Incognitoolithusis anoogenusofmedioolithidfossilbird egg.It is notable for bearing evidence of predation, possibly from a bird pecking the eggshell.[1]
| Incognitoolithus Temporal range:
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|---|---|
Egg fossil classification
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| Basic shell type: | Ornithoid |
| Morphotype: | Ornithoid-ratite |
| Oofamily: | †Medioolithidae |
| Oogenus: | †Incognitoolithus Hirsch, Kihm & Zelenitsky, 1997 |
| Oospecies | |
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Distribution
editIncognitoolithusfragments are found at two localities in theDeBeque FormationinGarfield County, Colorado.Both localities are dated to theEarly Eocene.[1]
History
editEggshell fragments ofIncognitoolithuswere discovered in 1977 and 1979 during two separate field seasons. The oospeciesI. ramotubuluswas first described in 1997 byKarl Hirsch,Allen KihmandDarla Zelenitsky.[1]
Description
editI. ramotubulusis known from over 200 eggshell fragments which may represent a single disintegrated egg. When complete, the egg is estimated to have been 10–12 cm (3.9–4.7 in) long and 7.5–9 cm (3.0–3.5 in), making it significantly larger than the next largest known Eocene bird egg in North America, which measured only 6.4 x 8.9 cm. The eggshell is 1.27–1.43 mm thick and consists of two structural layers, unlike most modernratiteeggs (which have a third layer, the external layer). The outer layer, called the continuous layer, is three times the thickness of the inner layer (the mammillary layer).[1]It is one of the few fossil eggs to have only two layers and a smooth eggshell.[2]
Incognitoolithushas a distinctive pore system. It has both branching and unbranching pores. The openings of these pores on the surface of the eggshell matches the "aepyornithid"type: Pores open in small pits or in grooves which may accommodate multiple pore openings.[1]
Paleobiology
editParentage
editThe pore arrangement and structure ofIncognitoolithusis similar to that ofAepyornis.[3]The microstructure and lack of ornamentation are similar to modernratiteeggs. However, since no embryonic remains or parental remains were found withIncognitoolithus,it is impossible to infer what kind of bird laid the eggs.[1]
Predation
editMultiple fragments ofIncognitoolithushave been found with holes interpreted as peck marks. While it is possible that these were made by a parent assisting the hatching, this behavior is very rare in modern birds. More likely, they are the result of predation. Experiments on modern chicken eggs by Hirschet al.in 1997 found thatIncognitoolithus'sholes are most consistent with those from a bird's peck. However, the dynamics of a thick eggshell likeI. ramotubulusdiffer from those of chicken eggs, so the possibility that the holes are tooth marks of a mammal or reptile cannot be ruled out.[1]
See also
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References
edit- ^abcdefgHirsch, Karl; Kihm, Allen; Zelenitsky, Darla (1997). "New Eggshell of Ratite Morphotype with Predation Marks from the Eocene of Colorado".Journal of Vertebrate Paleontology.17(2): 360–369.Bibcode:1997JVPal..17..360H.doi:10.1080/02724634.1997.10010980.JSTOR4523812.
- ^Tanaka, Kohei; Zelenitsky, Darla; Saegusa, Haruo; Ikeda, Tadahiro; DeBuhr, Christopher; Therrien, François (2016). "Dinosaur eggshell assemblage from Japan reveals unknown diversity of small theropods".Cretaceous Research.57:350–363.Bibcode:2016CrRes..57..350T.doi:10.1016/j.cretres.2015.06.002.
- ^Bibi, Faysal; Shabel, Alan; Kraatz, Brian; Stidham, Thomas (2006). "New fossil ratite (Aves: Palaeognathae) eggshell discoveries from the Late Miocene Baynunah Formation of the United Arab Emirates, Arabian Peninsula".Palaeontologia Electronica.9(1): 2A.