| Proconodontida | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Infraphylum: | Agnatha |
| Class: | †Conodonta |
| Subclass: | †Cavidonti |
| Order: | †Proconodontida Sweet, 1988 |
| Synonyms | |
| |
Proconodontida is anorder ofconodonts which originated in the lateCambrian (Furongian) and persisted partly through theOrdovician.[1] The ancestral proconodont,Proconodontus, was one of the earliest euconodonts ("true conodonts") to appear. Proconodonts are often equated with the broader groupCavidonti, which occupies one side of a basal division in the evolution of early euconodonts in the Cambrian. All other euconodonts occupyConodonti, the other side of the Cambrian split.[1]
Proconodontida may be ancestral to another order,Belodellida.[1] Belodellids originate in the Ordovician and survive up to theDevonian[1] or even thePermian (ifCaenodontus qualifies as a member of the order).[2]
Cavidonts were simple conodonts, tending to maintain smooth and thin-walled elements with ahyaline structure. They were often coniform (horn- or tooth-shaped) with a semi-symmetrical or elliptical cross-section.[1][3] The basal cavity was deeper than in early members of theirsister taxon Conodonti. The apparatus is quinquimembrate at most (with five or fewer different element forms) and P elements are infrequent.[1]
Lateral keels and subtle lines of serrations are frequently found in the hook-shaped elements of bellodelids, while other proconodonts rarely deviate from one or more basic conical structures.[1] The Ordovician proconodontFryxellodontus is occasionally considered ancestral toPolonodus andpygodontids, which had more unusual elements covered with ridges, nodes, and denticles.[4][1]
Cavidonti and its interrelationships were first established by Sweet (1988).[1] Many families and larger groups areparaphyletic and not yet evaluated by cladistic analyses.[5]
A different taxonomic arrangement, proposed by Dzik (1991), does not use Cavidonti as a grouping. Instead, it classifies proconodontids (families Proconodontidae, Cordylodontidae, and Fryxellodontidae) as members of the orderPanderodontida and the superfamilyCordylodontacea. The order Belodellida is broken up and removed from their status as descendants of proconodontids. Bellodellidae and the component taxa of Dapsilodontidae (Besselodus andDapsilodus) were moved into the superfamilyPanderodontacea, closer toPanderodontidae andStrachanognathidae. Ansellidae is given a more distant placement among thePrioniodontida.[9] A 1994 reevaluation ofPanderodus argued that Belodellidae may have close affinities to Panderodontida, whileBesselodus andDapsilodus are best classified within the orderProtopanderodontida.[10]
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