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436:, although scientists don't know what kind of animals laid them. No modern reptile is known to lay their eggs on the seafloor, so these eggs likely originated in a different environmental setting. Ken Carpenter notes that while it's not possible to be completely sure how these eggs ended up on the seabed, some possibilities include carcasses of dead
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rather than the more typical form of calcite composing the eggshells of other reptile groups. Aragonite is unstable, so heat and pressure can convert it into the more stable form of calcite. One common form of diagenesis affecting fossil turtle eggs is the conversion of aragonite, which is unstable,
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and can change what minerals will precipitate out of the water. The organic material in the eggshell itself can lead to the precipitation of calcite out of solution. This often causes fossil eggshell to be covered in a thin layer of calcite that complicates the identification process. However, since
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beforehand. Even eggs that successfully hatch can fossilize. In fact, not only is this possible it's actually common. Many fossil dinosaur eggs are preserved with their tops broken open by the escaping hatchling. Of course not all open fossil eggs made it to a happy ending. Some contain fossil feces
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together. Simple experiments have demonstrated that under certain conditions eggshell can be transported for 68 kilometers or 42 miles with little loss of size. The durability of eggshell under transport means that pieces of fossil eggshell aren't necessarily discovered in deposits geographically
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More complete eggs in the process of fossilization are gradually buried until the weight of the sediment overtop them causes them to crack. These cracks allow even more sediments to fill the eggs. Sometimes, though, fossilization can begin fast enough to prevent the eggs from being cracked. This
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can be incorporated into fossil eggshells, but this process is damaging to the shell's internal structure due to the difference in size between silica molecules and the calcite molecules. In addition to calcite and silica other minerals can be present in small amounts in fossil eggs, especially
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eggshells are usually chiefly composed of calcite anyway the eggshell itself is mostly composed of the original calcite it had in life. The lack of change in composition and structure despite undergoing fossilization allows scientists to study the original structure of the shell.
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and begin to power their metabolisms using different energy sources. These processes can result in certain minerals being precipitated out of the groundwater selectively. The bacteria also dispose of metabolic waste using ions. Ken
Carpenter observes that one common method links
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environments as one of the best places to find fossils of dinosaur eggs. Dinosaurs would bury their eggs on the floodplain where the periodic floodwaters would carry the sediments that would bury and preserve the egg.
250:. Whether or not hatching was successful, water and wind would fill the egg with sediment through any large openings. Not all fossil egg specimens are of complete specimens, though. According to egg paleontologist
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begin when the egg either hatches or dies. Eggshell fragments are robust and can often travel great distances before burial. More complete egg specimens gradually begin to fill with sediment, which hardens as
457:. These eggs were likely buried in the debris by large tortoises. Not all volcanic debris deposits are capable of preserving eggs, however, because acids in these sediments can dissolve eggshell.
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into the regular calcite characterizing other kinds of reptile eggs, which makes them difficult to identify. In eggs laid by other types of reptile, the pressure from being buried imposes a
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and/or preservation begin. As noted, insects can be among the first scavengers of a dead egg, but deeply buried specimens may not be accessible to them and will be decomposed solely by
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composing the eggshell generally remains unchanged, allowing scientists to study its original structure. However, egg fossils buried under sediments at great depth can be subjected to
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In northeastern Spain is a deposit of beach sands estimated to be home to over 300,000 fossil eggs. According to paleontologist Ken
Carpenter these eggs were laid by
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dinosaurs who chose the site based on how easy beach sand would be to dig nests into and because such sands would absorb enough heat to help incubate the eggs.
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Many dinosaur eggs have been preserved in sandstone formed from the sands of ancient deserts in modern
Mongolia and northern China. The presence of
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preserved in their life brooding position suggests that sandstorms may have been the primary way that the eggs found in the deposits were buried.
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pattern on the calcite when viewed through a microscope. In more extreme cases the eggshell's internal structure can be obliterated completely.
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being washed out to sea and releasing its eggs when by splitting open, carried out to sea by floods, or drifting out on mats of vegetation.
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debris deposits although not lava deposits. At least two clutched of hard-shelled turtle eggs preserved in this manner are known from the
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out of solution. If enough minerals make it inside the egg can become sturdy enough to withstand the weight of the overlying sediments.
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The formation of fossil eggs begins with the original egg itself. Not all eggs that end up fossilizing experience the death of their
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Hayward, J.L., K.F. Hirsch, and T.C. Robertson. (1991). Rapid dissolution of avian eggshells buried by Mount St. Helens ash.
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When the egg is buried deeply enough, the bacteria decomposing the egg are cut off from
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Eggs, Nests, and Baby
Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past)
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through pores or cracks in the shell. Throughout the fossilization process the
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that can alter the structure of its shell through a process called
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After burial eggs can still be altered. This process is called
630:"Discussion," Hayward, Hirsch, and Robertson (1991); page 177.
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639:"How to Fossilize an Egg," Carpenter (1999); pages 114–115.
621:"How to Fossilize an Egg," Carpenter (1999); pages 111–112.
612:"How to Fossilize an Egg," Carpenter (1999); pages 110-111.
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Fossil eggs are known from sedimentary rocks deposited in
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648:"How to Fossilize an Egg," Carpenter (1999); page 115.
603:"How to Fossilize an Egg," Carpenter (1999); page 111.
589:"How to Fossilize an Egg," Carpenter (1999); page 114.
577:"How to Fossilize an Egg," Carpenter (1999); page 108.
565:"How to Fossilize an Egg," Carpenter (1999); page 113.
551:"How to Fossilize an Egg," Carpenter (1999); page 112.
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environments. Turtle eggs are known from the marine
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Study of the decomposition and fossilization of eggs
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51:introducing citations to additional sources
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41:Relevant discussion may be found on the
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258:that cements the eggshell's calcite
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379:Carpenter has also described the
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34:relies largely or entirely on a
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529:Timeline of egg fossil research
449:Fossil eggs have been found in
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664:, Indiana University Press.
308:. During conditions of high
660:Carpenter, Kenneth (1999).
218:due to overly deep burial,
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300:water. The acids dissolve
356:Depositional environments
343:ammonia to power their
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267:they originated from.
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383:deposited in ancient
284:decomposition in the
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304:like calcite out of
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129:is the study of the
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521:Paleontology portal
190:(known formally as
120:Oolithes spheroides
171:chemical processes
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422:Stonesfield Slate
337:calcium carbonate
292:from atmospheric
276:process involves
252:Kenneth Carpenter
222:health problems,
181:Laying and burial
159:calcium carbonate
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103:November 2015
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58:Find sources:
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36:single source
32:This article
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489:iron sulfide
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271:Preservation
236:temperatures
216:asphyxiation
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693:Egg fossils
430:Oxford Clay
375:Floodplains
362:Beach sands
345:metabolisms
314:precipitate
224:dehydration
214:eggs, like
155:percolating
151:precipitate
687:Categories
679:6:174–178.
655:References
497:iron oxide
467:diagenesis
461:Alteration
434:Gault Clay
393:Sand dunes
385:floodplain
341:nitrogento
310:watertable
220:congenital
200:scavenging
192:coprolites
175:diagenesis
73:newspapers
698:Taphonomy
535:Footnotes
471:aragonite
400:Oviraptor
381:mudstones
306:limestone
143:taphonomy
43:talk page
507:See also
501:hematite
451:volcanic
408:Seafloor
368:sauropod
349:alkaline
302:minerals
260:crystals
244:bacteria
232:drowning
167:pressure
148:minerals
677:Palaios
228:disease
212:reptile
87:scholar
668:
493:pyrite
480:Silica
424:, and
414:marine
321:oxygen
196:larvae
187:embryo
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499:, or
282:plant
278:acids
248:fungi
204:flies
94:JSTOR
80:books
666:ISBN
485:iron
432:and
333:Ca2+
298:rain
296:and
286:soil
265:nest
246:and
210:and
208:bird
169:and
163:heat
139:eggs
133:and
66:news
491:or
331:to
198:of
137:of
49:by
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