Australia's Saltwater Crocodiles Have Problems With Water Temperatures Above 31.5 C

Australia's saltwater crocodiles appear to be in hot water, with a University of Queensland study linking climate warming to shorter dives, putting the crocs' survival at risk.

Professor Craig Franklin of the UQ School of Biological Sciences said saltwater crocodiles exposed to long-term elevated water temperature spent less time submerged once water temperature exceeded 31.5 degrees Celsius.

"We thought that crocodiles - like many animals - would adjust to temperature changes so life continues," he said.

"However, we were surprised to find they had little capacity to compensate for water temperature changes and seemed to be hard-wired to operate at certain temperatures.

"We are not sure what this means, but it's likely that if the water is too hot, crocodiles might move to cooler regions, or will seek refuge in deep, cool water pockets to defend their dive times."

Lead author and PhD student, Essie Rodgers, said crocodiles spend up to 11 hours a day submerged. Their diving capacity is important to avoid predators, to forage, for sleep/recovery and for social interactions, which all occur underwater.

"Crocodiles are ectothermic animals - where environmental temperatures strongly influence their body temperatures," she said.

Ms Rodgers said the study exposed crocodiles to three water temperatures reflecting differing climate change scenarios- current summer, 28°C; moderate climate warming, 31.5°C; and high climate warming, up to 35°C.

"Acute increases in water temperature resulted in significantly shorter crocodile dives," she said.

link.

What Crocodylomorphs Survived the KT/K-Pg Asteroid Impact Extinction in Europe

Review of the Late Cretaceous-early Paleogene crocodylomorphs of Europe: Extinction patterns across the K-PG boundary

Authors:

Puértolas-Pascual et al

Abstract:

Although the European dinosaur succession during the latest Cretaceous and its relationship with the Cretaceous-Paleogene (K-Pg) mass extinction has been the focus of recent work, other continental vertebrates, such as crocodylomorphs, have received less attention. The European continental record of crocodylomorphs in general, and of eusuchians in particular, is relatively dense through the Maastrichtian until the K-Pg boundary. Traditionally it has been argued that continental crocodylomorphs were minimally impacted by the K-Pg extinction, but they were substantially affected in Europe with the disappearance of endemic eusuchians such as Hylaeochampsidae, Allodaposuchus and their close relatives, and non-eusuchians such as Doratodon or Theriosuchus. Despite extensive sampling in Danian continental deposits, only scarce fragmentary crocodylomorph remains have been cited. It is not until the late Paleocene and Eocene that a recovery in continental crocodylomorphs is observed. The presence of taxa such as planocraniids, the alligatoroids Diplocynodon and Hassiacosuchus, and stem crocodyloids during this period provide the first reliable continental records of Crocodylia in Europe and is best explained by post-extinction immigration from Asia or North America. By contrast, marine forms such as Thoracosaurus are found on both sides of the K-Pg boundary in Europe. The adaptation of these marine animals to different environments, from shallow seas to more transitional or fluvial environments, could be the key to their success and survival across the K-Pg boundary, as seen in other marine crocodylomorph clades such as Dyrosauridae.

Miocene Neogene Peruvian Amazon had Seven Different Crocodile Species

Thirteen million years ago, as many as seven different species of crocodiles hunted in the swampy waters of what is now northeastern Peru, new research shows. This hyperdiverse assemblage, revealed through more than a decade of work in Amazon bone beds, contains the largest number of crocodile species co-existing in one place at any time in Earth's history, likely due to an abundant food source that forms only a small part of modern crocodile diets: mollusks like clams and snails. The work, published today in the journal Proceedings of the Royal Society B, helps fill in gaps in understanding the history of the Amazon's remarkably rich biodiversity.

"The modern Amazon River basin contains the world's richest biota, but the origins of this extraordinary diversity are really poorly understood," said John Flynn, Frick Curator of Fossil Mammals at the American Museum of Natural History and an author on the paper. "Because it's a vast rain forest today, our exposure to rocks--and therefore, also to the fossils those rocks may preserve--is extremely limited. So anytime you get a special window like these fossilized "mega-wetland" deposits, with so many new and peculiar species, it can provide novel insights into ancient ecosystems. And what we've found isn't necessarily what you would expect."

Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, filled with lakes, embayments, swamps, and rivers that drained northward toward the Caribbean, instead of today's pattern of eastward river flow to the Atlantic Ocean. Knowing the kind of life that existed at that time is crucial to understanding the history and origins of modern Amazonian biodiversity. But although invertebrates like mollusks and crustaceans are abundant in Amazonian fossil deposits, evidence of vertebrates other than fish have been very rare.

Since 2002, Flynn has been co-leading prospecting and excavating expeditions with colleagues at fossil outcrops of the Pebas Formation in northeastern Peru. These outcrops have preserved life from the Miocene, including the seven species of crocodiles discussed in Proceedings B. Three of the species are entirely new to science, the strangest of which is Gnatusuchus pebasensis, a short-faced caiman with globular teeth that is thought to have used its snout to "shovel" mud bottoms, digging for clams and other mollusks. The new work suggests that the rise of Gnatusuchus and other "durophagous," or shell-crunching, crocodiles is correlated with a peak in mollusk diversity and numbers, which disappeared when the mega-wetlands transformed into the modern Amazon River drainage system.

"When we analyzed Gnatusuchus bones and realized that it was probably a head-burrowing and shoveling caiman preying on mollusks living in muddy river and swamp bottoms, we knew it was a milestone for understanding proto-Amazonian wetland feeding dynamics," said Rodolfo Salas-Gismondi, lead author of the paper and a graduate student at the University of Montpellier, in France, as well as researcher and chief of the paleontology department at the National University of San Marcos' Museum of Natural History in Lima, Peru.

Besides the blunt-snouted crocodiles like Gnatusuchus, the researchers also recovered the first unambiguous fossil representative of the living smooth-fronted caiman Paleosuchus, which has a longer and higher snout shape suitable for catching a variety of prey, like fish and other active swimming vertebrates.

"We uncovered this special moment in time when the ancient mega-wetland ecosystem reached its peak in size and complexity, just before its demise and the start of the modern Amazon River system," Salas-Gismondi said. "At this moment, most known caiman groups co-existed: ancient lineages bearing unusual blunt snouts and globular teeth along with those more generalized feeders representing the beginning of what was to come."

link.

Two New Miocene Crocodilian and Hippolike Anthracothere Found in Panama

University of Florida paleontologists have discovered remarkably well-preserved fossils of two crocodilians and a mammal previously unknown to science during recent Panama Canal excavations that began in 2009.

The two new ancient extinct alligator-like animals and an extinct hippo-like species inhabited Central America during the Miocene about 20 million years ago. The research expands the range of ancient animals in the subtropics — some of the most diverse areas today about which little is known historically because lush vegetation prevents paleontological excavations — and may be used to better understand how climate change affects species dispersal today. The two studies appear online today in the same issue of the Journal of Vertebrate Paleontology.

The fossils shed new light on scientists' understanding of species distribution because they represent a time before the formation of the Isthmus of Panama, when the continents of North and South America were separated by oceanic waters.

"In part we are trying to understand how ecosystems have responded to animals moving long distances and across geographic barriers in the past," said study co-author Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History on the UF campus. "It's a testing ground for things like invasive species – if you have things that migrated from one place into another in the past, then potentially you have the ability to look at what impact a new species might have on an ecosystem in the future."

The research was funded by the National Science Foundation Panama Canal Partnerships in International Research and Education project, which supports paleontological excavation of the canal during construction expected to continue through 2014.

"We're very fortunate we could get the funding for PIRE to take advantage of this opportunity — we're getting to sample these areas that are completely unsampled," said Alex Hastings, lead author of the crocodilian study and a visiting instructor at Georgia Southern University who conducted the research for the project as a UF graduate student.

Researchers analyzed all known crocodilian fossils from the Panama Canal, including the oldest records of Central American caimans, which are cousins of alligators. The more primitive species, named Culebrasuchus mesoamericanus, may represent an evolutionary transition between caimans and alligators, Hastings said.

"You mix an alligator and one of the more primitive caimans and you end up with this caiman that has a much flatter snout, making it more like an alligator," Hastings said. "Before this, there were no fossil crocodilian skulls known from Central America."

Christopher Brochu, an assistant professor of vertebrate paleontology in the department of geoscience at the University of Iowa, said "the caiman fossil record is tantalizing," and the new data shows there is still a long way to go before researchers understand the group.

"The fossils that are in this paper are from a later time period, but some of them appear to be earlier-branching groups, which could be very important," said Brochu, who was not involved with the study. "The problem is, because we know so little about early caiman history, it's very difficult to tell where these later forms actually go on the family tree."

The new mammal species researchers described is an anthracothere, Arretotherium meridionale, an even-toed hooved mammal previously thought to be related to living hippos and intensively studied on the basis of its hypothetical relationship with whales. About the size of a cow, the mammal would have lived in a semi-aquatic environment in Central America, said lead author and UF graduate student Aldo Rincon.

"With the evolution of new terrestrial corridors like this peninsula connecting North America with Central America, this is one of the most amazing examples of the different kind of paths land animals can take," Rincon said. "Somehow this anthracothere is similar to anthracotheres from other continents like northern Africa and northeastern Asia."

Researchers also name a second crocodilian species, Centenariosuchus gilmorei, after Charles Gilmore, who first reported evidence of crocodilian fossils collected during construction of the canal 100 years ago. The genus is named in honor of the canal's centennial in 2014.

Crocodilians Dispersed Differently Than Mammals in the Americas

The uplift of the Isthmus of Panama 2.6 million years ago formed a land-bridge that has long thought to be the crucial step in the interchange of animals between the Americas, including armadillos and giant sloths moving up into North America and relatives of modern horses, rabbits, foxes, pigs, cats, dogs, and elephants down into South America.

However, in the March 2013 issue of the Journal of Vertebrate Paleontology, researchers from the University of Florida and the Smithsonian Tropical Research institute describe fossil crocodilians that shed a surprising new light on the history of interchange and animal distributions between the Americas.

The fossils are partial skulls of two new species of caiman, relatives of alligators, who live exclusively in South America today. They were discovered in rocks dated from 19.83 and 19.12 million years old and that were exposed by excavations associated with the expansion of the Panama Canal.

"These are the first fossil crocodilian skulls recovered from all of Central America. They fill a gap in evolution between the alligators of North America and the caimans of South America. It's quite incredible." states lead author Alex Hastings, a fossil crocodilian specialist at Georgia Southern University.

The presence of the fossils in Panama indicates that caimans dispersed North from South America by the early Miocene, which is over ten million years earlier than the spread of mammals. This discovery is additionally important because caimans lack the ability to excrete excess salt from their bodies and are restricted to freshwater environments. As a result, they could have only dispersed a short distance across sea water, which supports a recent hypothesis that Central and South America were much closer to each other 19 million years ago than previously thought, and paints a new picture of the past histories of American animals.

Says co-author Jonathan Bloch, a vertebrate paleontologist at the Florida Museum of Natural History, "We are starting to understand that while the mammals in Panama 19-21 million years ago were very similar to those found in Mexico, Texas, and Florida at that time, the reptiles tell a different story. Somehow, they were able to cross over from South America when it was completely isolated by seaways—this is one of the mysteries that will drive future inquiry and research in this region."

More Pakasuchus kapilimai Pictures

Via NatGeo.

Pakasuchus kapilimai: a heterodont notosuchine

Fossils of an ancient crocodile with mammal-like teeth have been discovered in the Rukwa Rift Basin of Tanzania, scientists report in this week's issue of the journal Nature. The unusual creature is changing the picture of animal life at 100 million years ago in what is now sub-Saharan Africa.

"If you only looked at the teeth, you wouldn't think this was a crocodile. You would wonder what kind of strange mammal or mammal-like reptile it is," said study lead author Patrick O'Connor, associate professor of anatomy in the Ohio University College of Osteopathic Medicine.

The scientists describe the new species of notosuchian crocodyliform as a small animal—"its head would fit in the palm of your hand," O'Connor said—that wasn't as heavily armored as other crocodiles, except along the tail. Other aspects of its anatomy suggest it was a land-dwelling creature that likely feasted on insects and other small animals to survive.

O'Connor and his international research team, funded by the U.S. National Science Foundation and the National Geographic Society, found a complete specimen of the crocodile in 2008, and now have recovered portions of seven different individuals in southwestern Tanzania. The tooth row with molar-like teeth initially puzzled many experts. Other ancient and living crocodiles typically boast relatively simple, conical teeth that serve to seize and tear prey; they swallow flesh in large chunks.

The molar teeth of the new species, named Pakasuchus (Paka is the Ki-Swahili name for cat and souchos is Greek for crocodile), possessed shearing edges for processing food, similar in form to the teeth of some mammalian carnivores.

"Once we were able to get a close look at the teeth, we knew we had something new and very exciting," O'Connor said.

The research team's discovery that the animals had heavily plated tails but relatively unarmored bodies with gracile limbs suggests that the creatures were quite mobile. They probably actively foraged on land, unlike water-dwelling crocodiles.

The new species isn't a close relative of modern crocodilians, but is a member of a very successful side branch of the crocodyliform lineage that lived during the Mesozoic Era, O'Connor said.

While the specimens of the newly discovered animal and its close relatives are unusual, the study suggests that the creatures were abundant during the middle Cretaceous, from around 110 million until 80 million years ago.

Also at Nat Geo.

Salties Use Ocean Currents for Oceanic Travel

How did the world's largest living reptile, the saltwater crocodile, reach so many South Pacific islands separated by huge stretches of water despite being a poor swimmer?

Apparently, like a surfer catching a wave, these goliaths can ride currents on the ocean surface to cross large areas of open sea, researchers now reveal.

[...]

There were already many anecdotal accounts of large crocodiles sighted far out at sea, but nothing confirmed. Now, for the first time, using sonar transmitters and satellite tracking, scientists now find that saltwater crocodiles actually do ride surface ocean currents for long-distance travel, enabling them to voyage from one oceanic island to another.

"Because these crocodiles are poor swimmers, it is unlikely that they swim across vast tracts of ocean," said researcher Hamish Campbell, a behavioral ecologist from University of Queensland in Australia. "But they can survive for long periods in saltwater without eating or drinking, so by only traveling when surface currents are favorable, they would be able to move long distances by sea."

[...]

Working at the remote Kennedy River in northeastern Australia, the team of scientists - which included the late Steve Irwin, "The Crocodile Hunter" - tagged 27 adult seawater crocodiles with sonar transmitters, employing 20 underwater receivers deployed along a 39-mile-long stretch of the river (63 km) to track the reptiles' every move for more than 12 months. They found both male and female adult crocodiles undertook long-distance journeys, regularly traveling more than 30 miles (48 km) from their home area to the river mouth and beyond into open sea.

The scientists also discovered the "salties" always began long-distance travel within an hour of the tide changing, allowing them to go with the flow. They halted their journeys by hauling out onto the river bank or diving to the river bottom when the currents turned against them.

[...]

After they made their discovery on the river, Campbell and his colleagues re-analyzed archival data from the few crocodiles that have been satellite tracked while undertaking ocean travel. By overlaying the reptiles' movements with surface current estimates, they found the strategy of ocean-swimming crocodiles was similar to what they employed with rivers.

One satellite-tagged crocodile, 12.6-foot-long male (3.8 meters) - left the Kennedy River and travelled 366 miles (590 km) over 25 days, timing its journey to coincide with a seasonal current system that develops in the Gulf of Carpentaria.

Another croc - a 15.8-foot-long male (4.8 meters) - traveled more than 255 miles (411 km) in only 20 days through the Torres Straits, which are notorious for strong water currents. When the reptile arrived at the straits, the currents were moving opposite to his direction of travel - he then waited in a sheltered bay for four days and only passed through the straits when the currents switched to favor his journey.

These findings could explain why this crocodile species did not split into many other species despite occupying islands across such a large range, where in principle populations could have been isolated and diverged from their relatives over time.

"Regular mixing between the island populations probably occurs," Campbell said. "Crocodilians have crossed major marine barriers during their evolutionary past."

awesome.

Cretaceous Gondwanan Crocodyliform Diversity

A suite of five ancient crocs, including one with teeth like boar tusks and another with a snout like a duck's bill, have been discovered in the Sahara by National Geographic Explorer-in-Residence Paul Sereno. The five fossil crocs, three of them newly named species, are remains of a bizarre world of crocs that inhabited the southern land mass known as Gondwana some 100 million years ago.

Sereno, a professor at the University of Chicago, and his team unearthed the strange crocs in a series of expeditions beginning in 2000 in the Sahara. Many of the fossils were found lying on the surface of a remote, windswept stretch of rock and dunes. The crocs galloped and swam across present-day Niger and Morocco when broad rivers coursed over lush plains and dinosaurs ruled.

"These species open a window on a croc world completely foreign to what was living on northern continents," Sereno said. The five crocs, along with a closely related sixth species, will be detailed in a paper published in the journal ZooKeys and appear in the November 2009 issue of National Geographic magazine. The crocs also will star in a documentary, "When Crocs Ate Dinosaurs," to premiere at 9 p.m. ET/PT Saturday, Nov. 21, on the National Geographic Channel.

Extensively covered here, here, here, here, here, and here at least. Paper here.

why I hate theropods: Iharkutosuchus makadii

Another heterodont crocodylian, a eusuchian no less! The freakin thing thinks its a therapsid or something. Go READ!

Another Armadillosuchus Rendition

Hopefully this is more accurate than that other one I found. The teeth are certainly interesting. Are there more Armadillosuchus restorations out there? Link to the paper. Nick Gardner's post is excellent, too.

Armadillosuchus Rendition

It looks like a cros between a croc, an armadillo and a fscking wolf. Was the fossil even close to that complete?

Armadillosuchus, Brazilian Cretaceous Croc

Fossils found in Brazil are from a crocodile resembling a large armadillo that was a predator in the area around modern-day Sao Paulo state 90 million years ago, researchers said on Tuesday.

The 6.6-foot-long (two-meter-long), 265-lb (120-kg) crocodile, named the "Armadillosuchus," appears to have been unique to that area, the researchers at Rio de Janeiro's Federal University said.

The creature displayed some characteristics of an armadillo, with bony plates on its neck and back.

It had a carapace, a wide skull, a short, narrow snout, and relatively small, specialized teeth that make it distinct from any other crocodile discovered, the university said.

"The Armadillosuchus is only found in the interior of Sao Paulo state and this is a surprise, partly because it challenges the idea that crocodiles are found in hot and humid climates," UFRJ paleontologist Ismar de Souza Carvalho told reporters.

"In this case, they are crocodiles that live in a climate that is quite hot, dry and arid," he added.

The crocodile lived during the Cretaceous period, when temperatures would have reached about 113 degree Fahrenheit (45 degrees Celsius), the researchers said.

Regular blogging will resume soon. Promise.

PS. First tank passed the pressure test.

Some Experimental Paleobiology: Alligators Development And Hypoxia

During the last 540 million years, the earth's oxygen levels have fluctuated wildly. Knowing that the dinosaurs appeared around the time when oxygen levels were at their lowest at 12%, Tomasz Owerkowicz, Ruth Elsey and James Hicks wondered how these monsters coped at such low oxygen levels. But without a ready supply of dinosaurs to test their ideas on, Owerkowicz and Hicks turned to a modern relative: the alligator. 'We knew testing the effects of different oxygen levels would work with alligators,' Owerkowicz explains, 'because crocodilians have survived in their basic shape and form for 220 million years. They must be doing something right to have survived the oxygen fluctuations.' Choosing to start at the beginning of alligator development, the trio decided to try incubating alligator eggs at different oxygen levels, to find out how the youngsters grew and developed and publish their results on April 17 2009 in The Journal of Experimental Biology at http://jeb.biologists.org.

Receiving newly laid alligator eggs from Elsey at the Rockefeller Wildlife Refuge, Owerkowicz divided the eggs into groups incubated at 12% (low) oxygen, 21% (normal) oxygen and 30% (high) oxygen, and waited to see what would happen. After almost 10 weeks of waiting, the eggs began hatching and Owerkowicz could see that there were no obvious differences between the alligators that developed in normal and high oxygen atmospheres.

Abstract:

Atmospheric oxygen level affects growth trajectory, cardiopulmonary allometry and metabolic rate in the American alligator (Alligator mississippiensis)

Tomasz Owerkowicz1,*, Ruth M. Elsey2 and James W. Hicks1

1 Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
2 Rockefeller Wildlife Refuge, Louisiana Department of Wildlife and Fisheries, Grand Chenier, LA 70643, USA

* Author for correspondence (e-mail: towerkow@uci.edu)

Accepted 3 February 2009

Recent palaeoatmospheric models suggest large-scale fluctuations in ambient oxygen level over the past 550 million years. To better understand how global hypoxia and hyperoxia might have affected the growth and physiology of contemporary vertebrates, we incubated eggs and raised hatchlings of the American alligator. Crocodilians are one of few vertebrate taxa that survived these global changes with distinctly conservative morphology. We maintained animals at 30°C under chronic hypoxia (12% O2), normoxia (21% O2) or hyperoxia (30% O2). At hatching, hypoxic animals were significantly smaller than their normoxic and hyperoxic siblings. Over the course of 3 months, post-hatching growth was fastest under hyperoxia and slowest under hypoxia. Hypoxia, but not hyperoxia, caused distinct scaling of major visceral organs–reduction of liver mass, enlargement of the heart and accelerated growth of lungs. When absorptive and post-absorptive metabolic rates were measured in juvenile alligators, the increase in oxygen consumption rate due to digestion/absorption of food was greatest in hyperoxic alligators and smallest in hypoxic ones. Hyperoxic alligators exhibited the lowest breathing rate and highest oxygen consumption per breath. We suggest that, despite compensatory cardiopulmonary remodelling, growth of hypoxic alligators is constrained by low atmospheric oxygen supply, which may limit their food utilisation capacity. Conversely, the combination of elevated metabolism and low cost of breathing in hyperoxic alligators allows for a greater proportion of metabolised energy to be available for growth. This suggests that growth and metabolic patterns of extinct vertebrates would have been significantly affected by changes in the atmospheric oxygen level.

So. Does this support Ward's hypothesis about hypoxia strongly effecting vertebrate evolution or not? There are some hints, but I have to wonder about this...has anyone done anything like this for the monotremes?

My post "Gasping for Paleo Air" touches on some of this, btw, as there is evidence that the hypoxic levels may not have dropped as low as what has been hypothesized (17/18% instead of 11/12%) because vegetation won't burn under a certain oxygen level and there is ample evidence for forest fires at multiple geological time periods.

Birds, Alligators and Thumbs

Bird wings only have three fingers, having evolved from remote ancestors that, like humans and most reptiles, had five fingers. Biologists have typically used embryology to identify the evolutionary origin (homology) of structures; the three fingers of the bird wing develop from cartilage condensations that are found in the same positions in the embryo as fingers two, three and four of humans (the index, middle and ring fingers). However, the morphology of the fingers of early birds such as Archaeopteryx corresponds to that of fingers one, two and three in other reptiles (thumb, index and middle finger). The fossil record clearly shows that fingers four and five (ring and pinky finger) were lost and reduced in the dinosaur ancestors of birds.

Further, the lack of expression of the HoxD-11 gene in the first finger of the wing makes it most similar to finger one (the "thumb") of the mouse, consistent with comparative morphology. However, the mouse is only distantly related to birds; crocodilians, in turn, are bird's closest living relatives.

To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues, working at the lab of Gunter Wagner at Yale, have examined the expression of this gene in alligators; they found the expression to be, as in mice, absent only in finger one (the "thumb").

Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body. A famous example is the case of the fruitfly mutant antennapaedia, which develops legs on its head instead of antennae. The new work by Vargas et al. rekindles the hypothesis that a "hometic frameshift" occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four.

MB's strike again, Zach!

Were the Basal Archosaurs Endothermic?

As most of you know, I am rather interested in the mass extinctions of life on our planet. It's not so much the morbidity. It has a lot more to do with the fact that there's a massive scale murder mystery involved and how life deals with the die offs is really an exercise in world building. Or rebuilding. My interest in all this can be traced back to, of course, the perennial question of what killed the dinosaurs. Every kid that loved the dinos wondered what did the deed. However, that interest waned as I got older and got involved with other interests and projects: solars sails, supercomputers, rockets, architecture and gob smacking sized lasers. I probably would have just read a bit here and there on paleontology and paleoanthropology if not for Dr Benton's book, When Life Nearly Died. From then on, I'd been turned back to being intensely curious about mass extinctions and the worlds that begat them. If not for reading that, I wouldn't have started down the paleo path that has brought so many readers to my blog.



While I was researching my new interest, gobbling up any and all new books on the subject that I could afford, I came across what Dr Peter Ward had to say about crocodilian evolution while reading Out of Thin Air. I was more than a bit surprised and incredulous at the prospect that crocodiles' ancestors would have been endothermic and that the crocs lost that. I couldn't wrap my head around the idea that sometime, something had given up such a metabolic advantage. I had only encountered this idea in Ward's book and not having all the time in the world (or knowledge enough as yet) to read the literature, I was extraordinarily skeptical. Then I started encountering the idea elsewhere.


Part of my resistance also stemmed from the fact that of the two extent archosaur lineages, one (crocs et al) is ectothermic and the other (Aves) is endothermic. The other nearest retatives, the other diapsids (lizards, snakes and the tuatara), were ectothermic, so, therefore, in my mind, the obviously basal condition was ectothermy. It seemed plain. It seemed obvious. Why argue over the settled? Well, then along came science.


The first bit that started to defy my expectations was what Ward pointed out: the crocs and relatives have a heart that was designed much more so for an endotherm and later modified for their unique ecological role and the behavior, long submergence with minimal activity to facilitate ambush predation. I did initially dismiss this as merely a case of the crocs lineage having split off while the prerequisite traits for endothermy were being acquired before endothermy arose in actuality. Note: I never doubted that dinosaurs were endothermic. Birds are the closest thing and they're definitely hot blooded. Some people did. Others did not, and those that did not began to wonder just how to tell whether or not something is warmed blooded from the fossil record. Once they felt they had established that the dinosaurs were endothermic, they began to study further and further back on the archosaurian family tree to establish just where it did arise. Dr Kevin Padian and his merry bad of paleo pirates were doing exactly just that and with their latest paper maybe have converted me from a 'huh. that's what they think' to 'wow. they're probably right.' So what exactly was in that paper?


Padian et al went out and sampled bones to look for growth patterns for numerous basal archosauriformes. They sliced and prepared various fossilized bones. What they were looking for was how the bones were grown. Ectotherms' bones grow in a manner that looks not all that dissimilar to tree rings. Slice a crocodile's or lizard's or turtle's bone cross wise and you would see these rings, albeit only if you looked very closely. Endotherms' bones don't do this. They have a rather different, nearly homogeneous structure. They examined the bones from numerous archosaurs and relatives. They had hoped to find out what the basal condition for the archosaurs was, ectothermic or endothermic. Their results were quite interesting and, honestly, a little unexpected.


The authors looked at a total of twelve members of Archosauromorpha. There was one outlier, purposefully, from Rhynchosauria in the form of Scanphonyx. The remainder were from the Archosauriformes. The intent was that the authors could compare something more distantly related to the remainder of the archosauriformes and have some idea what the basal and derived conditions were. Of these twelve specimens studied, four had very strong indications of the layered growth ring patterns in their bones. One had a case where it appeared initially there was a fast growth phase and then developed layered growth approach. Another they stated was poorly preserved, but appeared to have layers of the same sort of tissue growth of what we would normally find in endotherms: ie, if I am understanding what they stated correctly, this was something odd and unique in the form of a compromise. One more specimen needed to be double checked, but it looked strongly like a purely endothermic growth pattern. The remaining six had purely nonlayered bone growth structure. So who was who?

The first four that were strongly layered were Scanphonyx, "Mandasuchus," Hesperosuchus, and Luperosuchus. The one that seemed to switch growth patterns was Chanaresuchus. The one that had the odd and possibly misunderstood by me growth pattern was Herrerasaurus. The one that needed to be double checked, but looked like it was not layered was Ornithosuchus. The remainder were "Teleocrater," Erythrosuchus, Euparkeria, Thecodontosaurus, and Lesothosaurus. Now take a moment and go back to look at the cladogram. Now wrap your brain around that one


There are some basic statements that can be made at this time. It appears that the basal condition for the ancestors of archosauromorpha were ectothermic. This is a common, basal characteristic of all amniotes and the endothermic condition is derived: we knew that. The question here was when endothermy arose in archosaurs and their relatives. The answer to that is that it needs more study because the archosaurs and their ancient relatives were out having an adaptive radiation party during the Triassic. We knew that too. However, it appears that they were doing this metabolically and in their growth patterns as well.


It looks as though the archosauriforms were on the cusp of endothermy for some time and crossed over fairly early in their evolution if "Teleocrater" and Erythrosuchus are any indication. Yet if you look closely you will see that in some cases later, this condition was lost. Pseudosuchia, frex, seems to have largely dumped it. The authors concluded that only the Ornithodirans, pterodactyls and dinosaurs, were to eventually keep the derived metabolic condition.


The authors do warn that their sample is small and there needs to be more research done. There need to be more samples from specimens of the same critters they studied - they warned that "Mandasuchus" had different bone deposition patterns in different bones and that some of the specimens they had were not well preserved, rex, Herrerasaurus - and that there needs to be more specimens of different genuses in the archisauriformes to be be studied. I would argue that more from the broader archosauropmorpha need to be studied to make sure that Rhynchosauria is not the exception rather than the rule for more basal members of the lineage. If their hypothesis holds up, then there are some interesting implications.


The first is that endothermy was an innovation in the archosaurian line after the Permian Extinction that arose some time during the Triassic. One hypothesis was that endothermy was a reaction in both the therapsids and archosaurs to the events leading up to and during the PT Extinction. That doesn't appear to be the case. The therapsids picked this up prior to the Permian Extinction. The causes for these lineages adopting this metabolic change are for different reasons. That's a big deal.


Second, it really did happen, the crocs went from a warm blooded to cold blooded metabolism. As hard as it was - and, in some ways, still is - to accept, the evidence really is mounting. The archosaurian ancestors hit on the warm bloodedness and then dumped it as they adapted into a mode of life where it was unnecessary. The final confirmation of this would be if there were pseudogenes associated with metabolic functions. We ought to know relatively soon since crocs are getting their genome sequenced now.


Finally, yep, the dinosaurs were warm blooded. People just need to get over that fact. Their ancestors were. Their daughters - aves - are.

Deal with it:


images blatantly stolen from Scott, Zach, Mark, and wikipedia. The cladogram is from the paper (Padian 's Paleo Pirates et al) itself.

Guarinisuchus munizi: An African Croc in SoAm

A fossil of a new species of prehistoric crocodile found in Brazil and presented here Wednesday has led scientists to believe the reptile benefited from the [KT mass] extinction ... to migrate from across the Atlantic.

Guarinisuchus munizi -- the "warrior of the seas," as the crocodile has been dubbed -- is believed to have had its origins in Africa some 200 million years ago.

But the remains of a jaw, skull and vertebra discovered in Palaeocene deposits of northeastern Brazil suggests the species set off for new territory 62 million years ago, according to researchers.

"They left the African continent and are believed to have occupied zones in South America, and later regions in North America," paleontologist Maria Somalia Viana told a media conference in Rio de Janeiro.

She added that, back then, "Africa and the northeast point of Brazil were much closer than today."

The reptile, which grew to around three meters (10 feet) and was perfectly adapted to living in the ocean, apparently took advantage of the extinction of bigger marine lizards called mosasaurs to dominate the waters, another paleontologist, Alexander Kellner, said.

The Guarinisuchus munizi became "the main predators, together with sharks, in shallow marine Palaeocene environments" the researchers from the federal universities of Pernambuco and Rio de Janeiro theorized in their paper published in the Proceedings of the Royal Society B.

hmmm. How well adapted was it to the ocean? Was it like geosaurus? Or was it more like the modern salt water crocodile?

Oregonian Jurassic Marine Croc

The Mesozoic Ecology Gets a Little More Colorful

But what if there were big terrestrial predatory crocodilians during the Mesozoic? Surely such animals would have been interacting with predatory dinosaurs: living in the same places, preying on the same prey, and scavenging from the same carcasses.

[...]

The remains we have of such sebecosuchians as Baurusuchus shows that they were large animals, with body lengths exceeding 3.5 m and approaching 4 m in Stratiotosuchus. If the idea of a 4-m-long terrestrial predatory Cretaceous non-dinosaurian reptile doesn't grab your imagination, shame on you. It is veeery tempting to wonder whether, and how, sebecosuchians and theropods interacted: surely they must have. I wanted to mention this idea in my 2001 review article on crocodilians, but my reviewer urged me to remove it. Candeiro et al. (2006) however, have hinted at this idea, noting that, in some Late Cretaceous South American faunas, terrestrial crocodilians 'had a more important ecological role to play as the main carnivorous group ... than did theropods' (p. 937).

This is from Darren Naish's post.

The question is, of course, what was the earliest terrestrial gigantoform croc for the Mesozoic? Were they strictly a Maastrichtian-only phenomenon? Is this a sign of the proposed dinosaur decline 10 million years before the KT Boundary? Or was something like this around the whole time? It'd be very interesting if there was a Jurassic example!