Age determination of dinosaurs
Encyclopedia
Age determination in dinosaur
s is mainly used to determine the approximate age of a dinosaur when the animal died.
. For very large individuals, growth rates were extrapolated to dinosaur proportions using regression analysis. The results of these investigations have been extremely variable as they depend on mass estimates and growth rates that are highly at odds with one another.
For example, longevity estimates for the sauropod Hypselosaurus
priscus range from a few decades to several hundred years. Recently, however, it has been shown that most dinosaur bones have growth lines that are visible in thin sectioned material viewed under a polarized light source.
, and lines of arrested growth (LAGs). Histological examinations have revealed that annuli are composed of thin layers of avascular bone with parallel-aligned bone fibers. The growth line annuli are found compressed between broad vascularized regions of bone with randomly oriented fibrillar patterns, known as zones.
Lines of arrested growth, similar to annuli, are found between zones are avascular. They are, however, much thinner, and have relatively fewer bone fibers by volume.
Studies on extant vertebrate
s indicate that the vascularized zones form during moderate to rapid skeletogenesis, and that abrupt metabolic disruptions of bone formation can trigger growth line deposition.
Both types of growth lines may be deposited in synchrony with endogenous biorhythms. For example, captive crocodilians exposed to constant temperature, diet, and photoperiod, still exhibit the periodic and cyclical skeletal growth banding of their wild counterparts. Consequently, it is assumed that many paleontologists that the growth lines of dinosaurs reflect annual rhythms, and that they may be used to determine individual ages. However, in the large and long bones of many dinosaurian taxa, resorption of internal and external bone proceeds even as new cortical bone continues to be deposited, so that growth lines deposited early in development may need to be inferred.
mongoliensis was 10 or 11 years. The prosauropod Massospondylus
carinatus 15 years of age, the sauropod Bothriospondylus
madagascariensis 43 years, the coelophysoid Megapnosaurus
rhodesiensis 7 years, and the maniraptor Troodon
formosus 3-5 years of age respectively. These data are being used in conjunction with mass estimated in order to infer the metabolic status and growth rates of dinosaurs.
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s is mainly used to determine the approximate age of a dinosaur when the animal died.
History
Early attempts to estimate the longevity of dinosaurs used allometric scaling principles. Ages were determined by dividing individual mass estimates by rates of growth for similar, extant taxaTaxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
. For very large individuals, growth rates were extrapolated to dinosaur proportions using regression analysis. The results of these investigations have been extremely variable as they depend on mass estimates and growth rates that are highly at odds with one another.
For example, longevity estimates for the sauropod Hypselosaurus
Hypselosaurus
Hypselosaurus was a long titanosaurid sauropod that lived in Europe during the Late Cretaceous Period .Hypselosaurus was scientifically described by geologist Pierre Émile Philippe Matheron in 1846 and formally named in...
priscus range from a few decades to several hundred years. Recently, however, it has been shown that most dinosaur bones have growth lines that are visible in thin sectioned material viewed under a polarized light source.
Growth lines
Two types of growth lines exist: annuliAnnulus (zoology)
In zoology, an annulus is an external circular ring. Annuli are commonly found in segmented animals such as earthworms and leeches. The bodies of these annelids are externally marked by annuli that are arranged in series with each other....
, and lines of arrested growth (LAGs). Histological examinations have revealed that annuli are composed of thin layers of avascular bone with parallel-aligned bone fibers. The growth line annuli are found compressed between broad vascularized regions of bone with randomly oriented fibrillar patterns, known as zones.
Lines of arrested growth, similar to annuli, are found between zones are avascular. They are, however, much thinner, and have relatively fewer bone fibers by volume.
Studies on extant vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s indicate that the vascularized zones form during moderate to rapid skeletogenesis, and that abrupt metabolic disruptions of bone formation can trigger growth line deposition.
Both types of growth lines may be deposited in synchrony with endogenous biorhythms. For example, captive crocodilians exposed to constant temperature, diet, and photoperiod, still exhibit the periodic and cyclical skeletal growth banding of their wild counterparts. Consequently, it is assumed that many paleontologists that the growth lines of dinosaurs reflect annual rhythms, and that they may be used to determine individual ages. However, in the large and long bones of many dinosaurian taxa, resorption of internal and external bone proceeds even as new cortical bone continues to be deposited, so that growth lines deposited early in development may need to be inferred.
Results in dinosaurs
The results of pioneering efforts to age dinosaur fossils using growth ring counts suggest that the longevity of the basal ceratopsian PsittacosaurusPsittacosaurus
Psittacosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of what is now Asia, about 130 to 100 million years ago. It is notable for being the most species-rich dinosaur genus...
mongoliensis was 10 or 11 years. The prosauropod Massospondylus
Massospondylus
Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...
carinatus 15 years of age, the sauropod Bothriospondylus
Bothriospondylus
Bothriospondylus is an dubious genus of sauropod dinosaur. It lived during the Late Jurassic.The type species, Bothriospondylus suffossus, was described by Richard Owen in 1875. The specific epithet suffossus means "undermined" in Latin, a reference to the fact that pleurocoels had hollowed out...
madagascariensis 43 years, the coelophysoid Megapnosaurus
Megapnosaurus
Megapnosaurus was a dinosaur of the theropod family Coelophysidae, formerly called Syntarsus , living during the Early Jurassic. It was renamed by American entomologist Dr. Michael Ivie , Polish Australian Dr...
rhodesiensis 7 years, and the maniraptor Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
formosus 3-5 years of age respectively. These data are being used in conjunction with mass estimated in order to infer the metabolic status and growth rates of dinosaurs.