? Less temporally dramatic, what if the seasonality of a region changed in such a way as to lengthen the mating season, or change the territoriality of a species? Would these events, be recorded in the fossil record? Undoubtedly yes!

Responsiveness of Vertebrates to Environment
Many studies of vertebrates have suggested that climate is the single best indicator of modern species richness. Over the past decade several different theories have been suggested in hopes of establishing a clear and precise relationship between organismal change and the environment. Some of these hypotheses are relatively familiar, such as Van Valen’s “Red Queen model,” and Vrba’s “Turnover-pulse model,” but others less so… Regardless, the majority of these models work to resolve one key question; how synchronous are climate and biotic change?

Vertebrates, and in particular mammals, are highly responsive to changes in the environment. Climate fluctuation can lead to an incredible amount of variation in the diet choice, distribution and even morphology of vertebrates. Even within Humans, biological anthropologists have identified trends associated with body size and appendage length based on climate; they refer to this correlation as Bermand and Allan’s Rule. It suggests that human populations occupying regions closer to the equator statistically contain individuals with larger body size and longer limbs relative to those who inhabit more pole-ward regions. This variation has arisen primarily to promote more efficient thermoregulation as to reduce body heat loss in cooler regions, and to promote cooling in warmer climates. Some vertebrates posses even finer genetic plasticity changing morphologically with what could be termed “hair triggers.”

One of the most highly variable vertebrates is the Pocket gopher (Thomomys spp). These gophers have been intensively studied as indicators of environmental change. Their populations, and individual morphology, have been shown to vary with in a period of less than ten years. The most easily recognized change in morphology is their body size - which fluctuates with everything from altitude to diet. Body size, in turn, has a noticeable effect on territory, fertility of females and distribution of the population (Hadly, 1996). These physiological changes, and the fossils they have left behind, have been intensely studied in relation to Late-Holocene Climatic changes.

Thomomys spp

One site in particular, Lamar Cave, located with in the boundaries of Yellowstone National Park, has been used by Elizabeth Hadley to make correlations to such historic climate changes as the Medieval Warm Period (MWP). Through comparison of fossil dental plates with those of modern descendants, Hadley has been able to demonstrate that during the MWP pocket gophers of this region had the smallest body size than at any other point in the paleontological record. Using similar comparisons she was also able to identify trends in morphology that correlated with the Little Ice Age (LIA) and other events including neoglaciation (Hadly, 1996). The response of vertebrates is not limited to the highly plastic morphology of pocket gophers. Many other vertebrates respond equally as readily to climate change. However, morphological change is not necessarily required of a species in order for it to serve as a climate proxy. During their lifespan, all organisms make detailed records of their environment. Through the fundamental life processes of cellular growth and repair vertebrates have the potential to generate detailed records of their environment. Just as the old cliché exemplifies, “you are what you eat.” This record can later be resurrected and deciphered from their fossil remains to help clarify the picture of the climate and chemistry they endured while alive.

Isotopes
Examinations of isotopic records are commonplace for many paleontologists. Uncountable volumes have been written on Foram 18-O isotopes and their relationship to periods of increased glaciation, or similar correlations of speleothems and 13-C, but accurate isotopic records of both of these elements can be obtained from other sources as well - including vertebrates.

Carbonate apatite is a primary constituent of both skeletal bones and dentition in the vertebrates. It is incorporated into the organism through diet and water uptake. The process is riddled with various “vital effects” but has nonetheless been found to be very accurate. In fact, many conservationist use this isotopic signature in vertebrates to better decipher the life histories of contemporary vertebrates in hopes of aiding in their preservation. For example, remains from the world’s largest cavefish (Milyeringa veritas) have been used by Australian conservationists to better examine and comprehend the environment and ecosystem which the fish inhabits. The cavefish lives in deep columns of water that are rich in dissolved limestone. The depths of the water column posses various corresponding incremental concentrations of dissolved materials and by examining the isotopic signatures of the fish’s skeletal apatite, conservationists were able to discover the exact depth the fish occupies.

Milyeringa veritas

Uptake of elements within vertebrates (O, C, Sr & others) generates a highly detailed record of environmentally available isotopes, and as one might guess, availability is indicative of climate.

As another example, Thure Cerling and others at the University of Utah have refined the technique of laser ablation to such quality and precision that they can use it to vaporize the apatite found in vertebrate teeth, and then analyze the gas to determine its isotopic components. They can examine the teeth to such resolution as to be able to report the dietary preferences of mammals between C3 and C4 plants. Previously, samples of fossil teeth or skeletal structures were far to rare to permit them to be thrown into a TIMS for examination, but now that laser ablation has reached such a high level of efficiency isotopic analysis can be made in the smallest and rarest of specimens with minimum impact on the fossil itself. Laser ablation can be used to examine the minute layer of enamel on the smallest of rodents and the most voluble of fossils on display at museums with little difficulty.

As a side note - many scientists have recently discovered that skeletal tissues, which possess apatite, are very susceptible to diagenic processes that can cause recrystalization and alter results, but dental samples seem to be far more reliable when it comes to maintaining their original isotopic signatures. This coupled with the knowledge acquired in the past few decades in regards to the incorporation of specific 18-O and 13-C isotopes into biological entities has brought to light a highly detailed and accurate record of climate change.

Similar techniques have been used to examine bone fragments from marine vertebrates. Some alteration of samples occurs during fossil formation in paleo-seawater environments which forces users of this technique to integrate other proxies of isotopic variation in their final estimates as a “check,” but as the technique begins to advance some of this error is likely to be eliminated. Others have also verified the validity of the use of dental enamel as an isotopic record. Schmitz and his colleagues examined fossil shark teeth from two different locations in Mississippi (one strata being mixed marine, the other brackish-water). Both samples demonstrated nearly identical isotopic signatures, even though they had been deposited in different strata, one with a high salinity concentration - previously shown to accelerate diagenesis. They also examined skeletal remains from marine vertebrates, but there seemed to be a significant error associated with those found in the marine strata.

Isotopic signatures can be very useful in the interpretation of paleoclimate, but in certain cases the mere presence of an organism at a given location - biogeography - can report volumes of information in regards to past climate.

Biogeography
The vertebrate fossil record can be extrapolated in terms of the diversity, divergence and variation of distinct animal groups over a geographic region to display, with accuracy, the impact of environmental change. Similarly, known vertebrate biogeographic patterns can be used to demonstrate specific climatic fluctuation both locally and on the global scale.

The Cenozoic has been marked by tremendous variation of climate. During the early portions of the Cenozoic high temperatures were the standard with the highest to be found in the Early to Middle Eocene, since then a falling temperature trend has been the rule. It was during the Eocene-Oligocene transition that Antarctica became isolated and sea levels dropped dramatically with the accumulation of ice caps, this had the effect of changing terrestrial habitats significantly. Throughout the Cenozoic, similar patterns of fluctuating glacioeustatic sea level events would continue to occur. Evidence of this can be found across the globe.

Thailand, in South-East Asia, is one of many regions that accurately record these glacioeustatic events through its vertebrate fossil record. Thailand is especially significant in that it separates two distinct biogeographical regions (Fig 1). The Indochinese region is located to the north of Thailand and the Sundaic region is located to the south. These two regions have significantly different climates and zoological compositions. Up until about 800kyr B.P. fluctuation of sea level was somewhat constant in the region of Thailand, with the average being somewhere around 70m below the modern, and the greatest change being no more than 100m below the modern. However, near the 800kyr B.P. mark level dropped more dramatically, some fluctuations going as low as 170m below modern sea levels. This had the effect of constructing a land bridge between the Indochinese and Sundaic biogeographical regions, thus permitting the migration of a large variety of animals, including mammals. Through careful comparison of the fossils these migrating animals left behind, and the extant species found in both the Indochinese and Sundaic regions, certain conclusions can be established in regards to their phylogenies. The presence of fossil mammals with Indochinese affinity in the Sundaic regions, and the presence of Sundaic mammals in Indochina suggest some mode of migration in the past that is prevented in modern times by the sea acting as a barrier. Through radio dating of remains, an estimated time for the existence of the land bridge can be calculated, thus the fossil mammals provide dates for periods of reduced sea levels, and in turn, periods of increased glaciation.

FIGURE 1--- Land bridge linking distinct biogeographical regions in Thailand

Thailand is not unique in its ability to provide vertebrate proxies of climate change. Similar scenarios have been played out across the globe. Grenada offers another example of vertebrate biogeography acting as an indicator of sea level change due to increased glaciation.

Grenada has a rather sparse population of indigenous mammals at present, and bats represent the majority of these species. However, paleontologists have recently uncovered a variety of fossil mammals near the Grenadine coast dating from the Pliocene. These species, such as representative capybaras and sloth, did not arise independently on Grenada and then become extinct. Their lineages suggest that they arrived on Grenada from the South American mainland, where their descendants can still be found today. Grenada is located on the Southern Antilles Arc Platform, an elongate sub ocean structure that extends some 180km. This arc provides a base for several small islands and at its closest point comes to with in 40km of South America. During the Pliocene, a combination of low sea levels and tectonic activity provided a land bridge that may have conjoined Grenada with South America thus allowing for the migration of mammals. Through accurate dating of these fossil remains and of the associated tectonic activity estimates for late Pliocene glaciations can be made.


Through biogeographic research, other evidence can be in found with the target of determining periods of climatic change that are independent of sea level, and glacioeustaic events. Many other factors can have the effect of generating temporary corridors that permit faunal exchange. A “corridor” is simply a narrow tract, or pathway, which allows for the exchange of animals from one side to another. These corridors can be created by various means, including the growth of a forest.


The western Canadian ice-free corridor is a continuous tract of land that extends from Alberta, Northward to the Arctic Ocean (fig 2). This corridor separates Eastern and Central Canada from the Western Coastal portions of the Country. At one point in the past this corridor was closed to faunal exchange do to the advancing Laurentide ice sheet; however, near the close of the Pleistocene the ice retreated significantly enough to open the corridor temporarily, before finally closing again. This second closing of the corridor was not due to advancing ice caps, but rather to the growth of Boreal forests.

FIGURE 2---- Ice-free corridor, shaded region

These forests impeded the exchange of fauna between the Bering Strait (and in turn Asia) located in the North West, and Eastern Canada. This meant that any faunal exchange would need to occur between the Plains of the United States and the Bering Strait, which, as coincidence would have it, was a corridor itself. Evidence for this “faunal funneling” can be found through out the plains. The presence of fossil mammals such as wooly mammoths, camels, horses, buffalo, lemmings and even lions give support for the corridor closing during this period. These animals marked their migratory trails with their very own remains, which are now found as fossils - littering their previous routes. Through accurate dating it can be determined exactly when this western Canadian corridor was closed by the growth of forests, and reductively, when climate would support such lush growth.

Interpretation of paleoclimate is a highly important field of study. Not only is it required to better understand the physical and biological history of our planet, but also to endow us with the knowledge needed to prepare for tomorrows’ inevitable changes. The Cenozoic has been marked by extreme change of temperature and climate as a whole, many such changes visible on a short-term scale. This period in geological history has seen everything from periods of hot and dry, to glaciation. To better understand the past and future effects on humans we must discover how it impacted the existence of other animals, in particular, other mammals. To better understand their evolutionary responses to climate, careful analysis of their fossil record must be made. Their physiology, morphology, biochemistry and even behavioral responses record every detail of their natural histories and the climates that they endured. Organisms change through time; the trick to rendering these records lays in the accurate translation of their fossil remains. To accomplish this end, the vertebrate indicators of climate change are an essential and indispensable tool and I very much look forward to reading more about them in May.

RECCOMENDED READING

Alberdi, M. et al. 2001. Vertebrate taphonomy in circum-lake environments: Three cases in the Guadix-Baza Basin (Granada, Spain). Paleogeogrphy, Paleoclimatology, Paleoecology. 165:1-26.

Badgley, C; Behrensmeyer, A. 1995. Preservational, Paleoecological and evolutionary patterns in the Paleogene of Wyoming-Montana and the Neogene of Pakistan. Paleogeography, Paleoclimatology, Paleoecology. 115: 319-340.

Badgley, C; Behrensmeyer, A. 1995. Two long geological records of continental ecosystems. Paleogeography, Paleoclimatology, Paleoecology. 115:1-11.

Barnosky, A. 2001. Distinguishing the effects of the Red Queen and the Court Jester on Pliocene Mammal Evolution in the Northern Rocky Mountains. Journal of Vertebrate Paleontolgy. 21:172-185.

Barrat, J; etal. 2000. Strontium isotopes in biogenic phosphates from a Neogene marine formation: implications for paleoseawater studies. Chemical Geology. 168:325-332.

Bromage, T.; etal. 1995. Paleobiography of the Molawi Rift: Age and vertebrate paleontology of the Chiwando beds, northern Molawi. Journal of Human Evolution. 28:37-57.

Bussuyt, F; Milankovitch, M. 2001. Amphibians as Indicators of Early Territory “ Out- of -India” Dispersal of Vertebrates. Science. 292:93-100.

Cerling, T; Sharp,Z. 1996. Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablution. Paleogeography, Paleoclimatology, Paleoecology. 126:173-186.

Coope, G.R. et al. 1997. Climatic and Environmental Reconstructions based on fossil assemblages from Middle Devension (Weichselion) deposits of the river Thames at South Kensington, Central London, UK. Quaternary Science Reviews. 16:1163-1195.

Cruzan, M and Templeton, A. 2000. Paleoecology and Coalescence: phylographic analysis of hypothesis from the fossil record. TREE. 15:491-496.

Dennistan, R. etal. 1999. Integrating stalagmite, vertebrate and pollen sequences to investigate Holocene vegetation and climate change in the southern Midwestern United States. Quaternery Research. 52:381-387.

Flynn, J; Wyss, A. 1998. Recent advances in South American mammalian paleontology. TREE. 11:449-454.

Gao, C. et al. 2000. Last interglacial and Devension deposits of the river Great Ouse at Toolpack Form, Fenstanton, Cambrideshire, UK. Quarternary Science Reviews. 19:787-810.

Kerr, J; Packer, L. 1999. The environmental basis of North American species richness patterns among Epicauta (caleoptera: Meloidae). Biodiversity and Conservation. 8:617-628.

MacDonald, G; McLeod, T. 1996. The Holocene closing of the ‘ice-free’ corrider: A Biographical Perspective. Quarternary International. 32:57-95.

MacPhee, R.; Singer, R.; Diamond, M. 2000. Late Cenozoic land mammals from Grenada, lesser Antilles Island-Arc. American Museum Novitates. 3302:1-20.

Scasso, R.; Castro, L. 1999. Cenozoic phosphatic deposits in North Patagonia, Argentina: Phosphogenesis, sequence-stratigraphy and paleooceanography. Journal of South American Earth Sciences. 12:471-487.

Schmitz, B. et al. 1997. Testing 87Sr/86Sr as a paleosalinity indicator on mixed marine, brackish-water and terrestrial vertebrate skeletal apatite in late Paleocene-early Eocene near coastal sediments, Mississippi. Chemical Geology. 140:275-287.

Vigne, Jean-Denis. 1996. Small mammal fossil assemblages as indicators of environmental change in northern Corsica during the last 2500 years. Journal of Archeological Science. 23:199-215.

Wing, S; Alroy, J; Hickey, L. 1995. Plant and mammal diversity in the Paleocene to early Eocene of the Bighorn Basin. Paleogeography, Paleoclimatology, Paleoecology. 115:117-155.


Elizabeth A. Hadly (1997). Evolutionary and ecological response of pocket gophers (Thomomys talpoides) to late-Holocene climatic change Biological Journal of the Linnean Society, 60 (2), 277-296 DOI: 10.1111/j.1095-8312.1997.tb01496.x

William F. Humphreys (2001). Milyeringa veritus (Eleotridae), a remarkably versatile cave fish
from the arid tropics of Northwestern Australia.
Environmental Biology of Fishes, 62 (1/3), 297-313 DOI: 10.1023/A:1011880726946