{{Taxobox
| name = Troodontids
| fossil_range = Jurassic - Cretaceous
| image = Troodont.jpg
| image_width = 250px
| image_caption = ''Troodon'' by Frederik Spindler
| regnum = Animalia
| phylum = Chordata
| classis = Sauropsida
| superordo = Dinosauria
| ordo = Saurischia
| subordo = Theropoda
| infraordo = Deinonychosauria
| familia = '''Troodontidae'''
| familia_authority = Gilmore, 1924
| subdivision_ranks = Genera
| subdivision = 
See text.
| synonyms =
* Saurornithoididae <small>Barsbold, 1974</small>
}}

'''Troodontidae''' is a family of theropod eggs and embryos, and complete juveniles) have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like ''Sinovenator'', demonstrate striking anatomical similarities with ''Archaeopteryx'' and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.

==Physical characteristics==
Troodontids were a group of small- to medium-sized theropods (~1-100 kg) with unusually long legs compared to other theropods, with a  large, curved claw on their retractable second toes, similar to the "sickle-claw" of the dromaeosaurids. However, the sickle-claws of troodontids were not as large or recurved as in their relatives, and in some instances could not be held off the ground and "retracted" to the same degree. In at least one troodontid, ''Borogovia'', the second toe could not be held far off the ground at all and the claw was straight, not curved or sickle-like.

Troodontids had unusually large brains among dinosaurs, comparable to those of living flightless birds. Their eyes were also unusually large, and pointed forward, indicating that they had very strong, paleontologists believe that they were predatory omnivorous or herbivorous.<ref name="holtzetal1998">Holtz, T.R., Jr., Brinkman, D.L. and Chandler, C.L. (1998). "Denticle morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur ''Troodon''." ''Gaia'', '''15''': 159-166.[http://www.geol.umd.edu/~tholtz/gaiatroo.pdf]</ref> In contrast, a few species, such as ''Byronosaurus'', had large numbers of needle-like teeth, which seem best-suited for picking up small prey, such as birds, lizards and small mammals.

==Paleobiology==
Many troodontid nests, including eggs that contain fossilized embryos, have been described. Hypotheses about troodontid reproduction have been developed from this evidence (see ''Troodon'', "Reproduction"). 

A few troodont Mei'' and ''Sinornithoides'', demonstrate that these animals roosted like birds, with their heads tucked under their forelimbs.<ref name="Xu&Norell2004">Xu and Norell, (2004). "A new troodontid dinosaur from China with avian-like sleeping posture." ''Nature'', '''431''': 838-841.</ref> These fossils, as well as numerous skeletal similarities to birds and related feathered dinosaurs, support the idea that troodontids probably bore a bird-like feathered coat. The discovery of a fully-feathered, primitive troodontid (''Jinfengopteryx'') lends support to this.

In 2004, Mark Norell and colleagues described two partial troodontid skulls (IGM 100/972 and IGM 100/974) found in a nest of oviraptorid eggs in the Djadokhta Formation of Mongolia. The nest is quite certainly that of an oviraptorosaur, since an oviraptorid embryo is still preserved inside one of the eggs. The two partial troodontid skulls were first described by Norell et al. (1994) as dromaeosaurids, but reassigned after further study.<ref name="Mackovicky2004"></ref> The troodontids were either hatchlings or embryos, and fragments of eggshell are adhered to them although it seems to be oviraptorid eggshell.  The presence of tiny troodontids in an oviraptorid nest is an enigma. Hypotheses explaining how they ended up in an oviraptorid nest include that they were the prey of the adult oviraptorid, that they were there to prey on oviraptorid hatchlings, or that some troodontids may have been nest parasites.<ref name="Norelletal1994"></ref>

==Troodontids and bird evolution==

Troodontids are important to research on the origin of birds because they share many anatomical characters with early birds. Crucially, the substantially complete fossil identified as WDC DML 001 ("Lori"), is a troodontid from the Late Jurassic Morrison Formation, close to the time of ''Archaeopteryx''. The discovery of this Jurassic troodont is positive physical evidence that derived deinonychosaurs were present very near the time that birds arose, and basal paravians must have evolved much earlier. This fact strongly invalidates the "temporal paradox" cited by the few remaining opponents of the idea that birds are closely related to dinosaurs.

{{Taxobox
| color = pink
| name = 傷齒龍科
| fossil_range = 侏儸紀到白堊紀
| image = Troodont.jpg
| image_width = 250px
| image_caption = 傷齒龍
| regnum = 動物界 Animalia
| phylum = 脊索動物門 Chordata
| classis = 蜥形綱 Sauropsida
| superordo = 恐龍總目 Dinosauria
| ordo = 蜥臀目 Saurischia
| subordo = 獸腳亞目 Theropoda
| infraordo = 恐爪龍下目 Deinonychosauria
| familia = '''傷齒龍科 Troodontidae'''
| familia_authority = Gilmore, 1924
}}

'''傷齒龍科'''（Troodontidae）是群類似鳥類的獸腳亞目恐龍。

在過去數十年，傷齒龍科的化石很少發現而且零碎，因為牠們曾多次被分類於虛骨龍類的幾乎每個主要支系裡。

最近發現了大量的傷齒龍科化石，以及許多新物種。這些新發現包含數個完整且呈天然狀態的標本，以及保存羽毛的標本、蛋巢、包含胚胎的蛋、以及完整的未成年體。

關於傷齒龍科生理結構的研究，尤其是最原始的物種如中國獵龍，證實牠們與始祖鳥、原始的馳龍科恐龍有極相似的生理結構，並證實了這些動物都是近親，共同形成近鳥類演化支。

==生理特徵==
傷齒龍科恐龍是群體型小到中型的獸腳類恐龍，體重在100公斤以內；相對於其他獸腳類恐龍，牠們擁有較長後肢；牠們的第二腳趾擁有可收縮的大型、彎曲趾爪，類似馳龍科的鐮刀狀趾爪。然而，傷齒龍科的趾爪並未如馳龍科的那樣大型、彎曲；在某些例子裡，這些趾爪無法收縮到同樣程度，也無法在行走時遠離地面。至少有某一種傷齒龍科恐龍，無聊龍，牠們的第二趾爪筆直，行走時無法遠離地面。

傷齒龍科恐龍的獨特出在於牠們的大型腦部，可與現代的無法飛行鳥類相比。牠們的眼睛相當大，方向往前，顯示牠們擁有相當好的立體視覺。傷齒龍科恐龍的耳部在獸腳類恐龍中相當獨特，牠們擁有異常大的中耳空間，顯示牠們擁有準確的聽力。中耳空間接近鼓膜，有助於偵測低頻率的聲音。<ref name ="currie1985">Currie, P. J. (1985). "Cranial anatomy of ''Stenonychosaurus inequalis'' (Saurischia, Theropoda) and its bearing on the origin of birds." ''Canadian Journal of Earth Sciences'', '''22''': 1643-1658.</ref>傷齒龍科恐龍的耳朵位置並不對稱，頭顱骨兩側的耳朵位在不同的高度，這個特徵只有某些貓頭鷹才有。耳部的極度特化顯示傷齒龍科恐龍以類似貓頭鷹的方式來獵食，使用聽力來確定小型獵物的位置。<ref name="castanhinha&mateus2006">Castanhinha, R., and Mateus, O. (2006). "On the left-right asymmetry in dinosaurs." ''Journal of Vertebrate Paleontology'', '''26''' (Supp. 3): 48A.</ref> 雖然大部分古生物學家認為傷齒龍科恐龍是肉食性掠食者，但某些物種（尤其是傷齒龍）的小型、粗糙邊緣牙齒，以及U形顎部，顯示某些物種可能是雜食性或草食性動物。<ref name="holtzetal1998">Holtz, T.R., Jr., Brinkman, D.L. and Chandler, C.L. (1998). "Denticle morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur ''Troodon''." ''Gaia'', '''15''': 159-166.[http://www.geol.umd.edu/~tholtz/gaiatroo.pdf]</ref>相反地，少如物種如拜倫龍，擁有眾多的針狀牙齒，相當適合獵食小型動物，例如：鳥類、蜥蜴、以及小型哺乳類。

少數傷齒龍科的化石，包含寐龍與中國鳥腳龍的標本，證實這些動物以類似鳥類方式棲息，將頭部埋藏在前肢下方。<ref name="Xu&Norell2004">Xu and Norell, (2004). "A new troodontid dinosaur from China with avian-like sleeping posture." ''Nature'', '''431''': 838-841.</ref>這些化石與眾多類似鳥類與有羽毛恐龍的骨骸，支持了傷齒龍科恐龍身上覆蓋者類似鳥類羽毛的理論。完全覆蓋羽毛的原始傷齒龍科恐龍金鳳鳥的發現，更進一步支持這個理論。

目前已發現許多傷齒龍科的蛋巢，包含內含胚胎的恐龍蛋。目前已有一些關於傷齒龍科繁衍能力的理論。在1994年，馬克·諾瑞爾（Mark Norell）等人敘述了兩個傷齒龍科的部份顱骨（編號IGM 100/972與IGM 100/974），兩個顱骨都發現於蒙古的德加多克塔組，位在一個蛋巢裡面，這個蛋巢中有一個恐龍蛋，內有偷蛋龍科的胚胎，因此確定是偷蛋龍科的蛋巢。而這兩個顱骨最初被諾瑞爾等人敘述成馳龍科的化石，而後重新歸類於傷齒龍科。<ref name="Mackovicky2004"></ref>這兩個傷齒龍科顱骨是剛出生幼體或胚胎，上附有蛋殼碎片，但似乎是偷蛋龍科的蛋殼。為何偷蛋龍科的蛋巢會出現兩隻年幼的傷齒龍科，令人費解。目前的解釋有：牠們是成年偷蛋龍科的獵物、牠們以偷蛋龍科幼體為食、或者傷齒龍科具有巢寄生現象。<ref name="Norelletal1994"></ref>