Sciurumimus: A New Feathered Megalosauroid

Image: Helmut Tischlinger

Remember this fossil? It has just been described!

So far, all discovered feathered dinosaurs have been coelurosaurs (Concavenator is controversial). Recently named from Germany is the Late Jurassic (150 million years ago or so) megalosauroid Sciurumimus albersdoerferi. There is a twist; however, Sciurumimus has been preserved with filamentous integumentation, similar to dinosaurs such as Dilong, Sinosauropteryx and Beipiaosaurus.

This finding could connect the feathers found in coelurosaurian dinosaurs with the feather-like structures preserved in ornithischians such as Tianyulong and Psittacosaurus. The name Sciurumimus literally means “squirrel mimic” because of its bushy tail, covered in protofeathers, which resembles that of a squirrel.

Sciurumimus probably had a different diet than most megalosauroids, due to its different dentition. It was probably insectivorous, but could eat other small animals. The preserved specimen is a baby and is only twenty-eight inches long.

Abstract

Recent discoveries in Asia have greatly increased our understanding of the evolution of dinosaurs’ integumentary structures, revealing a previously unexpected diversity of “protofeathers” and feathers. However, all theropod dinosaurs with preserved feathers reported so far are coelurosaurs. Evidence for filaments or feathers in noncoelurosaurian theropods is circumstantial and debated. Here we report an exceptionally preserved skeleton of a juvenile megalosauroid, Sciurumimus albersdoerferi n. gen., n. sp., from the Late Jurassic of Germany, which preserves a filamentous plumage at the tail base and on parts of the body. These structures are identical to the type 1 feathers that have been reported in some ornithischians, the basal tyrannosaur Dilong, the basal therizinosauroid Beipiaosaurus, and, probably, in the basal coelurosaur Sinosauropteryx. Sciurumimus albersdoerferi represents the phylogenetically most basal theropod that preserves direct evidence for feathers and helps close the gap between feathers reported in coelurosaurian theropods and filaments in ornithischian dinosaurs, further supporting the homology of these structures. The specimen of Sciurumimus is the most complete megalosauroid yet discovered and helps clarify significant anatomical details of this important basal theropod clade, such as the complete absence of the fourth digit of the manus. The dentition of this probably early-posthatchling individual is markedly similar to that of basal coelurosaurian theropods, indicating that coelurosaur occurrences based on isolated teeth should be used with caution.

References

* Rauhut, O.W.M., et al. (2012). “Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany”. PNAS, in press. DOI: 10.1073/pnas.1203238109.

* July 2, 2012. “Newly discovered dinosaur implies greater prevalence of feathers”. Science Codex. Retrieved July 2, 2012, from http://www.sciencecodex.com/newly_discovered_dinosaur_implies_greater_prevalence_of_feathers-94354

An Osteological Review of Alioramus

Abstract - The Late Cretaceous tyrannosaurid theropod Alioramus has long been one of the most puzzling large carnivorous dinosaur taxa, largely because for several decades it has been represented only by a single, fragmentary specimen that seems to represent a long-snouted and gracile individual but is difficult to interpret. The discovery of a substantially complete skeleton of Alioramus at the Tsaagan Khuushu locality in the Maastrichtian Nemegt Formation of Mongolia, recovered during the 2001 American Museum–Mongolian Academy of Sciences expedition and described as a new species (Alioramus altai) in 2009, definitively shows that this mysterious taxon is a distinct form of longirostrine tyrannosaurid that lived alongside the larger and more robust Tarbosaurus. Here we describe and figure this remarkably preserved skeleton in detail. We provide exhaustive descriptions and photographs of individual bones, and make extensive comparisons with other tyrannosauroids. This monographic description provides further evidence that Alioramus is an unusual long-snouted, gracile, and slender-limbed taxon with an unpredecented degree of cranial ornamentation among tyrannosaurids and an extremely pneumatized skeleton.

Anatomical comparisons indicate that the long skull of Alioramus is an autapomorphic feature that is proportionally longer (relative to femur length) than in any other known tyrannosaurid specimen, including juveniles, and that Alioramus is morphologically distinctive relative to similarly sized individuals of the contemporary and sympatric Tarbosaurus. The holotype specimen of A. altai belongs to a young individual, and many differences between it and the other known specimen of Alioramus (the holotype of A. remotus) may represent ontogenetic variation. The unusual longirostrine skull of Alioramus was largely produced by lengthening of the snout bones (maxilla, nasal, dentary, lacrimal, jugal), rather than the orbiotemporal bones (frontal, postorbital, squamosal, quadratojugal). The long snout, gracile skull bones, comparatively small attachment sites for jaw muscles, and lack of interlocking sutures and a robust orbital brow would have precluded the holotype individual from employing the characteristic “puncture-pull” feeding style of large-bodied adult tyrannosaurids, in which the muscular jaws, thick teeth, and interlocking sutures enabled individuals to bite with enough force to fracture bone. Whether adult Alioramus could utilize “puncture-pull” feeding awaits discovery of mature individuals of the genus. The coexistence of the long-snouted Alioramus and robust and deep-snouted Tarbosaurus, which are found together at the Tsaagan Khuushu locality, demonstrate that multiple large tyrannosaurids were able to live in sympatry, likely because of niche partitioning due to differences in craniofacial morphology and functional behavior.

Reference - Brusatte, S.L., Carr, T.D., Norell, M.A. (2012). "The Osteology of Alioramus, A Gracile and Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia". Bulletin of the American Museum of Natural History, 366: 1-197. doi: 10.1206/770.1.

Characteristic 'Death Poses' in Theropods May Have Been the Result of a Cerebral Disorder Producing Muscle Spasms After Death

Opisthotonic postures, more colloquially known as "death poses" are a common occurrence in theropod and bird fossils. They are characterized by, in life, what would be a certainly impossible feat: the neck arching backward at an incredibly sharp angle, to the point of where the head is even touching the back; the tail arching forward in many ways the neck does, even to when the tail and the head are close to touching; and the hindlimbs appear rigid and stiff.

An explanation for such phenomena has not yet reached the surface, however, paleontologists do know that these are muscle spasms creating the "death pose", not the geological/geographical conditions of its site or the way it was buried or fossilized. Conversely, the exact cause of the spasms are unknown. Or are they? A recent paper in the journal Palaeobiodiversity and Palaeoenvironments may have found the answer. Mental disorders having to do with the cerebral hemisphere of the brain may have caused the spasms postmortem,* according to the article, which was written by paleontologists Achim G. Reisdorf and Michael Wuttke.

To test this theory, they analyzed two basal coelurosaurs, Compsognathus longipes (below) and Juravenator starki, of which are both known for their "death poses". By analyzing the biomechanical constraints of the two dinosaurs plus experiments concerning decomposition tested using deceased domestic fowls, it has been found that muscle spasms are postmortem phenomena.

* The cerebrum has many functions, of which one is the complete control of your physical body, including via muscles.

Compsognathus longipes in the opisthotonic
posture, also known as the "death pose".
Image taken by Wikipedia user Ballista, here.

Abstract - More or less complete and articulated skeletons of fossil air-breathing vertebrates with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. Additionally, the tail is typically drawn over the body, while the limbs have a rigid appearance. In palaeontological literature, this “opisthotonic posture” of such fossils still requires a causal interpretation in an etiological context. According to this hypothesis, there is a presumption of a cerebral disorder generating perimortem muscle spasms that are preserved by rapid burial or other sequestration of a skeleton in the fossil record. We re-evaluate this “opisthotonic posture hypothesis” by analysing the non-avian theropods Compsognathus longipes and Juravenator starki from the famous South Franconian plattenkalks of the Upper Jurassic Solnhofen Archipelago. Decay experiments with the extant domestic fowl Gallus gallus L. and analysis of the theropods’ constructional morphological constraints reveal that the opisthotonic posture is not a peri- but a postmortem phenomenon. By analysing the timeline of decomposition, it is possible to recognise different stages of decay, depending on the varying decay resistance of soft tissues. Adipocere formation must have blocked further decay until embedding was completed by minimal sedimentation. Analyses of the palaeoenvironment of the basins of the Solnhofen Archipelago show that the conditions of deposition of individual basins cannot be considered to be similar, even inside the same time frame. Therefore, a generalised approach of looking at the depositional setting must be excluded. Assumptions by Faux and Padian (2007) that the accepted palaeoenvironmental reconstruction of the Solnhofen Fossillagerstätte has to be questioned in the light of the opisthotonic posture hypothesis enforce the need for a review of palaeoecological factors of the Franconian Plattenkalks from a taphonomic perspective.

Reference - Reisdorf, A.G., Wuttke, M. (2012). "Re-evaluating Moodie’s Opisthotonic-Posture Hypothesis in Fossil Vertebrates Part I: Reptiles—the taphonomy of the bipedal dinosaurs Compsognathus longipes and Juravenator starki from the Solnhofen Archipelago (Jurassic, Germany)". Palaeobiodiversity and Palaeoenvironments, in press. doi: 10.1007/s12549-011-0068-y.