Age determination in

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

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 Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932. Overview Allome ...

scaling principles. Ages were determined by dividing individual mass estimates by rates of growth for similar, extant

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

. 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. 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: '' annuli'', and ''lines of arrested growth'' (LAGs).Francillion-Viellot H., ''et al.'', (1990). Microstructure and mineralization of vertebrate skeletal tissues. In ''Skeletal Biomineralization: Patterns, Processes, and Evolutionary Trends'' (J. G. Carter, Ed.). Vol. 1, pp. 471-530. Van Nostrand-Reinhold, New York. 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 Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

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

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns exposed to constant temperature, diet, and photoperiod, still exhibit the periodic and cyclical skeletal growth banding of their wild counterparts. Consequently, it is assumed by many

paleontologists Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

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 Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic ...

Psittacosaurus ''Psittacosaurus'' ( ; "parrot lizard") is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 126 and 101 million years ago. It is notable for being the most species-rich non-avian dinosaur gen ...

'' ''mongoliensis'' was 10 or 11 years. The

prosauropod Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had l ...

Massospondylus ''Massospondylus'' ( ; from Greek, (massōn, "longer") and (spondylos, "vertebra")) is a genus of sauropodomorph dinosaur from the Early Jurassic. (Hettangian to Pliensbachian ages, ca. 200–183 million years ago). It was described by S ...

carinatus'' 15 years of age,Chinsamy, A. (1994). Dinosaur bone histology: Implications and inferences. In ''Dino Fest'' (G. D. Rosenburg and D. L. Wolberg, Eds.), pp. 213-227. The Paleontological Society, Department of Geological Sciences, Univ. of Tennessee, Knoxville. the sauropods ''

Lapparentosaurus ''Lapparentosaurus'' is a genus of sauropod dinosaur from the Middle Jurassic. Its fossils were found in Madagascar (Isalo III Formation). The type species is ''L. madagascariensis''. Discovery and naming In 1895 Richard Lydekker named a new s ...

'' and ''

Narindasaurus ''Narindasaurus'' (meaning "lizard of Narinda Bay") is a genus of turiasaurian sauropod dinosaur from the Middle Jurassic Isalo III Formation of Madagascar. The type species, ''N. thevenini'' was formally described by Royo-Torres ''et al.'' in 2 ...

'' 43 years, the

coelophysoid Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...

Megapnosaurus ''Megapnosaurus'' (meaning "big dead lizard", from Greek μεγα = "big", 'απνοος = "not breathing", "dead", σαυρος = "lizard") is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago dur ...

rhodesiensis'' 7 years, and the

maniraptor Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoro ...

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77 mya). It includes at leas ...

formosus'' 3-5 years of age respectively.Varricchio, D. V. (1993). Bone microstructure of the Upper Cretaceous theropod dinosaur ''Troodon formosus. J. Vertebr. Paleontol.'' 13, 99-104. These data are being used in conjunction with mass estimated in order to infer the metabolic status and growth rates of dinosaurs.

References

{{reflist, 2 Dinosaur paleobiology Senescence in non-human organisms