Huracan, Jiangzuo & Flynn & Wang & Hou & Deng, 2023
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publication ID |
https://doi.org/ 10.1206/3996.1 |
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persistent identifier |
https://treatment.plazi.org/id/3F7387AE-FFD2-FFB3-FED2-B6B9FCC1F97A |
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treatment provided by |
Felipe |
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scientific name |
Huracan |
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COMPARISON OF HURACAN TO INDARCTOS AND AGRIOTHERIUM
The type species of Huracan was originally viewed as assignable to Agriotherium but with some Indarctos -like characters ( Hunt, 1998). Indeed, the overall morphologies of species of Huracan are most similar to Agriotherium . Both genera share several characters: short rostrum, small anterior premolars, large P4 parastyle, short M2 talon, presence of a premasseteric fossa, and absence of an entepicondylar foramen of the humerus.
Nevertheless, Huracan also exhibits several characters that are never observed in or are extremely rare in typical Agriotherium . The most significant distinguishing character is the Indarctos -like m1 entoconid and metaconid complex in Huracan . In Huracan (as in Indarctos ), there are always three cusps in this region, representing the metaconid and a subdivided entoconid. Nearly all Agriotherium , except one specimen of A. africanum (PQL 50446), possess no metaconid (most cases) or only an extremely weak metaconid ( A. africanum: PQL 50006; A. hendeyi: AMNH F :AM 63098) ( Jiangzuo and Flynn, 2019). Beyond this character, Huracan also differs from Agriotherium in: P4 with more frequently subdivided hypocone; proportionally longer M1 and M2, and larger M2 talon ( fig. 18 View FIG ); p4 mostly lacking the medial ridge; and presence of a posterocentral accessory cusp, well developed and distinguished from the medial ridge of the I1/I2. Among these characters, M1 and M2 shapes are intermediate between the typical Indarctos and typical Agriotherium conditions. In terms of the M2/M1 length ratio, the M2 of H. coffeyi is shorter than any species of Indarctos , without overlap ( fig. 18 View FIG , table 3), but some specimens overlap with A. africanum in talon size. In terms of talon size, using the ratio of M2 TL/L, H. coffeyi overlaps with species of both Indarctos and Agriotherium . The standard error for this ratio in H. coffeyi is 9.4 × 10 -3, larger than that represented across the entire genus Indarctos (7.1 × 10 -3), suggesting extensive intraspecific variability of talon size in H. coffeyi . The second character (p4 without medial ridge) is shared between most individuals of Huracan and Indarctos , although a few Hh3-aged H. coffeyi specimens and several Hh4-aged H. schneideri specimens have this ridge. The last character (presence of I1/I2 posterocentral accessory cusp) is an autapomorphy, as it is absent in both Indarctos and Agriotherium . Huracan differs from Indarctos in the peculiar I1/I2 morphology of the new taxon; more reduced anterior premolars, larger P4 parastyle, proportionally shorter M1 and M2 with a shorter talon, presence of a distinct anterior accessory cusp on p4, more elongate m1, and presence of a premasseteric fossa on the mandible. Most of these characters are shared with Agriotherium , but do not occur in Indarctos and Ursavus (outgroup), representing synapomorphies indicating a closer relationship of Huracan to Agriotherium than to Indarctos . Some characters show variability, e.g., the I3 medial cingulum often bears a distinct central groove in Huracan , which also is the case in Indarctos (at least in all material from Lufeng and unpublished material from
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TAXA
Huracan qiui
Huracan roblesi
Ningxia, North China), but the groove seems to be absent in all material of Agriotherium (based on published specimens and unpublished material from Yushe).
In terms of cranial characters, Agriotherium has the shortest and most robust rostrum relative to Huracan and Indarctos ( fig. 19 View FIG ), with Huracan intermediate between Agriotherium and Indarctos . Two ratios can be used to measure relative rostrum length: relative diastema length between C/c and P4/p4 and cheek tooth (including molars and P4/p4) row length, i.e., L21/L9 of the cranium and L5/L4 of the mandible (see the definitions of L4, L5, L9 and L 21 in Materials and Methods). Both ratios in H. coffeyi (means of 0.36, and 0.33, respectively; see the ratios and variation of each value in tables 6, 11) are smaller than those of Indarctos (means of 0.42 and 0.38, respectively; see the ratios and variation of each value in tables 6, 11), indicating a generally shorter rostrum, although there is considerable overlap in their ranges.
Huracan , Agriotherium , and Indarctos share many derived traits relative to ursid outgroups, e.g., large body size, reduced anterior premolars, enlarged carnassial, m1 with expanded talonid, etc. Within this clade of Huracan , Agriotherium , and Indarctos , Huracan shares only retained primitive characters with Indarctos but possesses some derived characters shared with Agriotherium . Huracan thus represents a morphologically intermediate taxon between the two genera, providing an important link in understanding transformations between the morphology of the previously well-known taxa Indarctos and Agriotherium , although the presence of autapomorphies clearly indicate that it was not directly ancestral to Agriotherium (neither morphologically nor temporally, as Agriotherium also had already appeared in both Asia and North America prior to the first occurrence of Huracan ), but rather represents the closest sister group to Agriotherium .
Another hypothesis about the origins of Agriotherium was that it evolved from some kind of hemicyonid bear ( Qiu et al., 1991; Morales et al., 2005; Abella et al., 2014). However, the dentitions of hemicyonids differ markedly from that of Agriotherium . In comparison to Agriotherium , P4s of hemicyonids lack a parastyle (most taxa) or only possess a cingulumlike structure in the parastylar region (a very few specimens of Plithocyon , especially in P. armagnacensis ). In hemicyonids, the M1 and M2 are more transversely widened and have a well-developed lingual cingulum, M2 never develops a talon and is always smaller than M1, lower molars are overall narrower, the m1 talonid is not especially wide, and the m1 buccal contour only slightly undulates or is straight ( Frick, 1926; Ginsburg and Morales, 1998; Hunt 1998). Concerning cranial morphology, hemicyonid skulls are less stout, possess an alisphenoid canal, and the mastoid process is never exaggeratedly developed ( Frick, 1926). In all of these aspects, Agriotherium is much more similar to Indarctos and Huracan than to hemicyonids. The limited similarities between Agriotherium and hemicyonids include a P4 inner lobe with single cusp and M2 lacking a talon. But as discussed above, these traits also show a continuous range of variation from Indarctos - type through Huracan - type to Agriotherium - type, and the latter type is convergent with hemicyonids, presumably reflecting common adaptations in these two lineages toward a more carnivorous diet. Postcranial morphology further suggests that hemicyonids were better adapted to a cursorial locomotor pattern than any other bear ( Frick, 1926), even relative to the quite cursorial morphology exhibited independently by Huracan and Agriotherium .
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