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The Terminology of Amniote Temporal Vacuities

1983; Kansas Academy of Science; Volume: 86; Issue: 1 Linguagem: Inglês

10.2307/3628423

1938-5420

Hobart M. Smith, David Chiszar, Michael J. Frey,

Amphibian and Reptile Biology

Attention is focussed upon the extensive variation in temporal vacuities of amniotes, applying terms to types exemplified in extant turtles, squamatans, birds and mammals. Turtles, long accepted as anapsid, exhibit varying degrees of temporal notching (keiroid), either posterior (opisthokeirold) or inferior (pleurokeiroid), or both. The prefixes meio-, meso-, metaand hyperare used to designate appropriate degrees of notching. In squamatans, the divisions hemidiapsid (more specifically, infrahemidiapsid), anadiapsid and eudiapsid are designated. In birds the eudiapsid and suprahemidiapsid conditions are noted, and in mammals the eusynapsid and anasynapsid divisions of the synapsid condition. That reptiles explored virtually every conceivable sort of temporal vacuation in their protracted and diverse radiation has been known for several centuries. Several types of vacuity persisted so long in vertebrate history and became represented by so many species, genera, families and even several orders and classes, that they are universally viewed as fundamental in amniote evolution. It was therefore fully appropriate that distinctive names be applied to the basically different sorts of vacuities, and thus the concepts are perpetuated by such long-established terms as anapsid, synapsid, diapsid, parapsid and euryapsid, each referring to a distinctive type of temporal vacuity. The terminology representing the diversity of temporal vacuities arose in reference to fossils, and although extended in application to extant groups, the specializations that are particularly notable in living taxa have not received proportionate attention. The diapsid condition characteristic of birds, and the synapsid condition perpetuated in mammals, have as a matter of fact not diverged greatly from the ancestral reptilian condition, and therefore require little refinement of terminology. On the contrary, two modem groups of reptiles, the turtles and the squamatans (lizards, snakes, amphisbaenids) have indeed evolved so extensively from the primitive anapsid and diapsid conditions as to be unrecognizable as such in their extreme forms. This content downloaded from 207.46.13.122 on Thu, 25 May 2017 17:59:44 UTC All use subject to http://about.jstor.org/terms VOLUME 85, NUMBER 1 49 TESTUDINID TEMPORAL VACUITIES Turtles, for example, are regarded quite properly as anapsid, as are fishes and amphibians as well as the extinct reptiles (cotylosaurs, mesosaurs) that along with the order Testudines constitute the subclass Anapsida. However, all except the most primitive turtles (e.g., sea turtles) exhibit greater or lesser amounts of either supratemporal or infratemporal (or both) emargination (as opposed to temporal fossation), with extremes breaching any of the postorbital, posttemporal, or infratemporal arcades. In some species two arcades are known to be incomplete, and very likely in a few (not now known) all three may be. The extensive modification seen in turtles of the basic anapsid cranial architecture equals or exceeds the entire ramification of types of temporal fossae occurring in other amniotes, yet no differentiating terminology has been applied to the varied character states that are readily distinguished. It is proposed here that the following terminological categories be recognized among turtles and other anapsid vertebrates. 1. keiroid: the condition characterized by presence of any sort of temporal (either supraor infra-) emargination. Derived from the Greek word KELpav transliterated as keiro, meaning to cut out or to destroy (fide Brown, 1956: 247). 2. akeiroid: the euanapsid condition, involving no or an insignificant amount of temporal notching, as in Dermochelys (Fig. 1) and Chelonia (Fig. 2). 3. opisthokeiroid: the condition characterized by presence of a supratemporal emargination. Several degrees of such emargination may be recognized, as follows. 4. meiopisthokeiroid: the condition characterized by a small supratemporal emargination, as in Platysternon (Fig. 3). 5. mesopisthokeiroid: the condition characterized by a moderate supratemporal emargination, as in Chelydra (Fig. 4). 6. metopisthokeiroid: the condition characterized by an extensive supratemporal emargination, leaving a narrow postorbital arcade, as in Cyclemys (Fig. 5). 7. hyperopisthokeiroid: the condition characterized by extension of the supratemporal emargination through either the postorbital arcade (as in Kinixys belliana, Fig. 6) or the infratemporal arcade (as in Terrapene carolina, Fig. 7; Cuora galbinifrons, Fig. 8; Heosemys depressa, Fig. 9; and Trionyx spiniferus, Fig. 10). 8. pleurokeiroid: the condition characterized by the presence of an infratemporal emargination, posterior to the orbit. Numerous species exhibit some degree of both pleurokeiroidy and opisthokeiroidy. The extent ofemarThis content downloaded from 207.46.13.122 on Thu, 25 May 2017 17:59:44 UTC All use subject to http://about.jstor.org/terms 50 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE gination in pleurokeiroidy varies greatly, just as in opisthokeiroidy, as follows. 9. meiopleurokeiroid: the condition characterized by a small infratemporal emargination (as in Cyclemys, Fig. 5, and in Chinemys reevesi, Fig. 10, in both of which it is combined with a metopisthokeiroid condition). 10. mesopleurokeiroid: the condition characterized by a moderate infratemporal emargination (as in Cuora galbinifrons, Fig. 8; Terrapene carolina, Fig. 7; Kinixys belliana, Fig. 6, where it is combined with a hyperopisthokeiroid condition; Testudo graeca, Fig. 12, where it is combined with an extreme metopisthokeiroid condition; and Podocnemis expansa, Fig. 13, where it is combined with a mesopisthokeiroid condition). 11. metapleurokeiroid: the condition characterized by an extensive infratemporal emargination, leaving but a narrow posttemporal arcade (as in Elseya dentata, Fig. 14, and in Batrachemys nasuta, Fig. 15). This and the following condition occur only in pleurodire turtles. 12. hyperpleurokeiroid.: the condition characterized by a breach of the posttemporal arcade by extension of the infratemporal emargination to unite with the supratemporal emargination (as in Chelodina longicollis, Fig. 16). Progressive lines of modification are clearly evident in comparisons of species of polytypic genera, and of related genera. Three generalities are evident: (1) that the primitive condition is the absence of emargination; (2) that supratemporal emargination occurs in both cryptodire and pleurodire lines of phylogeny, but is less common and less extreme in the latter group; and (3) that infratemporal emargination also occurs in both cryptodire and pleurodire lines of phylogeny, but is less common and much less extreme in the former group. SQUAMATE TEMPORAL VACUITIES Lizards, snakes and amphisbaenians constitute the order Squamata, which quite properly is regarded as being diapsid throughout, but in this group, contrary to other diapsid groups, the temporal fossae are so enlarged that in most examples, if not all, either the infratemporal arcade, or both the infratemporal and supratemporal arcades, are incomplete, vestigial or absent. We here propose that the condition wherein the infratemporal arcade only is not intact, as in most lizards (Fig. 17) and amphisbaenians, be designated hemidiapsid, the prefix hemi- referring to the presence of but one of the normal two intact arches. For the serpentine (and occasional saurian) condition, in which both supratemporal and infratemporal arcades are absent (Fig. 18), we propose the term anadiapsid. Those reptiles (e.g., crocodilians, rhynchocephalians) retaining both arcades are properly regarded as eudiapsid (Fig. 19). This content downloaded from 207.46.13.122 on Thu, 25 May 2017 17:59:44 UTC All use subject to http://about.jstor.org/terms VOLUME 85, NUMBER 1 51 AVIAN AND MAMMALIAN TEMPORAL VACUITIES Birds are conveniently regarded universally as diapsid, and mammals as synapsid, but in both classes certain groups exhibit incomplete arcades, much as most squamatans. In most birds, for example, the supratemporal arcade is incomplete (Fig. 21) resulting in continuity of the infratemporal and supratemporal fossae; primarily in the parrots and their kin (Psittacidae) is the supratemporal arcade complete (Fig. 20). In no group is the infratemporal arcade incomplete. Thus although most birds are in reality hemidiapsid, they differ from hemidiapsid squamatans in which it is the infratemporal arcade rather than the supratemporal that is incomplete. We suggest that these two conditions be distinguished by the terms suprahemidiapsid (for the avian condition) and infrahemidiapsid (for the squamatan condition). Most mammals, with a single temporal fossa-a condition designated as synapsid-retain the infratemporal arcade intact (Fig. 22). In a few groups, however, notably among insectivores, that arcade is incomplete (Fig. 23). We suggest that the common condition be distinguished by the term eusynapsid from the unusual condition, with an incomplete infratemporal arcade, that we here term anasynapsid.