In Silesaurid Dinosauriform Asilisaurus, Size was NOT a Good Predictor of Maturity

Paleontologists at Virginia Tech have found that muscle-scarred fossil leg bones of one of the closest cousins of dinosaurs that lived approximately 240 million years ago can shine new light on a large unknown: How early dinosaurs grew from hatchlings to adults.

Published this month in the Journal of Vertebrate Paleontology, the findings are surprising: dinosaurs and their close relatives had much more variation in growth patterns then ever expected, and this variation does not appear to be related to differences between males and females.

Lead author Christopher Griffin, a geosciences master's student in the College of Science, focused his study on muscle scars etched into the fossil bones of the Asilisaurus kongwe, a dinosaur cousin that lived roughly 10 million years earlier than the oldest known dinosaurs.

"Variation in muscle scars were thought to indicate sexual difference in early dinosaurs, but we know that in many modern animals these features are related to growth, not sex," said Griffin of Redding, California. "Because of this, we thought that similar variations that we saw in Asilisaurus would not turn out to split into two groups, which would be evidence for a sex difference, and instead be more on a spectrum. As we looked at more Asilisaurus fossils of different sizes, because we had such a great sample size, we found this to be supported: with a large sample size, they don't split into two clean groups."

Added Sterling Nesbitt, study co-author and an assistant professor with the Virginia Tech Department of Geosciences: "The earliest dinosaurs grew just like their closest relatives, and there are very few features that make dinosaurs unique from their closest relatives."

Asilisaurus lived during the Triassic Period, roughly 240 million years ago in present-day Africa. With four legs and a long tail, the animal was about the size of a Labrador retriever, and likely maxed at 65 pounds, according to previous studies of the animal. Its exterior skin appearance remains unknown.

Fossils of Asilisaurus kongwe - a combination of Swahili and Greek works meaning "ancient ancestor reptile" - are vital because a large number of specimens were found, largely intact and varying in size and age. Such findings are so rare that paleontologists have struggled with understanding how the first dinosaurs grew, as most species of early dinosaur are known from only a handful of fossils.

The Asilisaurus fossils initially were discovered during a 2007 expedition in southern Tanzania, with additional field excursions taking place for the next eight years.

The length of the field excursions and the number of specimens of fossils resulted in several smaller individual specimens appearing to be more mature than larger finds, and individuals of the same size appeared to be at different stages of growth.

In studying the anatomy and bone tissue of Asilisaurus and how each changed during growth, Griffin and Nesbitt found the although these individual animals lived in roughly the same location at the same time, they grew differently. Griffin compared this finding to any modern family with siblings and cousins differing in height or body mass, for instance, one brother smallish, and another taller; one naturally muscular, another prone to thinness.

Griffin and Nesbitt studied bone scars on the Asilisaurus leg bones, focusing on spots where muscles and tendons attach to bone.

link.

Anisian Triassic Dinosauriform Asilisaurus kongwe Just Complicated Dinosauriform Ontogeny

The femoral ontogeny and long bone histology of the Middle Triassic (?late Anisian) dinosauriform Asilisaurus kongwe and implications for the growth of early dinosaurs

Authors:

Griffin et al

Abstract:

The ontogeny of early-diverging dinosauromorphs is poorly understood because few ontogenetic series from the same species-level taxon are known and what is available has not been extensively documented. The large numbers of skeletal elements of the silesaurid Asilisaurus kongwe recently recovered from Tanzania provide an opportunity to examine the ontogenetic trajectory of the earliest known member of Ornithodira and one of the closest relatives to Dinosauria. We examined the ontogeny of the femur and the histology of a series of long bone elements. We observed bone scar variation in a series of femora (n = 27) of different lengths (73.8–177.2 mm). We hypothesize that most femora follow a similar developmental trajectory; however, we observed sequence polymorphism in the order of appearance and shape of bone scars, and we quantified this polymorphism using ontogenetic sequence analysis (OSA). Additionally, five femora, three tibiae, a fibula, and a humerus were thin-sectioned to examine osteological tissues. No lines of arrested growth (LAGs) are present in any specimen, and there is little histological information about the ontogenetic stage of femora, although none have slowed or ceased growth. The woven-fibered bone present in the cortex of elements sectioned is similar to that of the earliest dinosaurs. This sequence polymorphism provides an alternate hypothesis for the robust/gracile dichotomy found in early dinosaurs often interpreted as sexual dimorphism. The shared femoral features found in Asilisaurus and early dinosaurs suggest that this ontogenetic pattern is plesiomorphic for Dinosauria, and that size is a poor predictor of maturity in early dinosauriforms.

Giving a Crap: Understanding Polish Norian-Rhaetian Triassic PaleoEcologies Through Carnivore Coprolites

Coprolites of Late Triassic carnivorous vertebrates from Poland: An integrative approach

Authors:

Zatoń et al

Abstract:

Vertebrate coprolites derived from Upper Triassic terrestrial deposits of southern Poland have been subjected to various analytical methods in order to retrieve information about their composition, producer’s diet and nature of the microscopic structures preserved in the groundmass. Morphologically, the coprolites have been classified into four morphotypes, of which only three were further analysed due to their good state of preservation. Their groundmass are composed of francolite, a carbonate-rich apatite, in which abundant coccoid structures are preserved. Based on various microscopic and organic geochemical techniques, they are interpreted as fossilized bacteria which could have mediated the phosphatization of the faeces. The thin sectioning revealed that the coprolites consist of those containing exclusively bone remains, and those preserving both bone and plant remains. Those coprolites preserving only vertebrate remains are suggestive for exclusive carnivorous diet of the producers. However, the interpretation of coprolites consisting of both vertebrate and plant remains is more debatable. Although they may attest to omnivory, it cannot be excluded that potential producers were carnivorous and occasionally ingested plants, or accidentally swallowed plant material during feeding. The latter may involve predation or scavenging upon other herbivorous animals. The potential producers may have been animals that foraged in or near aquatic habitats, such as semi-aquatic archosaurs and/or temnospondyls. This is supported by the presence of ostracode and other aquatic arthropod remains, and fish scales within the coprolites, as well as by the presence of specific biomarkers such as phytanic and pristanic acids, which are characteristic constituents of fish oil. The preservation of such labile organic compounds as sterols, palmitin, stearin or levoglucosan attests for rapid, microbially-mediated mineralization of the faeces at very early stages of diagenesis.

How Dinosauriform Silesaurus Grew

Skeletal variation and ontogeny of the Late Triassic Dinosauriform Silesaurus opolensis

Authors:

Piechowski et al

Abstract:

A principal component analysis (PCA) performed for a set of 24 measurements on 33 femora and 15 measurements on 20 ilia of Silesaurus opolensis from the early Late Triassic of Krasiejów, southern Poland, shows that this sample is highly variable but probably monospecific. Most of the morphological variation is concentrated in the muscle attachments and proportions of bones, which significantly change in both size and position during ontogeny. Despite the small sample size, femora of smaller individuals have less flattened shafts and a more sinusoidal appearance. In many large specimens, proximal parts of muscle tendons are ossified at their attachment site on femora and remain attached to the bone in the largest specimens. The specimens with attached ossifications are interpreted as mature females that were statistically larger than proposed males. It is suggested that ossifications developed in females under calcitonin control. The intrapopulation variability of ilia is high, but less dependant on ontogeny. The population represented by a few specimens from the lower level at Krasiejów may represent a different stage in the evolution of the species than that from the upper horizon.

Carnian Triassic Dinosauriform Silesaurus did not Chew Tough Food

Dental microwear of a Late Triassic dinosauriform, Silesaurus opolensis

Authors:

Kubo et al

Abstract:

Silesaurus opolensis belongs to Silesauridae, the closest sister group to dinosaurs. The present study analyzed the dental microwear patterns of Silesaurus opolensis. Low pit-to-scratch ratios imply they did not feed on hard objects. Unimodal distributions of both wear-facet and non-facet scratch orientations indicate simple orthal jaw movement. Scratch orientation and density differ between microscopic regions in Silesaurus, and unlike hadrosaurid dinosaurs, the microwear patterns of small areas are not identical to those of whole teeth.

The Origins of Dinosaurs in the Triassic

The origins of Dinosauria: much ado about nothing

Author:

Langer

Abstract:

Research this century has greatly improved our knowledge of the origin and early radiation of dinosaurs. The unearthing of several new dinosaurs and close outgroups from Triassic rocks from various parts of the world, coupled with improved phylogenetic analyses, has set a basic framework in terms of timing of events and macroevolutionary patterns. However, important parts of the early dinosauromorph evolutionary history are still poorly understood, rendering uncertain the phylogenetic position of silesaurids as either non-dinosaur Dinosauriformes or ornithischians, as well as that of various early saurischians, such as Eoraptor lunensis and herrerasaurs, as either noneusaurischians or members of the sauropodomorph or theropod lineages. This lack of agreement in part derives from a patchy distribution of traits among early members of the main dinosauromorph lineages and requires a more meticulous assessment of characters and homologies than those recently conducted. Presently, the oldest uncontroversial dinosaur records come from Late Triassic (Carnian) rocks of South America, southern Africa and India, hinting at a south-western Pangaea origin of the group. Besides, macroevolutionary approaches suggest that the rise of dinosaurs was a more gradual process than previously understood. Obviously, these tentative scenarios need to be tested by new fossil finds, which should also help close the major gaps recognized in the fossil record of Triassic dinosauromorphs.

The Norian Triassic Dinosaur & Dinosauriform Biota of Poland

Basal dinosauriform and theropod dinosaurs from the mid–late Norian (Late Triassic) of Poland: implications for Triassic dinosaur evolution and distribution

Authors:

Niedźwiedzki et al

Abstract:

The rise of dinosaurs during the Triassic is a widely studied evolutionary radiation, but there are still many unanswered questions about early dinosaur evolution and biogeography that are hampered by an unevenly sampled Late Triassic fossil record. Although very common in western North America and parts of South America, dinosaur (and more basal dinosauriform) remains are relatively rare in the Upper Triassic deposits of Europe, making any new discoveries critically important. One of the most diverse dinosauriform assemblages from Europe comes from the Poręba site in Poland, a recently described locality with exposures of the Zbąszynek Beds, which have a palynomorph assemblage characteristic for the mid–late Norian in the biostratigraphic schemes of the Germanic Basin. Using a synapomorphy-based approach, we evaluate several isolated dinosauriform specimens from Poręba. This assemblage includes a silesaurid, a herrerasaurid and remains of another type of theropod (potentially a neotheropod). The Poręba herrerasaurid is the first record of this rare group of primitive dinosaurs from Europe and one of the youngest records worldwide, whereas the silesaurid is the youngest record of a silesaurid from Europe. These findings indicate that silesaurids persisted alongside true dinosaurs into the mid–late Norian of Europe and that silesaurid–herrerasaurid–neotheropod assemblages (which are also known from the Norian of North America, at low latitudes) were more widespread geographically and latitudinally than previously thought. Silesaurid–herrerasaurid–neotheropod assemblages may have been a common ecological structuring of dinosaurs during their early evolution, and their widespread distribution may indicate weak palaeolatitudinal controls on early dinosaur biogeography during the latest Triassic.

Ignotosaurus fragilis, a New Silesaurid Dinosauriform From Carnian/Norian Argentina

Ignotosaurus fragilis, a New Silesaurid Dinosauriform from the Late Triassic of Argentina and the Vertebrate Succession of the Ischigualasto Formation - See more at:

Authors:

Martinez at el

Abstract:

The Upper Triassic (Carnian–Norian) Ischigualasto Formation has yielded a diverse vertebrate fauna that records the initial phase of dinosaur evolution. Radioisotopic dates from ash layers within the formation provide a chronostratigraphic framework, and stratigraphic and sedimetological studies have subdivided the formation into four members and three abundance-based biozones. We describe two new basal dinosauromorphs, an unnamed lagerpetid and a new silesaurid, Ignotosaurus fragilis, gen. et sp. nov., which increase to 29 the number of vertebrates in the Ischigualasto fauna. We provide a census of 848 fossil specimens representing 26 vertebrate taxa logged to stratigraphic intervals of 50 m. This temporally calibrated census shows that abundance and taxonomic diversity within the Ischigualasto Formation does not change suddenly but rather appears to gradually decline in response to climatic deterioration. The only abrupt shift in faunal composition occurs at the end of the second of three biozones, when the abundant cynodont Exaeretodon is replaced by the rare dicynodont Jachaleria.

I don't see the paper yet at the JVP website.

A hat tip link to Chinleana.

Ladinian Triassic Silesaurid Found in Chile

link in Spanish.

A New Silesaurid Dinosauriform From Anisian Triassic Zambia

A new silesaurid from the upper Ntawere Formation of Zambia (Middle Triassic) demonstrates the rapid diversification of Silesauridae (Avemetatarsalia, Dinosauriformes)

Authors:

1. Brandon R. Peecook (a)
2. Christian A. Sidor (a)
3. Sterling J. Nesbitt (a)
4. Roger M. H. Smith (b)
5. J. Sebastien Steyer (c)
6. Kenneth D. Angielczykd

Affiliations:

(can't see them...for some reason I have lost access to JVP)

Abstract:

Recent discoveries have shown that non-dinosaurian dinosauromorphs were morphologically diverse, globally distributed, and have a stratigraphic range extending into the Upper Triassic. Silesauridae, the sister group to Dinosauria, contains at least seven species. Here we describe Lutungutali sitwensis, gen. et sp. nov., the first silesaurid from the upper portion of the Ntawere Formation of the Luangwa Basin, Zambia. The upper Ntawere Formation has been correlated with subzone C of the Cynognathus Assemblage Zone of the Karoo Basin in South Africa and the Lifua Member of the Manda beds in the Ruhuhu Basin in Tanzania, both of which are considered Anisian in age and the latter has yielded the silesaurid Asilisaurus kongwe. The results of our phylogenetic analysis, including a new pelvic character, allies Lutungutali with Upper Triassic silesaurids such as Silesaurus, Sacisaurus, and Eucoelophysis rather than with the possibly coeval Asilisaurus. The Zambian silesaurid shares a laterally oriented brevis fossa on the ilium and a transversely thin ischium in cross-section with Upper Triassic forms. Silesaurids were more diverse during their early evolution in the Anisian than previously suspected. Lutungutali and Asilisaurus are the two oldest known members of the bird-line archosaurs represented by body fossils. Together they show that a subclade of bird-line archosaurs was diversifying soon after its origin, building further support for the rapid diversification of Archosauria in the wake of the Permo-Triassic extinction.

Didn't someone raise the idea silesaurids were actually basal orinthschians? Did that not pan out?