As promised! I'll be splitting this into two sections, with the other posted sometime over Thanksgiving weekend (Friday or Saturday most likely), after which I will continue the series on the Western Interior Seaway the following week.
But today, meet boar croc, duck croc, and dog croc!
Crocodiles are animals that inspire the extremes out of us--loathed by some and yet worshipped as gods by others through the recorded history of humanity. But crocodiles as we know them now are only a hint of the remarkably diverse lineage they once were. Crocodylomorpha, the clade containing both modern day crocodiles and all their extinct relatives first appeared in the Late Triassic, and truly began to explode in diversity and form in the Jurassic and Cretaceous periods. We have found seafaring crocodiles, like the Metriorhynchidae, a strange armadillo-like crocodile from Brazil fittingly named Armadillosuchus, amongst countless other strange and interesting species.
This last week saw the release of an absolutely gigantic paper (running 147 pages in length, and encompassing nearly a decade of research) by paleontologist Paul Sereno that described several new crocodilian fossils from the ancient Sahara, millions of years before the familiar desert we know was formed.
1. Kaprosuchus
One of these forms, a 20 foot long animal with massive caniform style teeth, was dubbed Kaprosuchus, or 'boar croc' (once again, for very good reason!). What makes this particular animal most distinct at first glance are the remarkably differentially sized teeth, something very uncommon for crocodilians--most tend to have very uniform dentition.
Looking at the form, there were several inferences Sereno made about the beast: firstly, the nasals (the bones just behind the frontmost, or rostral portion of the snout) were fused together, likely an adaptation to minimize stress from great bite forces. Secondly, in crocodilians the nares, or 'nostril holes' are placed on the top of the head in an effort to assist aquatic based predation, letting them breathe air from the surface while still submerging themselves underwater as much as possible. Though Kaprosuchus kept this general form, the nostrils were greatly retracted to the point that they was just in front of the eyes, which also differed in their placement when compare to modern day crocodilians (they're raised on a shelf of bone, indicative of a slightly more forward facing field of vision). When combined with a rugose surface that may have held some kind of keratin based structure (the material that makes up an eagle's talons), he suggested the snout may have been used as a tool for impact with potential prey.
However, though when compared to the preferentially aquatic crocodilians we know of today it seems likely that Kaprosuchus was a terrestrial predator, no postcranial (anything other than the skull) material has been found, so (though likely) it's an inference that still requires further testing!
2. Anatosuchus
Though first described by Paul Sereno in 2003, new material was uncovered that offered quite a few insights into the nature of this somewhat bizarre animal. Dubbed 'duck croc' as a reference to the shape of its skull (which well... looks like a duck), the new material is particularly fascinating because it allows observation of the growth stages of these crocodilians: the holotype (the material from which all other future comparisons are based on, used when naming a species) was based upon a subadult skull, and as many can tell when looking at human babies today, age can bring all sorts of skeletal changes.
Firstly, the distance between the eyes relative to the rest of the skull changed with age--when young, the bone between Anatosuchus's eyes was roughly equal in width to the to the bone forming the 'skull table' in the back of the skull. In adulthood, the distance between the eyes expanded monumentally relative to the back, so that it was comparatively twice as wide relative to the skull table!
Other changes were found--the antorbital fenestra (a large hole in the side of the skull in archosaurs like avian and non-avian dinosaurs) was much more exposed as a juvenile and shrank towards adulthood. They gained teeth as they aged, with 15 teeth in the maxilla (one of the two tooth bearing bones in the upper jaw) as a subadult and 19 as an adult (though it's possible that the difference could be due to variation in the population, it's probably more likely that it's ontogenic, or due to changes through age). The lower jaws became more 'U-Shaped' (ducklike!) as they age.
Its limbs were relatively longer than those of modern day crocodilians and its hands were expanded, connecting to the shoulder and hip sockets such that it probably stood upright. Looking at the shape of its teeth, the placement of the jaws, its small size (roughly three feet in length), its wide hands, and the existence of structures that potentially housed special nerves for sensory input, it was suggested that this animal likely dug for invertebrates and amphibians/fish.
3. Araripesuchus wegeneri
Though a genus first described quite some time ago, several remarkable new specimens and species were uncovered by Paul Sereno in the Elrhaz Formation of Niger (roughly 110 million years old). As with Anatosuchus, the limbs preserved suggest that it had an upright posture, allowing for decent land based locomotion abilities.
Its teeth were strange in that unlike many other crocodilians, they lacked the compression and curvature characteristic of most carnivorous species, and were set in the jaws in a manner that would be relatively detrimental for live prey capture. Combined with the heavy blunt and worn ends of the tooth crowns, it seems very likely that it was either omnivorous or herbivorous.
Combined with distinctive cranial material, one of the more fascinating finds was comprised of a series of three well relatively articulated skeletons combined with cranial elements of two other animals all preserved in a single sandstone block. Some the bones were disarticulated and transported after death, but because their axial (vertebral) columns were all so well aligned and because each of their amazingly well preserved tails have a distinctive 'waved' articulation, it suggests that they were all buried together in a single event. However, whether or not they represent a single 'family' unit is something that we'll likely never know.
Tune in next week for pancake croc and rat croc!
All images taken from the published description except for the first two which can be found here and here.